CZ278110B6 - Process for preparing fuel based on rape-seed oil fatty acid methyl esters for self-igniting engines - Google Patents

Abstract

Rapeseed oil is processed by re-esterification with methanol in the presence of potassium hydroxide as the catalyst. The initial substances are brought to the reaction in the ratio of rapeseed oil:methanol:potassium hydroxide of 1:1.1 to 1.75 of the equivalent : 1.4 to 1.6 % by weight related to rapeseed oil. Re-esterification is performed at a temperature of 20 to 25 degrees C. From the upper layer of the reesterification product methanol is removed by vacuum evaporation at a temperature of 20 to 25 degrees C and the excluded precipitate containing the prevailing part of potassium hydroxide, originally dissolved in the upper layer, is mechanically separated. The methanol vapours are collected in the condenser.

Description

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The rapeseed oil is treated by re-esterification with methanol in the presence of potassium hydroxide catalyst. The starting materials are fed to the reaction in a ratio of rapeseed oil: methanol: potassium hydroxide = 1: 1.1 to 1.75 equivalents; 1.4 to 1.6 wt. % based on rapeseed oil. The re-esterification is carried out at a temperature of 20 to 25 ° C. Methanol is removed from the upper layer of the re-esterification product by vacuum evaporation at 20-25 ° C and the precipitate containing the major part of the upper layer of the initially dissolved potassium hydroxide is mechanically separated. Methanol vapors are collected in a condenser.

Method for producing fuel for self-ignition engines based on rapeseed oil fatty acid methyl esters

Technical field

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of fuel for self-ignition engines based on fatty acid methyl esters (so-called biodiesel) from rapeseed oil by re-esterification with methanol under catalysis with potassium hydroxide.

BACKGROUND OF THE INVENTION

The use of fatty acid esters as fuel for self-ignition (Diesel) engines is known. When these esters are obtained from natural material (various types of vegetable and animal fats and oils), the resulting product is called biodiesel.

These natural materials are used as biodiesel to a lesser extent as such, but this requires modification of engines designed for conventional diesel. Much more often. however, they chemically and physically modify, primarily by catalytic re-esterification, in which the original mixture of triglycerides of higher fatty acids produces a mixture of esters of these acids and glycerin by reaction with various lower monohydric alcohols (methanol, ethanol, propanol). For such biodiesel it is not necessary to modify conventional diesel engines.

In Europe, rapeseed oil is one of the most commonly used natural starting materials. The esterifying agent is most often methanol, and potassium hydroxide is the most commonly used catalyst.

Various processes for making this type of biodiesel are the subject of a number of patents: DE-CS 3149170, DE-OS 3150988, FR-A 2492402, DE-OS 3122453, US-PS 2360844, 2383632, 2383633.

Individual procedures differ mainly in temperature (25 to 25 ° C)

100 ° C), a stoichiometric ratio of rapeseed oil: methanol and the amount of catalyst. The rapeseed oil: methanol ratio ranges from 1: 1 (German Patent DE 3727981 from 1988) to 1: 1.75 equivalents, i.e. from 1: 3 to 1: 5.25 moles. The amounts of potassium hydroxide, expressed as a weight by weight, of rapeseed oil are 1 to 7%. The methods used can be divided into batch and continuous. In both cases, a solution of potassium hydroxide in methanol is mixed with rapeseed oil, at the same time being re-esterified to a mixture of fatty acid methyl esters (biodiesel) and separation of the heavier glycerol layer from biodiesel. The separation of the glycerin layer from the bismuth by gravity is accelerated by centrifugation or coalescing filters. Unreacted methanol and potassium hydroxide should be removed from the biodiesel. Some procedures remove methanol and potassium hydroxide simultaneously by washing with water or suitably acidified water. The disadvantage of this procedure is the difficult separation of biodiesel from the wash waters (emulsion formation) and the need to wash the wash waters (regeneration or removal of methanol, removal of potassium hydroxide). Other processes remove methanol and potassium hydroxide from the biodiesel at higher temperature and reduced pressure, then on a cation exchange column.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved method of re-esterifying rapeseed oil to biodiesel. It consists in proposing an optimal ratio of reaction components and optimum conditions for the rapeseed oil reesterification with methanol in the presence of potassium hydroxide. At the same time, the invention also provides a process for treating crude biodiesel obtained from re-esterification as the top product layer.

