JP2006508148A - Alkyl ester production method - Google Patents

Abstract

A method is provided for producing alkyl esters from a mixture of glycerides and free fatty acids derived primarily from degreased waste. The mixture is first solvated in low boiling alcohol and then the pH of the solution is adjusted to about 1-2 by addition of acid, resulting in acid catalyzed alkyl esterification. The acidic solution is then treated with a concentrated alkoxide solution, raising the pH of the solution to pH 12, resulting in base-catalyzed transesterification of the glycerides contained in the mixture. The resulting solution is then treated with acid, reducing the pH of the solution to about 2, resulting in acid-catalyzed esterification of the remaining saponification byproduct. The alcohol solvent is removed by distillation or other suitable technique, and the resulting alkyl ester is separated from any remaining residue and the remaining acid is neutralized.

Description

(Field of Invention)
The present invention relates to mixtures of glycerides and free fatty acids, in particular mixtures of glycerides and free fatty acids from grease stop (grease trap) waste, tallow, animal fats, vegetable lipids and other high fatty acid-containing lipids. Relates to a process for producing alkyl esters from In addition to these lipids, it has been found to be extremely effective in the efficient production of alkyl esters from lower fatty acids, higher glyceride containing lipids.

(Background of the invention)
Alkyl esters of fatty acids found in natural lipids, commonly known as biodiesel, are increasingly recognized as promising fuel alternatives for diesel engines. They are known to reduce particulate, hydrocarbon pollutant emissions and improve the lubricity of diesel engines. Biodiesel can also be successfully used as a lubricant, hydraulic fluid, and as a multipurpose solvent.

  In addition, biodiesel is attractive from a commercial and environmental standpoint because the raw materials applicable to the present invention are renewable oilseed feedstock, used vegetable oil, palm oil, coconut (coconut palm). ) Oil, soda oil as a fat-rich by-product of vegetable essential oil, soapstock material, tallow, animal oil or from greased waste, these are usually landfilled and others Discarded at a waste disposal facility.

  The widespread adoption of biodiesel as an alternative to petroleum-based diesel fuel is hampered by inefficient methods for biodiesel production. Known methods for the production of biodiesel include incomplete esterification of all fatty acids in the starting material, long-term purification methods such as water washing, relatively long reaction times, glycerol co-production and Limited by associated contamination and separation difficulties and saponification of starting materials under certain reaction conditions.

  The Boocock method for forming methyl esters from vegetable oils is based on the formation of a single-phase reaction mixture using a co-solvent such as tetrahydrofuran (THF) or methyl tetrabutyl ether (MTBE). Efforts were made to accelerate the reaction time for the catalyzed methyl alcoholysis of the seed process acid and then base. Boocock reports that 99% recovery of the methyl ester is achieved using this method. Glycerol is a by-product, and the resulting alkyl ester usually requires extensive purification, including washing the alkyl ester with water.

  Methods such as Haas for synthesizing fatty acid methyl esters from soap feeds include another two-step process in which the soap feed is first saponified and then Esterify in acidic alcohol solution. Haas et al. Report that 60% recovery of fatty acid methyl esters is achieved using this method. However, this method is characterized by a large consumption of reagents.

  The present invention attempts to overcome, at least in part, some of the above-mentioned drawbacks and provide new advantages including low or no glycerol production, and this method comprises low capital equipment costs and Follow plant mobility.

(Summary of Invention)
According to a first aspect of the invention, there is provided a method for producing an alkyl ester from a mixture of glycerides and free fatty acids, which comprises:
a) adding an acid to the alcoholic solution of the mixture and reducing the pH of the solution from about 1 to 2 to effect acid catalyzed alkyl esterification;
b) treating the solution from step a) with a concentrated alkoxide solution and raising the pH of the solution to about 12, resulting in base-catalyzed transesterification of the glycerides contained in the mixture;
c) treating the solution from step b) with an acid and reducing the pH of the solution to about 2, resulting in acid-catalyzed esterification of the residual saponification by-product from step b);
d) removing alcohol from the solution from step c); and
e) separating the resulting alkyl ester.

