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Kinetic modeling of rapid enzymatic hydrolysis of crystalline cellulose after pretreatment by NMMO

  • Mahdi Khodaverdi
  • Azam JeihanipourEmail author
  • Keikhosro Karimi
  • Mohammad J. Taherzadeh
Bioenergy/Biofuels/Biochemicals

Abstract

Pretreatment of cellulose with an industrial cellulosic solvent, N-methylmorpholine-N-oxide, showed promising results in increasing the rate of subsequent enzymatic hydrolysis. Cotton linter was used as high crystalline cellulose. After the pretreatment, the cellulose was almost completely hydrolyzed in less than 12 h, using low enzyme loading (15 FPU/g cellulose). The pretreatment significantly decreased the total crystallinity of cellulose from 7.1 to 3.3, and drastically increased the enzyme adsorption capacity of cellulose by approximately 42 times. A semi-mechanistic model was used to describe the relationship between the cellulose concentration and the enzyme loading. In this model, two reactions for heterogeneous reaction of cellulose to glucose and cellobiose, and a homogenous reaction for cellobiose conversion to glucose was incorporated. The Langmuir model was applied to model the adsorption of cellulase onto the treated cellulose. The competitive inhibition was also considered for the effects of sugar inhibition on the rate of enzymatic hydrolysis. The kinetic parameters of the model were estimated by experimental results and evaluated.

Keywords

Enzymatic hydrolysis Kinetic modeling N-Methylmorpholine-N-oxide Pretreatment Substrate reactivity 

List of symbols

Eb

Adsorbed cellulase (mg cellulase/l)

Ef

Free cellulase (mg cellulase/l)

Kads

Dissociation constant (l/g cellulose)

S

Cellulose concentration (mg/ml)

C

Cellulose concentration at a given time (mg/ml)

C0

Cellulose concentration at time zero (mg/ml)

E1b

Bound concentration of cellulase on cellulose (mg protein/ml)

Eif

Concentration of free enzymes in solution (mg protein/ml) (i = 1 for cellulase; i = 2 for β-glucosidase)

E1T

Total endogluconase/cellobiohydrolase concentration (mg protein/ml)

E2T

Total β-glucosidase concentration (mg protein/ml)

G

Glucose concentration (mg/ml)

G2

Cellobiose concentration (mg/ml)

kir

Reaction rate constants (ml/mg h), in which i = 1 for cellulose to cellobiose; i = 2 for cellulose to glucose; i = 3 for cellobiose to glucose

KiIG

Inhibition constants of glucose on enzymes (mg/ml), in which i = 1, 2, and 3 (i is the same as that in k ir)

KiIG2

Inhibition constants of cellobiose on enzymes (mg/ml), in which i = 1 and 2 (i is the same as that in k ir)

K3M

Substrate (cellobiose) saturation constants (mg/ml)

ri

Reaction rate (mg/ml h), where i = 1, 2, and 3 (i is the same as that in k ir)

Notes

Acknowledgments

The present study was financially supported by Sparbanksstiftelsen Sjuhärad (Sweden). The help and advice provided by Dr. Magnus Lundin in modeling part of this study is greatly appreciated.

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Copyright information

© Society for Industrial Microbiology 2011

Authors and Affiliations

  • Mahdi Khodaverdi
    • 1
  • Azam Jeihanipour
    • 1
    • 2
    Email author
  • Keikhosro Karimi
    • 3
  • Mohammad J. Taherzadeh
    • 1
  1. 1.School of EngineeringUniversity of BoråsBoråsSweden
  2. 2.Department of Chemical and Biological EngineeringChalmers University of TechnologyGöteborgSweden
  3. 3.Department of Chemical EngineeringIsfahan University of TechnologyIsfahanIran

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