WO2009075762A1

WO2009075762A1 - Process for producing biodiesel and fatty acid esters

Info

Publication number: WO2009075762A1
Application number: PCT/US2008/013354
Authority: WO
Inventors: Xiangsheng S. Meng; Paraskevas Tsobanakis; Ian C. Purtle
Original assignee: Cargill, Incorporated
Priority date: 2007-12-11
Filing date: 2008-12-04
Publication date: 2009-06-18
Also published as: AR069616A1

Abstract

Fatty acid esters are manufactured in a reaction between a fatty acid source and at least one reagent. The source and the reagent are of limited mutual solubility. The reaction is conducted in a reactor involving at least two tubes. At least one of the tubes spins relatively to the other. The reaction may include spinning at least one of the tubes for a reaction time to generate a product medium, removing product medium from the reactor, and separating the removed product medium into at least one lipophilic phase and at least one hydrophilic phase.

Description

Process for Producing Biodiesel and Fatty Acid Esters

Xiangsheng Meng, Paris Tsobanakis and Ian Purtle

Cross Reference to Related Application

[0001] This application is an international application which claims priority to US provisional application 61/007,069, filed 11 December 2007, entitled PROCESS FOR PRODUCING BIODIESEL AND FATTY ACID ESTERS, which is hereby incorporated by reference in its entirety.

Field of The Invention

[0002] The invention discloses a method for the manufacturing of a fatty acid ester. Specifically, the ester is manufactured in a reaction between a fatty acid source and at least one reagent, which are of limited mutual solubility. More specifically, the reaction is conducted in a reactor involving at least two tubes, wherein at least one of said tubes spins relatively to the other.

Background of The Invention

[0003] Production of fatty acids methyl esters (FAME, also referred to as biodiesel) from renewable resources, such as natural fats and oils, has received considerable attention, mainly because of concern about the future supply of petroleum. Typically, biodiesel is manufactured by trans-esterification of vegetable oil with methanol and is catalyzed by a basic catalyst. Since the oil and methanol are of limited mutual miscibility, the reaction takes place in a two-phases system and is therefore slow. Traditionally, reaching high oil conversion yield requires multiple steps, long residence time in the range of hours, elevated temperatures, large excess of methanol and a strong basic catalyst, such as sodium methoxide. Multiple steps, long residence time and large excess of methanol lead to large reactor volume and thus to high investment cost. The elevated temperature involves energy cost and chemical degradation that reduces yields and adds impurities to be separated in subsequent steps. Sodium methoxide is an expensive catalyst. At the end of the reaction, the reaction mixture contains biodiesel, unreacted methanol and glycerol byproduct. Glycerol has limited solubility in biodiesel so that settling forms two phases, a more lipophilic (and lighter) one containing essentially the biodiesel and a hydrophilic (heavier) one with the glycerol. Phase separation is slow, typically of several hours, requiring large settler volume, which adds to the investment cost. The unreacted methanol is separated, typically by distillation, and recycled to the reaction. The higher the excess, the greater are the separation and recycle costs. [0004] Being hydrophilic in nature, the majority of the base catalyst used in the biodiesel production ends up in the glycerol phase. In order to increase the economic value of the glycerol byproduct, the base catalyst in the hydrophilic phase has to be neutralized and removed. In the conventional biodiesel production, the lighter biodiesel phase is washed by acidic water solution (adding hydrochloric acid)) after separation from the heavier glycerol phase to remove the excess methanol and a small amount of dissolved base catalyst and glycerol. The water washing solution is combined with the glycerol phase and reacted with hydrochloric acid to neutralize the base catalyst there. After neutralization, the methanol in the glycerol phase is recovered by evaporation and recycled back to the biodiesel production. Then, water in the glycerol phase is evaporated, followed by the glycerol distillation to reject the salts formed on catalyst neutralization (e.g. NaCl or KCl) and other impurities. The whole glycerol purification process is a highly-energy intensive, highly corrosive and therefore a costly process. The usage of HCl to neutralize the base catalyst requires all mixing tanks, pipes and distillation columns to be made from high-cost and corrosion-resistant materials such as titanium.

[0005] An objective of the present invention is an improved process for the manufacturing of fatty acid esters for applications such as in biodiesel. More specifically, the objective is manufacturing such esters at reduced cost, e.g. as a result of shorter reaction time, operating at lower temperatures, consumption of less and/or cheaper catalyst, possibly via catalyst recovery and producing high quality coproducts.

Summary of The Invention

[0006] According to the method of the present invention, fatty acid esters are manufactured in a reaction between a fatty acid source and at least one reagent, the method being characterized in that the source and the reagent are of limited mutual solubility and in that said reacting is conducted in a reactor involving at least two tubes, wherein at least one of said tubes spins relatively to the other.

