Combined Subcritical/Supercritical And Fermentation Of Biomass For Ethanol Production

With the rising demand for liquid fuels and environment protection, the production technology of fuel ethanol from biomass is in great potential. Supercritical technology provides an effective method for the reutilization of biomass. The disposal and reutilization of biomass were realized by combined subcritical/supercritical and fermentation technology. To obtain high reducing sugar yield and concentration by subcritical/supercritical reaction and ethanol by fermentation, the influence factors, detoxification of liquefaction products and fermentation conditions were investigated.In this paper, the biomass was liquefied by subcritical/supercritical technology and the effects of temperature and solid liquid ratio on reducing sugar yield and concentration were studied. The results were as follows: (1) In the condition of 343℃, solid liquid ratio 1:3.7, the reducing sugar yield and concentration of bagasse can reach the maximum value 30.4% and 141.55g/L; (2) The reducing sugar yield and concentration of rice straw can reach the highest value 20.6% and 119.98g/L in the condition of 332℃, solid liquid ratio 1:3.6; (3) In the condition of 335℃, solid liquid ratio 1:6.5, the reducing sugar yield and concentration of wheat can reach the maximum value 23.75%,62.17g/L; (4) The reducing sugar yield and concentration of corn can reach the highest value 33.72% and 106.65g/L in the condition of 312℃, solid liquid ratio 1:3; (5) In the condition of 319℃, solid liquid ratio 1:5, the reducing sugar yield and concentration of cole can reach the maximum value 34.21% and 79.86g/L.The detoxification methods of liquid in the subcritical/supercritical water were improved: The liquid from subcritical/supercritical reaction was excessive neutralized using calcium hydroxide while pH reached 8-9, accurately regulating to 5.0 using phosphoric acid. Then 3% of volume rate of add activated carbon were added in, after stirring for 30 minutes at 50℃and filtered.The influence factors of fermentation of biomass liquefied in subcritical/supercritical water after detoxification to produce ethanol were discussed in this thesis, such as the effect of detoxification and domestication and inoculation volume of Saccharomyces cerevisiae and nutrient content. The results showed that the solution after detoxification was more conductive to fermentation and the ethanol production was improved by 35.6%. The ethanol concentration produced by Saccharomyces cerevisiae after domestication rose from 32g/L to 42.9g/L. The possible reason was that the detoxification inhibiting fermentation of the liquid was incomplete. The best inoculation volume was 10%, the pH reached 5.0 in the end of fermentation. Through the ethanol concentration, the best nutrients ratio are: MgSO₄·7H₂O 0.1g/L, KH₂PO₄ 0.15g/L, (NH₄)₂SO₄ 0.4g/L, and did the verification experiment, the ethanol concentration was 52.6g/L. The bagasse of 20g was liquefied in 343℃, the reducing sugar yield and concentration were 30.4% and 141.55g/L. So 2.09g of reducing sugar were required to produce each gram of ethanol, that was 6.88g of bagasse were required to produce each gram of ethanol. The utilization ratio of reducing sugar was 47.85%. The reducing sugar and ethanol concentration produced by cellulose were 75.94% and 36.12% .