Transesterification plant

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Transesterification plant in Motherwell , Scotland

A transesterification plant is a plant for the transesterification of vegetable oil with methanol to biodiesel and glycerine .

Chemistry of the process

Example of the acid-catalyzed transesterification of a natural triglyceride (above) in fats and oils. The fatty acid residue marked blue is saturated, the green marked is single, the red marked triple unsaturated . In the equilibrium reaction, glycerine is split off and FAME (bottom) is formed, a mixture of fatty acid methyl esters, in the example three different ones.

The transesterification takes place by reacting vegetable oils with methanol according to the reaction equation opposite. The mixture of the resulting methyl esters is called fatty acid methyl ester (FAME) or biodiesel; glycerine is obtained as a by-product.

raw materials

Rapeseed oil is mainly used as the raw material for biodiesel production in Europe , soybean oil is mainly used in the USA , and palm oil , especially in the summer months . Many manufacturing processes require refined oil that has undergone a refining process. In the refining impurities such as gums, free are fatty acids , carotenes and tocopherols removed.

During degumming , additions containing lecithin are hydrolyzed by adding water and acids. The resulting sludge is separated. In the subsequent deacidification step, free fatty acids (FFA) and other acidic components such as phenols are removed. Deacidification can be carried out either by alkaline saponification or by distillation. The fine cleaning steps used are bleaching with hydrogen peroxide and deodorization using steam.

Processes that are more tolerant of the quality of the raw materials used usually require more complex processes at the end of the transesterification in order to clean the biodiesel produced.

Industrial plants

Modern industrial plants have an annual capacity of at least 100,000 tons per year.


The transesterification is usually catalyzed using an alkaline method. To avoid secondary reactions caused by water, the main catalysts used are anhydrous alcoholates, which are used as an approximately 30% strength solution of sodium or potassium alcoholate in methanol.

Apparatus used

A typical transesterification plant requires storage tanks for the raw materials and end products, heat exchangers for heating the reaction mixture, stirred tanks for mixing the catalyst and methanol ( static mixers in larger plants ). Furthermore, reactors and apparatus for the phase separation of raw biodiesel and glycerine, filtration systems and distillation apparatus for the separation of biodiesel and methanol and residual moisture are required.

Procedural steps

The process can be roughly divided into the steps of transesterification , separation of biodiesel and glycerin , washing of biodiesel, drying of biodiesel and processing of glycerin and recovery of methanol. Many of the process steps are multi-stage. In large industrial plants, transesterification is carried out in a continuous process. The process can be monitored by online near infrared (NIR) analysis.

Transesterification and separation

As a first step, the transesterification catalyst and methanol are mixed. These are mixed with vegetable oil and pumped into a continuous stirred tank reactor, two or more of which can be connected in series. The transesterification takes place there. The typical reaction temperature is around 50 to 65 ° C. The process takes place under normal pressure. As a rule, methanol is used in a stoichiometric excess. However, stirred tank reactors are only used in smaller systems with a capacity of up to 100 kt per year. In larger plants, static mixers or in-line mixers are usually used instead of stirred tank reactors.

A heavy basic phase containing glycerine, methanol and methanolate collects in the lower part of the reactor and is drawn off and temporarily stored. The biodiesel phase also contains methanol, unreacted rapeseed oil and soaps. To complete the reaction, catalyst and methanol are again added to the ester mixture in a further reactor and then separated again. The light ester phase (“raw biodiesel”) is then washed.

Biodiesel washing and drying

Impurities in the ester phase such as methanol, soaps and glycerine are removed by adding water in continuous washing columns. The by-products are stored in an intermediate storage tank. The remaining water is separated from the biodiesel in a settler. The final drying stage of the biodiesel usually takes place as vacuum drying, for example in a thin-film evaporator.

Processing of the glycerine and recovery of the methanol

Glycerine and methanol are separated from one another by distillation in a column. The condensed methanol phase is fed back into the process. The crude glycerine remaining as bottom product is acidified. The impurities methanolate and soap are converted into methanol, salt and free fatty acid by this step. The pure glycerine can be separated from the impurities in a sedimentation vessel.

Individual evidence

  1. ^ Oil refining in central oil mills ( memento from July 19, 2009 in the Internet Archive ).
  2. Overview of the biodiesel production capacities (status: 2002) ( Memento of the original from July 20, 2009 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot /
  3. ^ Transesterification catalysts at Degussa ( Memento from August 29, 2006 in the Internet Archive ).

Web links