Microstructured ZSM-11 Catalyst on Stainless Steel Microfibers for Improving Glycerol Dehydration to Acrolein

Abstract

Glycerol is a byproduct from the biodiesel manufacturing. Glycerol dehydration into more valuable acrolein is desirable and essential since it improves the economics of the biodiesel production and offers a sustainable route to replace the market favorite chemical from petroleum process. Zeolites with the dominant Brønsted acid sites have been wildly used in glycerol dehydration, since Brønsted acid sites are flexible and interacting with the center hydroxyl of glycerol towards acrolein production. In this research, microstructured ZSM-11 catalysts have been developed by direct growth of zeolite crystals on a macroscopic 3D network of sinter-locked stainless-steel microfibers. It showed remarkable stability and acrolein selectivity improvement as compared to conventional ZSM-11 zeolite, due to the short residence time to limit the secondary reactions and enhanced mass transfer to minimize the coke formation. The acidity of zeolites has been optimized via tuning the SiO2/Al2O3 ratios in a wide range from 78 to 283. The highest glycerol conversions and acrolein selectivity were observed over the catalyst with a SiO2/Al2O3 molar ratio of 131. The higher temperature at 300 o C was necessary to achieve better catalytic conversion and improve the acrolein formation. At the high-flow of carrier gas, the coke formation was suppressed due to the enhanced diffusion of big-size products out of the zeolite pores.

Tuning of Selectivity for Sustainable Production of Acrolein from Glycerol

“…It is well-known that there are two main competing routes in the dehydration of glycerol: (i) formation of acrolein on Brønsted acid sites and (ii) formation of acetol on Lewis acidic sites (Scheme 3). The mechanisms of acrolein and acetol formation on these sites were first proposed by Alhanash et al [16] who used Cs 2.5 H 0.5 PW 12 O 40 as a catalyst and then confirmed by many authors using metal oxides, [17,18] zeolites, [19,20] metal phosphides, [21] and HPAs. [22] In general, the dehydration of glycerol on Brønsted acid sites starts with the protonation of the secondary oxygen atom which has a higher negative charge compared to the terminal oxygen atoms (Scheme 3a).…”

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

“…The catalysts were developed and optimized to exhibit high water tolerance. It was shown that in addition to decreasing the viscosity of the feed, the presence of large amounts of water was essential to promote the formation of acrolein in high selectivity and inhibit the formation of carbonaceous deposits on the catalyst. − …”

“…A plethora of catalysts were prepared and evaluated in gas-phase fixed-bed flow reactor, such as zeo­lites and molecular sieves, − hetero­poly acids, ,,,− niobium-based, ,,− vanadium-based, ,− tungsten-based, ,,,,− ,,,− and other transition metal-based…”

“…Xu and colleagues evidenced that the presence of micropores in binary metal oxide catalysts was detrimental to acrolein selectivity because of a reduced diffusion ability . Lu et al described a procedure in rupture, which consisted in directly growing microporous ZSM-11 zeolite on a stainless steel (SS) microfiber . By comparison to the classical ZSM-11, the new catalyst gave enhanced stability and selectivity for acrolein since its microfibrous structure improved the diffusion/mass transfer of compounds, thereby inhibiting side-reactions and coke formation.…”

Progress of the Catalytic Deactivation of H‐ZSM‐5 Zeolite in Glycerol Dehydration

“…Some examples are phenol, dihydrofuran, cyclopentanone, methylcyclopentenone, cyclohexenone, tetrahydropyran-2-carbaldehyde and 2-oxepanone. [10,28,77,82,83] Such compounds are obtained mainly through oligomerization (aldol condensation) reactions from oxygenated products and intermediates, in which oxygen is removed in the form of water. [65,78,79] Afterward, these compounds are converted to aromatics from multiple steps of oligomerization, cyclization, dehydration, dehydrogenation, H-transfer, alkylation and other reactions.…”