Furans production from biomass

The great and increasing interest in the production of furan derivatives from biomass resources is due to the wide range of chemical intermediates and end products that can be produced from these compounds [179]. HMF, for instance, is the key intermediate to bridge the gap between biomass resources and biochemicals (Figure 6.35) [180]. 

Production of Furans from Biomass-derived Sources... 

Finally, the HMF rehydration and ring cleavage product levulinic acid (LA) 4, which can be produced from HMF, XMFs, or directly from biomass, has also entered into the mainstream of renewable chemistry. With its easy availability and a derivative chemistry that rivals that of the furans, LA is currently leading the charge towards commercialization within the furanics movement, and piloted approaches to its production and applications are described. 

This efficient conversion is a good example of the potential of gold catalysis to produce useful chemicals from biomass-derived starting materials. Methylfuroate formed from furfural is useful for flavor and fragrance applications and has potential as an industrial solvent. FDMC derived from HMF is a monomer that could replace the terephthalic acid used for making polyester plastics. The course of the reaction is quite different from when a platinum catalyst is used because furan dicar-baldehyde is the product from the Pt-catalyzed oxidation of HMF in water. 

As discussed in detail in Chapter 1 [1], the chemical-catalytic approach to biomass valorization is poised to come to the fore of biorefinery operations due to its advantages over microbial and thermochemical processing of lignocellulosic feedstocks. Below, we consider three mainstream platform chemicals, collectively referred to as furanics, that are derived from the acid-catalyzed dehydration of carbohydrates. The first, 5-(hydroxymethyl)furfural, or HMF 1, is an icon of the biorefinery movement. With derivatives that branch out over multiple product manifolds, HMF is a recognized commercial opportunity for whoever can manage to produce it economically, and approaches towards the realization of this aim will be discussed. 

As furan derivatives, both furfural and 5-hydroxymethylfurfural (HMF) are readily prepared from renewable biomass. Furfural can be easily obtained from a variety of biomass containing pentoses, mainly including com cobs, oats and rice hulls, sugar cane bagasses, cotton seeds, ohve husks and stones, and wood chips. Furfuryl was first produced in the early nineteenth century and right now the annual production is 300,000 tons [101]. On the other hand, HMF is another major promising furan derivative due to its rich chemistry and potential availability from hexose carbohydrates or from their precursors such as fructose, glucose, sucrose, cellulose, and inulin [14]. 

Furfural is the starting material for the industrial production of almost all furan compounds and is industrially produced from a pentosan-rich biomass like corn cobs, oat hulls, almond husks, cottonseed hull bran, birch wood, bagasse and sunflower husks in large quantities (>200,000 mt/a). Several process improvements have been developed at pilot scale in recent years which lead to higher yields (up to 80%) due to reduced side reactions and improved product recovery [12,13]. 

Pyrolysis of biomass is carried out under inert atmosphere and forms, depending on the residence time and temperature, char, oil, and gas. Pyrolysis with long residence time at low temperamre (400°C) produces a black solid (charcoal), while fast pyrolysis at high temperarnre (500°C) favors the formation of a black liquor (bio-oil). The short contact times (<2s at ca. 500" C) thus maximize the liquid yield. Fast pyrolysis is preferred by the chemical industry because of the relative ease of handling liquids. However, bio-oil produced by pyrolysis of bulk biomass contains more than 400 different components like carboxylic acids, ketones, aldehydes, sugars, furans, (substituted) phenols, aromatics, and tar (Table 1). Separation of useful chemicals from this complex pool is very difficult. As an alternative, pyrolysis can also be used as a first step for generating heat or electricity, followed by combusting the pyrolytic products. Excellent papers and reviews that describe fast pyrolysis in more detail are available [27-32]. 

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