[0007] More specifically, the method involves the steps of (a) forming in the reactor a reaction medium comprising the fatty acid source and a reagent; (b) spinning at least one of the tubes for a reaction time to generate a product medium; (c) removing product medium from the reactor, and (d) separating the removed product medium into at least one lipophilic phase and at least one hydrophilic phase. [0008] According to an embodiment of the invention, the fatty acid source is selected from a group consisting of triglycerides, diglycerides, monoglycerides, free fatty acids, fatty acid salts and phospholipids, preferably triglyceride. According to an embodiment of the invention, the reagent is selected from a group consisting of alcohols with single or multiple hydroxyl functions and their esters, hydroxycarboxylic acids and their esters, hydroxyamines and their esters and mixtures thereof. According to another embodiment, the reagent is water soluble, preferably methanol, ethanol and their mixtures.

[0009] According to an embodiment of the invention, the reaction medium comprises a catalyst. Suitable catalysts include basic compounds, but not limited to, alkaline metal hydroxides and carbonates such as sodium hydroxide and carbonate, potassium hydroxide and carbonate, alkaline metal alcoholates such as sodium methoxide and ethoxide, potassium methoxide and ethoxide, alkaline earth metal hydroxides and oxides, such as magnesium, calcium, strontium and barium hydroxides, magnesium, calcium, strontium and barium oxides, barium alcoholates such as barium methoxide and ethoxide, ammonia, ammonium hydroxide, alkylammonium hydroxide, amines, zeolites, and their combinations.

[0010] According to an embodiment of the invention the reaction time is less than 10 seconds. The preferred reaction temperature is in the range between about 2O⁰C and about 6O⁰C. According to another embodiment of the invention the concentration of the catalyst in the reaction medium is in a range between about 0.1 and about 10 percent.

[0011] According to an embodiment of the invention the molar ratio between the source and the reagent is in the range between about 1 and about 10. According to another embodiment of the invention separating the product medium into two phases is essentially completed within about 60 minutes.

[0012] According to an embodiment of the invention the catalyst used is volatile, and the method also includes the steps of separating unreacted reagent by distillation, separating catalyst by distillation, and recycling both to the reactor. According to another embodiment of the invention catalyst recycle uses reaction with carbon dioxide to form a carbonate, a bicarbonate or their combination.

[0013] According to an embodiment of the invention the catalyst used is solid, separating catalyst by filtration and/or centrifugation, and recycling to the reactor. [0014] According to an embodiment of the invention the catalyst used is basic compound, removing and separating catalyst uses reaction with carbon dioxide to form a carbonate, a bicarbonate or their combination.

[0015] According to an embodiment of the invention the catalyst used is basic compound, removing and separating catalyst uses reaction with sulfuric acid to form a sulfate.

[0016] According to an embodiment of the invention the reaction product is a methyl or an ethyl ester of fatty acid and meeting ASTM specification for biodiesel.

Detailed Description of The Invention

[0017] The present invention discloses a method for manufacturing of fatty acid esters, e.g. methyl esters, ethyl esters or their combinations. Also suitable are esters of fatty acids with polyols, such as glycerol, ethylene glycol and propylene glycol. Also suitable are esters of fatty acids with hydroxy-carboxylic acids. The method involves reacting a fatty acid source with at least one suitable reagent. Particularly desired are products that meet the ASTM specifications for biodiesel. One of ASTM the specifications is total glycerol in biodiesel less than 0.25%.

[0018] A characteristic of the method of the present invention is that the fatty acid source and the reagent are of limited mutual solubility. This means that, on mixing the fatty acid source with the reagent in the weight/weight (or molar) ratios and at the temperature selected for the reaction, at least two phases are observed. Typically, at least two of the observed phases are liquid at the reaction temperature, but a solid phase and/or a vapor phase are also optional.

[0019] Another characteristic of the method of the present invention is that the reaction is conducted in a reactor involving at least two tubes, wherein at least one of said tubes spins or rotates relatively to the other. A specific example of such reactor is the Spinning Tube in Tube (STT™) reactor as disclosed in US Patents 5,279,463, 5,538,191, 6,471,392, 6,723,999, 6,742,774, 6,752,529 and 6,994,330 and Patent Applications 20040013587, 20040052158 and 20050033069 incorporated here by reference and as manufactured by Kreido Laboratories. [0020] According to a preferred embodiment of the invention, the method involves the following steps: (a) forming in the reactor a reaction medium comprising the fatty acid source, the reagent and optionally also a catalyst; (b) spinning at least one of the tubes for a reaction time to generate a product medium; (c) removing product medium from the reactor, and (d) separating a product from the removed product medium.

[0021] In the present invention, free fatty acids, their salts, various mixtures of those, their esters and their amides, those include acids with additional functional groups, e.g. dicarboxylic acids and carboxylic acids carrying hydroxyl, carboxyl and/or amino functions are suitable fatty acid sources. Examples for suitable sources include triglycerides, diglycerides, monoglycerides, free fatty acids, fatty acid salts and phospholipids. In some cases, the preferred fatty acid sources are triglyceride, such as oils and fats. Suitable oils include, but not limit to, soybean oil, rapeseed oil, corn oil, sunflower oil, linseed oil, cottonseed oil, peanut oil, palm oil, palm kernel oil, oak oil, almond oil, apricot oil, walnut oil, babassu oil, perilla oil, oiticica oil, castor oil, olive oil, safflower oil, canola oil, groundnut oil, sesame oil, coconut oil, and etc. Suitable fats include animal fat, beef tallow, chicken oil, sheep oil, lard, suet, goose fat, fish oil, milk fat, butterfat, and etc.