(Description of the invention)
The present invention is generally found in grease-free waste, tallow, animal fat, palm oil, coconut oil, and other naturally occurring lipids found in waste or fresh unused vegetable oil and tallow. A process for reacting a mixture of fatty acids and glycerides with a short chain alcohol such as methanol, ethanol, propanol, or butanol to produce the corresponding alkyl ester is described.

  Grease deterrents include highly variable mixtures of organic fats, greases and vegetable oils, consisting of high free fatty acids and mono-, di-, and triglyceride content, detergents, water, soap, inorganic It will be understood that it is contaminated by solid and particulate materials. Throughout this specification, the terms free fatty acids (FFA) and glycerides are included in anti-grease waste, tallow, animal fats and other naturally occurring lipids, and are available for alkyl esterification as a whole. Is used to mean a free fatty acid content of mono-, di-, and triglycerides. Typically, anti-grease waste contains between 80 and 100% free fatty acids and glycerides.

  Alcohols include low boiling alcohols, preferably methanol, ethanol, propanol, and butanol, in their single chain and isomerized forms. However, it is anticipated that much longer chain alcohols can be utilized in the same manner in accordance with the present invention.

  A mixture of free fatty acids and glycerides in alcoholic form in the form of grease extracted from greasy waste, tallow, animal oils and other naturally occurring animal or vegetable lipids, or Stir to form a miscible single phase alcoholic solution of the mixture.

  Depending on the composition of the mixture, an immiscible suspension of lipids may be formed in the alcohol. In this case, the suspension is continuously agitated to prevent the lipid and alcohol from separating into two distinct phases. For the purposes of the present invention, the suspension to be agitated should be considered and treated as an alcoholic solution of a mixture of lipids and glycerides.

  Neither type of mixture depends on or requires a co-solvent in the process. However, the use of such co-solvents does not detract from the reaction or its final alkyl ester product. The use of a co-solvent slightly increases the reaction rate, but the reaction is very rapid and is completed in the absence of co-solvent.

Preferably, the mixture of free fatty acids and glycerides is dissolved in a similar volume of alcohol to give an alcoholic solution of about 50% v / v of the mixture. In this direction, the alcohol is present in a molar excess of the total free fatty acid content, preferably in the range from 1:10 to 1:25.
The reaction proceeds satisfactorily with a lower or higher proportion of alcohol to lipid, but the reaction proceeds optimally at about 50% v / v.

  Certain mixtures of free fatty acids and glycerides, such as tallow and vegetable oils, may not form a monophasic alcoholic solution. However, vigorous stirring of the two-phase homogeneous solution during the reaction procedure yields similar results with respect to alkyl ester production.

  The alcoholic solution of the mixture is first treated with an acid catalyst to provide acid catalyzed alkyl esterification, and then treated with a base catalyst to provide base catalyzed transesterification of the glycerides contained in the mixture. The resulting reaction mixture is finally treated with an acid catalyst, resulting in an acid-catalyzed alkyl esterification of the residual saponification byproduct obtained from the previous processing step.

  Preferably, the steps of acid-catalyzed esterification and base-catalyzed transesterification are carried out under reflux conditions, but said steps are also carried out at ambient temperature, although longer reaction times are required unless high pressure is used. You can also.

  The method of the present invention is preferably carried out at ambient atmospheric pressure. However, the process can be carried out successfully under higher pressures with the use of pressure vessels or under autoclave conditions.

  Acid catalysts include, but are not limited to, high concentrations of strong inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and perchloric acid. Preferably, the ratio of added acid catalyst to total fatty acid content is about 1:20 in the first acid catalyzed alkyl esterification reaction step and about 1 in the second acid catalyzed esterification reaction step. : 5.

