Impact of Macroporosity on Catalytic Upgrading of Fast Pyrolysis Bio‐Oil by Esterification over Silica Sulfonic Acids

Abstract

Fast pyrolysis bio‐oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom‐ and energy‐efficient route to upgrade pyrolysis bio‐oils. Propyl sulfonic acid (PrSO3H) silicas are active for carboxylic acid esterification but suffer mass‐transport limitations for bulky substrates. The incorporation of macropores (200 nm) enhances the activity of mesoporous SBA‐15 architectures (post‐functionalized by hydrothermal saline‐promoted grafting) for the esterification of linear carboxylic acids, with the magnitude of the turnover frequency (TOF) enhancement increasing with carboxylic acid chain length from 5 % (C3) to 110 % (C12). Macroporous–mesoporous PrSO3H/SBA‐15 also provides a two‐fold TOF enhancement over its mesoporous analogue for the esterification of a real, thermal fast‐pyrolysis bio‐oil derived from woodchips. The total acid number was reduced by 57 %, as determined by GC×GC–time‐of‐flight mass spectrometry (GC×GC–ToFMS), which indicated ester and ether formation accompanying the loss of acid, phenolic, aldehyde, and ketone components.

A Novel and Versatile Grafting Procedure: Toward the Highest Possible Sulfonation Degree of Mesoporous Silica

“…[36,41] This absorption band at 3743 cm −1 disappears after the CVD functionalization with the MPTMS linker molecules (purple spectrum) proving that all isolated silanol groups of the silica material reacted with the MPTMS molecules via condensation reaction. [26,42] Comparing the KIT-6-SH with the KIT-6-SO 3 H DRIFT spectrum, the shift of the bands at 2941 and 2842 cm −1 to higher wavenumbers and the absence of the thiol assigning band at 2561 cm −1 indicates the successful, quantitative oxidation of the thiol to sulfonic acid groups. All additional absorption bands in the DRIFT spectrum of KIT-6-SH could be clearly assigned to MPTMS.…”

Unravelling mass transport in hierarchically porous catalysts

“…Hierarchical porous solids, typically comprising interpenetrating bimodal mesoporemicropore or macropore-mesopore networks, extend control over molecular transport, adsorption, and reaction. 3 For example, the introduction of mesoporosity into zeolites improves their lifetime, 4,5 and activity and selectivity for (bio) fuels 6,7 or ne chemicals 8 production, while macropores promote esterication 9 and selective alcohol oxidation 10 over sulfonic acid and Pd mesoporous SBA-15 silicas respectively, CO 2 hydrogenation over Cu alumina, 11 and transesterication over Mg-Al hydrotalcites. 12 This is conceptually akin to fractal networks in Nature, 13 wherein the transport of matter is optimised by rapid convective ow through large channels, that in turn supply a network of smaller channels through which diffusion is constrained.…”

Zirconia catalysed acetic acid ketonisation for pre-treatment of biomass fast pyrolysis vapours

“…3 Crude bio-oils must therefore be upgraded to remove corrosive components and stabilise them prior to any final hydrodeoxygenation step to enhance their calorific value. Ketonisation, [14][15][16] involving the condensation of two acid molecules to form a ketone, CO 2 and H 2 O (Scheme 1), and esterification [17][18][19] involving the reaction of carboxylic acids with alcohols (already present or from external addition), are promising routes to lower the acidity of crude bio-oil. Ketonisation is advantageous since it can be conducted in the vapor phase without additional reactants, thereby enabling a catalyst bed close-coupled to the fast pyrolysis unit to remove acids from pyrolysis vapour prior to condensation as a biooil.…”