[0022] According to a preferred embodiment, oil or fat is provided and is hydrolyzed prior to the reaction with the reagent. Hydrolysis forms glycerol and free fatty acids, which are separated by known methods, such as decantation, centrifugation or extraction (free fatty acids and glycerol are of very small mutual solubility). The hydrolysis, also referred to as oil/fat splitting, can be catalyzed chemically (e.g. using acid as a catalyst) or biologically (e.g. using a lipase). Alternatively, the hydrolysis is conducted at somewhat higher temperatures with no need for catalyst usage. The formed free acids are used as sources in the reaction of the present invention. The embodiment of using no catalyst and that of using a biological catalyst have an advantages over those of using a chemical catalyst and that of manufacturing the fatty acid esters by direct reaction between oil/fat and a reagent. The main advantage is forming a much more pure glycerol coproduct, saving on its purification cost.

[0023] According to a particularly preferred embodiment, hydrolysis of fat/oil to generate free fatty acid and glycerol of high purity is conducted in a spinning-tube reactor, e.g. similar to the one used for the reaction between the fatty acid source and the reagent. [0024] Suitable reagents include organic molecules carrying at least one hydroxyl function and products of such molecules, such as esters. Examples of suitable reagents include monohydric alcohols, such as methanol, ethanol, propanol, iso-propanol, butanol, sec-butanol and tert-butanol. Other suitable alcohols are polyhydric ones, such as ethylene glycol, propylene glycol, glycerol, erythritol, inositols and sugar alcohols. Esters of such monohydric and polyhydric alcohols are also suitable. Also suitable are hydroxycarboxylic acids, such as glycolic, lactic and 3-hydroxy propionic acid and their esters. Other suitable reagents include hydroxyamines, hydroxy amino acids and their derivatives. Mixtures of such reagents are also suitable. In many of the processes the reagent is water soluble, preferably methanol, ethanol and their mixtures. Water-soluble reagents can reach in water at 25C concentrations of at least 15% by weight.

[0025] According to an embodiment of the invention, the reaction medium comprises a catalyst. Suitable catalysts include basic compounds, but not limited to, alkaline metal hydroxides and carbonates such as sodium hydroxide and carbonate, potassium hydroxide and carbonate, alkaline metal alcoholates such as sodium methoxide and ethoxide, potassium methoxide and ethoxide, alkaline earth metal hydroxides and oxides, such as magnesium, calcium, strontium and barium hydroxides, magnesium, calcium, strontium and barium oxides, barium carbonate, barium alcoholates such as barium methoxide and ethoxide, ammonia, ammonium hydroxide, alkylammonium hydroxide, amines, compounds carrying amine, amide and/or pyrrolidone functions, zeolites, and their combinations. Suitable catalysts are either hydrophilic (water and alcohol soluble, such as alkaline metal hydroxides) or lipophilic (e.g. organic amines). The catalyst could be introduced in any form, e.g. in liquid or solid form. Suitable solid catalysts also include basic metal oxides and resins. An important advantage of the method of the present invention is that the reaction can be conducted at relatively low temperatures, where practically any basic resin is stable. Obviously, resins of high thermal stability, such as Reillex, are also suitable. The inventors have surprisingly found that catalysts which are not working well in conventional method (producing many undesirable byproducts) are suitable in the method of the present invention, e.g. metal hydroxides. Such catalysts are of considerably lower cost than those used in conventional methods, e.g. metal methoxides. The method of the present invention enables further reduction of catalyst-related cost by minimizing or avoiding the need of neutralization and by enabling catalysts recycle, as explained in the following.

[0026] Any concentration of catalyst that facilitates the reaction is suitable. The inventors have surprisingly found that, in the process of the present invention, high reaction rates are obtained at relatively low concentrations of catalyst. The preferred catalyst concentration depends on the fatty acid source, on the reagent, on the selected catalyst and on the reaction medium, e.g. solvent if used, and reaction conditions, e.g. temperature. Typical suitable catalyst concentrations in the reaction medium for reacting oils and methanol are in a range between about 0.1 and about 1 percent for alkaline metal hydroxides.

[0027] A particularly advantage is process embodiments wherein fatty acid esters such as biodiesel can be formed in so short reaction time such as 1 second or less from the fatty acid source such as soybean oil, the reagent such as methanol or ethanol and a metal hydroxide catalyst in the spinning tube reactor.

