Butenes recovery system

UOP/HYDRO Olefins Butenes from natural gas, methanol Methanol to olefins (MTO) process uses fluidized-bed reactor and efficient product recovery system NA NA... 

Purification. For polymerization, butadiene that is at least 99 mol% pure is required. Although alkynes are the most troublesome impurities, separation of the butadiene from other C4 products is also necessary. Simple fractional distillation is effective for removing the light (C3) and heavy (C5) ends from butadiene, but not for removing the various C4 species because of the closeness of the boiling points to each other and to butadiene. Further complicating purification, butadiene forms azeotropes with re-butane and 2-butene. The most widely used recovery systems are extraction with aqueous cuprous ammonium acetate (CAA) and solvent extractions with furfural, acetonitrile, dimethylformamide, dimethylacetamide, or AT-methylpyrrolidinone (65,66). 

The concept of biphasic catalysis requires that the catalyst and product phases separate rapidly to achieve a practical approach to the recovery and recycling of the catalyst. It is obvious that simple aqueous/hydrocarbon systems form two phases under nearly all operating conditions and thus provide rapid product-catalyst separation. Ultimately, however, the application of water-soluble catalysts is limited to low-molecular-mass substrates which have appreciable water-solubility. The problem is illustrated by the data in Table 1, which gives the solubility of some simple alkenes in water at room temperature [1], Although hydrocarbon (alkene)-solubility in water increases at higher temperature, most alkenes do not have sufficient solubility to give practical reaction rates in catalytic applications. The addition of salts further decreases the solubility of hydrocarbons in water. Substrate solubility in water is a significant issue and it is no accident that so-far the practiced and proposed commercial applications of water-soluble catalysts for hydroformylation are limited to propene and butene. 

The high efficiency of the recovery process ensures that Rh losses are only in parts per billion. Similarly, 1-butene, which like propylene has adequate solubility in water, is also hydroformylated efficiently with the Rh-TPPTS catalyst system. 

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