Solids concentration hemicellulose hydrolysis

These results could suggest that what has been traditionally been described as "biphasic" behavior may reflect a combination of chemical reaction and mass transfer effects, with each limiting xylan reaction and removal at different stages or modes of operation. This effect might be better described by a model that incorporates reaction of solids to form soluble species as a function of temperature and acid concentration coupled with a second mass transfer step that is affected by flow. On this basis, we plan to investigate whether the pore leaching model could be simplified and adapted in this way to better describe hemicellulose hydrolysis. 

Because the hemicellulose fraction of biomass materials can be separated from lignin and cellulose by dilute acid treatment, cellulose becomes more reactive towards cellulase. Hemicellulose hydrolysis rates vary with acid concentration, temperature, and solid-to-liquid ratio. With most lignocellulosic materials, complete hemicellulose hydrolysis can be achieved in 5-10 min at 160°C or 30-60 min at 140 °C. Dilute acid hydrolysis forms the basis of many pretreatment processes for example, autohydrolysis and steam explosion are based on high-temperature dilute acid catalyzed hydrolysis of biomass. 

Traditional hemicellulose hydrolysis kinetic models cannot account for a change in hemicellulose sugar yields with solids concentration and suffer from inconsistencies that bring into question their mechanistic accuracy. Thus, although current models can be usefiil for a given flow regime, their ability to describe different systems such as flowthrough reactors on a consistent basis is unproven (29). 

Corn fiber is composed of approximately 20% starch, 35% hemicellulose, 18% cellulose, 11% protein, 3% oil, and 6% ash. The hemicellulose is primarily composed of xylose (-55%) and arabinose (-36%). Corn fiber can be fractionated using combinations of enzymatic and thermochemical (heat plus acid or base) methods. Many different hydrolysis schemes have been carried out on the corn fiber to obtain various industrially useful components. The hydrolysis step creates mainly oligosaccharides, with lower concentrations of monosaccharides and degradation products. These oligosaccharides are further hydrolyzed to monosaccharides by a secondary hydrolysis. In this experiment, the corn fiber was hydrolyzed at 30% solids at 140°C for 30 minutes followed, optionally, by an acid hydrolysis or enzyme hydrolysis. The most optimal hydrolysis method was the initial thermochemical hydrolysis method without the further acid or enzyme hydrolysis. The glucose and xylose monosaccharides present in the hydrolysates were fermented to ethanol by a recombinant strain of Saccharomyces cerevisiae 424A to produce up to 58 g/L of ethanol in the fermentation broth. 

The effect of three high-solids hydrolysis metfiods on corn fiber were determined by the monomer sugar concentrations and the solubilization percentage. Generally, the hydrolysis of corn fiber proceeds, as severity of treatment increases, in the order of starch, hemicellulose branches, hemicellulose xylose backbone, and then cellulose (4). 

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