Mathematical modeling of cellulose conversion to ethanol by the simultaneous saccharification and fermentation process

  • George P. Philippidis
  • Diane D. Spindler
  • Charles E. Wyman
Session 4 Bioengineering Research

Abstract

Ethanol, a promising alternative fuel, can be produced by the simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass, which combines the enzymatic hydrolysis of cellulose to glucose and the fermentation of glucose to ethanol by yeast in a single step.

A mathematical model that depicts the kinetics of SSF has been developed based on considerations of the quality of the substrate and enzyme, and the substrate-enzyme-microorganism interactions. Critical experimentation has been performed in conjunction with multiresponse nonlinear regression analysis to determine key model parameters regarding cell growth and ethanol production. The model will be used for rational SSF optimization and scale-up.

Index Entries

Cellulose hydrolysis SSF modeling biomass conversion ethanol production 

Nomenclature

a

Growth-associated ethanol formation constant (g/g)

αs

Surface area occupied by unit mass of cellulase (m2/g)

αt

Available surface area of cellulose (m2/L)

b

Nongrowth-associated specific ethanol production rate (g/g/h)

(B)

Concentration of cellobiose (g/L)

(C)

Concentration of cellulose (g/L)

(E)

Concentration of ethanol (g/L)

(E1)

Concentration of cellulase in solution (g/L)

(E1*)

Concentration of cellulase adsorbed on cellulose (g/L)

(E2)

Concentration of β-glucosidase (g/L)

(G)

Concentration of glucose (g/L)

kd

Specific rate of cell death (h-1)

k1, k2

Specific rate of cellulose and cellobiose hydrolysis, respectively (h-1)

Ke

Constant in cellulase adsorption Eq. 2 (g/L)

Ki

Constant of cell growth inhibition by the substrate (glucose) (g/L)

Km

Michaelis constant of β-glucosidase for cellobiose (g/L)

K1B, K2B

Inhibition constants of cellulase and β-glucosidase by cellobiose, respectively (g/L)

K1E, K2E, K3E

Inhibition constants of cellulase, β-glucosidase, and cell growth by ethanol, respectively (g/L)

K1G, K2G

Inhibition constants of cellulase and β-glucosidase by glucose, respectively (g/L)

K1L, K2L

Constants for cellulase and β-glucosidase adsorption to lignin, respectively (L/g)

K3

Monod constant of glucose for cell growth (g/L)

K4

Monod constant of glucose for ethanol synthesis (g/L)

(L)

Concentration of lignin (g/L)

m

Specific rate of substrate consumption for maintenance requirements (h-1)

µm

Maximal specific growth rate (h-1)

r1,r2,r3

Volumetric rate of cellulose, cellobiose, and glucose utilization, respectively (g/L/h)

t

Time (h)

(X)

Concentration of cell mass (g/L)

γXG

Average yield coefficient of cell mass on substrate (glucose) (g/g)

Φ

Cellulose reactivity coefficient (dimensionless) Subscripts

t

Total value

Copyright information

© Humana Press Inc. 1992

Authors and Affiliations

  • George P. Philippidis
    • 1
  • Diane D. Spindler
    • 1
  • Charles E. Wyman
    • 1
  1. 1.Biotechnology Research Branch, Fuels and Chemicals Research and Engineering DivisionNational Renewable Energy LaboratoryGolden

Personalised recommendations