Abstract

Vegetable oils and fats are valuable mixtures whose dominant components are triacylglycerols, but whose processing behavior is governed by much smaller concentrations of phospholipids, free fatty acids, soaps, water, metals, pigments, oxidation products, waxes, partial glycerides, and suspended solids. Refining must remove selected impurities while retaining neutral oil, tocopherols, sterols, and other desirable minor components. Biodiesel production has a related objective: convert acyl groups to fatty acid alkyl esters while controlling glycerol, alcohol, catalyst, soap, metals, water, oxidation stability, and cold flow behavior. Oleochemical conversion expands the same chemistry to hydrolysis, esterification, interesterification, structured lipids, fatty acids, soaps, and glycerol based coproducts [6,7,8,9].

11. Vegetable Oil Refining, Biodiesel, and Oleochemical Conversion

11.1 Introduction

Vegetable oils and fats are valuable mixtures whose dominant components are triacylglycerols, but whose processing behavior is governed by much smaller concentrations of phospholipids, free fatty acids, soaps, water, metals, pigments, oxidation products, waxes, partial glycerides, and suspended solids. Refining must remove selected impurities while retaining neutral oil, tocopherols, sterols, and other desirable minor components. Biodiesel production has a related objective: convert acyl groups to fatty acid alkyl esters while controlling glycerol, alcohol, catalyst, soap, metals, water, oxidation stability, and cold flow behavior. Oleochemical conversion expands the same chemistry to hydrolysis, esterification, interesterification, structured lipids, fatty acids, soaps, and glycerol based coproducts [6,7,8,9].

The recurring engineering difficulty is phase contact. Water must reach hydratable phospholipids. Acid must reach calcium and magnesium associated phospholipids. Caustic must contact free fatty acids without remaining in concentrated droplets long enough to saponify neutral oil. Enzymes must reach an oil water interface without being thermally or mechanically deactivated. Methanol and catalyst must contact triacylglycerols even though the initial oil rich and alcohol rich phases are poorly miscible. In each case, the intrinsic chemistry can be faster than the transport of material to the interface [5,6,7,8].

Hydrodynamic cavitation is produced when liquid velocity and local pressure are manipulated so that vapor and gas cavities form, grow, and subsequently collapse as pressure recovers. The useful process effects include droplet breakup, boundary layer renewal, pressure pulses, localized liquid jets, intense velocity gradients, deagglomeration, and bulk hydraulic energy dissipation. These effects can reduce contact time and reagent overdosage, but they can also create persistent emulsions, heat, oxidation, erosion, plugging, vibration, and unwanted cavitation in the pump. Process benefit therefore exists only inside a defined operating window [1,2,3,4,5,6].

The technology should be evaluated as one operation within a sequence of metering, contact, hold, phase transformation, and separation. An inline cavitation device cannot compensate for inaccurate reagent concentration, unstable feed flow, insufficient chemical residence time, an overloaded centrifuge, or poor sampling. Conversely, a well integrated contactor can remove a mixing bottleneck that otherwise forces a plant to use excessive acid, caustic, water, enzyme, catalyst, alcohol, adsorbent, or residence volume.

Figure 11.1. Credible integration points for controlled hydrodynamic cavitation in vegetable oil refining and biodiesel production. The device is shown as a contacting operation followed by a hold or separation step.

This chapter asks five practical questions. First, what transport or reaction limitation is the device intended to remove? Second, which hydraulic variables actually create and control the low pressure region? Third, how does the dispersion evolve during the downstream hold? Fourth, which measurements prove a net improvement in quality and yield? Fifth, do recoverable savings in product, chemicals, water, time, and capacity exceed energy, maintenance, and capital costs?11.2

11.2.Vegetable Oil Feedstocks and Conventional Refining

11.2.1 Composition and refining objectives

Crude oil is normally more than 90 percent triacylglycerol by mass, yet a small impurity fraction controls color, flavor, stability, processing loss, catalyst demand, wastewater load, and deodorizer performance. Hydratable phospholipids become associated with an aqueous phase after controlled water addition. Nonhydratable phospholipids often occur as calcium or magnesium salts of phosphatidic acid and related compounds and require acid, chelation, electrolyte treatment, or enzymatic conversion before they can be removed effectively [7,8,21,22].

Free fatty acids are removed by alkali neutralization or by steam stripping during physical refining. Alkali neutralization produces soap, which acts as both the desired heavy phase carrier and an emulsifier that can entrain neutral oil. Metals such as iron, copper, calcium, and magnesium influence oxidation, gum chemistry, bleaching, and downstream catalyst behavior. Waxes and high melting components determine haze and cold stability. Water, suspended solids, and entrained gas influence viscosity, nucleation, pressure loss, and separation. A cavitation design basis must therefore use measured feed properties at operating temperature rather than a nominal oil name.

Figure 11.3. Conceptual composition of crude vegetable oil. The minor fraction is expanded conceptually because it controls most refining decisions. Actual composition depends on oil type, storage, extraction, and prior treatment [7,8].

Table 11.2. Major crude oil constituents, refining consequences, and relevance to cavitation assisted contacting.

Constituent	Process consequence	Refining objective	Cavitation relevance
Triacylglycerols	Primary valuable product	Maximize recovery and avoid hydrolysis or saponification	Excessive shear, heat, oxygen, or caustic contact can reduce yield or stability
Hydratable phospholipids	Form gums after water contact	Hydrate and create a separable heavy phase	Fine water dispersion accelerates contact, followed by coalescence and floc growth
Nonhydratable phospholipids	Associated with calcium, magnesium, and acidic phospholipids	Convert to hydratable or extractable forms	Small acid dose requires rapid and uniform distribution
Free fatty acids	Increase refining loss and acid value	Neutralize selectively or remove by physical refining	Micromixing can reduce caustic excess, while overcontact can saponify neutral oil
Soaps and partial glycerides	Strong interfacial stabilizers	Remove without entraining oil	Create the emulsion paradox and constrain useful dose
Trace metals	Promote oxidation and poison catalysts	Transfer to water, gums, or adsorbent	Acid contact and adsorbent dispersion can improve removal
Pigments and oxidation products	Color, flavor, and stability defects	Adsorb during bleaching or strip during deodorization	Adsorbent wetting may improve, but oxidation must be monitored
Water, gas, and solids	Hydrolysis, fouling, unstable flow, and nucleation changes	Control before each stage	Strongly influence pressure field, plugging, and cavitation onset
Waxes and high melting compounds	Haze and poor cold behavior	Crystallize and filter	Excessive shear can fragment crystals and reduce filterability

11.2.2 Feedstock variability

Soybean oil is a common degumming feed because it can contain substantial phospholipid concentrations. Rapeseed and canola oils have different phospholipid and sulfur containing minor components. Sunflower and corn oils may require careful wax and color control. Rice bran oil can develop high free fatty acid content rapidly after milling if lipase is not inactivated. Palm oil normally contains less phospholipid than soybean oil but may contain high free fatty acids, moisture, metals, and thermal history effects. Castor oil has much higher viscosity because of hydroxylated fatty acids. Used cooking oil contains water, food particles, oxidation products, polymers, free fatty acids, and highly variable contaminant loads [7,8,9].

The same device setting can therefore produce different pressure drop, cavitation intensity, droplet size, and heat rise in different oils. A design that operates stably in warm soybean oil can plug or fail to cavitate in a colder, more viscous feed. Alcohol addition changes vapor pressure and compressibility. Water and suspended particles change the nuclei population. Scale up should preserve a product response rather than assume that a fixed pressure drop is universally transferable.

Table 11.3. Minimum feed characterization for design and acceptance testing.

Property	Reason for measurement	Recommended reporting basis
Density and viscosity	Determine velocity, Reynolds number, pressure loss, pumping, and separation	Measured at each operating temperature
Vapor pressure or boiling tendency	Affects cavitation onset and alcohol flashing	Estimated or measured for actual mixture
Water and entrained gas	Influence nuclei, hydrolysis, pressure stability, and phase volume	Mass fraction plus sampling method
Free fatty acids or acid value	Determines caustic or esterification demand	Mass fraction and mg KOH per g
Phosphorus, calcium, magnesium, and iron	Define gum chemistry and pretreatment demand	mg per kg with analytical uncertainty
Soap and partial glycerides	Control emulsion stability and separator loading	mg per kg or mass fraction at defined sample point
Suspended solids and waxes	Affect plugging, erosion, and filtration	Particle loading and size distribution
Oxidation state	Provides baseline for quality protection	Peroxide value, p anisidine value, induction period, and conjugated dienes

11.2.3 Conventional process train and realistic boundaries

A conventional chemical refining train includes heating and conditioning, water or acid degumming, centrifugal separation, caustic neutralization, one or more water washes, vacuum drying, bleaching, filtration, and deodorization. Physical refining removes free fatty acids in the deodorizer but requires very low phosphorus, metals, soap, and moisture upstream. Hydrodynamic cavitation is most credible in liquid liquid contacting, reaction initiation, and selected solid dispersion duties. It does not replace centrifugation, vacuum drying, filtration, deodorization, alcohol recovery, or final product testing.

