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Impact of dual temperature profile in dilute acid hydrolysis of spruce for ethanol production.

Bösch P, Wallberg O, Joelsson E, Galbe M, Zacchi G - Biotechnol Biofuels (2010)

Bottom Line: The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH.When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH.Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Lund University, P,O, Box 124, SE-221 00 Lund, Sweden. ola.wallberg@chemeng.lth.se.

ABSTRACT

Background: The two-step dilute acid hydrolysis (DAH) of softwood is costly in energy demands and capital costs. However, it has the advantage that hydrolysis and subsequent removal of hemicellulose-derived sugars can be carried out under conditions of low severity, resulting in a reduction in the level of sugar degradation products during the more severe subsequent steps of cellulose hydrolysis. In this paper, we discuss a single-step DAH method that incorporates a temperature profile at two levels. This profile should simulate the two-step process while removing its major disadvantage, that is, the washing step between the runs, which leads to increased energy demand.

Results: The experiments were conducted in a reactor with a controlled temperature profile. The total dry matter content of the hydrolysate was up to 21.1% w/w, corresponding to a content of 15.5% w/w of water insoluble solids. The highest measured glucose yield, (18.3 g glucose per 100 g dry raw material), was obtained after DAH cycles of 3 min at 209 degrees C and 6 min at 211 degrees C with 1% H2SO4, which resulted in a total of 26.3 g solubilized C6 sugars per 100 g dry raw material. To estimate the remaining sugar potential, enzymatic hydrolysis (EH) of the solid fraction was also performed. EH of the solid residue increased the total level of solubilized C6 sugars to a maximum of 35.5 g per 100 g dry raw material when DAH was performed as described above (3 min at 210 degrees C and 2 min at 211 degrees C with 1% H2SO4).

Conclusion: The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH. When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH. Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis. A two-step steam pretreatment with EH gave rise to a considerably higher sugar yield in this study.

No MeSH data available.


Flow diagram of the sugar solubilization by pretreatment at a combined severity factor (CS) of 3.17 followed by enzymatic hydrolysis (EH).
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Figure 8: Flow diagram of the sugar solubilization by pretreatment at a combined severity factor (CS) of 3.17 followed by enzymatic hydrolysis (EH).

Mentions: EH of the total slurry was performed for selected samples to evaluate which sugar yield was potentially obtainable. The highest level of solubilized hexoses, (that is, 36.4 g per 100 g DM (55% of theoretical value)), was found for DAH at a CS of 3.17 (corresponding to 1% H2SO4, for 7 min at 202°C). Figure 7 shows a plateau of 35 g per 100 g DM for a CS of 2.95 to 3.38 with an assumed peak at 3.02 to 3.17. At a CS of 3.40 and higher, a rapid decline in hexoses was measured. The maximum yield of glucose after EH was 28.8 g per 100 g DM at a CS of 3.17 (57.5% of theoretical value), from which 14.6 g per 100 g DM was released by EH. The best-case scenario is shown in detail by Table 3 with a supporting process flow diagram (Figure 8).


Impact of dual temperature profile in dilute acid hydrolysis of spruce for ethanol production.

Bösch P, Wallberg O, Joelsson E, Galbe M, Zacchi G - Biotechnol Biofuels (2010)

Flow diagram of the sugar solubilization by pretreatment at a combined severity factor (CS) of 3.17 followed by enzymatic hydrolysis (EH).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2908586&req=5

Figure 8: Flow diagram of the sugar solubilization by pretreatment at a combined severity factor (CS) of 3.17 followed by enzymatic hydrolysis (EH).
Mentions: EH of the total slurry was performed for selected samples to evaluate which sugar yield was potentially obtainable. The highest level of solubilized hexoses, (that is, 36.4 g per 100 g DM (55% of theoretical value)), was found for DAH at a CS of 3.17 (corresponding to 1% H2SO4, for 7 min at 202°C). Figure 7 shows a plateau of 35 g per 100 g DM for a CS of 2.95 to 3.38 with an assumed peak at 3.02 to 3.17. At a CS of 3.40 and higher, a rapid decline in hexoses was measured. The maximum yield of glucose after EH was 28.8 g per 100 g DM at a CS of 3.17 (57.5% of theoretical value), from which 14.6 g per 100 g DM was released by EH. The best-case scenario is shown in detail by Table 3 with a supporting process flow diagram (Figure 8).

Bottom Line: The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH.When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH.Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Lund University, P,O, Box 124, SE-221 00 Lund, Sweden. ola.wallberg@chemeng.lth.se.

ABSTRACT

Background: The two-step dilute acid hydrolysis (DAH) of softwood is costly in energy demands and capital costs. However, it has the advantage that hydrolysis and subsequent removal of hemicellulose-derived sugars can be carried out under conditions of low severity, resulting in a reduction in the level of sugar degradation products during the more severe subsequent steps of cellulose hydrolysis. In this paper, we discuss a single-step DAH method that incorporates a temperature profile at two levels. This profile should simulate the two-step process while removing its major disadvantage, that is, the washing step between the runs, which leads to increased energy demand.

Results: The experiments were conducted in a reactor with a controlled temperature profile. The total dry matter content of the hydrolysate was up to 21.1% w/w, corresponding to a content of 15.5% w/w of water insoluble solids. The highest measured glucose yield, (18.3 g glucose per 100 g dry raw material), was obtained after DAH cycles of 3 min at 209 degrees C and 6 min at 211 degrees C with 1% H2SO4, which resulted in a total of 26.3 g solubilized C6 sugars per 100 g dry raw material. To estimate the remaining sugar potential, enzymatic hydrolysis (EH) of the solid fraction was also performed. EH of the solid residue increased the total level of solubilized C6 sugars to a maximum of 35.5 g per 100 g dry raw material when DAH was performed as described above (3 min at 210 degrees C and 2 min at 211 degrees C with 1% H2SO4).

Conclusion: The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH. When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH. Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis. A two-step steam pretreatment with EH gave rise to a considerably higher sugar yield in this study.

No MeSH data available.