[0028] Particularly advantageous are process embodiments wherein the catalyst does not exist in the product medium exiting the reactor or is easily separated from that product medium. One objective is saving on catalyst cost by recycling catalyst to the reaction medium, optionally after some purification or bleeding to avoid impurities build up. Another objective is minimizing contamination with the catalyst. Such contamination could be of the product ester, the coproduct, e.g. glycerol, or both. In many of the process embodiments the catalyst is hydrophilic in nature and accumulates in the hydrophilic phase formed on separation of the product medium. Thus, e.g. in case of forming fatty acid esters in reaction between oils/fats and methanol or ethanol, wherein the catalyst is a hydroxide or methoxide of an alkaline metal or alkaline earth metal, the hydrophilic phase is a glycerol-containing medium and the catalyst concentrates in that medium. Typically, the basic catalyst is neutralized at the end of the reaction, e.g. with an acid to form a salt. Since the glycerol molecular weight is small compared with that of the oil, the weight ratio between the catalyst (or its neutralization product) and the glycerol is relatively high so that the glycerol is contaminated with relatively large concentration of catalyst. That is particularly problematic when the coproduct is intended for use, e.g. glycerol as such or as a starting material for other compounds, such as glycols, acrylic acid, glyceric acid, etc. Several embodiments of the method of the present invention minimize or avoid these difficulties, saving on catalyst cost, catalyst neutralization cost and product/coproduct purification.

[0029] According to a preferred embodiment, the catalyst is bound to at least one surface of the reactor that comes in contact with the fatty acid source, the reagent or both and is kept thereby in the reactor. Binding could use, e.g. glue or a layer of polymeric binder. At the end of the reaction, the product medium is removed from the reactor, while the catalyst stays there for the next reaction. [0030] According to another preferred embodiment, the catalyst is insoluble in the product medium and is separated from the product medium at the end of the reaction, e.g. by means of filtration or centrifugation. Alternatively, an insoluble catalyst is kept in the reactor, e.g. by means of a filter during the removal of the product medium at the end of the reaction. An insoluble catalyst according to the present invention is a catalyst with less than 5% weight in glycerol at 25C.

[0031] According to still another embodiment, the catalyst is of high molecular weight, e.g. a polyamine and is separated by means of membrane separation, e.g. ultrafiltration, from the product medium, from the lipophilic phase, and/or from the hydrophilic phase. Typically, said high molecular weight catalyst has a molecular weight of at least about 3,000 Dal tons.

[0032] According to a preferred medium, the catalyst is volatile, e.g. having, at a given temperature, partial vapor pressures lower than those of the manufactured esters and/or lower than those of coproduct glycerol. Examples for such volatile catalysts are ammonia and low molecular-weighty amines. According to an embodiment of the method of the present invention, a volatile catalyst is used and the method comprises a step of distilling catalyst from the product medium at the end of the reaction.

[0033] According to an embodiment of the method, the reagent used in the reaction is volatile and is used in excess. The unreacted reagent is separated from the product medium, e.g. by distillation. In a preferred embodiment of the present invention, both the catalyst and the reagent are volatile and both are separated from the product medium by distillation, either simultaneously or sequentially. In a preferred embodiment, both the volatile catalyst and the volatile excess reagent are recycled to the reaction medium, preferably together.

[0034] In another preferred embodiment, the catalyst is absorbed on an absorbent and is recovered from the absorbent and recycled to the reaction of the present invention. Alternatively, the absorbed catalyst is recycled with the absorbent to the reaction of the present invention.

[0035] In another preferred embodiment, the catalyst is neutralized at the end of the reaction with CO2, rather than with a strong mineral acid, such as hydrochloric acid. A carbonate salt, a bicarbonate salt or a mixture of those is formed. In a preferred embodiment, at least part of the formed salt precipitates out of the product medium or out of the hydrophilic phase formed on separating the product medium and is separated as such. In many cases, separation of catalyst in that way improves with increasing the concentration of the C02-treated medium. Separation of the salt forms a purer product, coproduct or both. This embodiment also saves on the cost of the neutralizing mineral acid. The separated carbonates and/or bicarbonate have commercial value for various applications. In a preferred embodiment, it is reused as a catalyst in the reaction as such or after some modification. Various modifications could be suitable. According to a preferred embodiment a bicarbonate salt is heated and converted to a carbonate of higher basicity (and CO2 that could be reused for catalyst neutralization). According to another preferred embodiment, the carbonate formed on CO2 treatment is of an alkaline metal and is reacted after separation with an oxide or hydroxide of an alkaline earth metal. A carbonate of an alkaline earth metal and a hydroxide of the alkaline metal are formed. According to a preferred embodiment, the hydroxide is used as a catalyst as such or after modification, e.g. conversion to methoxide. The carbonate, according to another preferred embodiment, is heat treated and converted into CO2 and hydroxide of the alkaline earth metal for reuse.

[0036] In another preferred embodiment, the catalyst is neutralized at the end of the reaction with sulfuric acid, rather than with hydrochloric acid. An insoluble sulfate salt is formed and is separated from the product medium e.g. by means of filtration or centrifugation.