  Base catalysts include, but are not limited to, alcoholic solutions of sodium hydroxide and / or potassium hydroxide, or sodium or potassium that dissolves in selected short chain alcohols. Preferably, a 10% w / w alkali metal alkoxide solution is used as the base catalyst such that the ratio of added base catalyst to total fatty acid content is about 1: 5.

  The alcohol is separated from the resulting reaction mixture by distillation or by separation using a microfiltration membrane, with or without the aid of vacuum, and the two-phase heterogeneity of alkyl ester and solid phase. The remaining mixture is removed. The alkyl ester is separated from the solid phase by decantation and further purified by filtration or by filtration alone.

  If the alcohol is removed from the reaction mixture by distillation or microfiltration and the alkyl ester is separated from the solid phase by decantation or filtration, the alkyl ester is treated with a weak base or alternatively Residual acids remaining in the alkyl ester phase can be effectively neutralized by ion exchange or microfiltration. It is expected that the pH of the alkyl ester phase will be neutralized to about pH 6-7.

  The neutralization step is accomplished by the addition of a small amount of sodium bicarbonate or calcium carbonate or magnesium carbonate to the alkyl ester phase. Other well-known means for neutralizing pH, such as elution of the liquid phase via separation by ion exchange resins or membranes, have been successfully used to effect neutralization of residual acid in the alkyl ester phase. It is expected to be used for

  The residual water is then removed by conventional means such as passage of an alkyl ester phase over a hygroscopic desiccant, desiccant, or the alkyl ester is steamed at atmospheric pressure or under reduced pressure. It can be removed by heating enough to remove or by microfiltration. Depending on the ultimate intended use of the alkyl ester, a small amount of entrained water is acceptable and its removal may not be necessary.

  Surprisingly, the inventor has shown that the alkyl esters produced by the process of the present invention remain uncontaminated by glycerol by-products from the acid catalyzed esterification and base catalyzed transesterification reactions according to the present invention. I found it. An exception was found from the treatment of fresh, unused vegetable oils, whereby small amounts of good quality glycerol were easily separated. The amount of glycerol byproduct was less than 8% of the starting oil and was significantly less than that produced by other esterification processes. Significant glycerol production did not occur when processing other lipids such as palm oil, coconut oil, animal tallow or greasy waste. The residual product after separation of the alkyl ester showed no signs of glycerol by gas chromatography tests.

The invention will now be illustrated according to the following examples.
(Example)
One single phase 1: 1 v / v methanolic solution of anti-grease waste (800 mL) in methanol (800 mL) was prepared. GC / MS analysis of the grease stop waste showed that the main components of the grease stop waste were octadecanoic acid and n-hexadecanoic acid. The pH of the methanolic solution of grease stop waste was 4, reflecting a high fatty acid content.

  A high concentration of sulfuric acid (98%) (8.5 g) was added to the methanolic solution with stirring, resulting in a solution pH between 1 and 2. The methanolic solution was refluxed for 30 minutes.

  A 10% w / w NaOH solution of sodium methoxide in methanol (160 mL) was then added dropwise to the stirred and refluxed methanolic solution, resulting in a final pH of 12.

  Concentrated sulfuric acid (98%) (21 mL) was added dropwise to the stirred and refluxed methanolic solution to give a final pH of 2.

  Excess methanol was removed by distillation. The resulting methyl ester (825 mL) was separated from the semi-solid basal residue (64.5 g) by decantation and finally filtered to remove fine sediment. It was assessed that there was a better conversion to methyl ester than 91% of the waste trap grease.

  A similar amount of degreased waste was treated according to the present invention as described in the examples above, where ethanol was used as the solvent rather than methanol. It has been found that a similar degree of degreasing waste conversion to the corresponding ethyl ester is achieved.

  Furthermore, similar experiments using a solution of potassium alkoxide rather than a sodium hydroxide solution produced results similar to those illustrated in the above examples.

  From the reaction mixture, the residual sediment formed using ethanol and potassium hydroxide was less crustiform than the sediment described in the examples, but it was easily removed from the ethyl ester by filtration. Isolated on.