Figure 11.4. Conventional vegetable oil refining train and credible intensification locations. The contacting step can be modified without eliminating the downstream hold, separation, drying, bleaching, filtration, or deodorization operations.

The integration point must be chosen from the downstream requirement. A device placed immediately before a centrifuge can create droplets too small to separate within the available residence time. A device placed before an acid hold can improve conversion while allowing later aggregation. A separate mild water contacting stage can provide hydration without reapplying the full acid contact dose. The plant should therefore be designed backward from the required separator inlet condition.

11.3 Engineering Fundamentals and Reactor Configurations

11.3.1 Flow, pressure, and cavitation onset

For incompressible flow, volumetric flow rate is related to flow area and mean velocity by the continuity equation:

$$Q=Au$$

(11.1)

When a flow area decreases, velocity increases. A pressure form of the mechanical energy balance between two locations is:

$$p_1+\frac{1}{2}\rho u_1^2+\rho g{z}_1=p_2+\frac{1}{2}\rho u_2^2+\rho g{z}_2+\mathrm{\Delta }{p}_{loss}$$

(11.2)

The static pressure can fall near or below the local vapor pressure in a throat, annular gap, rotating cavity, vortex core, or jet. The cavitation number is commonly written as:

$${\sigma }_c=\frac{p_{ref}-p_v}{\frac{1}{2}\rho u_{ref}^2}$$

(11.3)

Lower values generally indicate a greater tendency to cavitate, but comparisons are valid only when reference pressure, velocity location, temperature, and vapor pressure are defined consistently. In oil systems, dissolved gas and volatile alcohol can make the cavity content different from pure oil vapor. The Reynolds number provides a first indication of flow regime:

$$Re=\frac{\rho u{D}_h}{\mu }$$

(11.4)

Reynolds number alone does not define cavitation intensity, because pressure recovery, nuclei, turbulence scale, and geometry determine where cavities grow and collapse. The Rayleigh Plesset equation expresses the radial dynamics of an ideal spherical bubble:

$$R\ddot{R}+\frac{3}{2}{\dot{R}}^2=\frac{1}{\rho }[p_B(t)-p_{\infty }(t)-\frac{4\mu \dot{R}}{R}-\frac{2\gamma }{R})$$

(11.5)

The equation demonstrates why pressure history, viscosity, surface tension, and gas content matter. Industrial cavities are not isolated spheres and often occur near walls, interfaces, particles, and rapidly changing turbulent structures. The equation is therefore a physical guide, not a complete reactor model [1,2,3,4,5].

Figure 11.5. Idealized cavity life cycle through a low pressure and pressure recovery region. Useful collapse should occur inside a controlled zone rather than at a pump inlet or vulnerable wall.

11.3.2 Hydraulic power, energy dose, and heat

The hydraulic power dissipated across the active device is:

$$P_{hyd}=\mathrm{\Delta }pQ$$

(11.6)

The approximate electrical input to the pressure generating pump is:

$$P_{el}=\frac{\mathrm{\Delta }pQ}{{\eta }_p}$$

(11.7)

For one pass, the idealized specific electrical energy is:

$$e_s=\frac{\mathrm{\Delta }p}{\rho {\eta }_p}$$

(11.8)

Hydraulic energy ultimately becomes sensible heat, kinetic energy, pressure recovery loss, acoustic emission, vibration, surface work, and deformation of dispersed phases. If all pressure loss becomes sensible heat in an adiabatic pass, the upper estimate of bulk temperature rise is:

$$\mathrm{\Delta }T\approx \frac{\mathrm{\Delta }p}{\rho c_p}$$

(11.9)

A modest single pass temperature rise can become large during recirculation. Temperature is not a secondary utility variable. It changes viscosity, vapor pressure, enzyme activity, methanol flashing, reaction rate, oxidation, and centrifuge density difference. Pressure drop, pass count, flow, power, and temperature rise must be reported together.

11.3.3 Reactor families

Static devices include multi hole orifices, venturis, nozzles, annular restrictions, and vortex chambers. Dynamic devices include rotor stator gaps, rotating cavities, slots, teeth, and shockwave power reactors. Adjustable inline devices use a movable restriction or controlled backpressure to preserve a target pressure field across changing throughput. Not every high shear mixer cavitates. Evidence should include the pressure field, vapor or acoustic signature where available, and a repeatable process response.

Figure 11.6. Representative hydrodynamic cavitation reactor families and their low pressure mechanisms.

Figure 11.7. Patent drawing of an adjustable annular reactor for vegetable oil degumming. US 9,290,717 B1 [20].

Table 11.4. Comparison of principal reactor families.

Family	Low pressure mechanism	Advantages	Main cautions
Multi hole orifice	Parallel jets followed by abrupt expansion	Compact, interchangeable, and readily numbered up	Plugging, local erosion, broad residence distribution, and high pump load
Venturi	Converging section, throat, and diffuser recovery	Smooth recovery and continuous service	Longer body and sensitivity to diffuser angle and backpressure
Vortex device	Swirling core creates an axial low pressure zone	Extended cavity residence and no small parallel holes	Complex multiphase flow and difficult scale up
Rotor stator or SPR	Rotating gaps, cavities, slots, or teeth	Adjustable intensity and high throughput	Moving parts, seals, vibration, heat, and wear
Adjustable inline restriction	Movable throat and controlled recovery pressure	Can maintain a hydraulic fingerprint over changing flow	Proprietary characterization and need for site acceptance
Compression decompression reactor	Pressure increase followed by rapid controlled release	Can produce fine droplets and repeated pressure cycles	Cavitation may be promoted or intentionally avoided, depending on geometry

11.3.4 Process architectures and treatment history

A single pass system provides the clearest treatment history and the lowest risk of overprocessing. Recirculation increases the number of contacts but broadens the distribution of passes: some material can receive many more exposures than the average. A slipstream retrofit treats only a fraction of the plant flow and therefore requires reliable mixing of treated and untreated material. Series reactors can create sequential pressure histories. Parallel reactors increase capacity but require flow balancing.

Figure 11.8. Single pass, recirculation, and slipstream process architectures. The design must define how many exposures each fluid element receives.

Increasing hydraulic dose does not guarantee increasing benefit. Contact and conversion generally improve at first, while separation, oxidation stability, temperature control, equipment life, and power consumption can deteriorate beyond an optimum. The useful setting is the lowest dose that reaches the chemical and separation endpoint.

Figure 11.9. Conceptual operating window for cavitation assisted oil processing. The process optimum lies between undercontact and persistent emulsion, heat, oxidation, or wear.

11.4 Mechanisms of Process Intensification

11.4.1 Droplet breakup and interfacial area

Most refining duties disperse a small aqueous phase into a continuous oil phase. For spherical droplets represented by Sauter mean diameter d32 and dispersed phase volume fraction phi, the specific interfacial area is approximated by:

$$a=\frac{6\varphi }{d_{32}}$$

(11.10)

Reducing d32 from 300 micrometres to 30 micrometres increases interfacial area by a factor of ten at the same reagent dose. This geometric effect is the most direct explanation for rapid contact. It also explains the separation penalty: the same reduction produces droplets with lower settling velocity and much larger stabilizing surface.

Figure 11.10. Specific interfacial area increases inversely with Sauter mean droplet diameter at fixed dispersed phase fraction.

A conceptual transfer rate can be written as:

$$\frac{dC}{dt}=k_{L}a(C^{\ast }-C)$$

(11.11)

Cavitation can increase both interfacial area and liquid side mass transfer coefficient $k_L$ by renewing the boundary layer. The equation remains useful even when reaction, adsorption, flocculation, and nonideal equilibrium occur simultaneously.

