Improving carbon retention in biomass conversion by alkylation of phenolics with small oxygenates

Alkylation of phenolics with alcohols is an efficient way to retain carbon from small oxygenates in the liquid products of pyrolysis bio-oil. In this contribution, we have investigated the alkylation of m-cresol with several alkylating agents over H-Beta zeolite. The alkylation activity follows the sequence 2-propanol > propylene > 1-propanol. In all cases, propylene is the actual alkylation agent since the alcohols dehydrate at a faster rate than the rate of alkylation. A two-stage process is proposed to convert fractions of bio-oil rich in small aldehydes and ketones together with phenolics. In the first stage, aldehydes and ketones are selectively hydrogenated to alcohols. In the second stage, the resulting alcohols alkylate the phenolic compounds and get incorporated into the upgraded liquid. To illustrate this concept, two consecutive catalyst beds have been used. The first bed contains a metal catalyst for the selective hydrogenation. Among several catalysts investigated, Cu/SiO2 and Pt–Fe/SiO2 were found to exhibit good selectivity to hydrogenate the aldehyde and ketone, respectively, while preserving the aromatic ring of the phenolic compound. The second bed contains an H-Beta zeolite for the alkylation stage.

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► Alkylation is an efficient method to retain C from small oxygenates in liquid fraction of bio-oil.
► m-Cresol alkylation activity follows the sequence 2-propanol > propylene > 1-propanol.
► A hydrogenation/alkylation two-stage process is proposed to utilize small aldehydes and ketones.
► The combination Pt–Fe/SiO2 + H-beta was found to be effective for the two-stage process.