Amy Falcon and Jingxin WangDivision of Forestry & Natural Resources

West Virginia UniversityMorgantown, WV USA

Optimizing Urea Concentration for Woody Biomass

Pretreatment

Current Issue

• Coal, natural gas, oil and woody biomass are the most common sources of energy

• Pretreatment is the cost limiting factor in the conversion of woody biomass into sugars for fuels

• Reliable/cost effective method of treating biomass for extraction of sugars for fuels

Pretreatment Technologies

• Steam Explosion

• Hot Water

• AFEX (Ammonia Fiber Explosion)

• Acid Hydrolysis

• Alkaline Hydrolysis

• Organosolv

Advantages/Disadvantages

ADVANTAGES DISADVANTAGES

Hot Water Can completely recover

hemicellulose from hardwoods

Low equipment corrosion

Less degradation into inhibitory

byproducts

Dissolves only 40-60% of the

total biomass2

AFEX • Increases accessible surface area, • removes lignin and hemicellulose to

an extent• does not produce inhibitors for

downstream processes

• Not efficient for biomass with high lignin content

Acid Hydrolysis • Hydrolyzes hemicellulose to xylose and other sugars

• alters lignin structure

• High cost• Equipment corrosion• Formation of toxic

substances

Pretreatment with Urea

• Easier & safer to use on-site

• Readily available

• Pure ammonia must be recovered

• Ammonia is an eye, skin and respiratory tract irritant

• Transportation and storage issues with ammonia

Pretreatment with Urea

• Urea pretreatment, like ammonia, should extract hemicellulose; disrupt lignin structure

• Cellulose molecules are treated, but remain in solid form

Pretreatment with Urea

• Highly soluble in water

• 2 molecules of ammonia for each urea

• Hydrolysis of urea is a first order reaction with respect to urea

• Rapid reaction rate around 130°C, up to 180°C

• Conversion rate of urea decreases with increasing initial urea concentration

Sahu, J. N., K. Mahalik, et al. (2008). "Equilibrium and Kinetic Studies on the Hydrolysis of Urea for Ammonia Generation in a Semibatch Reactor." Industrial & Engineering Chemistry Research 47(14): 4689-4696.

Experimental Design

• Response Surface Model Factors: – Holding time (40, 60, 80 minutes)

– Urea concentration (0, 10, 20%)

– Temperature(160, 170, 180C)

Box-Behnken Design

Methods

• Urea extraction process

– Dissolve urea in water (7/1 water to wood ratio)

– Combine with wood in reactor under temperature and pressure

Methods

• NREL-LAP “Determination of Structural Carbohydrates and Lignin in Biomass”

– Lignin fractionates into acid-soluble and acid-insoluble portions

– Polymeric carbohydrates are hydrolyzed into monomeric carbohydrates

Methods

• Nelson-Somogyi Method

– For estimation of glucose by reducing sugars

– Based on the absorbance (540nm) of a colored complex between copper oxidized sugar and arsenomolybdate

– Amount of carbohydrate present determined by comparison with a calibration curve

Glucose Standard Curve

• Read absorbance at 540nm

y = 109.9x - 5.1159R² = 0.9682

0

20

40

60

80

100

0 0.2 0.4 0.6 0.8 1 1.2

Glu

cose

Co

nce

ntr

atio

n (

µg/

µl)

Absorbance

Glucose Standard Curve

Results

• Determine which variables are significant

Results

• Determine optimal model

Average Glucose Concentration =

0.38 + 1.311*Concentration - 0.0494*Concentration2

Results

• Optimal urea concentration = 13.27%

20151050

9

8

7

6

5

4

3

2

1

0

Concentration

Mean

of

Avera

ge G

luco

se C

on

cen

trati

on

Main Effects Plot for Average Glucose ConcentrationFitted Means

Results

• Optimal glucose concentration:

0.379

8.548

16.388

18.366

14.703

6.845

0

5

10

15

20

0 10 13 13.27 13.5 20

Glu

cose

Co

nce

ntr

atio

n (

g/L)

Urea Concentration (%)

Concentration Curve

20151050

9

8

7

6

5

4

3

2

1

0

Concentration

Mean

of

Avera

ge G

luco

se C

on

cen

trati

on

Main Effects Plot for Average Glucose ConcentrationFitted Means

Results (to be determined...)

• HPLC analysis of all sugars present in hydrolysis

• Soluble sugars from optimal conditions

• Amount on Nitrogen present, and where it is located

• Lignin content

• Ash content

Conclusion

• Temperature and time are insignificant in the separation of glucose from woody biomass using urea pretreatment

• Urea concentration is the only significant factor

• Out of 140 g/L woody biomass, 18.366 g/L of glucose is separated (~13% glucose)

Thank you for your time and attention!