Soy methyl ester

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Soybean oil methyl ester
Soybean oil biodiesel
other names

Soy methyl ester (SME)

Brief description Fuel for self-igniting piston engines (diesel fuels), solvents
origin

biosynthetic

CAS number

67784-80-9

properties
Physical state liquid
viscosity

7.5 mm² / s (at 20 ° C)

density

0.88 kg / L (at 20 ° C)

Calorific value

32.36 MJ / L = 37.2 MJ / kg (at? ° C)

safety instructions
GHS labeling of hazardous substances
no classification available
H and P phrases H: see above
P: see above
UN number 1202
Hazard number 30th
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Soybeans

Soy methyl ester (SME; also soy oil methyl ester ) is a mixture of methyl esters of saturated and unsaturated fatty acids , each with 16 to 22 carbon atoms. It is a clear, thin, flammable liquid that cannot be mixed with water.

In North America and thus worldwide, SME made from soy makes up the largest share of biodiesel , in Europe SME made from imported soy ranks second after rapeseed methyl ester . Fully refined SME is also used as a solvent in industrial production .

Manufacturing

When methanol is added to the soy oil, the soy methyl ester is produced in a catalytic reaction ; Furthermore, raw glycerine is produced, which is processed into pharmaceutical glycerine through further purification and distillation . The SME formation takes place by reacting soybean oil with methanol according to the following reaction equation:

Transesterification for the synthesis of RME + glycerine

Pre-treatment of the soybean oil

After the initial and auxiliary products have been delivered, the soybean oil used is cleaned. First, the crude oil is deacidified by adding phosphoric acid with elimination of phosphatides. This creates mucilage that is separated from the oil with the help of a centrifuge . In the next process step, the remaining soap is washed out of the neutralized oil and then dried in a vacuum dryer . Before the crude oil is put into a washing centrifuge, caustic soda is added. In this way, the previously added phosphoric acid and the remaining fatty acids are completely neutralized . Following centrifugation, the slimy substances are separated off in a separator .

Transesterification process

The main process of methyl ester production, transesterification , is based on the chemical reaction of triglycerides with methanol to form a mixture of methyl esters and glycerine, which is accelerated in the presence of an alkaline catalyst. The transesterification takes place in two reactors connected in series, which are each provided with different reaction chambers in order to achieve the highest possible conversion to the methyl ester. Both methanol and the catalyst sodium methylate are fed to the reactors in parallel to enable the transesterification process as desired. At normal pressure and temperatures around 60 ° C in the 1st reactor and about 50 ° C in the 2nd reactor, the ester bonds of the triglycerides are broken and reconnected with the alcohol, with the heavier glycerine settling on the bottom of the reactor. With the help of phase separators , the methyl ester and glycerine can be separated from one another due to their different densities .

Cleaning the product

The phase with the ester also contains methanol, glycerine, catalysts, soaps and other components. The water-soluble substances are removed by a washing process before the SME is then dried in vacuum dryers and is finally available for economic recycling.

Areas of application

Bus with soy diesel ads

SME has a significantly lower viscosity than untreated soybean oil; therefore it can be used as a substitute for the mineral diesel fuel without having to adapt the diesel engine . However, the plastic parts that come into contact with fuel must be resistant to the methyl ester.

In the manufacture of engine and transmission housings in the automotive industry , casting molds are used that are made from molding sand and resins. For this so-called cold box system, SME, but also RME ( rapeseed methyl ester ), is used on a larger scale as a binder for the resin component. This enables emissions of problematic solvents in the BTX fraction ( benzene , toluene and xylene ) to be reduced; Furthermore, the use of methyl esters should also lead to technical advantages over the classic cold box systems.

literature

Individual evidence

  1. ↑ Viscosity of biodiesel at hydrogeit .de
  2. ^ Norbert Schmitz, Jan Henke, Gernot Klepper: Biofuels: A comparative analysis . Ed .: Agency for Renewable Raw Materials . 2nd Edition. Gülzow 2009 ( fnr-server.de [PDF; 2.0 MB ; accessed on January 13, 2017]).
  3. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.