Biodiesel production

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

• 4.1 transesterification and separation
• 4.2 biodiesel washing and drying
• 4.3 processing of the glycerol and the recovery of the methanol

Chemistry of the process

The transesterification is carried out by reacting vegetable oils with methanol after the adjacent reaction equation. The mixture of methyl esters obtained are called fatty acid methyl esters ( FAME) or biodiesel, as a by-product of glycerin.

Raw materials

As a raw material for biodiesel production takes place in Europe, mainly rapeseed oil use in the U.S. mainly soybean oil, especially in the summer months, palm oil. Many manufacturing processes require refined oil that has been subjected to a treatment process. In the refining impurities such as mucilage, free fatty acids, carotenes and tocopherols are removed.

In the degumming lecithin-containing admixtures through water and addition of acid are hydrolyzed. The resulting sludge is separated. In subsequent acid removal are free fatty acids (FFA; engl free fatty acids. ) And other acidic ingredients such as phenols removed. The acidification can be accomplished either by alkaline hydrolysis or by distillation. As a final purification step, the bleaching with hydrogen peroxide and the deodorization be used by water vapor.

Methods that are more tolerant of the quality of the raw materials used, usually need at the end of the transesterification elaborate processes to purify the resulting biodiesel.

Industrial plants

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

Catalysts

The transesterification is catalyzed usually alkaline. Find To avoid side reactions caused by water as catalysts mainly anhydrous alcoholates use, which are used as a 30 % solution of sodium or potassium in methanol.

Equipment used

A typical transesterification requires storage tanks for the raw materials and end products, heat exchanger for heating the reaction mixture stirred vessel for mixing of catalyst and methanol (static mixer in larger systems ). Furthermore, reactors and apparatus for phase separation of crude biodiesel and glycerol, filtration systems and stills are needed for the separation of biodiesel and methanol and residual moisture.

Process steps

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

Transesterification and separation

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

In the lower part of the reactor, a heavy basic phase, the glycerol, and methanol is drawn off and contains methoxide collected and stored. The biodiesel phase, further comprising methanol, unreacted canola oil, and soaps. To complete the reaction catalyst and methanol are added to the acetate mixture and subsequently separated again in a further reactor again. The lightweight acetate phase ( "crude biodiesel " ) is washed afterwards.

Biodiesel washing and drying

Impurities in the ester phase, such as methanol, glycerol and soaps are removed by adding water to the continuous washing column. The extension products are stored in an intermediate storage tank. In a settler, the remaining water is separated from the biodiesel. The last drying stage of the biodiesel is generally as vacuum drying, for example in a thin film evaporator.

Working up of the methanol and recovery of the glycerin

In a column glycerol and methanol are separated by distillation. The condensed methanol phase is recycled to the process. The remaining crude glycerol as the bottom product is acidified. The impurities and soap are transferred methanolate by this step in methanol, salt, free fatty acid. Pure glycerol can be separated in a settling vessel from the impurities.