11.4.2 Stress criteria for breakup

Droplet deformation and breakup depend on the ratio of disruptive inertial or viscous stress to restorative interfacial tension. Three useful groups are:

$$We=\frac{{\rho }_c{u}_{rel}^{2}d}{\gamma }$$

(11.12)

$$Ca=\frac{{\mu }_{c}u}{\gamma }$$

(11.13)

$$Oh=\frac{{\mu }_d}{\sqrt{{\rho }_d\gamma d}}$$

(11.14)

The Weber number compares inertia with interfacial tension, the capillary number compares viscous stress with interfacial tension, and the Ohnesorge number reflects the role of dispersed phase viscosity. In turbulent breakup, a Hinze type estimate for maximum stable droplet diameter is:

$$d_{\max }=C_H{\left(\frac{\gamma }{{\rho }_c}\right)}^{\frac{3}{5}}{\epsilon }^{-\frac{2}{5}}$$

(11.15)

The local energy dissipation rate varies strongly within a real reactor, so one average value cannot represent every droplet. Measurements should report the full droplet size distribution, not only a mean.

11.4.3 Micromixing and boundary layer renewal

A concentrated acid or caustic droplet can create a local reagent concentration far above the bulk average. Rapid deformation and boundary layer renewal distribute the reagent before undesirable side reactions dominate. In acid degumming this helps acid reach metal associated phospholipids. In neutralization it can reduce local caustic excess. In biodiesel it accelerates initial transfer of methoxide into the oil rich phase. The benefit is greatest when the initial limitation is interfacial transport rather than intrinsic chemistry.

Collapse induced pressure pulses and liquid jets can also deagglomerate enzyme preparations, gums, and adsorbent particles. The downstream requirement may be the opposite: large hydrated gum flocs, coalesced water droplets, separated glycerol, or filterable adsorbent cake. A useful system therefore creates a fine dispersion in the contactor and then deliberately permits phase growth downstream.

Figure 11.11. Required temporal sequence: fine contact in the device, chemical or enzymatic conversion in a controlled hold, floc or droplet growth, and low shear transfer to the separator.

11.4.4 Residence time and recirculation

The nominal residence time of a vessel is:

$$\tau =\frac{V}{Q}$$

(11.16)

For a well mixed recirculation loop with liquid volume VL, the average number of passes during processing time t is:

$$N_p=\frac{Qt}{V_L}$$

(11.17)

These expressions do not capture bypassing, short circuiting, or the distribution of passes. Tracer testing is recommended when scale up depends on hold time or recirculation history. A nominal average of three passes does not mean that every fluid element receives exactly three contacts.

11.4.5 Heat, radical chemistry, and oxidation

Bulk heating lowers viscosity and can accelerate hydration, reaction, and separation. Excessive temperature can flash methanol, deactivate enzymes, reduce density difference, and accelerate lipid oxidation. In water rich microzones, cavity collapse can form reactive species. In unsaturated oil, the same chemistry can initiate peroxide formation and degrade tocopherols. The 2026 acoustic cavitation study by Kalenchak and coworkers provides a useful warning: fast neutralization was achieved, but oxidation markers were more favorable when the process was protected by nitrogen [37].

Oxidative verification should include peroxide value, p anisidine value, conjugated dienes, total oxidation value where used, tocopherols, volatile aldehydes, and induction period. A reduction in phosphorus or reaction time that produces a meaningful loss of oxidative stability is not a successful outcome.

11.4.6 The emulsion paradox

The emulsion paradox is the dominant practical constraint. Reaction benefits from small droplets and high interfacial area. Separation benefits from larger droplets, low surfactant concentration, and limited turbulence. Phospholipids, soaps, partial glycerides, and some oxidation products stabilize interfaces precisely while impurities are being transformed. The design response is to use the minimum hydraulic dose, stop intense contact after the endpoint, provide a defined hold, reduce shear before the centrifuge, and evaluate droplet size at several locations.

Table 11.5. Mechanisms, expected benefits, measurements, and risks.

Mechanism	Expected benefit	Measurement	Risk if excessive
Droplet breakup	Larger interfacial area and faster reagent contact	Droplet size distribution immediately after device	Persistent emulsion and poor separation
Boundary layer renewal	Higher volumetric mass transfer coefficient	Reaction time at equal reagent dose and endpoint	Continued contact after endpoint
Micromixing	Lower local reagent concentration peaks	Lower excess acid, base, enzyme, or catalyst	Neutral oil saponification or enzyme damage
Deagglomeration	Improved use of enzymes, gums, or adsorbent	Particle or floc distribution	Excess fines and high filter resistance
Pressure pulses and liquid jets	Rapid interface renewal and localized cleaning	Acoustic, vibration, and process response	Erosion, vibration, and noise
Bulk energy dissipation	Lower viscosity and faster kinetics	Motor power and temperature rise	Heat load, methanol loss, or oxidation
Reactive chemistry	Possible contaminant conversion	Oxidation and trace species markers	Lipid oxidation and shelf life loss

11.5 Integration into Vegetable Oil Refining

11.5.1 General integration architecture

A robust installation separates four functions: accurate reagent metering, intense but brief contact, controlled chemical or biological hold, and phase separation. The oil flow must be stable and the reagent concentration must be verified. The hold vessel provides time for hydration, acid conversion, enzyme action, neutralization, floc development, or coalescence. The separator must receive a droplet and floc distribution within its hydraulic and solids loading capacity.

Table 11.6. Stage specific objectives and acceptance endpoints.

Stage	Contacted phase	Primary endpoint	Downstream constraint
Water degumming	Water in crude oil	Residual phosphorus at equal or lower water dose	Hydrated gums must aggregate without high neutral oil loss
Acid or deep degumming	Acid followed by water or base	Phosphorus, calcium, and magnesium	Adequate acid conversion and hold before centrifugation
Enzymatic degumming	Enzyme in aqueous microphase	Enzyme dose or time at equal phosphorus and yield	Enzyme activity, pH, temperature, and separation
Alkali neutralization	Caustic contacting free fatty acids and residual acid	Free fatty acids and soap at lower caustic excess	Avoid triglyceride saponification and oil entrainment
Water washing	Wash water contacting soap and salts	Soap and salts at reduced water use	Avoid stable surfactant rich emulsion
Adsorbent dispersion	Bleaching earth, silica, or carbon	Color, metals, and phosphorus at lower dose	Avoid particle fragmentation and filter resistance

11.5.2 Water degumming

Water degumming consists of heating crude oil, metering water, mixing, providing a hydration hold, and separating the heavy gum phase. Cavitation can distribute water rapidly and reduce the distance a phospholipid molecule must travel to reach an interface. The endpoint is not a fine water dispersion. It is low residual phosphorus, rapid gum separation, low moisture in oil, and low neutral oil in gums [7,8].

Development should begin with a conventional baseline at the same feed, water dose, temperature, hold, and centrifuge setting. Cavitation should be introduced at low dose and one pass. Water or hold time should be reduced only after the baseline phosphorus and oil recovery are matched. Too much water increases the heavy phase volume, drying duty, wastewater, and emulsion stability. Cavitation changes contacting but does not remove the chemical optimum for water dose.

11.5.3 Acid and deep degumming

Acid degumming converts metal associated phospholipid forms into more hydratable or extractable species. Phosphoric and citric acids are common choices. Because acid dose is small relative to oil flow, distribution is critical. A fine acid dispersion can complete conversion rapidly, but adding acid and all hydration water before an excessively intense device can produce a stable acidic emulsion. Practical sequences include acid contact followed by an acid hold and later water addition, diluted acid and water contact in one stage, or separate contact stages with different doses.

The stoichiometric acid requirement depends on the measured calcium, magnesium, residual base, and phospholipid chemistry. A compact general expression is:

$$n_{acid,st}=\sum _i{\nu }_i{n}_i$$

(11.18)

Here ni represents the amount of each neutralized or complexed species and nu i is the acid stoichiometric coefficient. In practice, online flow control is combined with frequent phosphorus, calcium, magnesium, and acid strength measurements. A low outlet phosphorus value obtained by transferring excessive neutral oil to the heavy phase is not an economic improvement.

Figure 11.12. Patent disclosed degumming sequence with acid conditioning, base addition, cavitation, hold, and separation. US 9,321,983.

11.5.4 Enzymatic degumming

Enzymatic degumming uses phospholipases to convert phospholipids to products with improved hydration, separation, or oil yield. Phospholipase A forms a lysophospholipid and a free fatty acid. Phospholipase C can release diacylglycerol and a water soluble phosphorylated head group. The selected enzyme changes both the chemistry and the yield accounting. A simplified phospholipase A reaction is:

$$\text{phospholipid}+H_{2}O\to \text{lysophospholipid}+\text{free fatty acid}$$

(11.19)

The enzyme acts at an oil water interface. Cavitation can increase interfacial accessibility, but enzymes can lose activity under excessive temperature, repeated shear, interfacial stress, or recirculation. The correct comparison is lower enzyme dose or shorter hold at equal final phosphorus, metals, oil yield, and enzyme activity.

