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Isfahan University of Tech team reports new efficient pretreatment method for rice straw to boost yield of cellulosic ethanol

Researchers at Isfahan University of Technology (Iran) report the efficient production of cellulosic ethanol from rice straw using a new sodium carbonate pretreatment method. In a paper published in the ACS journal Energy & Fuels, they presented results indicating an hydrolysis yield of 97% and the resulting production of 175 g of ethanol per 1 kg of rice straw.

Rice straw was treated with sodium carbonate (Na2CO3)prior to enzymatic hydrolysis and fermentation. All pretreatments were performed in a high-pressure reactor at 90, 120, 150, and 180 °C by 0.25, 0.5, and 1 M sodium carbonate solution. Afterward, enzymatic hydrolysis of the untreated and all treated straws were conducted at 45 °C for 72 h with enzyme loading of 20 FPU cellulase and 30 IU β-glucosidase per gram of substrate. The best pretreatment conditions were obtained to be 0.5 M Na2CO3 at 180 °C for 120 min.

Material balance flow diagram for pretreatment and simultaneous saccharification and fermentation (SSF) for the straw treated with 0.5 M Na2CO3 at 180 °C for 120 min. Credit: ACS, Salehi et al. Click to enlarge.

This pretreatment improved the released glucose from 9.5 g/L for the untreated straw to 43.5 g/L for the treated one. On the other hand, the treatment showed significant improvement on ethanol production from rice straw applying simultaneous saccharification and fermentation. Ethanol production was enhanced from 90.2 to 351.4 g/L by the treatment. The analysis showed that the treatment with sodium carbonate at elevated temperature can significantly reduce the lignin and xylan contents and the cellulose crystallinity and also convert cellulose type I to type II, which is more amenable for enzymatic hydrolysis.

...considering the average ratio of rice straw to harvested grain to be 1.25 and based on annual rice production it can be claimed that more than 200 billion liters of bioethanol can be produced annually from rice straw using an inexpensive chemical without the necessity of neutralization and pollutant production.


  • S. M. Amin Salehi, Keikhosro Karimi, Tayebeh Behzad, and Nafiseh Poornejad (2012) Efficient Conversion of Rice Straw to Bioethanol Using Sodium Carbonate Pretreatment. Energy & Fuels doi: 10.1021/ef301476b



Now all they need is a yeast that produces its own cellulase and β-glucosidase, and a design for a system which produces the process heat from non-fossil sources.


How about burning some of the rice straw for process heat.


Very inefficient use of captured energy.  Instead of a fraction of a percent of incident radiation going into straw for process heat, you could easily get 50% with solar collectors.

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