[0037] In any of the above-listed alternative embodiments, costs related to catalyst neutralization and purchase are minimized or substantially avoided. Some of those embodiments are characterized in that the hydrophilic phase formed after phase separating the reaction phase is essentially free of catalyst or have a less catalyst. Other embodiments are characterized in that such essentially catalyst free hydrophilic phase is formed by a method other than glycerol distillation. The use of high cost material of construction, typical to the conventional process, is avoided since hydrochloric acid is not used for neutralization and since distillation from chloride solution is not required.

[0038] In the above-listed embodiment of the neutralization of the catalyst with CO2, rather than hydrochloric acid, the hydrophilic phase can be purified by distillation in the presence of the formed carbonate, bicarbonate or a mixture of carbonate and bicarbonate. The use of high cost material of construction, typical to the conventional process, is avoided since hydrochloric acid is not used for neutralization and since distillation from chloride solution is not required. [0039] The inventors have surprisingly found that the rate of reaction conducted according to the embodiments of the present invention is much higher than the reaction conducted in presently known methods. Thus, while a typical time of reaction conducted by conventional methods is about hours, it typically approaches completion in the method of the present invention in less than 10 seconds, more preferably less than 5 seconds, most preferably less than 1 second.

[0040] The inventors have also found that, according to the present invention, high conversion yields are reached at relatively low temperatures. The preferred reaction temperature is in the range between about 2O⁰C and about 6O⁰C. Thus, while a typical temperature of reaction conducted by conventional methods is 6O⁰C and above, it typically approaches completion in the method of the present invention at temperatures lower than 6O⁰C, more preferably lower than 4O⁰C, most preferably at room temperature or below than 25⁰C. Conducting the reaction at reduced temperature has an important advantage in saving on energy cost. In particular cases, an even more important advantage is minimizing the amount of degradation products formed during the reaction. This leads to higher yields and lower purification costs.

[0041] A known method, in case of reactions reaching equilibrium, is to use one of the reactants in excess to achieve high yields of converting the other reactant. The formed product medium is then processed to remove the excess reactant for recycling to reaction and for product purification. Thus, on production of biodiesel in a reaction between triglycerides and methanol, excess methanol is used. In known methods for biodiesel production about 6 to 24 moles of methanol are used per mole of triglyceride (excess of about 100 to 700 percents). The inventors have surprisingly found that, in the method of the present invention much lower excess is required, which saves on the cost of further treatment, e.g. by methanol distillation from the product medium. Thus, in the process of the present invention, typically 6 moles or less of reagent are used per mole of fatty acid in the source.

[0042] Thus, the method of the present invention has the following advantages, among others. It saves on catalyst consumption, uses catalysts of lower cost and saves on costs related to catalyst neutralization and separation. It is conducted at temperatures lower than in alternative methods, saving on energy cost and minimizing reagents degradation, which also saves on purification costs. It doesn't require high excess of the reagents, saving thereby on costs related to product purification and reagent recycle. Reaction duration is much shorter than in conventional processes. Yet, all those improvements are achieved without compromising on conversion yields. A typical conversion yield in the process of the present invention is at least about 95%, more preferably at least about 97%, most preferably at least 99%.

[0043] Another surprising advantage of the method of the present invention is related to phase separation of the product medium. As indicated, a characteristic of the invention is that the fatty acid source and the reagent are of limited mutual solubility. Typically, the reaction product, the fatty acid ester, and coproduct are also of limited miscibility. For example, in cases where the fatty acid source is a triglyceride and the reagent is methanol, the product is a fatty acid methyl ester and the coproduct is glycerol. The former is of low hydrophilicity, while the latter is highly hydrophilic. Typically, the reagent is used in excess so that part of it is left in the product medium at the end of the reaction. In many cases, the reagent is also hydrophilic and of low miscibility with the reaction product. At the end of the reaction, the product medium is typically separated into two phases, both of them are liquid in most cases. In a typical commercial process, phase separation is relatively slow, requiring long residence time and therefore large and expensive settling vessels. In others, centrifugation could be used at added cost, particularly since explosion proof equipment is typically required. The inventors have surprisingly found that, in conducting the reaction according to the method of the present invention, phase separation is rapid. Thus, compared with typical phase separation time of about hours, the phases in the method of the present invention are typically separated in less than about 30 minutes, more preferably in less than about 20 minutes, most preferably less than about 10 minutes.

[0044] The present invention provides a methyl or an ethyl ester of fatty acid meeting ASTM specification for biodiesel.

[0045] The invention will be more readily understood by reference to the following examples. There are, of course, many other forms of this invention which will become obvious to one skilled in the art, once the invention has been fully disclosed, and it will accordingly be recognized that these examples are given for the purpose of illustration only, and are not to be construed as limiting the scope of this invention in any way.