The rapeseed oil reesterification according to the invention is carried out at a ratio of rapeseed oil: methanol: potassium hydroxide = 1: 1.1 to 1.75 equivalents: 1.4 to 1.6% by weight (based on rapeseed oil) at room temperature preferably in the range of 20 to 25 ° C. To this end, a solution of potassium hydroxide in methanol prepared in the above ratio of the components according to the invention is introduced into the intensively stirred crude rapeseed oil presented in an appropriate amount. The resulting mixture is stirred vigorously for 2 to 5 minutes and then allowed to settle for about 1 to 2 hours until two sufficiently sharply distinguished layers are formed which are separated. The top layer contains a major proportion of biodiesel, as well as methanol and potassium hydroxide. It is subjected to further processing. The backsheet contains glycerin as the major component. The process according to the invention is not processed.

The treatment of the upper layer consists in separating the residual methanol and the catalyst. According to the invention, the methanol separation is carried out by vacuum evaporation of methanol, preferably at a pressure of 1 to 50 mmHg and at the above room temperature. Preferably, this vacuum evaporation is carried out as the biodiesel level increases, for example by stirring or spraying. A precipitate is formed which contains the major part of the upper layer of the initially dissolved potassium hydroxide. This precipitate can be easily mechanically separated from the biodiesel. Methanol vapors are collected in a condenser.

The optimum ratio of the reaction components is important both in terms of biodiesel yield and feasibility of processing the re-esterified mixture. Higher amounts of methanol have been found to accelerate re-esterification and increase biodiesel yield, but unreacted methanol extends sedimentation time, entrains potassium hydroxide and biodiesel into the lower glycerol layer, dilutes the biodiesel and the bottom layer, and incurs higher costs in eliminating methanol from both layers. A lower amount of methanol results in too low a conversion and thus a high density and viscosity of the resulting biodiesel. Lower amounts of potassium hydroxide retard the re-esterification and separation of both layers, higher amounts of catalyst cause problems in the necessary elimination from both layers.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

1000 cm ³ (916 g) of crude sedimented rapeseed oil was charged to a 1.5 dm ³ glass batch reactor. Under vigorous stirring, a solution of 13.74 g of potassium hydroxide in 146.3 cm ³ (116.2 g) of methanol was added in one portion. The mixture was stirred vigorously for two minutes. It was then left to stand still. The sedimentation with layer separation lasted 1.5 hours. The biodiesel layer was subjected to vacuum evaporation. Evacuation was carried out at a pressure of about 1000 Pa and a room temperature of 20-22 ° C for two hours. The volatile methanol was collected into a condenser. The precipitate containing the catalyst was removed by filtration. The resulting biodiesel had the following parameters: yield 94.4 wt. % to rapeseed oil, density (25 ° C) 0.883 gc ^-3 , viscosity (20 ° C) 8.67 mm ² <s ^-1 , conversion to rapeseed oil 92% (liquid chromatography), conversion to methyl esters 94.5% (liquid chromatography), 95.5% (gas chromatography), flash point in a sealed crucible 160 ° C, methanol content 0.06 wt. % potassium hydroxide content 3 mg per kg biodiesel, sulfur content 0.037 wt. %, pour point -15 C.

Industrial applicability

The biodiesel parameters prepared by the process of the present invention comply with international regulations. The potassium hydroxide content of the biodiesel, using the claimed process, is a small fraction (in the case of Example 1, 0.64% by weight) of the potassium hydroxide content of the crude product obtained from the re-esterification, without using any additional equipment or reagent. The sulfur content is given by the sulfur content of the rapeseed oil which cannot be influenced.

Claims (3)

PATENT CLAIMS A process for producing fuel for self-igniting rapeseed oil fatty acid methyl ester engines by reesterification with methanol under potassium hydroxide catalysis and treating the top layer of the reesterification product, characterized in that the reesterification is carried out at room temperature of 20-25 ° C and starting materials are reacted in a ratio of rapeseed oil: methanol: potassium hydride = 1: 1.1 to 1.75 equivalents: 1.4 to 1.6 wt. % based on rapeseed oil, that methanol was removed from the upper layer of the re-esterification product by vacuum evaporation at a pressure of 666-1333 Pa and at room temperature, and that the precipitate containing most of the upper layer of initially dissolved potassium hydroxide was mechanically separated. 4 Method for producing fuel for self-igniting rapeseed oil fatty acid methyl ester engines according to claim 1, characterized in that, during re-esterification, a solution of potassium hydroxide in methanol is added simultaneously to the crude sedimented rapeseed oil under intensive stirring and the mixture is stirred for a further 2 to 5 minutes. stirring vigorously. Method for producing fuel for self-ignition engines based on rapeseed oil fatty acid methyl esters according to the claims 1 and 2, characterized in that the vacuum evaporation of methanol is carried out as the fuel level increases, for example by stirring or spraying.