Scientific Design SD Process

The aqueous maleic acid is freed from water by an azeotropic distillation with o-xylene and converted to MA in the process. The process is designed to minimize thermal isomerization of maleic acid to fumaric acid. MA from this step and from direct condensation are combined and refined by distillation. 

The flow diagram is shown in Fig. 2-2. In the process,a mixture of benzene and preheated air passes through a multitube reactor cooled by a circulating salt bath. A fixed bed of granular catalyst is used. The conversion of benzene is not complete. 

AIR FILTER AIR DRYER AIRBLOWER PREHEATER WASH TOWER 

The MA is recovered as a solid 4- liquid in switch condensers. After the condensers are switched, MA is melted for refining by batch distillation. Recovery is 90%, the remaining 10% MA being removed in a two-stage scrubber with water and dilute alkali. 

Unconverted benzene is recovered from the exhaust gases in an activated carbon unit. The benzene so obtained is returned to the feedstock. These recovery steps, all combined, make the exhaust gases dust and odor free. 

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The effluent stream contains a low concentration of MA in the gas phase (1.5% by weight). Part of this is recovered as a solid by cooling the effluent as in the Ruhroll process. The Scientific Design (SD) process, on the other hand, collects MA as a molten liquid by cooling the stream above the dew point of water. This prevents formation of any significant concentration of maleic acid produced by hydrolysis which may potentially isomerize to fumaric acid. (See Chapter 1.) The molten MA is collected as such in the Scientific Design process.Alternatively, the molten MA can be collected on ceramic supports as claimed by Monsanto. 

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