Examples

[0046] Sample Analysis, Lipid Profile by GC/FID. Lipid Profile analysis was used to determine the compound classes of the sample. The sample size was approximately 65 mg. The samples were dried down to obtain the sample residues. Moisture and volatiles were removed from the samples by centrifugation under vacuum. An internal standard (IS) of heptadecanyl stearate (HDS) was used at 10 mg. Samples were silylated with N,O,-bis-(trimethylsilyl) trifluoroacetomaide (BSTFA) with 1% trimethylchlorosilane and pyridine. Aliquots (20 μL) were diluted with 980 μL of toluene. The trimethylsilane (TMS) ethers were analyzed by cool on-column (COC) gas chromatography (GC) with a non-polar column stationary phase (DB-5HT, 15m x 0.25mm x 0.10 μm) coupled to a flame ionization detector (FID). The temperature program was 110⁰C (0.2 min) to 14O⁰C at 30°C/min to 340⁰C at 10°C/min (10 min). Hydrogen was the carrier gas, and inlet pressure was 6.7 psi at 1 10⁰C in the constant flow mode. The detector temperature was 370⁰C. Samples were analyzed a single time.

General Procedure for Biodiesel Reaction in the STT ^M Reactor

[0047] The base catalyst (NaOH, KOH, NaOMe or amines) was premixed with the methanol (or ethanol) before pumping into the STT™ reactor. The soybean oil was preheated to the same temperature as one set for the STT™ reactor before pumping into the STT™ reactor. The soybean oil and the catalyst containing methanol (or ethanol) streams were pumped into the reactor using syringe pumps. About 100-500 ml samples were collected for each experiment. The most samples collected from the reactor were settled for about 2 hours to have a clear phase separation. Then, the top biodiesel phase was taken for water washing (about a 2:1 phase ratio of biodiesel to water) to remove the contained methanol, catalyst and glycerol, and also to stop further transesterification reaction. The washed biodiesel was then centrifuged for 10 minute at 4000 rpm. The clean biodiesel after centrifuge was taken for further analysis by GC.

Examples 1 to 9

[0048] These experiments were conducted in a batch top STT™ reactor (Magellan™) using soybean oil and methanol with NaOH or amine as a catalyst. The Magellan STT™ reactor has a reaction volume of 1.5 ml with a capability of rotating 12,000 rpm. A gap between the stator and the rotor is about 0.3 millimeter or 300 microns. A 2-times excess or a 6/1 molar ratio of methanol to oil (or 1 to 4 volume ratio of methanol to oil) was used for the test with 0.1% to 1.0% NaOH (based on mass of oil) catalyst. When butylamine and diethylamine were used as catalyst, 10% catalyst based on the mass of soybean oil and 6- times excess methanol were applied. The reaction temperature varied from 25⁰C to 6O⁰C. The reaction time varied from 2 seconds to 10 seconds. Two feed streams of soybean oil and methanol with dissolved catalyst were pump into the reactor at one end of the STT™ reactor by two syringe pumps. The reaction product was collected in another end of the reactor. Two phases (biodiesel and glycerol) in the product stream were separated in about 10 minutes after exiting the reactor. Both phases have the light yellow colors (same as the color). The top phase was taken for analysis of biodiesel composition. The glycerol phase was not analyzed. The biodiesel samples collected in this set of experiments were not treated by water wash. The samples were analyzed by GC several days later. Therefore, a conversion to biodiesel from triglyceride may be little higher than the real conversion when the samples were treated by water wash to stop the further reaction. The Table 1 shows the reaction conditions and results of the biodiesel production from soybean oil and methanol with the base catalysts using the STT™ reactor.

[0049] With 0.5-1.0% NaOH catalysts, a 6/1 molar ratio of methanol to oil (or 1/4 volume ratio), 2-10 seconds reaction time and 25-6O⁰C reaction temperatures, soybean oil was quantitatively converted to fatty acid methyl esters (FAME) or biodiesel. The TAG and DAG contents in the biodiesel were not detectable, the MAG content was low varying from 0.28% to 0.37%, and glycerol concentration in biodiesel was low varying from 0.4% to 0.53%. These parameters indicate that biodiesel produced by STT™ reactor meets ASTM specification if free glycerol in biodiesel is removed by water wash. Light amines (butylamine and diethylamine) were also used as the catalysts in the production of biodiesel in the STT™ reactor although the yields were lower than that of using NaOH as a catalyst. However, the yield is much higher than that when a conventional reactor was used. The reported yield of biodiesel was very low (<5%) when amine, such as triethylamine, was used as catalyst. The benefit for using light amine as a catalyst is that the amine catalyst can be recycled together with methanol.

