Catalytic upgrading of succinates to itaconic acid.

摘要

A novel process and catalysts to produce itaconic acid via condensation of succinic acid or its derivatives and formaldehyde were comprehensively studied.; The nature of sites on the support played an important role in the formation of citraconates in the vapor phase reaction. Neither highly acidic nor basic sites on the support favored the reaction. The highly acidic supports were found to be very active for cracking succinates into carbon dioxide, but not for condensation to citraconic anhydride. The basic supports gave little citraconic anhydride but catalyzed the Cannizzaro reaction of formaldehyde to methanol and formic acid, thus preventing formaldehyde from participating in the desired condensation. In contrast, γ-alumina, a mildly acidic support, without any salt added showed significant activity for the formation of citraconates from succinates. Results from different feedstocks over γ-alumina at the base case (standard) conditions are summarized in Table below.; Summary of Results from Different Feedstocks over γ-Alumina; cwl="69:112:112:95:74" wdm="100" dispwid="7.56in"> row> cell>S.N. cell>Feedstock cell>Yield of citraconates (%) cell>Conv of succinates (%) cell>Selectivity (%) row rht="0.36in"> cell>1 cell>DMS + trioxane cell chj="c">35 cell chj="c">48 cell chj="c">73 row> cell>2 cell>SAN + trioxane cell chj="c">44 cell chj="c">67 cell chj="c">66 row> cell>3 cell>MMS + trioxane cell chj="c">26 cell chj="c">40 cell chj="c">78 row> cell>4 cell>DMS + Formalin cell chj="c">29 cell chj="c">42 cell chj="c">70 row> cell>5 cell>DMS + Formcel cell chj="c">34 cell chj="c">56 cell chj="c">61 ; The decay in catalyst activity was much slower with Formalin. Yields of citraconic anhydride and conversion of DMS dropped off very slowly over time for reaction times out to five hours. Coking on the catalyst was also much less with Formalin, likely because the water present steam-cleaned the catalyst during the reaction. Coking involves both the succinate species and formaldehyde. Citraconic anhydride yield stabilizes following acid site deactivation. Upon deactivation, the alumina catalyst was regenerated by exposure to air at 500°C for five hours. The yields of citraconic anhydride were identical before and after the regeneration process, which demonstrated the robust nature of the oxide catalysts and their ability to be regenerated.; Yield of citraconic anhydride increased with increasing reaction temperature, but selectivity lower