One-Step Butadiene Synthesis via Gas-Phase Prins Condensation of Propylene with Formaldehyde over Heteropolyacid Catalysts

Abstract

Gas-phase continuous synthesis of butadiene from propene and formaldehyde has been studied over heteropolyacids (HPA) supported on silica. Silicotungstic acid (SiW) is found to be the most active and selective among other HPA. At low SiW loadings, catalysts have low selectivity due to the formation of a butanal by-product, while at high loadings (≥40 wt %), selective butadiene formation and stable performance are achieved. Strong Brønsted acid sites associated with intrinsic SiW protons are shown to be more active in butadiene synthesis as compared with Si–OH2 + sites formed by the interaction of HPA protons with a silica support. The kinetic study and product cofeeding experiments suggest that propene activation or C–C bond formation is the rate-determining step and that both butadiene and butanal are formed over strong acid sites starting from a common intermediate. Over weaker acid sites, condensation of butanal with formaldehyde leads to 2-ethylacrolein. Besides that, the reaction is complicated by butadiene interaction with formaldehyde leading to 2,3-dihydropyran, propene oligomerization and cracking, formaldehyde decomposition toward CO and H2, and extensive coke formation leading to catalyst deactivation. However, the optimization of reaction temperature, SiW loadings, and the content of water in reaction media allows us to achieve a butadiene selectivity up to 64% and stable catalyst performance with time on stream.

Sulfonic Acid-Functionalized Brønsted Ionic Liquid-Catalyzed Isoprene Production via Prins Condensation between Methyl Tert-Butyl Ether and Formaldehyde in Their Stoichiometric Ratio

“…As the formation rates of both intermediates were dependent on the concentration of FA, based on the apparent rate equations (eqs –), a high formaldehyde concentration benefited the DMD route. The byproduct 3,6-2H-4-methyl-2­(H)-pynan was formed together with isoprene, which was the product of the Diels–Alder reaction between isoprene and formaldehyde. , Although it was the secondary product originating from isoprene, the yield with time was similar to that of isoprene, indicating that the rate of the Diels–Alder reaction should be much higher than the rates of decomposition of DMD and dehydration of 3mbo. Besides, large amounts of oxygenated products formed by the Prins reaction between olefin and formaldehyde and dimerization reaction products between isobutene and isoprene were detected by GC, GCMS, and LPMS (Figure S2).…”

Revealing Formaldehyde-Mediated Methanol-to-Aromatics Reactions over Zn-Modified Zeolites by Observing the Oxygenated and Polyunsaturated Intermediates

“…Prins and Diels–Alder pathways to aromatics: The pathway starts from the Prins reactions between HCHO ( 1 ) with olefins (C n H 2 n ), such as ethene ( 2 ), propene ( 8 ), and butenes ( 31 , 34 ), which would generate the corresponding dienes (C n +1 H 2 n ) ( 20 , 25 , 32 , 33 , 35 ) . The highly reactive dienes were going to form the aromatic precursor via self-polymerization or the Diels–Alder reaction with another olefin molecule, followed by direct dehydrogenation or hydrogen transfer to aromatics .…”

In-Depth Understanding of Highly Active Silicotungstic Acid Catalysts for Ethanol Dehydration to Ethylene under Industrially Favorable Conditions

“…The theoretical and actual concentration of Brønsted acid sites can be calculated from the actual loading of STA and FTIR spectra of adsorbed pyridine. 48,50 Figure 5 shows the relationship between the theoretical and detected Brønsted acid amount and STA loading. The amount of obtainable Brønsted acid sites by pyridine FTIR is almost directly proportional to the STA loading.…”