•  In this last lecture for the petrochemicals module, we demonstrate the process technology for Maleic anhydride and DDT.

•  Maleic anhydride is manufacture from benzene by butane oxidation.

•  DDT is a pesticide and is manufactured from benzene, chlorine and ethanol using sulphuric acid as a catalyst.

•  We next present the process technology for maleic anhydride. Along with this compound, fumaric acid is also produced as another product.

25.2 Maleic anhydride & Fumaric acid

25.2.1 Reactions

• •  Benzene + O₂ (Air) → Maleic anhydride + H₂O + CO_2.

•  Reaction is exothermic.

•  Operating temperature is 400 – 500°C.

•  Catalyst is V₂O₅

•  For fumaric acid, the reaction is Maleic acid → Fumaric acid.

•  Fumaric acid is an isomer of Maleic acid.

•  HCl is used as a catalyst for the isomerisation reactor at normal pressure and temperature.

25.2.2 Process technology (Figure 25.1)

• •  The process technology is similar to phthalic anhydride production.

•  Benzene or butane is first vaporized in excess air.

•  Then the mixture enters the catalytic tubular reactor (with shell arrangement). The catalytic reactor is circulated with salt solution so as to absorb the heat generated using the reaction.

•  The reactor products enter a waste steam recovery boiler where the boiler water is converted to steam.

•  The product vapors eventually enter an integrated heat exchanger to exchange heat with the pre-heated feed stream.

•  Eventually, the vapors are condensed followed with gravity settling to remove tar as a product in the gravity settling. The vapors then enter a water scrubber to obtain 40% maleic acid solution. The leaving gases consist mainly of CO₂.

•  The maleic acid from the absorber is partially sent to a dehydrator that removes water using azeotropic distillation principle. The purified maleic anhydride product is further sent to vacuum distillation to obtain the maleic anhydride product.

•  The dilute maleic acid solution is partially sent to an isomerisation unit where HCl is used as the isomerisation catalyst.

•  After reaction, the product is sent to a centrifuge that separates water from the fumaric acid.

•  Eventually, fumaric acid is sent to a drier to obtain dry fumaric acid.

25.2.3 Uses :

Maleic anhydride can be used as a highly reactive and versatile raw material. It can be used in the manufacture of alkyd resins, which in turn are used for making paints and coatings. It can also be used in making agricultural chemicals like herbicides, pesticides and plant growth regulators.