  Tests have found that the residue in the dirty form is composed primarily of sodium sulfate with a minor entrained methyl ester combined with 9% sodium sulfate summed by the weight of the starting grease stop waste. It was done. Therefore, the conversion of grease stop waste to methyl ester exceeded 91%. The total processing time to the final product alkyl ester is less than 1 hour. Furthermore, it has been found that increasing the amount of acid in the first step speeds up the reaction time, thereby reducing the overall reaction processing time.

  The process is not sensitive to or is not impaired by residual water that contaminates the starting lipids.

  It is a fast and efficient process and method, which increases the dosage of the catalyst (dispensing amount) and / or by many well known methods including increased heating, pressure and agitation, It can be made even faster by increasing the kinetics of the reaction.

  The final product alkyl ester does not require water washing, thereby eliminating time-consuming and fouling main processing steps common to other processes. Glycerol byproduct production is eliminated in most lipid feedstocks tested. The methods and processes allow for the design of commercial equipment, which should be low in capital costs, small in size, with high production rates, and as a mounted truck, trailer unit or static Should be able to move as a secure facility.

Modifications and variations are considered to be within the scope of the invention, as will be apparent to the skilled recipient. The processes and methods allow for the alkyl esterification of lipids as described variously.

Claims (13)

A process for producing alkyl esters from a mixture of glycerides and free fatty acids comprising:
a) adding an acid to the alcoholic solution of the mixture and reducing the pH of the solution from about 1 to 2 to effect acid catalyzed alkyl esterification;
b) treating the solution from step a) with a concentrated alkoxide solution and raising the pH of the solution to about 12, resulting in base-catalyzed transesterification of the glycerides contained in the mixture;
c) treating the solution from step b) with an acid and reducing the pH of the solution to about 2, resulting in acid-catalyzed esterification of the remaining saponification by-product from step b);
d) removing alcohol from the solution from step c); and e) separating the resulting alkyl ester.   2. A process according to claim 1, characterized in that the alcohol is removed from the solution from step c) by distillation.   2. A process according to claim 1, characterized in that the alcohol is removed from the solution from step c) by microfiltration.   An alcoholic solution of the mixture is formed by dissolving or stirring a mixture of glycerides and free fatty acids in a similar volume of alcohol, giving a solution of about 50% w / w alcohol in the mixture. The method according to any one of claims 1 to 3.   The process according to claim 4, characterized in that the alcohol has a low boiling point.   The alcohol includes methanol, ethanol, propanol, and butanol, and is selected from the group including n-propyl alcohol, n-butyl alcohol, isopropyl alcohol, isobutyl alcohol, sec-butyl alcohol, and t-butyl alcohol. The method according to claim 4 or 5.   Process according to any one of claims 1 to 6, characterized in that step a) is carried out under reflux conditions.   8. Process according to any one of claims 1 to 7, characterized in that step b) is carried out under reflux conditions.   9. A process according to any one of claims 1 to 8, wherein the acid is a strong inorganic acid including but not limited to sulfuric acid, hydrochloric acid, phosphoric acid, perchloric acid and mixtures thereof.   The high-concentration alkoxide solution comprises sodium hydroxide and / or potassium dissolved in the alcohol used in step a) or sodium or potassium dissolved in the alcohol used in step a) The method according to any one of claims 1 to 9.   11. The method of claim 10, wherein the high concentration alkoxide solution comprises a solution of about 10% w / w alkali metal alkoxide.   Residual acid remaining in the solution obtained from step d), or the alkyl ester obtained from step e) is treated by, but not limited to, microfiltration or ion treatment with the solution or alkyl ester with a weak base. 12. A process according to any one of the preceding claims, characterized in that it is neutralized to about pH 6-7 by other acid removal means including exchange. An alkyl ester produced from a mixture of glycerides and free fatty acids, obtained by the method according to any one of claims 1-12.