In Situ-Generated Supported Potassium Lactate: Stable Catalysis for Vapor-Phase Dehydration of Lactic Acid to Acrylic Acid

Abstract

We have studied unsupported, silica gel- and amorphous silica–alumina-supported catalysts derived from K salts for the vapor-phase dehydration of lactic acid (LA) to acrylic acid (AA). A catalytic study shows that the supported catalysts improve the activity and selectivity for the production of AA and decrease the selectivity for the production of propionic acid (PA). The silica–alumina-supported catalysts remain fairly stable in the catalytic performance during 90 h of reaction. The IR spectroscopic characterization combined with the catalytic study demonstrates that potassium lactate (C 3 H 5 KO 3 ) in situ generated from LA and a K salt is an important reaction intermediate for the production of AA and the catalytic stability is associated with the chemical stability of C 3 H 5 KO 3 and the activity for the regeneration of C 3 H 5 KO 3 in the catalytic cycle. On silica–alumina, C 3 H 5 KO 3 is well stabilized and smoothly regenerated during the reaction, leading to the good catalytic stability. This work suggests for the first time that lactate salt acts as the true catalytic active species for the dehydration of LA to AA. We also propose a predominant reaction pathway for the vapor-phase dehydration of LA to AA with K salt catalyst systems.

Stable catalysis of neutral silica-supported potassium lactate for vapour-phase dehydration of lactic acid to acrylic acid – critical role of the support

“…This is an indication that the reaction proceeds predominantly in a catalytic way with potassium lactate as the catalytic active species. 19 Meanwhile the selectivity to AD was observed to be lower than the selectivity to AA. After 28 h of reaction, the catalytic activity markedly declined, which is due to the poor stability of the unsupported potassium lactate under the reaction conditions.…”

“…On the other hand, considering the formation of true catalytic species starting with those precatalysts, those starting inorganic salts are supposed to transform to lactate salts and conjugate acids by the action of LA under the reaction conditions (eqn (4)). 19,23–32 Lactate n C 2 H 4 (OH)COOH + M n + → n C 2 H 4 (OH)COOM + n H + salt is likely the true catalytic species for the dehydration of LA to AA. 19 Upon the formation of lactate salt with the evaporation of conjugate acids or their derivatives such as H 3 PO 4 and H 2 SO 4 under the reaction conditions, the solid acidity of the catalyst systems depletes.…”

“…19,23–32 Lactate n C 2 H 4 (OH)COOH + M n + → n C 2 H 4 (OH)COOM + n H + salt is likely the true catalytic species for the dehydration of LA to AA. 19 Upon the formation of lactate salt with the evaporation of conjugate acids or their derivatives such as H 3 PO 4 and H 2 SO 4 under the reaction conditions, the solid acidity of the catalyst systems depletes. Eventually the H 0 of the catalyst systems may be dependent on the lactate salt only.…”

“…23 Our group has reported a significant catalytic formation of AA from vapour-phase LA dehydration over potassium lactate in situ generated from unsupported KNO 3 and assumed a related reaction pathway for the vapour-phase dehydration of LA to AA independently of solid acid. 19 From the work of Miller's and our groups, solid acid seems unnecessary assuming that a Brønsted acid is involved towards a vapour-phase LA dehydration reaction, as long as it is in the presence of a suitable catalyst system.…”

Continuous Flow Upgrading of Selected C2–C6Platform Chemicals Derived from Biomass

“…Supported catalysts such as NaNO 3 -modified mesoporous silica SBA-15 (Table , entry 23) or potassium lactate supported on silica-alumina (Table , entry 24) were also studied in fixed-bed reactors. In the latter case, despite a relatively low selectivity, the supported catalyst appeared to be remarkably stable as both selectivity and conversion dropped by only a few percents after 90 h on stream.…”