Resumen
The invention relates to a method for the trans-esterification of triglycerides with monoalcohols having a low molecular weight in order to obtain light alcohol esters using mixed catalysts. According to the invention, the trans-esterification of triglycerides, which are obtained from used frying oils or vegetable or animal oils, in order to obtain alcohol fatty acid esters having low molecular weight, was carried out with a mixed catalytic system comprising carboxylic acid salts and alkaline metal hydroxides. Said catalytic system can be used to reduce the conditioning steps and the process operating time. The process is performed under moderate pressure and temperature conditions in a continuous or discontinuous stirred tank-type reactor. The esters thus obtained can be used as fuel and dissolvents among other uses.
Reivindicaciones
1. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts characterized in that the triglycerides come from raw, refined or used vegetable oils, plant oils or animal fats, and mixtures thereof. 2. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the monoalcohols are preferably methanol and ethanol. 3. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the mixed catalytic system is comprised of alkaline metal hydroxides, preferably sodium and potassium, and of soaps obtained from free fatty acids contained in the starting materials by a process of neutralization. 4. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to claim 3, characterized in that the neutralization of the acidity of the raw materials is performed by the alkaline hydroxides forming the corresponding salts of carboxylic acids employed in the catalytic system. 5. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to claims 3 and 4, characterized in that the amount of alkaline hydroxides used, ranges between 0.1 and 1% of the reaction mass. 6. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to previous claims, characterized in that it uses continuous or discontinuous reactors, of the stirred-tank type, equipped with a filtration system at the exit of the reaction system. 7. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out at a temperature between 10 DEG and 100 DEG C and in a time between 5 and 300 minutes. 8. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out in one step introducing in the reactor an amount of alcohol ranging from 70 to 250% of the stechiometric amount. 9. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to claims 1 to 7, characterized in that the transesterification reaction is carried out in two steps: 1. 1. An amount of alcohol between 70 and 200% of the stechiometric amount is introduced in the reactor. 2. 2. The glycerine formed is separated from the reaction mixture and the required amount of alcohol is added to the reactor for this to encounter an amount between 100 and 250% of the stechiometric value. 10. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out in a discontinuous process in which the excess methanol or ethanol is separated from the reaction medium by a vacuum distillation operation. 11. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to claims 1 to 9, characterized in that the transesterification reaction is carried out in a continuous process in which the excess methanol or ethanol is separated from the reaction medium by vacuum distillation from the deposit chamber. 12. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to previous claims, characterized in that the reaction mixture is transferred to a deposit chamber to be subsequently purified and obtain the light alcohol esters (biodiesel) and by-products, which are made after this time in continuous mode. 13. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the mixture from the deposit chamber continuously feeds a separation system from which two phases are obtained: (A) the ester phase, mainly comprised of the ester, alcohols and soaps, and (B) the glycerine phase mainly comprised of glycerine, alcohol and soaps. 14. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the ester phase is rinsed with water or with a diluted solution of strong acid, being separated into: (A1). A phase comprised of the alcohol ester used for transesterification, to which an organic compound is added, to proceed to a drying operation followed by a filtration process obtaining an alkyl ester suitable for use as a combustion agent, fuel or solvent. (A2). An aqueous phase submitted to a neutralization operation followed by vacuum distillation. 15. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain light alcohol esters using mixed catalysts, according to claim 13, characterized in that the glycerine phase (B) is submitted to a vacuum distillation operation followed by neutralization with strong acid, preferably ortho-phosphoric acid giving rise to three by-products: (B1). Liquid phase that contains glycerine (B2). Liquid phase that contains fatty acids (B3). Solid phase that contains a sodium or potassium salt of the acid used in the neutralization. 16. Use of the esters obtained with the claimed transesterification process as combustion agents, fuels and solvents.
