Temperature lignocellulose acid

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. 

In a study by Rahman et al. (2007), the selectivity and xylose yield were developed to study individual and combined effect of parameters such as temperature, retention time and acid concentration at five different levels. The feedstock under study was oil palm empty fruit bunch fiber which is a lignocellulosic waste from palm oil mills and a potential source of xylose that can be used as a raw material for production of xylitol. It was found that under optimum conditions (i.e., temperature 119°C, reaction time 60 min and H SO concentration 2%), the xylose yield and selectivity were 91.3% and 18 g/g, respectively. The combined effect of temperature with reaction time and temperature with acid concentration was found to be more prominent than combined effect of reaction time and acid concentration. 

The CHAP process is based on the hydrolysis of lignocellulosic material by concentrated hydrochloric acid at low temperature and subsequent sugar fermentation. 

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. 

In summary, the chemicals to be laboratory-tested must be capable of reacting with lignocellulosic hydroxyls under neutral or mildly alkaline or acidic conditions at temperatures below 150°C. The chemical system should be simple and capable of swelling the structure to facilitate penetration. The complete molecule should react quickly with lignocellulosic components yielding stable chemical bonds, and the treated lignocellulosic must still possess the desirable properties of untreated lignocellulosics. 

Procedures bearing some similarity to the Philippou process were patented by Emerson in 1953 and 1963 104, 105). The first patent consisted of pretreatment of lignocellulosic particulate material with urea (0.7-11%), followed by addition of furfural (0.8-16%) and an acid or acid salt catalyst (1.0-16%), and pressing at elevated temperatures. The second involved a mixture of urea, furfural, lignin, petroleum resin, drying oil, wax, and an oxidation catalyst as a cross-linking mixture. 

Several processes, other than dilute acid hydrolysis, have been used to make biomass accessible to enzymatic breakdown for the generation of fermentable sugars. For ammonia disruption, the lignocellulose is exposed to ammonia at a high pressure and a temperature ranging from 25°C to The elevated... 

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. 

Fig. 19 shows the adsorption capacity attained with other precursors such as a bituminous and a subbituminous coal, vs. the heat treatment temperature and compared with wood [46]. It is clear that phosphoric acid activation must only be applied to lignocellulosic materials since the coals hardly develop any porosity. 

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