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The kinetics of inhibitor production resulting from hydrothermal deconstruction of wheat straw studied using a pressurised microwave reactor.

Ibbett R, Gaddipati S, Greetham D, Hill S, Tucker G - Biotechnol Biofuels (2014)

Bottom Line: A classical Arrhenius activation energy of 148 kJmol-1 has been determined for primary solubilisation, which is higher than the activation energy associated with historical measures of reaction severity.The gravimetric loss is primarily due to depolymerisation of the hemicellulose component of straw, but a minor proportion of lignin is solubilised at the same rate and hence may be associated with the more hydrophilic lignin-hemicellulose interface.However, furan degradation is found to be significant, which may limit ultimate quantities generated in hydrolysate liquors.

View Article: PubMed Central - HTML - PubMed

Affiliation: BBSRC Sustainable Bioenergy Research Centre, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK. roger.ibbett@nottingham.ac.uk.

ABSTRACT

Background: The use of a microwave synthesis reactor has allowed kinetic data for the hydrothermal reactions of straw biomass to be established from short times, avoiding corrections required for slow heating in conventional reactors, or two-step heating. Access to realistic kinetic data is important for predictions of optimal reaction conditions for the pretreatment of biomass for bioethanol processes, which is required to minimise production of inhibitory compounds and to maximise sugar and ethanol yields.

Results: The gravimetric loss through solubilisation of straw provided a global measure of the extent of hydrothermal deconstruction. The kinetic profiles of furan and lignin-derived inhibitors were determined in the hydrothermal hydrolysates by UV analysis, with concentrations of formic and acetic acid determined by HPLC. Kinetic analyses were either carried out by direct fitting to simple first order equations or by numerical integration of sequential reactions.

Conclusions: A classical Arrhenius activation energy of 148 kJmol-1 has been determined for primary solubilisation, which is higher than the activation energy associated with historical measures of reaction severity. The gravimetric loss is primarily due to depolymerisation of the hemicellulose component of straw, but a minor proportion of lignin is solubilised at the same rate and hence may be associated with the more hydrophilic lignin-hemicellulose interface. Acetic acid is liberated primarily from hydrolysis of pendant acetate groups on hemicellulose, although this occurs at a rate that is too slow to provide catalytic enhancement to the primary solubilisation reactions. However, the increase in protons may enhance secondary reactions leading to the production of furans and formic acid. The work has suggested that formic acid may be formed under these hydrothermal conditions via direct reaction of sugar end groups rather than furan breakdown. However, furan degradation is found to be significant, which may limit ultimate quantities generated in hydrolysate liquors.

No MeSH data available.


Related in: MedlinePlus

Influence of liquor ratio on kinetics of inhibitor formation following hydrothermal reactions at 200°C. a) Primary reactions of total solubilised mass: *, 4:1; ▲, 10:1; soluble lignin: x, 4:1; ●, 10:1; and acetic acid: ♦, 4:1; ■, 10:1. b) Secondary reactions of furans: ♦, 4:1; ■, 10:1; and formic acid: ▲, 4:1; ●, 10:1.
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Figure 6: Influence of liquor ratio on kinetics of inhibitor formation following hydrothermal reactions at 200°C. a) Primary reactions of total solubilised mass: *, 4:1; ▲, 10:1; soluble lignin: x, 4:1; ●, 10:1; and acetic acid: ♦, 4:1; ■, 10:1. b) Secondary reactions of furans: ♦, 4:1; ■, 10:1; and formic acid: ▲, 4:1; ●, 10:1.

Mentions: A further series of hydrolysate liquors were collected from hydrothermal reactions at a temperature of 200°C, at a lower water to biomass ratio of 4:1. The UV measurement of the liquors was again used and provided an indication of the evolution of the key soluble lignin and furanic compounds over time, shown in comparison with the corresponding 10:1 liquor ratio data in Figure 6. From the gravimetric weight loss determinations, in g/kg-dry biomass units, it appeared that the global solubilisation reactions proceeded at the same rate at the lower liquor ratio, within the limits of the experimental resolution, releasing the same amount of biomass material. The overall rate of lignin solubilisation was similar at both 4:1 and 10:1 liquor ratios, but a greater amount of lignin was apparently solubilised at lower liquor ratio. There was also a noticeable reduction in soluble lignin concentration as the reaction proceeded to longer times, which is presumed to be due to an increased likelihood of recondensation of reactive lignin species at higher biomass concentration. This was also mirrored in a slight reduction in overall weight loss at longer reaction times.


