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Effect of mixing on enzymatic hydrolysis of steam-pretreated spruce: a quantitative analysis of conversion and power consumption.

Palmqvist B, Wiman M, Lidén G - Biotechnol Biofuels (2011)

Bottom Line: In addition, the results were related to the power input needed to operate the impeller at different speeds, taking into account the changes in rheology throughout the process.A marked difference in hydrolysis rate at different impeller speeds was found.For example, the conversion was twice as high after 48 hours at 500 rpm compared with 25 rpm.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Lund University, Box 124, Se-221 00 Lund, Sweden. benny.palmqvist@chemeng.lth.se.

ABSTRACT

Background: When scaling up lignocellulose-based ethanol production, the desire to increase the final ethanol titer after fermentation can introduce problems. A high concentration of water-insoluble solids (WIS) is needed in the enzymatic hydrolysis step, resulting in increased viscosity, which can cause mass and heat transfer problems because of poor mixing of the material. In the present study, the effects of mixing on the enzymatic hydrolysis of steam-pretreated spruce were investigated using a stirred tank reactor operated with different impeller speeds and enzyme loadings. In addition, the results were related to the power input needed to operate the impeller at different speeds, taking into account the changes in rheology throughout the process.

Results: A marked difference in hydrolysis rate at different impeller speeds was found. For example, the conversion was twice as high after 48 hours at 500 rpm compared with 25 rpm. This difference remained throughout the 96 hours of hydrolysis. Substantial amounts of energy were required to achieve only minor increases in conversion during the later stages of the process.

Conclusions: Impeller speed strongly affected both the hydrolysis rate of the pretreated spruce and needed power input. Similar conversions could be obtained at different energy input by altering the mixing (that is, energy input), enzyme load and residence time, an important issue to consider when designing large-scale plants.

No MeSH data available.


Related in: MedlinePlus

Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times and response surface area and hydrolysis time for the two different enzyme loadings. (A, B) Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times (circles = 96 hours, diamonds = 48 hours, squares = 24 hours). (A) Solid lines = enzyme load of 20 FPU/g glucan; (B) dashed lines = 10 FPU/g glucan. (C, D) Response surface area, where conversion is a function of total energy input and hydrolysis time for the two different enzyme loadings, (C) 20 FPU/g glucan and (D) 10 FPU/g glucan.
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Figure 4: Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times and response surface area and hydrolysis time for the two different enzyme loadings. (A, B) Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times (circles = 96 hours, diamonds = 48 hours, squares = 24 hours). (A) Solid lines = enzyme load of 20 FPU/g glucan; (B) dashed lines = 10 FPU/g glucan. (C, D) Response surface area, where conversion is a function of total energy input and hydrolysis time for the two different enzyme loadings, (C) 20 FPU/g glucan and (D) 10 FPU/g glucan.

Mentions: A relationship between power number (P0) and Reynolds impeller number (Rei) was established from the power measurements and the rheological data provided by Wiman et al. [2] (Figure 2). The data were fitted to the equation previously suggested by Wassmer and Hungenberg [22] (P0 = K1/Rei + K2) to relate the power number to the Reynolds impeller number over a wide range of Rei. The fitted values for the parameters, K1 and K2, were 346.7 and 1.27 respectively. As the hydrolysis proceeded, the viscosity of the material decreased, which led to reduced power consumption (Figure 3a); that is, the viscosity reduction led to an increase in Reynolds impeller number, which in turn led to a decrease in power number (Figure 2). Clearly, the total dissipated energy during the hydrolysis increased drastically with increased impeller speed (Figure 3b). By increasing the enzyme dosage, the energy consumption could be reduced, because of faster hydrolysis of the material, which lowered the viscosity. It was therefore possible to reach similar conversions at different mixing energy input by altering residence time, impeller speed and/or enzyme load (Figure 4). In addition, it was clear that substantial amounts of energy were required to achieve only minor increases in conversion during the later stages of hydrolysis. A surface-response statistical model was used to illustrate the influence of energy input, residence time and enzyme loading on the conversion (Figure 4 c-d). First- and second-order terms were sufficient to describe the data satisfactorily (R2 = 0.991 and 0.980 respectively for the different enzyme loads).