Results from enzymatic refining trials, conducted with an initial phosphorus content of 322 mg/kg, showed that when cavitation was employed during the addition of the enzyme and water, phosphorus levels measured 59, 30, 26, and 21 mg/kg after 0, 30, 60, and 90 minutes, respectively. For comparison, without the use of cavitation, these figures were 96, 73, 60, and 88 mg/kg. Results from a series of experiments are also reported in which phosphorus content decreased from over 325 mg/kg to 84 mg/kg, calcium from over 160 mg/kg to 66 mg/kg, and magnesium from over 70 mg/kg to 14 mg/kg [26].

Figure 11.13. Data for enzymatic degumming with and without cavitation. [26].

Figure 11.14. Representative enzymatic degumming architecture showing acid conditioning, enzyme and water addition, cavitation contacts, short holds, heating, and separation. Author redrawn from [24,26].

Table 11.7. Vendor reported enzymatic degumming screening data from the supplied presentation [26].

Condition and time	Phosphorus, mg/kg	Calcium, mg/kg	Magnesium, mg/kg	FFA, percent
Incoming	322	167	70	0.63
Cavitation, 0 min	59	35	10	0.59
Cavitation, 30 min	30	20	5	0.74
Cavitation, 60 min	26	18	4	0.74
Cavitation, 90 min	21	14	3	0.73
No cavitation, 0 min	96	52	15	0.58
No cavitation, 30 min	73	40	11	0.74
No cavitation, 60 min	60	33	9	0.64
No cavitation, 90 min	88	40	14	0.72

A final process scheme was also proposed, involving treatment at 70°C using a 50% citric acid solution (at a dosage of 1300 mg per kg of raw material) and an enzyme (30 mg per kg), along with the addition of 2.5% water and the application of multiple cavitation cycles; notably, the total duration of the enzymatic treatment was less than one hour, in contrast to traditional methods, where it can take up to six hours. It is particularly noted that this process has not been optimized; therefore, the presented data should be viewed as a working hypothesis rather than a guaranteed recipe[26].

11.5.5 Compression and decompression cavitation degumming example

US 9,321,983 B2 discloses acid and base pretreatment followed by compression and rapid decompression cavitation. In one example, measured residual phosphorus decreased from 46 to 2.3 mg per kg, iron from 0.8 to 0.05 mg per kg, calcium from 35 to 2 mg per kg, and magnesium from 8 to below the reported detection value. The process used repeated decompression intervals after pressurization. [21].

Figure 11.15. Trace impurity reductions reported in a patent example for compression and decompression cavitation degumming [21].

Table 11.8. Patent example for compression and decompression degumming [21].

Analyte	Initial, mg/kg	Final, mg/kg	Calculated reduction
Phosphorus	46	2.3	95.0 percent
Iron	0.8	0.05	93.8 percent
Calcium	35	2	94.3 percent
Magnesium	8	reported as 0	approximately 100 percent

11.5.6 Alkali neutralization and water washing

Chemical refining removes free fatty acids by reaction with sodium hydroxide:

$$RCOO{H}_{oil}+NaO{H}_{aq}\to RCOONa+H_{2}O$$

(11.20)

The theoretical mass of sodium hydroxide for neutralizing free fatty acids can be estimated from:

$$m_{NaOH,st}=m_{oil}{w}_{FFA}\frac{M_{NaOH}}{M_{FFA}}+m_{NaOH,acid}$$

(11.21)

The excess factor is:

$$f_{ex}=\frac{m_{NaOH,actual}}{m_{NaOH,st}}$$

(11.22)

Rapid micromixing can reduce local concentration peaks and allow the excess factor to approach unity. The risk is direct: once free fatty acids and residual acid are neutralized, continued high interfacial area can increase triglyceride hydrolysis and saponification. The process should combine accurate free fatty acid measurement, verified caustic strength, ratio control, short contact, a defined hold, and timely separation.

Figure 11.16. Neutralization converts free fatty acid to soap, while excessive local caustic concentration or long contact can consume neutral oil. [7,23,25].

US 9,765,279 B2 discloses multiple localized shear cycles with millisecond relief intervals. The disclosed table demonstrates that nozzle size, stage count, shear rate, and time between cycles changed phosphorus, free fatty acid, and heavy phase volume. The strongest disclosed phosphorus values were obtained with multiple stages, while an unsuitable configuration produced high residual phosphorus and a larger heavy phase [23].

Table 11.9. Selected neutralization results disclosed in US 9,765,279 B2 [23].

Nozzle opening, mm	Stages	Approximate shear rate, 1/s	Heavy phase, vol percent	Phosphorus, mg/kg	FFA, percent
0.56	1	66,390	5.85	94.0	0.10
0.56	2	66,390	3.80	28.0	0.08
0.56	2	66,390	2.38	2.2	0.03
0.56	3	66,390	1.88	1.6	0.01
1.25	2	50,120	2.42	4.0	0.02
3.28	1	6,400	6.70	157	0.15

Water washing removes residual soap and salts after the first separator. The wash stage normally requires less intensity than the initial neutralization stage because soap concentration is high and interfacial stabilization is strong. A mild contactor may reduce wash water, but an intense device can create a wash emulsion that overloads the centrifuge. The wash endpoint should include soap, salts, moisture, light phase oil loss, and wastewater volume.

11.5.7 Reported refining results

The supplied refining presentations report industrial and trial data for several oil streams. One presentation reports, for corn, rapeseed, and soybean oils, reductions in acid dose of approximately 51.9, 37.7, and 24.4 percent; reductions in sodium hydroxide use of approximately 27.2, 57.2, and 26.7 percent; and soap reductions of approximately 69.5, 65.1, and 30.9 percent, respectively. Final phosphorus values were reported at 4 mg per kg for corn and 2 mg per kg for rapeseed and soybean oil [29].

Figure 11.17. Reported single pass testing across corn, rapeseed, and soybean oil streams. [29].

Table 11.10. Data from multi oil refining results [29].

Oil	Acid reduction	NaOH reduction	Soap reduction	Final phosphorus
Crude corn oil	51.91 percent	27.22 percent	69.50 percent	4 mg/kg
Degummed rapeseed oil	37.70 percent	57.17 percent	65.14 percent	2 mg/kg
Degummed soybean oil	24.44 percent	26.66 percent	30.86 percent	2 mg/kg

Another presentation reports a commercial neutralization installation with acid reduction of 45 percent, caustic reduction of 25 percent, a 0.40 percent yield increase at the first centrifuge, elimination of wash water, a 15 mg per kg reduction in phosphorus, and a 500 mg per kg reduction in soap. The presentation reports annual savings of about USD 1.44 million and a simple payback of 0.43 years [28,32].

Figure 11.18. Industrial Arisdyne controlled flow cavitation skid. Source [28,30

Figure 11.19. Floc rich dispersion and visible phase separation after treatment. [28,30].

11.5.8 Bleaching, winterization, and deodorization boundaries

Bleaching removes pigments, oxidation products, metals, soap, and residual phospholipids by adsorption onto activated clay, silica, carbon, or related media. Cavitation can improve wetting and break agglomerates, potentially reducing adsorbent dose. Excessive fragmentation can increase filter resistance and oil retained in spent earth. A trial should measure color, chlorophyll, phosphorus, metals, peroxide value, filter cycle time, spent earth oil, and pressure drop.

Winterization and dewaxing depend on controlled nucleation, crystal growth, and filtration. Cavitation can create nuclei but can also fragment crystals into fines that pass through or blind a filter. This application should be treated as exploratory and verified by crystal size distribution, cold test, haze, filterability, and oil loss. Hydrodynamic cavitation is not a replacement for steam deodorization. Its value is upstream removal of phosphorus, metals, soap, and oxidation precursors. Finished oil must still be evaluated for flavor, color, free fatty acids, trans isomers where relevant, tocopherols, sterols, peroxide value, p anisidine value, and oxidative stability.

11.6 Biodiesel Production by Intensified Contacting

11.6.1 Reaction chemistry and phase limitation

Biodiesel is commonly produced by transesterification of triacylglycerols with methanol in the presence of a catalyst:

$$TAG+3C{H}_{3}OH\rightleftharpoons 3RCOOC{H}_3+C_3{H}_5{(OH)}_3$$

(11.23)

The overall reaction proceeds through diacylglycerol and monoacylglycerol intermediates. At the beginning, the oil rich and methanol rich phases are poorly miscible, so observed rate is strongly influenced by interfacial area. As methyl esters and partial glycerides form, phase behavior changes and intrinsic kinetics become more important. Cavitation is particularly effective during the early mass transfer controlled period [9,16,17,18,19,33,34,35,36].

