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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

Evolution of soluble products formed following acid catalysed hydrothermal reaction of cold alkali hemicellulose extract from wheat straw. a) Acetic acid; b) xylose; and c) arabinose. Reaction in water: ●, 180°C; *, 200°C. Reaction in 1 wt% aqueous H2SO4: ♦, 160°C; ■, 180°C; ▲, 200°C.
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Figure 4: Evolution of soluble products formed following acid catalysed hydrothermal reaction of cold alkali hemicellulose extract from wheat straw. a) Acetic acid; b) xylose; and c) arabinose. Reaction in water: ●, 180°C; *, 200°C. Reaction in 1 wt% aqueous H2SO4: ♦, 160°C; ■, 180°C; ▲, 200°C.

Mentions: The trends in acetic acid concentrations in treatment liquors have also been studied by following the hydrothermal reactions of hemicellulose separated from straw, obtained by extraction as detailed in the Methods section. Kinetic data using the microwave reactor at temperatures of 180 and 200°C are shown in Figure 4a, for reactions in water and also in solutions of 1% sulphuric acid. With water as a reaction medium the concentration of acetic acid continued to evolve beyond the experiment time limit, mirroring the data for the whole straw. However, in the presence of the dilute acid catalyst the rate of evolution was faster, as expected, reaching an asymptote of similar concentration at both reaction temperatures. This supports the conclusion that a finite number of acetate substituents on hemicellulose are available for hydrolysis, with no suggestion of continuing liberation of acetic acid due to breakdown of terminal or monomer sugar groups [16]. This allows some confidence in estimation of the total potential acetic acid concentrations, which might be expected in hydrothermal process or fermentation liquors.


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)

Evolution of soluble products formed following acid catalysed hydrothermal reaction of cold alkali hemicellulose extract from wheat straw. a) Acetic acid; b) xylose; and c) arabinose. Reaction in water: ●, 180°C; *, 200°C. Reaction in 1 wt% aqueous H2SO4: ♦, 160°C; ■, 180°C; ▲, 200°C.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Evolution of soluble products formed following acid catalysed hydrothermal reaction of cold alkali hemicellulose extract from wheat straw. a) Acetic acid; b) xylose; and c) arabinose. Reaction in water: ●, 180°C; *, 200°C. Reaction in 1 wt% aqueous H2SO4: ♦, 160°C; ■, 180°C; ▲, 200°C.
Mentions: The trends in acetic acid concentrations in treatment liquors have also been studied by following the hydrothermal reactions of hemicellulose separated from straw, obtained by extraction as detailed in the Methods section. Kinetic data using the microwave reactor at temperatures of 180 and 200°C are shown in Figure 4a, for reactions in water and also in solutions of 1% sulphuric acid. With water as a reaction medium the concentration of acetic acid continued to evolve beyond the experiment time limit, mirroring the data for the whole straw. However, in the presence of the dilute acid catalyst the rate of evolution was faster, as expected, reaching an asymptote of similar concentration at both reaction temperatures. This supports the conclusion that a finite number of acetate substituents on hemicellulose are available for hydrolysis, with no suggestion of continuing liberation of acetic acid due to breakdown of terminal or monomer sugar groups [16]. This allows some confidence in estimation of the total potential acetic acid concentrations, which might be expected in hydrothermal process or fermentation liquors.

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