Carbon-Increasing Catalytic Strategies for Upgrading Biomass into Energy-Intensive Fuels and Chemicals

Abstract

Lignocellulosic biomass is the most abundant organic carbon source and has received a great deal of interest as renewable and sustainable feedstock for the production of potential biofuels and value-added chemicals with a wide range of designed catalytic systems. However, those natural polymeric materials are composed of short-chain monomers (typically C6 and C5 sugars) and complex lignin molecules containing plenty of oxygen, resulting in products during the downstream processing having low-grade fuel properties or limited applications in organic syntheses. Accordingly, approaches to increase the carbon-chain length or carbon atom number have been developed as crucial catalytic routes for upgrading biomass into energy-intensive fuels and chemicals. The primary focus of this review is to systematically describe the recent examples on the selective synthesis of long-chain oxygenates via different C–C coupling catalytic processes, such as Aldol condensation, hydroalkylation/alkylation, oligomerization, ketonization, Diels–Alder, Guerbet, and acylation reactions. Other integrated reaction steps including, for example, hydrolysis, dehydration, oxidation, partial hydrogenation, and hydrodeoxygenation (HDO) to derive corresponding key intermediates or final products are also reviewed. The effects of catalyst structure/type and reaction parameters on the catalytic performance along with relevant reaction mechanisms are in detail discussed. Apart from this, the formation of other useful compounds containing C–X bonds (X = O, N, and S) derived from biomass-based substrates for producing fuel additives and valuable chemicals is also briefly reviewed.

Development of Intermediates for High‐Energy Content New Biomass‐Derived Jet and Diesel Fuels with a Robust Rapid Green Reaction

“…After analyzing the chemical structure of the biomass‐derived molecules, we planned to develop the old Michael addition reaction for the new purpose of synthesizing high‐density jet and diesel fuels. Glucose and xylose are the main building blocks of terrestrial biomass that can be upgraded to a variety of biomass‐derived chemicals with C═C double bonds and carbonyl groups . These chemicals are potential Michael donors and Michael acceptors.…”

“…With optimized reaction conditions (Table , entry 9), the substrate scope of this TBAB/K 3 PO 4 ·3H 2 O catalytic solvent‐free Michael addition reaction with respect to Michael donors ( 1a – 1d ) and Michael acceptors ( 2a–2d ) was investigated. The Michael acceptors and donors were obtained from the small molecules derived from terrestrial biomass . For example, 1a can be obtained by simple esterification of malonic acid with ethanol; 2a, 2b, 2c, and 2d can be obtained by the esterification of acrylic acid with related alcohols.…”

“…The Michael acceptors and donors were obtained from the small molecules derived from terrestrial biomass . For example, 1a can be obtained by simple esterification of malonic acid with ethanol; 2a, 2b, 2c, and 2d can be obtained by the esterification of acrylic acid with related alcohols. As shown in Figure A, the reaction of secondary carbon linked to two electron withdrawing groups and active methylene compounds provided bis‐Michael adducts.…”

“…For example, 3a‐a , 3a‐b, 3a‐c, etc. can be converted into biofuels with chain length matching the gasoline range C 5 –C 13 and 3h‐a , 3h‐e , 3h‐f , etc. can be converted into cyclic hydrocarbon‐based high‐density aviation fuels …”

An efficient approach to produce 2,5‐diformylfuran from 5‐hydroxymethylfurfural using air as oxidant

“…The ongoing exhaustion of non‐renewable fossil resources and corresponding environmental concerns caused by their continuously growing consumption have urged developing new technologies to utilize renewable and green resources . Biomass, as the largest renewable carbon pool on earth, is anticipated to play a crucial role for a sustainable supply of energy and chemicals . Thus tremendous efforts have been set forth to develop novel technologies for the conversion of biomass to valuable chemicals .…”