Table 1. Reaction conditions and results of biodiesel production using STT™ reactor

ID Sample 1 Sample 2 Sample 3 Sample 4 Sample 15 Sample 6 Sample 7 Sample S: S Sampl

Temp. 60⁰C 25⁰C 5O⁰C 25⁰C 6O⁰C 25⁰C 6O⁰C 6O⁰C 6O⁰C

Rex time 10 sec 10 sec 10 sec 10 sec 10 sec 10 sec 2 sec 10 sec 5 sec

10% 10% 10% 1.0% 1.0% 0.1 % 1.0% 0.5% 0.5%

Catalyst BuNH₂ BuNH₂ Et₂NH NaOH NaOH NaOH NaOH NaOH NaOH

MeOH/Oil 18/1 18/1 6/1 6/1 6/1 6/1 6/1 6/1 6/1

TAG, % ND ND 0.86 ND ND 7.78 ND ND ND

DAG, % ND ND 4.54 ND ND 4.46 ND ND ND

MAG, % 0.83 0.86 1 1 .32 0.28 0.33 1.41 0.34 0.37 0.37

FFA, % 0.04 0.07 0.04 0.05 0.05 0.02 0.03 0.05 0.04

GIy. % 1 1 .62 10.85 6.20 0.53 0.52 0.69 0.46 0.40 0.44

FAME, % 58.38 60.62 64.13 100.00 100.00 79.75 100.00 100.00 l OO.OC

ND — Not detectable Examples 10 to 20

[0050] These experiments were also conducted in the Magellan STT™ reactor. All the experiments have a reaction time (or residence time) of 0.5 second, 1/6 molar ratio of oil to methanol, 1% NaOH or KOH as catalyst and 25C reaction temperature. The results of the experiments are shown in Table 2. The results demonstrate that soybean oil can be converted to biodiesel which meets ASTM specification after water wash to remove glycerol in biodiesel. KOH as a catalyst works better than NaOH as a catalyst. The results also show that if the biodiesel phase produced from the STT™ reactor was not washed by water, the transesterification can still take place slowly since there is dissolved catalyst and methanol in the biodiesel phase. This can be seen from the Examples 15 and 16. After water wash treatment, there were 0.638, 0.33 and 0.421 % TAG, DAG and MAG left in biodiesel. If the sample was allowed to settle for several days without water wash, the amount of TAG and DAG were reduced to the level that was not detectable. For the experiment of Example 1 1 , 50% NaOH solution was used to make 1 % NaOH catalyst instead of using dried NaOH. It seems that the conversion to biodiesel is slightly lower when 50% NaOH was used to make the catalyst. However, the dissolved glycerol in biodiesel is also lower. It is interested to point out that the lower rotation of the STT™ reactor gave a slightly better conversion for biodiesel than the higher rotation or the rotation of STT™ reactor varying from 6000 rpm to 12000 rpm has a little effect on the biodiesel conversion (the centrifuged Example 10 vs. Example 17 and the water washed Example 12 vs. Example 15 and Example 18).

Table 2. Reaction conditions and results of biodiesel production in the STT .TM reactor

*50% NaOH solution was used to make 1 % NaOH catalyst instead of using dried NaOH. ** 1% KOH was used as catalyst.

Examples 21 to 42

[0051] These experiments were conducted in the same batch top STT™ reactor (Magellan™). A 1/6 molar ratio of oil to methanol (or ethanol) was also used for all the experiments. NaOMe, NaOH, or TMAH (tetramethyl ammonium hydroxide) were used as a catalyst. The gap between the rotor and the stator of the STT™ reactor varies from 0.0125 inch (or 0.3 mm) to 0.0240 inch. If not mentioned, a gap in the STT™ reactor was 0.0125 inch for all the experiments. The results of these experiments were shown in Table 3. All samples analyzed in Table 3 were water washed then centrifuged. The water washed was done after the samples were collected and settled for about 2 hours. It can be found that the biodiesel produced in the STT™ reactor meets ASTM specification if 1% NaOH is used as a catalyst at either 6O⁰C for 0.5 sec residence time or 25⁰C for 1.0 sec residence time (Examples 23, 24, and 27). It was also confirmed that the rotation varying form 9000 rpm to 12000 rpm of the STT™ reactor has no effect or a little effect on the biodiesel production. The gap varies from 0.0125 inch to 0.0240 inch between the rotor and the stator of the STT™ reactor has no effect on biodiesel production (Examples 23, 38, 40 and 42). This means that the biodiesel production using the STT ^M reactor having a gap of 0.024 inch can produce more than 2 times biodiesel than the reactor having 0.0125 inch if the rest of the reaction conditions remain the same. When ethanol is used to make fatty acid ethyl ester (FAEE) biodiesel, with a molar ratio 1 to 6 for oil to ethanol, the ethyl ester biodiesel produced by the STT™ reactor also meets the ASTM specification if 1 % NaOH is used as a catalyst at either 6O⁰C for 0.5 sec residence time or 25⁰C for 1.0 sec residence time (Examples 26 and 41).

[0052] It should be pointed out that when 0.5% catalyst was used neither NaOCH₃ at 6O⁰C and 0.5 sec residence time nor NaOH at 6O⁰C and 1.0 sec residence time would not produce biodiesel which meets ASTM specification (Experiments 21 , 22, 33 and 34). It is also true for ethyl ester biodiesel if 0.5% NaOH is used as a catalyst even at 6O⁰C and 1.0 sec residence time (Examples 35 and 36). It is interested to note that a large gap (0.015-0.024 inch) between the rotor and the stator of the STT™ reactor gave the better results (Examples 37, 39 and 41) than those of using a small gap (0.0125 inch, Example 21). This may indicate that too small droplets produced by the STT™ reactor having a small gap may not be necessary, although a good mixing of two immicisible phases of oil and methanol is essential for the biodiesel production.