High free fatty acid feed reacts with base catalyst to form soap. It is commonly dried and subjected to acid esterification before base transesterification:

$$RCOOH+C{H}_{3}OH\rightleftharpoons RCOOC{H}_3+H_{2}O$$

(11.24)

Acid value is determined by titration and can be calculated as:

$$AV=\frac{56.1c_{KOH}{V}_{KOH}}{m_s}$$

(11.25)

Water formed during esterification must be controlled because it shifts equilibrium and promotes soap formation in the later base stage. The high free fatty acid patent US 7,935,157 B2 discloses series cavitation and holding stages for reducing free fatty acid content before transesterification [17]. The broader lesson is that cavitation accelerates contacting but does not change stoichiometry or equilibrium.

Table 11.11. Feed decision logic for biodiesel pretreatment.

Feed condition	Primary problem	Preferred preparation	Acceptance before base stage
Low FFA, dry refined oil	Initial methanol oil mass transfer	Direct base transesterification with accurate catalyst preparation	Water and FFA within validated plant limit
Moderate FFA	Catalyst consumption and soap	Drying plus acid esterification or controlled two stage process	Acid value reduced to validated threshold
High FFA waste oil or sludge oil	Severe soap formation, solids, water, oxidation	Filtration, drying, acid esterification, settling, and possible repeat stage	Low water, low solids, and FFA suitable for base conversion
Animal fats or high melting feed	Viscosity and crystallization	Heating, filtration, and temperature controlled contact	Stable liquid feed at reactor inlet
Mixed or variable waste feed	Uncertain composition and catalyst demand	Feed equalization, frequent analysis, and adaptive dosing	Stable feed envelope and traceable batch history

11.6.2 Reactor arrangements

Orifice and venturi loops are common in laboratory systems. A pump circulates oil, alcohol, and catalyst through one or more active geometries for a specified number of passes. Rotor stator and shockwave power reactors create repeated low pressure events in rotating gaps and can operate continuously. Patent disclosures include single pass, parallel, series, and recirculation arrangements, as well as staged processes that remove glycerol between reaction stages [16,18,19].

Figure 11.20. Continuous biodiesel process concept with cavitation assisted contact, reaction hold, glycerol separation, optional second contact, alcohol recovery, neutralization, drying, and polishing.

Figure 11.21. Patent disclosed series, parallel, and recirculation arrangements for biodiesel conversion. Author redrawn from US 7,754,905 B2 [16].

Figure 11.22. Patent drawing of feedstock, alcohol, and catalyst entering one or more controlled flow cavitation devices. US 7,754,905 B2 [16].

US 8,709,109 B2 discloses a pre reaction cavitation step, intermediate glycerol separation, and finishing in a pressurized reactor, with the objective of improving filterability and removing impurities with the glycerol rich stream [18]. US 9,000,244 B2 discloses a three stage system consisting of a high shear first reactor and lower shear finishing stages with separation and recycle [19]. These architectures reinforce a general principle: the high intensity contact should be brief, and slower conversion and separation should occur in equipment suited to those duties.

11.6.3 Published performance and proper comparison

Published outcomes must be compared carefully because yield, conversion, ester content, and product recovery are not equivalent. A reported 96 percent value can mean gas chromatographic FAME content, conversion of triacylglycerol, or gravimetric mass recovery. Feedstock, catalyst, alcohol ratio, temperature, reactor volume, pass count, and analytical method must accompany every result.

The 2022 orifice plate study by Vera Rozo and coworkers reported that a FAME criterion above 96.5 percent was reached in 17 minutes, compared with 120 minutes for the reported conventional reference [33]. The 2025 continuous shockwave power reactor study reported FAME above 96.5 percent for soybean and waste cooking oil over a matrix of rotor speed, flow, alcohol ratio, and catalyst type, with specific energy analysis included [34].

The 2026 modular reactor study by Andia Marron and coworkers reported a best biodiesel yield of 92.98 percent at 3.10 bar, an 8 to 1 methanol to oil molar ratio, 45 minutes, about 60 degrees Celsius, and 1 percent sodium hydroxide. The same study shows that increasing methanol ratio beyond the optimum did not improve yield [35].

Figure 11.23. Selected modular hydrodynamic cavitation reactor results as the function of inlet pressure and methanol to oil ratio. [35].

A useful noncavitating comparator is the 2024 continuous tubular reactor with a static mixer. It reported an experimental yield of 84.97 percent at a 6 to 1 molar ratio, 0.9 percent sodium hydroxide, and 6 minutes residence time [36]. This comparison is important because process intensification can result from any geometry that creates sufficient interfacial renewal. A cavitation claim should therefore demonstrate an advantage over an optimized static or dynamic mixer, not only over a poorly mixed batch.

Figure 11.24. Selected reported biodiesel outcomes. The metrics are not directly comparable because some sources report ester content, others conversion, and others gravimetric yield. The graph is a result map, not an efficiency ranking [16,33,34,35,36].

Table 11.12. Selected biodiesel studies and design implications.

Source	Feed and reactor	Reported outcome	Design implication
US 7,754,905 B2 [16]	Oil, methanol, base, one to four controlled cavitation devices	Examples above 98 percent conversion and up to 99.8 percent in series	Pressure history and number of devices can be staged
Vera Rozo et al. 2022 [33]	Soybean oil, orifice plate	FAME criterion above 96.5 percent after 17 min	Compare at equal analytical method and full specification
Vera Rozo et al. 2025 [34]	Soybean and waste cooking oil, continuous SPR	FAME above 96.5 percent in continuous operation	Steady metering and energy normalization improve industrial relevance
Andia Marron et al. 2026 [35]	Soybean oil, modular cavitation reactor	Best reported yield 92.98 percent at 3.10 bar and 8 to 1	Pressure and alcohol ratio interact and require optimization
Acevedo Quiroz et al. 2024 [36]	Soybean oil, continuous tubular static mixer	84.97 percent experimental yield in 6 min	Use an optimized noncavitating comparator

11.6.4 Reaction kinetics and scale interpretation

A simple first order representation of observed conversion is:

$$\frac{dX}{dt}=k_{obs}(1-X)$$

(11.26)

Temperature dependence is commonly represented by the Arrhenius equation:

$$k=k_0\exp (-\frac{E_a}{RT})$$

(11.27)

For a first order approximation, the Damkohler number is:

$$Da=k_{obs}\tau$$

(11.28)

In a mass transfer limited regime, kobs includes hydrodynamic effects and should not be interpreted as an intrinsic chemical rate constant. Increasing hydraulic intensity can increase kobs by increasing interfacial area, while the molecular kinetic constant remains unchanged. Once mass transfer is no longer limiting, further intensity increases power, heat, and wear without proportional conversion benefit.

11.6.5 Industrial results

The supplied biodiesel materials report an industrial comparison in which feed rate increased from about 700 to 800 lb per min, catalyst concentration decreased from 2.6 to 2.1 percent, and monoglycerides decreased from 0.59 to 0.28 percent in one comparison. A separate long term presentation reports capacity increase above 10 percent, catalyst reduction above 25 percent, and annual catalyst savings of approximately USD 0.45 to 1.35 million for a producer. These are vendor and customer reported values [28,30,31,32].

Figure 11.25. Industrial biodiesel comparison. Values are normalized to the conventional reference [28,30].

Figure 11.26. Arisdyne CFC biodiesel reactor system.[30,31].

Table 11.13. Reported industrial biodiesel comparison [28,30].

Metric	Conventional reference	CFC reported	Verification requirement
Feed rate	700 lb/min	800 lb/min	Mass flow calibration and steady state production
Catalyst concentration	2.6 percent	2.1 percent	Catalyst active concentration and total addition
Monoglycerides	0.59 percent	0.28 percent in one condition	Common sampling point and validated gas chromatography
Capacity increase	Baseline	More than 10 percent in customer feedback	Confirm that downstream recovery and purification remain within capacity
Annual catalyst savings	Not reported	USD 0.45 to 1.35 million	Recalculate using site catalyst price and actual production

11.6.6 Product quality and standards

High apparent yield does not establish biodiesel quality. ASTM D6751 24 covers B100 blendstock grades and specifies properties including flash point, residual methanol, water and sediment, viscosity, oxidation stability, sulfur, acid number, free glycerin, total glycerin, phosphorus, and metal limits [10]. European FAME production is governed by the contractual edition of EN 14214. A 2026 edition has entered standards catalogs, while some national catalogs and existing contracts continue to reference EN 14214:2012+A2:2019. Contracts should identify the exact edition and test methods rather than state only that product meets ASTM or EN [11,12].

