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Production of xylose sugars in high yield by acid-catalysed hydrolysis of bio-waste wood shavings

Lignocellulosic materials such as forest products (hardwood and softwood) and their residues are renewable resources of energy.

Recent reports estimated that up to 10.5 million tonnes of wood enters the waste stream each year in the UK. A very large proportion of this material comes from the construction and demolition sector. It has been estimated that utilizing two million tonnes of this material could generate2600 GWh of electricity each year and save 1.15 million tonnes of CO2.

The aim of this work was to investigate dilute acid hydrolysis of waste cellulosic biomass (wood shavings) with phosphoric acid. The process parameters that were investigated include variation in reaction temperature (135– 200 °C) and acid catalyst concentration (2.5–10% w/v).

Figure 1 shows the effect of temperature and H3PO4 concentration on xylose formation on the dilute acid hydrolysis of wood shavings over a range of combined severity factors. Yields up to 100% have been achieved under the opimum conditions.

 

FIGURE 1

Xylose formation increased with the increasing severity factor up to 7.5% H3PO4. Xylose degradation was not observed below a reaction temperature of 135 °C. From the severity data it was also found that the yield of xylose formation increases when the acid concentration
decreases with the greatest xylose was generated at the lowest acid concentrations and temperatures, demonstrating once again that hemicelluloses are very easy to hydrolyse.

Conclusions
The dilute acid hydrolysis of wood shavings using phosphoric acid gave a good performance for sugar production. This was mainly a combination of xylose, mannose and galactose. Excellent yield was achieved (100%) under the optimum conditions. However, for glucose, an average yield of 30% was obtained. Glucose was very difficult to hydrolyse, with almost all the glucose produced coming from the glucan present in the hemicelluloses. It can be concluded that the xylose sugars are easier to produce than glucose. It is concluded that ‘‘milder’’ reaction conditions (low acid concentration and temperature) give xylose yields approaching 100%.

For more details see:

Dilute phosphoric acid-catalysed hydrolysis of municipal bio-waste wood shavings using autoclave parr reactor system.

Orozco, A.M., Al-Muhtaseb A.H., Albadarin, A.B., Rooney, D., Walker, G.M. and Ahmad, M.N.

BIORESOURCE TECHNOLOGY, 102 (2011) 9076-9082