Table 3. Reaction conditions and results of biodiesel production in the STT ■TM

'Calculation from ASTM D6584-00

"Sample was washed Ih 50 πiin later than sample 26

Claims

ClaimsWe Claim:

1. A method for the manufacturing of a fatty acid ester, comprising reacting a fatty acid source and at least one reagent, characterized in that said source and said reagents are of limited mutual solubility and in that said reacting is conducted in a reactor involving at least two tubes, wherein at least one of said tubes spins relatively to the other.

2. The method of claim 1 , comprising the steps of

(a) forming in said reactor a reaction medium comprising said source and said reagent

(b) spinning at least one of said tubes for a reaction time to generate a product medium

(c) removing product medium from said reactor, and

(d) separating said removed product medium into at least one lipophilic phase and at least one hydrophilic phase.

3. The method of claim 2, wherein spinning is in a rate between about 50 rpm and about 12,000 rpm.

4. The method of claim 2, wherein the gap between said two tubes is in the range between about 0.2 mm and about 2.0 mm.

5. The method of claim 2, wherein said source is selected from a group consisting of triglycerides, diglycerides, monoglycerides, free fatty acids, fatty acid salts and phospholipids.

6. The method of claim 2, wherein said source is a triglyceride.

7. The method of claim 2, wherein said forming a reaction medium comprises the steps of

(a) hydrolyzing a triglyceride to form a hydrolyzate medium comprising fatty acids and glycerol

(b) separating fatty acids from glycerol in said hydrolyzate medium, and

(c) combing separated fatty acids with reagent.

8. The method of claim 2, wherein said reagent is selected from a group consisting of alcohols with single or multiple hydroxyl functions and their esters, hydroxycarboxylic acids and their esters, hydroxyamines and their esters and mixtures thereof.

9. The method of claim 2, wherein said reagent is selected from methanol, ethanol and mixtures thereof.

10. The method of claim 2, wherein said reaction medium comprises a catalyst.

11. The method of claim 10, wherein said catalyst is selected from a group consisting of basic compounds, alkaline metal hydroxides and carbonates, alkaline metal alcoholates, alkaline earth metal hydroxides, oxides and carbonates, barium alcoholates such as barium methoxide and ethoxide, ammonia, ammonium hydroxide, alkylammonium hydroxide, amines, compounds carrying amine, amide and/or pyrrolidone functions, zeolites, and combinations thereof.

12. The method of claim 10, wherein said catalyst is selected from a group of bases more volatile than glycerol, bases of low solubility in glycerol and bases of molecular weight greater than about 3,000 Daltons.

13. The method of claim 14, further comprising a step of catalyst separation from at least one of product medium and separated phases by at least one of distillation, filtration, centrifugation and membrane filtration.

14. The method of claim 15, further comprising a step of recycling separated catalyst to said reaction medium

15. The method of claim 10, wherein said catalyst is bound to an internal surface of said reactor.

16. The method of claim 2, wherein said reaction time is less than about 60 seconds.

17. The method of claim 2, wherein said reactor is maintained at a temperature in the range between about O⁰C and about 100⁰C.

18. The method of claim 10, wherein the weight ratio of said catalyst to said source is in a range between about 1 to 1000 and about 1 to 10.

19. The method of claim 2, wherein the molar ratio of said source to said reagent is in the range between about 1 to 1 and about 1 to 10.

20. The method of claim 2, wherein said separating into at least two phases is essentially completed within about 60 minutes.

21. The method of claim 10, wherein said catalyst is volatile, further comprising the steps of separating unreacted reagent by distillation, separating catalyst by distillation, and recycling both to the reactor.

22. The method of claim 10, further comprising a step of reacting catalyst or product of its modification with carbon dioxide to foπn at least one of carbonate and bicarbonate.

23. The method of claim 10, wherein said at least one of carbonate and bicarbonate is used for catalyst regeneration.

24. The method of claim 10, wherein said catalyst is basic compound, further comprising a step of reacting catalyst or product of its modification with sulfuric acid to form insoluble sulfate.

25. At least one of fatty acid methyl esters, fatty acid ethyl esters and mixtures thereof manufactured by the method of Claim 1 , characterized in meeting ASTM specification for biodiesel.

26. The method of claim 10, wherein said source is selected from a group consisting of triglycerides, diglycerides, monoglycerides, phospholipids and mixtures thereof and wherein a glycerol-comprising coproduct is formed.

27. The method of claim 1, wherein the reaction yield is at least 95%.

28. The method of claim 2, wherein said separating is essentially completed in less than 60 minutes.

29. The method of claim 1 , wherein said reacting is conducted in a continuous mode.