Sampling should begin only after the complete process reaches steady state. Hydraulic conditions can stabilize quickly, while methanol recovery, glycerol separation, wash systems, dryers, and tanks can require much longer. Every product claim should report FAME content, monoacylglycerol, diacylglycerol, triacylglycerol, free and total glycerin, residual methanol, acid number, water and sediment, viscosity, density, oxidation stability, phosphorus, sodium, potassium, calcium, magnesium, flash point, cloud point, and cold filter plugging or cold soak behavior as required by the contract [9,10,11,12].

Table 11.14. Biodiesel analytical program.

Quality group	Measurements	Reason
Conversion	FAME, monoacylglycerol, diacylglycerol, triacylglycerol	Separates chemical conversion from mass recovery
Glycerol control	Free glycerin and total glycerin	Indicates both reaction and glycerol separation
Volatiles and water	Residual methanol, water, sediment, flash point	Safety, storage, and specification compliance
Catalyst and metals	Sodium, potassium, calcium, magnesium, phosphorus, soap	Engine aftertreatment, ash, and purification
Fuel behavior	Viscosity, density, cloud point, cold filter plugging, cold soak filtration	Operability and handling
Stability	Acid number, peroxide markers where used, oxidation induction period	Storage and product life

11.7 Oleochemical Conversion Pathways

Hydrodynamic cavitation is applicable to oleochemical reactions in which immiscible phases or heterogeneous catalysts limit contact. The technology does not alter equilibrium or stoichiometry. It can shorten the time needed to approach equilibrium, reduce bulk heating demand, improve catalyst wetting, and change product distribution when mass transfer competes with reaction. More aggressive chemistry also increases the importance of corrosion, pressure containment, seal compatibility, and temperature control.

Figure 11.27. Oleochemical conversion platform and credible roles for intense liquid contacting.

11.7.1 Fatty oil hydrolysis

Hydrolysis converts triacylglycerol to fatty acids and glycerol:

$$TAG+3H_{2}O\rightleftharpoons 3RCOOH+C_3{H}_5{(OH)}_3$$

(11.29)

The reacting phases are initially poorly contacting. Cavitation can disperse water into oil, renew interfaces, and reduce external transport resistance. The product fatty acids and partial glycerides change interfacial behavior as conversion proceeds. The process must still provide the temperature, catalyst, pressure, and water ratio required by the selected hydrolysis route. Product selectivity, acid value, glycerol purity, corrosion, and energy are more informative than conversion time alone.

11.7.2 Esterification of high free fatty acid streams

Acid esterification is used for high free fatty acid feedstocks, fatty acid distillates, sludge oils, and soapstock derived fatty acids. The equilibrium reaction is shown in Equation 11.24. Cavitation can improve alcohol and acid catalyst contact, but water removal remains necessary. The 2022 open access sludge palm oil study illustrates the magnitude of pretreatment needed for extremely acidic material: heterogeneous and homogeneous acid routes reduced very high free fatty acid levels to about 1 percent under their respective optimized conditions [38].

11.7.3 Interesterification and structured lipids

Interesterification rearranges acyl groups without producing free glycerol in the same manner as conventional transesterification. Methyl acetate interesterification can be represented as:

$$TAG+3C{H}_{3}COOC{H}_3\rightleftharpoons 3RCOOC{H}_3+\text{triacetin}$$

(11.30)

Cavitation can improve contact among oil, acyl donor, and catalyst. In food fat processing, enzymatic interesterification changes triacylglycerol distribution, melting behavior, and solid fat content. The 2026 acoustic cavitation study reported accelerated enzymatic interesterification of fat blends and lower reaction time compared with its conventional reference, while also showing that oxidation control and enzyme protection are necessary [37]. Hydrodynamic systems should be evaluated with the same product distribution and quality measurements rather than only a viscosity or conversion endpoint.

11.7.4 Soapstock acidulation and fatty acid recovery

Soapstock contains soap, water, phospholipids, salts, and entrained neutral oil. Acidulation converts sodium carboxylate back to free fatty acid:

$$RCOONa+HCl\to RCOOH+NaCl$$

(11.31)

Intense contacting can distribute acid rapidly and reduce local overacidification, while the downstream process must allow fatty acid, aqueous salt, and neutral oil phases to separate. A complete balance should quantify recovered fatty acid, neutral oil, aqueous chemical oxygen demand, salt load, acid use, and emulsion stability. Gums deoiling and soapstock splitting are listed among commercial uses in the supplied long term presentation, but detailed independent data were not provided [28].

Table 11.15. Oleochemical pathways and cavitation design questions.

Pathway	Primary contact limitation	Potential cavitation role	Critical acceptance measurements
Hydrolysis	Water oil interface and catalyst distribution	Fine water dispersion and boundary renewal	Acid value, glycerol purity, selectivity, energy, corrosion
Acid esterification	Alcohol and acid contact with free fatty acids	Rapid dispersion and shorter approach to equilibrium	Residual FFA, water, methanol recovery, catalyst removal
Base transesterification	Methoxide transfer into oil rich phase	Rapid reaction initiation	FAME and complete glyceride profile
Methyl acetate interesterification	Acyl donor contact and catalyst distribution	High interfacial area without glycerol phase	FAME, triacetin, catalyst, residual donor
Enzymatic interesterification	Enzyme accessibility at interface	Improved contact at controlled stress	Triacylglycerol distribution, enzyme activity, oxidation, solid fat content
Soapstock acidulation	Acid distribution in surfactant rich mixture	Micromixing followed by low shear separation	Fatty acid recovery, neutral oil, salt water, emulsion loss

11.8 Process Design, Energy, and Scale Up

11.8.1 Design basis

The design basis should state the minimum, normal, and maximum feed flow; oil composition; temperature; density; viscosity; vapor pressure estimate; water; free fatty acids; phosphorus; calcium; magnesium; soap; solids; reagent concentration; required product quality; available upstream and downstream pressure; utilities; separator capacity; operating hours; cleaning plan; and allowable temperature rise. A device should not be sized only by tonnes per day. Two feeds at the same mass flow can require different throat area, pump head, backpressure, and residence history.

Table 11.16. Minimum process design basis.

Category	Required variables	Reason
Feed envelope	Flow, composition, viscosity, density, temperature, gas, solids	Defines hydraulic and fouling limits
Reagents	Concentration, density, ratio, injection pressure, temperature	Prevents dosing error and local overconcentration
Hydraulics	Inlet pressure, outlet pressure, pressure drop, flow, NPSH margin	Defines device and pump operating window
Thermal	Inlet and outlet temperature, heat capacity, cooling duty	Controls viscosity, enzymes, methanol, oxidation, and separation
Downstream equipment	Hold volume, residence distribution, separator capacity, filtration	Prevents contact improvement from becoming a separation failure
Product endpoints	Phosphorus, soap, FFA, yield, FAME, glycerides, stability	Defines acceptance rather than maximum intensity

11.8.2 Worked hydraulic energy example

Consider 100 metric tonnes per hour of oil with density 900 kg per cubic metre, a device pressure drop of 15 bar, and pump efficiency 0.75. The volumetric flow is:

$$Q=\frac{\frac{100000}{3600}}{900}=0.0309m^3{s}^{-1}$$

(11.32)

Hydraulic power is:

$$P_{hyd}=1.5\times {10}^6\times 0.0309=46.3kW$$

(11.33)

Estimated electrical power is:

$$P_{el}=\frac{46.3}{0.75}=61.7kW$$

(11.34)

The idealized specific electrical energy for one pass is:

$$E_s=\frac{61.7kWh}{100t}=0.617kWh{t}^{-1}$$

(11.35)

Three equivalent passes would require about 1.85 kWh per tonne before auxiliary pumps, cooling, controls, and downstream changes. This calculation does not predict process performance. It quantifies the cost of a selected pressure drop and pass count.

Figure 11.28. Idealized pressure drop and specific electrical energy per pass for oil density of 900 kg per cubic metre at several pump efficiencies. The graph is a hydraulic calculation, not a conversion prediction.

11.8.3 Scale up criteria

Exact geometric similarity is rarely practical because one very large throat would require extreme velocity and would not preserve turbulence structure or residence history. Industrial systems use numbering up, parallel channels, larger devices, or multiple stages. Scale up should preserve a product relevant operating window through several criteria: cavitation number, Reynolds number, pressure recovery, specific energy, temperature, residence distribution, droplet response, chemical Damkohler behavior, and separator loading [4,5].

