Selective Synthesis of Cyclohexanol Intermediates from Lignin-Based Phenolics and Diaryl Ethers using Hydrogen over Supp
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REVIEW ARTICLE
Selective Synthesis of Cyclohexanol Intermediates from Lignin‑Based Phenolics and Diaryl Ethers using Hydrogen over Supported Metal Catalysts: A Critical Review Sreedhar Gundekari1 · Sanjib Kumar Karmee1 Received: 8 July 2020 / Accepted: 9 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Depolymerisation of lignin produces concoction of aromatic compounds, such as, phenols, dihydroxybenzenes, alkylphenols, methoxyphenols, alkyl-methoxy substituted phenols, and diaryl ethers. This review presents an introduction on lignin, phenolic compounds and its value-added products, namely, cyclohexanols, cyclohexanones, and cyclohexanes obtained via hydrodeoxygenation/-hydrogenation reaction. The prior-art of catalytic interventions for selective preparation of cyclohexanols (a potential polymer and fuel intermediates) from lignin-based phenolic compounds are discussed. For this process, in-depth evaluation of nature of catalytic support, effect of reaction conditions (temperature and H2 pressure)/medium, active metallic sites, and mechanistic paths are performed. Keywords Lignin · Phenolic compounds · Hydrodeoxygenation · Hydrogenation · Hydrogenolysis · Metal catalysts · Cyclohexanols · Selectivity
1 Introduction Biomass is an alternative and sustainable source of organic carbon for the production of fuels, chemicals, and polymers. Lignocelluloses and triglycerides are well known feedstocks obtained from biomass [1]. Biomass conversion has many advantages: (i) it decreases foreign fuels and chemicals imports, (ii) it provides additional income for farmers, (iii) maintain or reduces GHGs emissions (carbon neutral), and (iv) opens up new opportunities for startups in science and technology [2, 3]. Bio-based building blocks and their catalytic transformation into value-added products have a positive impact on long-term environmental sustainability. Therefore, biobased-innovation and bioeconomy are creating immense interest among researchers, entrepreneurs and business communities [4]. * Sreedhar Gundekari [email protected]; [email protected] * Sanjib Kumar Karmee [email protected]; [email protected] 1
Thermo Chemical Conversion Technology Division, Sardar Patel Renewable Energy Research Institute (SPRERI), Near BVM Engineering College, Vallabh Vidyanagar, Post Box No. 2, Anand, Gujarat 388 120, India
Lignin is one of the components of lignocellulose biomass and consists of 10–35% by weight, and 40% by energy. Lignin is the second largest heterogeneous natural organic biopolymer [5]. It is considered as a waste co-product in paper, sugar, ethanol, and other bio-based industries. Globally, ~ 50 million tons/year of lignin is getting generated through pulping process. Many developed countries are now using renewable feedstocks viz. edible (starch) biomass known as a first-generation feedstock to non-edible (lignocellulose) second-generation biomass feedstock for bioethanol production. Some of the processes are valorizing biomass based feedstocks i
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