Since lignocellulose is mainly composed of cellulose, hemicellulose and lignin, it needs additional pretreatment in order to get sugar monomer ready for the fermentation process.

Typical process requires SHF (Separate Hydrolysis and Fermentation) of great complexity involving pretreatment, fractionation, delignification, hydrolysis and fermentation. Alternatively, pretreatment with proper steam explosion yields the hydrolysate, which can be enzymatically digested and fermented in a single reactor via SSF (Simultaneous Saccharification and Fermentation) method, as shown in Fig. 8.5.3, 8.5.4 and 8.5.5, involving only the pretreatment and hydrolysis/fermentation steps. The goal is to seek for the appropriate SSF that uses a commercially available cellulase enzyme and microorganism available in Thai market.

Source: C. Pomchaitaward et al, MTEC report (2007)

The steam explosion was applied to rice straw Supunburi1™ showing good carbohydrate recovery and high ethanol concentrations obtained in a single reactor with minimal enzyme and yeast supplementation. A 150 g of dried rice straw was steamed with pressure between 10 to 25 bar (with corresponding temperature 185 and 210 °С, respectively) for 5 minutes. Higher

steam pressure (or higher temperature) favored hemicelluloses solubilization. However, the

strong influence of steam pressure on the cellulose solubilization was not found.

pretreatment condition resulted in the production of a very small amount of sugar decomposition products, which enabled an effective fermentation of sugars to ethanol. In conclusion, mild steam pretreatment condition at 15 bars for 5 minutes results the highest hydrolysis yield.

This process substantially reduces the complexity of the overall rice straw to ethanol bioconversion, while simultaneously lowering the capital investment cost and time associated with the need for separate processes. Furthermore, it significantly lowers environmental impact due to less hazardous process chemicals and conditions involved. Last but not least, it provides an alternative for better energy efficiency in agricultural residue management.

Further information

C. Pomchaitaward et al, Feasibility Study of Ethanol Production from Lignocellulosic Materials via the Steam Explosion Pretreatment, MTEC in-house project report 2007 (chaiyapp@mtec. or. th)

S. Nivitchanyong, Alternative Energy Cluster, MTEC (siriluck@mtec. or. th)