Figure 11.29. Scale up must preserve a product relevant operating window. Matching only pressure drop, flow, or cavitation number can fail because the other phenomena change.

Table 11.17. Scale up criteria and verification methods.

Criterion	What should be preserved	Verification
Cavitation number	Comparable pressure and velocity relationship with same definition	Pressure and velocity at defined locations
Reynolds number	Comparable flow regime	Properties at operating temperature
Pressure recovery	Collapse location and backpressure	Axial pressure map or calibrated CFD
Specific energy	Minimum dose that reaches endpoint	Motor power per tonne of on specification product
Residence distribution	Number and distribution of intense contacts and holds	Tracer testing and pass accounting
Interfacial response	Droplet or particle distribution	Laser diffraction, microscopy, or focused beam measurement
Reaction behavior	Adequate post contact reaction time	Conversion versus time and temperature
Separator load	Heavy phase flow and droplet size within capacity	Centrifuge loss, torque, and phase quality

11.8.4 Computational modeling

Computational fluid dynamics can compare pressure minima, vapor fraction, velocity gradients, recirculation, and likely erosion locations. Common models couple turbulence with a vapor transport equation derived from simplified bubble dynamics. The results are sensitive to nuclei assumptions, mass transfer coefficients, turbulence closure, wall roughness, and boundary pressure. A model should be calibrated against measured pressure drop, flow, temperature, vibration or acoustic response, and visualization where possible. Oil properties and dispersed phase must be represented at operating temperature. A water model can rank geometries qualitatively but can misstate absolute behavior in oil.

11.9 Product Quality, Sampling, and Analytical Verification

11.9.1 Material balance before optimization

Small yield improvements can have large economic value, but they are also easily obscured by tank inventory, moisture, and sampling error. A plant should establish a closed material balance before attributing a 0.1 to 0.4 percent change to cavitation. For a refining stage, phosphorus removal is:

$${\eta }_P=\frac{C_{P,in}-C_{P,out}}{C_{P,in}}\times 100\text{\%}$$

(11.36)

Oil yield can be expressed as:

$$Y_{oil}=\frac{{\dot{m}}_{refinedoil}}{{\dot{m}}_{oilfeed}}\times 100\text{\%}$$

(11.37)

Both values can mislead. Low phosphorus can be achieved by transferring more oil into gums, while apparent yield can increase because of water, residual heavy phase, or inventory movement. Neutral oil in gums, soapstock, wash water, spent earth, filter cake, and off specification product must be tracked.

11.9.2 Sampling locations and timing

Cavitated dispersions evolve quickly. The sample point, valve geometry, sample line, delay before analysis, temperature, and agitation must be standardized. A narrow sampling valve can create more shear than the process under study. Recommended locations are feed before reagent, immediately after the device, after the chemical or enzymatic hold, both separator phases, and final product after drying or purification.

Figure 11.30. Sampling locations and material balance boundary. Every sample must be linked to the corresponding feed and residence delay.

A crossover trial is stronger than a simple before and after comparison. The plant alternates baseline and cavitation conditions after reaching steady state, for example A B B A, while unrelated changes are prohibited. Tank turnover time and downstream residence must be allowed before samples are assigned to a condition. Composite samples describe average product quality; synchronized grab samples are needed to study short time dynamics.

11.9.3 Analytical endpoints

Refining analysis should include phosphorus by a validated elemental method, calcium, magnesium, iron, soap, free fatty acids, moisture, insoluble impurities, color, chlorophyll where relevant, trace metals, oxidation markers, and oxidative stability. Heavy phase flow and composition are essential. Droplet and floc measurements support the mechanism but do not replace product and loss measurements.

For biodiesel, gravimetric yield is:

$$Y_{BD}=\frac{m_{recoveredbiodiesel}}{m_{oilfeed}}\times 100\text{\%}$$

(11.38)

This value does not equal conversion because recovered mass can contain unreacted oil, methanol, water, and soap. Gas chromatography is required to distinguish FAME, monoacylglycerol, diacylglycerol, and triacylglycerol. Free and total glycerin distinguish reaction and separation. Residual methanol, metals, water, acid number, oxidation stability, flash point, and cold flow properties establish final fuel behavior [9,10,11,12].

Table 11.18. Recommended verification program.

Objective	Primary measurement	Supporting measurements	Acceptance logic
Water or acid degumming	Residual phosphorus	Calcium, magnesium, moisture, oil in gums, heavy phase flow	Meet phosphorus target without increased oil loss or oxidation
Enzymatic degumming	Phosphorus and oil yield	Enzyme activity, FFA, reaction products, hold time	Lower dose or shorter time at equal quality and yield
Neutralization	FFA and soap in light phase	Caustic dose, neutral oil in soapstock, wash water, moisture	Reduce excess caustic and soap without greater saponification loss
Bleaching dispersion	Color and metals	Phosphorus, peroxide value, filter rate, spent earth oil	Equal quality at lower adsorbent dose without filtration penalty
Biodiesel reaction	FAME and glyceride profile	Free and total glycerin, catalyst, methanol, acid number	Meet complete fuel specification, not only mass yield
Equipment condition	Pressure drop and vibration trend	Motor power, temperature, metal particles, inspection	Stable hydraulic fingerprint without accelerating wear

11.10 Economics and Sustainability

11.10.1 Sources of recoverable value

Economic value can come from higher recovered oil or biodiesel, lower acid, caustic, enzyme, catalyst, alcohol, water, adsorbent, or filter aid, shorter residence time, more capacity through an existing bottleneck, lower wastewater or solid waste, reduced heating, fewer off specification batches, and avoided expansion capital. Yield is often the largest term at high throughput and also the term most vulnerable to measurement bias.

Energy per tonne of on specification product is more meaningful than pump energy per batch:

$$E_{spec,on}=\frac{E_{total}}{m_{onspecificationproduct}}$$

(11.39)

A simplified annual net value is:

$$V_{net}=m_{annual}{V}_{product}\mathrm{\Delta }Y+S_{chem}+S_{water}+S_{waste}+S_{capacity}-C_{electricity}-C_{maintenance}-C_{capital}$$

(11.40)

Simple payback is:

$$t_{PB}=\frac{C_{installed}}{V_{net}}$$

(11.41)

Net present value over N years at discount rate r is:

$$NPV=-C_{installed}+\sum _{j=1}^N\frac{C{F}_j}{{(1+r)}^j}$$

(11.42)

Reported paybacks below one year are possible when yield, chemicals, water, and capacity improve simultaneously. The calculation must be rebuilt with site specific oil value, operating hours, actual chemical concentration, measured power, maintenance, replacement parts, and confidence intervals.

Figure 11.31. Illustrative sensitivity ranking for a cavitation retrofit. The chart is a decision model example.

Table 11.19. Economic and sustainability accounting boundary.

Term	Potential benefit	Required evidence
Product yield	More refined oil or on specification biodiesel	Closed material balance corrected for water and inventory
Chemicals	Lower acid, base, enzyme, catalyst, alcohol, or adsorbent	Concentration corrected mass use per tonne
Water and waste	Lower wash water, wastewater, gums, soapstock, or spent earth	Measured flow and disposal or treatment cost
Capacity	More saleable product through existing plant	Downstream equipment remains within quality and loading limits
Energy	Lower heating or mixing, offset by pump and cooling	Calibrated motor and utility meters
Maintenance	Long wear life or reduced fouling	Inspection history, replacement interval, downtime
Coproducts	Lecithin, gums, glycerol, fatty acids	Actual recoverable value and quality
Environmental impact	Lower chemicals, water, waste, and product loss	Functional unit of one tonne on specification product

11.10.2 Sustainability interpretation

Hydrodynamic cavitation improves sustainability when reductions in chemical manufacture, water, wastewater, product loss, heating, and new tank volume exceed additional electricity and equipment replacement. It can worsen sustainability when a persistent emulsion increases waste, electricity has high carbon intensity, erosion causes frequent replacement, or oxidation shortens product life. The functional unit should be one tonne of on specification refined oil or biodiesel, not one tonne of feed. This credits yield and penalizes off specification output.

11.11 Equipment, Materials, Maintenance, and Safety

11.11.1 Pump selection and unwanted pump cavitation

Process cavitation should occur inside the intended device, not at the pump inlet. Net positive suction head available must exceed the required value over the full temperature, viscosity, tank level, gas content, and strainer condition range. A hot feed, low tank level, undersized suction line, fouled strainer, or volatile alcohol can initiate pump cavitation, causing unstable flow, noise, vibration, and impeller damage. Positive displacement pumps require relief protection. Centrifugal pumps should operate in a stable efficiency region and should not rely on uncontrolled throttling to create the process effect.

