Abstract
Biomass is a potential non-food, carbon-neutral, and abundant resource, which can be used as an alternative to fossil fuels during the sustainable preparation of various platform chemicals. Alkyl levulinates (ALs) have found widespread application as flavorings, plasticizing agents, and fuel additives, as well as synthetic precursors to various building blocks. Several processes have been investigated to transform biomass and its derivatives into ALs, which mainly include: (i) direct esterification of levulinic acid (LA) with alkyl alcohols and (ii) alcoholysis reactions of renewable biomass feedstocks and their derivatives, including furfuryl alcohol (FAL), chloromethyl furfural (CMF), and saccharides. This review focuses on illustrating the effects of the biomass pretreatment step, catalyst texture, possible mechanisms, acidities, and intermediates on the synthesis of ALs from sustainable resources covering a wide range of intermediates, including diethyl ether (DEE), 4,5,5-triethoxypentan-2-one (TEP), ethoxymethylfuran (EMF), ethyl-D-fructofuranoside (EDFF), and ethyl-D-glucopyranoside (EDGP).
Highlights
As the natural reserves of non-renewable resources such as petroleum, diesel, natural gases, and coal dwindle (Badgujar and Bhanage, 2015; Dhyani and Bhaskar, 2018) while causing unavoidable environmental issues, such as the emission of harmful gases and global-warming (Sun and Cheng, 2002; Wagh et al, 2016), extensive efforts must be devoted toward the search for alternative and renewable resources that are environmentally friendly
Similar conclusions have been reported by Huang et al when studying the conversion of furfuryl alcohol (FAL) into methyl levulinate (ML) (Huang et al, 2016)
Their investigations demonstrated that TMP was formed from MMF under specific reaction conditions, which indicates that both TMP and MMF promote the synthesis of ML
Summary
As the natural reserves of non-renewable resources such as petroleum, diesel, natural gases, and coal (fossil fuels) dwindle (Badgujar and Bhanage, 2015; Dhyani and Bhaskar, 2018) while causing unavoidable environmental issues, such as the emission of harmful gases and global-warming (Sun and Cheng, 2002; Wagh et al, 2016), extensive efforts must be devoted toward the search for alternative and renewable resources that are environmentally friendly. Alkyl levulinates (ALs) derived from biomass have shown great potential for biorenewable fuels like bio-lubricants (Mukherjee et al, 2015), chemicals synthesis (Mullen et al, 2013), polymer or resin precursors (Alloaoua et al, 2014; Cousinet, 2014), green solvents (Lomba et al, 2011), plasticizers (Bloom, 2007), food-flavor agents (Yontz, 2011), and pharmaceuticals (Tsucha and Yoshida, 1994) during the effective utilization of biomass (Table 1). Research on ALs has mainly concentrated on methyl, ethyl, and butyl levulinate (Mascal and Nikitin, 2010b). Among these three levulinates, ethyl levulinate (EL) exhibits enhanced solubility with diesel (Christensen et al, 2011)
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