Dilute acid pretreatment lignocellulosic material

Dilute acid pretreatment opens up the lignocelluloses structure as well as enhances the hydrolysis process, if right conditions are employed. It is a very popular method in which a very low concentration of acid (e.g., 0.1-1.0%) is used. Much research has explored the use of acid pretreatments of different lignocellulosic materials, focusing on chemical composition of the materials, operating time, concentration of acid. 

Acid hydrolysis has been successfully employed for pretreatment of lignocellulosic materials. Dilute sulfuric acid, used at either low or high temperature, achieves high xylan to xylose conversion. This is favorable to the overall economics, as xylan accounts for a large part of the total carbohydrates in the lignocellulosic materials. 

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. 

Another approach to improving cellulose filler dispersibility is described in U.S. Pat. No. 4,559,376 [37], according to which cellulose or lignocellulose material is subjected to a hydrolytic pretreatment using diluted hydrochloric or sulfuric acid. Essentially, the treatment converts cellulose or lignocellulose material to a fine... 

In cellulosic ethanol production processes, a pretreatment procedure is needed to disrupt the recalcitrant structure of the lignocellulosic materials so that the cellulose can be more efficiently hydrolyzed by cellulase enzymes [2], These pretreatments include physical, biological, and chemical ways, such as uncatalyzed steam explosion, liquid hot water, dilute acid, flow-through acid pretreatment, lime, ammonium fiber/freeze explosion, and ammonium recycle percolation [3, 4], Most of these methods involve a high temperature requirement, which is usually achieved through convection- or conduction-based heating. 

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