11.11.2 Erosion, corrosion, and materials

Cavitation erosion results from repeated pressure pulses and liquid jets near a surface. Resistance depends on hardness, toughness, microstructure, residual stress, corrosion environment, temperature, and collapse location. Austenitic stainless steels are common in food and biodiesel service, but no material is immune under sufficiently severe conditions. Replaceable inserts, hardened surfaces, cobalt or nickel alloys, and geometry that moves collapse away from walls can extend life.

ASTM G32 provides a vibratory apparatus method for comparative cavitation erosion testing, while ASTM G134 uses a cavitating liquid jet [13,14]. Neither reproduces every process chemistry or geometry. A practical program combines material screening, CFD identification of pressure recovery zones, pilot insert inspection, metal particle monitoring, and scheduled thickness or mass loss measurements. Acid, caustic, chlorides, methanol, water, and elevated temperature can create corrosion erosion synergy.

11.11.3 Food hygiene, cleanability, and compatibility

Edible oil equipment should avoid dead legs, crevices, uninspectable cavities, and product contaminating materials. The device should drain where practical and be included in cleaning validation. Vendor materials report anti plugging designs and limited need for clean in place on certain installations, but this must be verified for the actual solids and gum load [27,28,29,30,31].

Biodiesel and methanol require compatible seals, gaskets, hoses, coatings, and electrical classification. NREL guidance notes that material compatibility depends on biodiesel concentration, oxidation state, and exposure time; fluoropolymers and selected elastomers are commonly preferred, while certain natural rubbers, nitrile compounds, polypropylene, and reactive metals can be unsuitable in some service conditions [9]. Methanol containment, ventilation, grounding, bonding, relief, and fire protection must be addressed by the plant safety design.

11.11.4 Instrumentation and hydraulic fingerprint

Minimum instrumentation includes calibrated flow, inlet and outlet pressure, backpressure, temperature, motor power, reagent flow and concentration, vibration, and alarms for low suction pressure or high temperature. A hydraulic fingerprint records pressure drop, flow, power, temperature rise, vibration, and product response at an accepted operating point. Drift in this fingerprint can reveal erosion, plugging, valve movement, pump wear, gas ingress, or feed property changes before product becomes off specification.

Figure 11.32. Qualitative process risk matrix for cavitation assisted oil and biodiesel systems. Likelihood and consequence must be replaced by site specific hazard review values.

Table 11.20. Primary failure modes and controls.

Failure mode	Process consequence	Detection	Control
Pump inlet cavitation	Unstable flow and pump damage	Suction pressure, vibration, noise	NPSH margin, suction line design, level interlock
Overemulsification	High oil loss and centrifuge overload	Droplet size, turbidity, separator torque	Lower dose, shorter contact, controlled hold
Methanol flashing	Loss of liquid alcohol and pressure instability	Temperature and pressure trend, vent load	Backpressure, cooling, vapor recovery
Oxidation	Lower stability, color, flavor, or fuel life	Peroxide markers and induction period	Oxygen control, lower dose, lower temperature
Erosion	Pressure drift and metal contamination	Power trend, inspection, metal particles	Replaceable wear parts and controlled collapse location
Plugging	Increasing pressure and unstable flow split	Differential pressure	Filtration, larger passages, cleaning plan
Reagent dosing error	Incomplete conversion or side reactions	Mass flow ratio and analytical endpoint	Concentration verification and interlocks
Separator overload	High light phase loss or off specification oil	Heavy phase flow, torque, outlet analysis	Reduce feed or heavy phase load and allow coalescence

11.13 Conclusions

Hydrodynamic cavitation is best understood as a controllable short residence time contacting technology for vegetable oil refining, biodiesel production, and selected oleochemical reactions. Its principal effects are droplet breakup, interfacial renewal, micromixing, deagglomeration, pressure pulse generation, and hydraulic energy dissipation. These effects are relevant to degumming, neutralization, washing, adsorbent dispersion, transesterification, esterification, hydrolysis, and interesterification.

The most reliable architecture meters reagent accurately, applies only the dose needed for contact, provides a controlled hold for chemistry and phase transformation, and minimizes shear before separation. Optimizing the device while neglecting the hold vessel, centrifuge, filter, alcohol recovery, or purification train can convert a contact improvement into a separation failure.

Pressure drop alone is not a sufficient scale up criterion. Cavitation number, Reynolds number, reference pressure, pressure recovery, residence distribution, specific energy, temperature rise, droplet response, reaction behavior, and separator loading should be reported together. Fluid properties must be measured at operating temperature, and the effects of gas, water, alcohol, solids, and nuclei must be included.

Patent disclosures and vendor presentations provide valuable process architectures and quantitative hypotheses. They should be evaluated with a closed material balance, steady state sampling, complete product analysis, measured electrical power, and predeclared acceptance criteria. Vendor reported reductions in acid, caustic, catalyst, soap, monoglycerides, water, and oil loss can be economically important, but they are not substitutes for site specific verification.

The decisive engineering question is not whether cavities or rapid decompression can be generated. It is whether a repeatable hydraulic dose can be delivered without persistent emulsion, oxidation, methanol flashing, unwanted pump cavitation, erosion, plugging, excessive heat, or separator overload. When interfacial contact is the dominant limitation and downstream separation is engineered with equal care, cavitation can provide a practical route to lower reagent use, shorter residence time, increased throughput, and improved recovery.

Nomenclature

Unless stated otherwise, quantities are expressed in SI units. Symbols used only inside a chemical equation are defined in the accompanying text.

Table 11.22. Roman symbols and abbreviations.

Symbol	Definition	SI unit or status
a	Specific interfacial area	m²/m³
A	Flow cross sectional area	m²
AV	Acid value	mg KOH/g
C	Bulk concentration	application dependent
C*	Equilibrium or interfacial concentration	application dependent
CH	Breakup constant	dimensionless
cp	Specific heat capacity	J/(kg K)
CFD	Computational fluid dynamics	abbreviation
d	Droplet diameter	m
d₃₂	Sauter mean diameter	m
dmax	Maximum stable droplet diameter	m
Da	Damköhler number	dimensionless
Dh	Hydraulic diameter	m
Ea	Activation energy	J/mol
Eon	Energy per on specification product	kWh/t
es	Specific electrical energy	J/kg or kWh/t
FAME	Fatty acid methyl esters	abbreviation
fex	Caustic excess factor	dimensionless
g	Gravitational acceleration	m/s²
k	Reaction rate constant	time⁻¹
k0	Arrhenius preexponential factor	time⁻¹
kL	Liquid side mass transfer coefficient	m/s
kLa	Volumetric mass transfer coefficient	s⁻¹
m	Mass	kg
m annual	Annual feed throughput	kg/year or t/year
ṁ	Mass flow rate	kg/s
M	Molar mass	kg/mol
Np	Average number of passes	dimensionless
NPV	Net present value	currency
NPSH	Net positive suction head	m
Oh	Ohnesorge number	dimensionless
p	Static pressure	Pa
pref	Reference pressure	Pa
pv	Saturation vapor pressure	Pa
P hyd	Hydraulic power	W
P el	Electrical input power	W
Q	Volumetric flow rate	m³/s
R	Bubble radius or universal gas constant according to context	m or J/(mol K)
Re	Reynolds number	dimensionless
SPR	Shockwave power reactor	abbreviation
t	Time	s
TAG	Triacylglycerol	abbreviation
u	Mean liquid velocity	m/s
urel	Characteristic relative velocity	m/s
V	Liquid volume or economic value according to context	m³ or currency
V net	Annual net recoverable value	currency/year
We	Weber number	dimensionless
X	Fractional conversion	dimensionless
Y	Yield	dimensionless or percent
z	Elevation	m

Greek Letters

Symbol	Name	Meaning	SI unit
γ	Gamma	Interfacial tension	N/m
Δ	Delta	Finite change such as pressure drop or temperature rise	context dependent
ε	Epsilon	Turbulent energy dissipation rate per unit mass	W/kg
ηₚ	Eta	Pump efficiency	dimensionless
μ	Mu	Dynamic viscosity	Pa s
ν	Nu	Stoichiometric coefficient	dimensionless
φ	Phi	Dispersed phase volume fraction	dimensionless
ρ	Rho	Density	kg/m³
σc	Sigma	Cavitation number	dimensionless
τ	Tau	Residence time	s

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