Advances in understanding the humins: Formation , prevention and application

Abstract

The formation of dark-colored solids, as known as humins, was observed during acid-catalyzed dehydration of certain biomass platform molecules like fructose, glucose and 5-hydroxymethylfurfural (HMF). Humins structures were found to be precipitated as microspheres in the liquid phase and/or on the surfaces of solid catalyst and reactor walls. Humins formation begins with random and uncontrollable condensation of key intermediate molecules, namely, glucose, HMF, 1,2,4-Trihydroxybenzene (TB), 2,5-dioxo-6-hydroxyhexanal (DHH), etc. Further, mechanism network of humins formation also contains polymerization of soluble oligomers, growth of primary particles, physical absorption to soluble molecules and aggregation of particle groups. Humins formation retards the economy, safety and efficiency of cellulosic carbon conversion including wasting the substrates, blocking the reactor, causing deactivation of catalyst and absorbing the high-value molecules products. This necessitates the systematic elucidation of humins, including its formation mechanism network, characterization techniques and high-value utilization. This review organized significant studies of humins formation, including (i) background information of humins during different conversion process, (ii) different analytical techniques for humins characterization, (iii) the properties and formation mechanism of humins, (iv) prevention methods of humins formation and (v) exploration of high-value humins utilization.

Keywords

• Lignocellulosic Biomass
• Cellulose catalytic conversion
• Humins formation