The kinetics of inhibitor production resulting from hydrothermal deconstruction of wheat straw studied using a pressurised microwave reactor.

Ibbett R, Gaddipati S, Greetham D, Hill S, Tucker G - Biotechnol Biofuels (2014)

Influence of liquor ratio on kinetics of inhibitor formation following hydrothermal reactions at 200°C. a) Primary reactions of total solubilised mass: *, 4:1; ▲, 10:1; soluble lignin: x, 4:1; ●, 10:1; and acetic acid: ♦, 4:1; ■, 10:1. b) Secondary reactions of furans: ♦, 4:1; ■, 10:1; and formic acid: ▲, 4:1; ●, 10:1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230421&req=5

Figure 6: Influence of liquor ratio on kinetics of inhibitor formation following hydrothermal reactions at 200°C. a) Primary reactions of total solubilised mass: *, 4:1; ▲, 10:1; soluble lignin: x, 4:1; ●, 10:1; and acetic acid: ♦, 4:1; ■, 10:1. b) Secondary reactions of furans: ♦, 4:1; ■, 10:1; and formic acid: ▲, 4:1; ●, 10:1.
Mentions: A further series of hydrolysate liquors were collected from hydrothermal reactions at a temperature of 200°C, at a lower water to biomass ratio of 4:1. The UV measurement of the liquors was again used and provided an indication of the evolution of the key soluble lignin and furanic compounds over time, shown in comparison with the corresponding 10:1 liquor ratio data in Figure 6. From the gravimetric weight loss determinations, in g/kg-dry biomass units, it appeared that the global solubilisation reactions proceeded at the same rate at the lower liquor ratio, within the limits of the experimental resolution, releasing the same amount of biomass material. The overall rate of lignin solubilisation was similar at both 4:1 and 10:1 liquor ratios, but a greater amount of lignin was apparently solubilised at lower liquor ratio. There was also a noticeable reduction in soluble lignin concentration as the reaction proceeded to longer times, which is presumed to be due to an increased likelihood of recondensation of reactive lignin species at higher biomass concentration. This was also mirrored in a slight reduction in overall weight loss at longer reaction times.

Bottom Line: A classical Arrhenius activation energy of 148 kJmol-1 has been determined for primary solubilisation, which is higher than the activation energy associated with historical measures of reaction severity.The gravimetric loss is primarily due to depolymerisation of the hemicellulose component of straw, but a minor proportion of lignin is solubilised at the same rate and hence may be associated with the more hydrophilic lignin-hemicellulose interface.However, furan degradation is found to be significant, which may limit ultimate quantities generated in hydrolysate liquors.

View Article: PubMed Central - HTML - PubMed

Affiliation: BBSRC Sustainable Bioenergy Research Centre, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK. roger.ibbett@nottingham.ac.uk.

ABSTRACT

Background: The use of a microwave synthesis reactor has allowed kinetic data for the hydrothermal reactions of straw biomass to be established from short times, avoiding corrections required for slow heating in conventional reactors, or two-step heating. Access to realistic kinetic data is important for predictions of optimal reaction conditions for the pretreatment of biomass for bioethanol processes, which is required to minimise production of inhibitory compounds and to maximise sugar and ethanol yields.

Results: The gravimetric loss through solubilisation of straw provided a global measure of the extent of hydrothermal deconstruction. The kinetic profiles of furan and lignin-derived inhibitors were determined in the hydrothermal hydrolysates by UV analysis, with concentrations of formic and acetic acid determined by HPLC. Kinetic analyses were either carried out by direct fitting to simple first order equations or by numerical integration of sequential reactions.

Conclusions: A classical Arrhenius activation energy of 148 kJmol-1 has been determined for primary solubilisation, which is higher than the activation energy associated with historical measures of reaction severity. The gravimetric loss is primarily due to depolymerisation of the hemicellulose component of straw, but a minor proportion of lignin is solubilised at the same rate and hence may be associated with the more hydrophilic lignin-hemicellulose interface. Acetic acid is liberated primarily from hydrolysis of pendant acetate groups on hemicellulose, although this occurs at a rate that is too slow to provide catalytic enhancement to the primary solubilisation reactions. However, the increase in protons may enhance secondary reactions leading to the production of furans and formic acid. The work has suggested that formic acid may be formed under these hydrothermal conditions via direct reaction of sugar end groups rather than furan breakdown. However, furan degradation is found to be significant, which may limit ultimate quantities generated in hydrolysate liquors.

No MeSH data available.


Related in: MedlinePlus