Pretreatment of Corn stover and Hybrid poplar

1
Pretreatment of Corn stover and Hybrid poplar by
Sodium Hydroxide
Rajesh Gupta Y Y Lee Department of Chemical
Engineering Auburn University
Abstract NaOH and its
derivatives are used as pulping reagents, wherein
the spent NaOH is recovered in salt form and
reused. In this study, low concentration of NaOH
(approx. 1-5) was used for pretreatment of corn
stover and high lignin (HL) hybrid poplar. It was
done with the understanding that NaOH can be
recovered. In alkaline pretreatments, it is
technically feasible to retain most of
carbohydrates while removing large fraction of
lignin in the biomass. The enhancement of
digestibility is caused primarily by lignin
removal. Retention of hemicellulose after
pretreatment gives a significant economic benefit
since it eliminates the need of detoxifying
hemicellulose sugars. The main objective of this
study is to see if NaOH treatment can achieve
that goal. From the results, the optimum process
conditions were identified for each of the
feedstocks on the basis of carbohydrate retention
and digestibility of treated solid. Among the
noteworthy findings was that corn stover, after
treated with NaOH under moderate conditions,
attains near 100 glucan digestibility. On the
other hand, hybrid poplar required treatment
with much higher severity, in terms of
temperature and NaOH concentration, in order to
attain acceptable digestibility. It is found that
hydrogen peroxide supplementation in
pretreatment of hybrid poplar helps in retaining
the sugar in solids and further enhances the
delignification thus digestibility of solids.
Xylanase supplementation during the enzymatic
digestibility of treated hybrid poplar
drastically improves the sugars yields.
Corn Stover
High Lignin Hybrid Poplar
SEM Pictures of Untreated and treated Corn stover
Effect of NaOH treatment on composition and
Digestibility
Treatment Conditions Temperature ( 80C) Time
(24hrs)
SolidLiq.(110)
With Hydrogen Peroxide (5 conc. In Liquid)
Without Hydrogen Peroxide
Effect of NaOH treatment on composition and
Digestibility
Treatment Conditions Temperature ( 60C) Time
(24hrs) SolidLiq.(110)
Glucan Digestibility
Xylan Digestibility
NaOH treatment at very mild conditions
Enzyme Loading Cß-G Cellulase
(15FPU/g glucan) Cellobiase (30CBU/g glucan)
Treatment Conditions Concentration (1)
Temperature ( 60C)
Time (24hrs) Solid Liquid (110)
Effect of Xylanase supplementation
Composition and Digestibility( With and Without
Xylanase add.) of NaOH treated Corn stover
Treatment Conditions Temperature ( 80C) NaOH
Conc. (5)
H2O2 Conc. (5) Time (24hrs) SolidLiq.(110)
Glucan Digestibility
Xylan Digestibility
Enzyme Loading Cß-G Cellulase
(15FPU/g glucan) Cellobiase (30CBU/g glucan) C
ß-G X Cellulase (15FPU/g glucan)
Cellobiase (30CBU/g glucan) Xylanase (31.3mg
protein/g glucan)
Enzyme Loading Cß-G Cellulase
(15FPU/g glucan) Cellobiase (30CBU/g glucan) C
ß-G X Cellulase (15FPU/g glucan)
Cellobiase (30CBU/g glucan) Xylanase (31.3mg
protein/g glucan)
Overall Sugar Yield
Overall Sugar Yield
(Sugar yield from pretreatment liquor is not
included here)
(Sugar yield from pretreatment liquor is not
included here)
Enzymes Used Cellulase GC220 (Supplied by
Genencor Int.) Cellobiase Novo 188 ( Sigma cat
C-6150) Xylanase Multifect Xylanase (Supplied by
Genencor Int.)

• Summary (Contd.)
• HL hybrid poplar is more difficult to delignify,
  thus requires treatment
• conditions with high severity.
• Addition of 5 hydrogen peroxide in NaOH
  treatment increases the delignification,
• helps retaining the carbohydrates, and
  significantly improves the glucan
• digestibility.
• Hydrogen peroxide addition also reduces the Na
  conc. in pretreatment liquor.
• It appears that hydrogen peroxide promotes NaOH
  induced lignin degradation.
• As an oxidizing agent, hydrogen peroxide helps
  in stabilizing the reducing end
• in polysaccharide thus lowering the sugar
  degradation.

• Summary (Contd.)
• The effect of hydrogen peroxide is higher with
  higher conc. of NaOH.
• The overall sugar yield in enzymatic digestion
  of NaOH/H2O2 treated poplar is
• drastically improved by xylanase
  supplementation.

• Summary
• NaOH is very effective in delignification of
  corn stover. Treated under
• moderate conditions of 60C temp. and 1.5
  concentration, the glucan
• digestibility above 90 is obtained.
• Treated at 25C and 1NaOH, corn stover retains
  more carbohydrates
• in solids, and still gives 73 of overall sugar
  yield if enzymatic hydrolysis
• is done with xylanase addition.

• Acknowledgement
• US Department of Energy for funding the project
• (US/DOE No. DE-PS36-00GO10482)
• Members of CAFI-II team
• Genencor International Inc. for supplying enzyme