Catalysis of Organic..

334Rearrangement of 3,4-Epoxy-1-Butene to 2,5-DihydrofuranThe process is typically operated at 100-110ºC and at, or slightly above,atmospheric pressure. The rearrangement reaction is exothermic so CSTR-1 andCSTR-2 require heat removal. CSTR-3 is operated adiabatically and its large sizeallows for increased overall residence time and high conversion of 1 to products.When the oligomer level has built up sufficiently, a small purge stream is removedand sent to the Oligomer Removal Unit (ORU) for catalyst recovery. This unitemploys a 24-ft tall, 6-inch diameter Karr extractor and VM&P Naphtha extractionsolvent (mixed heptanes, B.P. 118ºC, specific gravity 0.76 g/mL). The alkanesolvent is introduced at the bottom of the continuous extractor and thecatalyst/oligomer concentrate at the top. Counter-current extraction occurs as theheavy catalyst and oligomer feed falls through the rising alkane while an axiallyattachedset of perforated plates agitates up and down (22). The oligomer (raffinate)is collected from the bottom of the column and is sent to the incinerator. Severalextraction process variables were optimized including extractor rates, reciprocationrate, plate spacing, mass-transfer direction, and temperature profile (23).CSTR-1Catalysts in alkaneCatalyst / OligomerConcentrateRecoveredalkaneKarrReciprocating-Plate,Counter-current,Continuous ExtractorRecoveredCatalystsMake upalkane extractionsolventOligomer toincineratorFigure 2. Oligomer Removal Unit (catalyst recovery).Because the low molecular weight oligomers are soluble in the alkane extractionsolvent, an unavoidably high concentration of oligomers is returned with recoveredcatalyst. Therefore during steady-state operation the reaction mixture is about onethirdoligomer!Table 3. Approximate steady-state process stream compositions.ComponentCSTR-3Reaction MixtureKarr ExtractorFeedRecoveredCatalyst StreamVolatiles 27%Oligomer 35% 48% 37%TOT 17% 23% 27%TOP18 21% 29% 36%