Effect of mixing on enzymatic hydrolysis of steam-pretreated spruce: a quantitative analysis of conversion and power consumption.

Palmqvist B, Wiman M, Lidén G - Biotechnol Biofuels (2011)

Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times and response surface area and hydrolysis time for the two different enzyme loadings. (A, B) Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times (circles = 96 hours, diamonds = 48 hours, squares = 24 hours). (A) Solid lines = enzyme load of 20 FPU/g glucan; (B) dashed lines = 10 FPU/g glucan. (C, D) Response surface area, where conversion is a function of total energy input and hydrolysis time for the two different enzyme loadings, (C) 20 FPU/g glucan and (D) 10 FPU/g glucan.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3113933&req=5

Figure 4: Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times and response surface area and hydrolysis time for the two different enzyme loadings. (A, B) Conversions obtained for enzymatic hydrolysis of pretreated spruce at corresponding energy input for three selected times (circles = 96 hours, diamonds = 48 hours, squares = 24 hours). (A) Solid lines = enzyme load of 20 FPU/g glucan; (B) dashed lines = 10 FPU/g glucan. (C, D) Response surface area, where conversion is a function of total energy input and hydrolysis time for the two different enzyme loadings, (C) 20 FPU/g glucan and (D) 10 FPU/g glucan.
Mentions: A relationship between power number (P0) and Reynolds impeller number (Rei) was established from the power measurements and the rheological data provided by Wiman et al. [2] (Figure 2). The data were fitted to the equation previously suggested by Wassmer and Hungenberg [22] (P0 = K1/Rei + K2) to relate the power number to the Reynolds impeller number over a wide range of Rei. The fitted values for the parameters, K1 and K2, were 346.7 and 1.27 respectively. As the hydrolysis proceeded, the viscosity of the material decreased, which led to reduced power consumption (Figure 3a); that is, the viscosity reduction led to an increase in Reynolds impeller number, which in turn led to a decrease in power number (Figure 2). Clearly, the total dissipated energy during the hydrolysis increased drastically with increased impeller speed (Figure 3b). By increasing the enzyme dosage, the energy consumption could be reduced, because of faster hydrolysis of the material, which lowered the viscosity. It was therefore possible to reach similar conversions at different mixing energy input by altering residence time, impeller speed and/or enzyme load (Figure 4). In addition, it was clear that substantial amounts of energy were required to achieve only minor increases in conversion during the later stages of hydrolysis. A surface-response statistical model was used to illustrate the influence of energy input, residence time and enzyme loading on the conversion (Figure 4 c-d). First- and second-order terms were sufficient to describe the data satisfactorily (R2 = 0.991 and 0.980 respectively for the different enzyme loads).

Bottom Line: In addition, the results were related to the power input needed to operate the impeller at different speeds, taking into account the changes in rheology throughout the process.A marked difference in hydrolysis rate at different impeller speeds was found.For example, the conversion was twice as high after 48 hours at 500 rpm compared with 25 rpm.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Lund University, Box 124, Se-221 00 Lund, Sweden. benny.palmqvist@chemeng.lth.se.

ABSTRACT

Background: When scaling up lignocellulose-based ethanol production, the desire to increase the final ethanol titer after fermentation can introduce problems. A high concentration of water-insoluble solids (WIS) is needed in the enzymatic hydrolysis step, resulting in increased viscosity, which can cause mass and heat transfer problems because of poor mixing of the material. In the present study, the effects of mixing on the enzymatic hydrolysis of steam-pretreated spruce were investigated using a stirred tank reactor operated with different impeller speeds and enzyme loadings. In addition, the results were related to the power input needed to operate the impeller at different speeds, taking into account the changes in rheology throughout the process.

Results: A marked difference in hydrolysis rate at different impeller speeds was found. For example, the conversion was twice as high after 48 hours at 500 rpm compared with 25 rpm. This difference remained throughout the 96 hours of hydrolysis. Substantial amounts of energy were required to achieve only minor increases in conversion during the later stages of the process.

Conclusions: Impeller speed strongly affected both the hydrolysis rate of the pretreated spruce and needed power input. Similar conversions could be obtained at different energy input by altering the mixing (that is, energy input), enzyme load and residence time, an important issue to consider when designing large-scale plants.

No MeSH data available.


Related in: MedlinePlus