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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.


C6 sugars and degradation products in the total slurry as a percentage of the total C6 sugars in the raw material (% mol/mol). Filled black triangle, glucose + mannose + galactose; filled black diamond, formic acid; filled black circle, levulinic acid; filled black square, hydroxymethylfurfuraldehyde (HMF).
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Figure 6: C6 sugars and degradation products in the total slurry as a percentage of the total C6 sugars in the raw material (% mol/mol). Filled black triangle, glucose + mannose + galactose; filled black diamond, formic acid; filled black circle, levulinic acid; filled black square, hydroxymethylfurfuraldehyde (HMF).

Mentions: The formation of sugar-derived degradation products increased significantly when the severity was increased: the pentoses xylose and arabinose were degraded to furfural, which was then further oxidized to formic acid [23]. The level of C5 sugars in the pretreated material declined rapidly, as shown in Figure 5. Whereas 75% mol/mol C5 sugars in the raw material could be recovered at a CS of 2.70, only 23% mol/mol were recovered at a CS of 3.93. Compared with the C5 sugars, the formation of furfural increased as the severity was raised. The low level of furfural in comparison to that of C5 sugars can be explained by its volatility; the furfural evaporated by flashing (that is, by release of pressure) and by its subsequent degradation to formic acid. The ratio of acetic acid increased only slightly, thus confirming the high degree of hemicellulose degradation under the specified conditions. Hexoses were degraded to HMF (ratio 1:1), which was then further degraded to formic acid and levulinic acid (ratio 1:1:1) [23]. The profile of the HMF formation (Figure 6) followed the same trend as the monosaccharide formation, but was slightly shifted along the CS axis. The peak of the HMF formation was found at severities of 3.4 to 3.6. This was believed to result from the rate of degradation of HMF to acids becoming higher than the formation of HMF as glucose formation was limited by the reaction of cellulose to glucose. Mannose also contributed to the formation of HMF. The formic acid formation followed the same trend as that of levulinic acid but was shifted by 3% mol/mol due to the contribution of the furfural degradation, which was evident even at the lowest of the investigated severity levels. The acid formation showed a steep increase in reaction rate at CS 3.40 and this coincided with the highest hexose yield and a leveling-off at the maximum of the HMF concentration.


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)

C6 sugars and degradation products in the total slurry as a percentage of the total C6 sugars in the raw material (% mol/mol). Filled black triangle, glucose + mannose + galactose; filled black diamond, formic acid; filled black circle, levulinic acid; filled black square, hydroxymethylfurfuraldehyde (HMF).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: C6 sugars and degradation products in the total slurry as a percentage of the total C6 sugars in the raw material (% mol/mol). Filled black triangle, glucose + mannose + galactose; filled black diamond, formic acid; filled black circle, levulinic acid; filled black square, hydroxymethylfurfuraldehyde (HMF).
Mentions: The formation of sugar-derived degradation products increased significantly when the severity was increased: the pentoses xylose and arabinose were degraded to furfural, which was then further oxidized to formic acid [23]. The level of C5 sugars in the pretreated material declined rapidly, as shown in Figure 5. Whereas 75% mol/mol C5 sugars in the raw material could be recovered at a CS of 2.70, only 23% mol/mol were recovered at a CS of 3.93. Compared with the C5 sugars, the formation of furfural increased as the severity was raised. The low level of furfural in comparison to that of C5 sugars can be explained by its volatility; the furfural evaporated by flashing (that is, by release of pressure) and by its subsequent degradation to formic acid. The ratio of acetic acid increased only slightly, thus confirming the high degree of hemicellulose degradation under the specified conditions. Hexoses were degraded to HMF (ratio 1:1), which was then further degraded to formic acid and levulinic acid (ratio 1:1:1) [23]. The profile of the HMF formation (Figure 6) followed the same trend as the monosaccharide formation, but was slightly shifted along the CS axis. The peak of the HMF formation was found at severities of 3.4 to 3.6. This was believed to result from the rate of degradation of HMF to acids becoming higher than the formation of HMF as glucose formation was limited by the reaction of cellulose to glucose. Mannose also contributed to the formation of HMF. The formic acid formation followed the same trend as that of levulinic acid but was shifted by 3% mol/mol due to the contribution of the furfural degradation, which was evident even at the lowest of the investigated severity levels. The acid formation showed a steep increase in reaction rate at CS 3.40 and this coincided with the highest hexose yield and a leveling-off at the maximum of the HMF concentration.

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.