Methane Adsorption by Different Biochars

Illinois Biochar Group Meeting

Yamini Sadasivam & Krishna R. Reddy University of Illinois at Chicago

04/05/2013

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Presentation Outline

Methane oxidation in landfill cover systems Biochar as a landfill cover material Ongoing research at UIC Batch adsorption testing

Types of biochars used Physical-chemical properties Testing protocol Results Major conclusions

Future goals & objectives

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Methane oxidation in landfill covers

Methane oxidation

CH4+2O2→CO2

+2H2O

Aerobic

Anaerobic

Landfill gas

CH4+CO2

O2

LFG emissions are among the major sources of greenhouse gases to the atmosphere

Traditionally soil covers were used to achieve microbial methane oxidation by methanotrophs Major issues with cracking of soil surfaces Inefficient performance in the absence of LFG extraction systems

Biocover materials with organic amendments were used to increase methane oxidation efficiency Major issues with material’s self-degradation Formation of EPS causing pores to clog & hindering the transport of gases Cannot contribute to methane adsorption

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Biochar – A Potential Landfill Cover Material

Methane oxidizing material

CH4 and CO2

Oxygen Exhaust gases

Porous material

Biocover

GDL

MSW

Biochar can be amended to landfill cover soils to enhance CH4 adsorption and oxidation

Biochar can be used

Biochar is advantageous over current compost biocovers

Enhanced CH4 adsorption

Greater porosity and specific surface area (limits pore clogging due to EPS formation)

Favors growth and CH4 oxidation activity of methanotrophs which can conveniently exist within the highly porous biochar

Enhanced gas transport through the pores Sustainable and cheap option to mitigate LFG

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Ongoing Biochar Research Goals

To quantify the physical, chemical and geotechnical characteristics of biochars and biochar-amended soils.

To determine the adsorption and enhanced gas transport properties of biochars and biochar-amended landfill cover soils for CH4 and oxygen.

To characterize the main factors that affect CH4 oxidation.

To investigate adsorption and oxidation of CH4 under various conditions such as biochar composition and size, soil composition, CH4 source strength, CH4 concentration, moisture content, and temperature.

To model the mechanisms of CH4 oxidation within biochars and biochar-amended landfill cover systems and determine kinetic parameters defining these mechanisms.

To conduct a full-scale field demonstration. To prepare guidance manual to design biochar and biochar-amended

landfill cover soil systems for landfill applications.

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Batch Adsorption Testing – Biochars used

1. BS : Biochar Solutions Inc.2. CK : Char King International3. AW : Aztec Wonder, LLC4. CE – WP1 : Wood pellets w/ash5. CE – WP2 : Wood pellets w/o

ash6. CE – AWP : Aged wood pellets7. GAC : granular activated

carbon

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Batch Adsorption Testing – Biochars used

Biochar Source

Feedstock Treatment Process

Treatment Temperature

Residence Time

Post-treatment

Biochar Solutions Inc.

Pine Wood Slow pyrolysis 350 - 6000C 6 hrs Screened through 3mm

mesh

Char-King International

90% pine & 10% fur wood

Fast pyrolysis > 5000C < 1 hr Activated with oxygen

Aztec Wonder, LLC

Aged oak & hickory wood

biochar

Pyrolysis – Missouri type concrete kiln

~ 5000C ---Mixed

w/innocula & sieved (1/4”)

Chip Energy Inc. Wood Pellets Gasification 5200C --- N/A

Wood Pellets --- --- --- Not subjected to fine ash filtration

Wood Pellets --- --- --- Fine ash separated

Feedstock & Production Processes:

In addition to biochars, GAC was obtained from Fisher Scientific and tested for its methane adsorption capacity

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Biochar type

pHMoisture Content (% d.w.)

Organic Content

(%)

Average Particle

Size (mm)

Specific Gravity

Water Holding Capacity (% total mass)

BS 8.5 0 29.2 0.7 1.1 54.66

CK 9.0 5.6 31.3 0.2 1.5 63.94

AW 8.2 49.2 76 0.9 1.2 49.96

CE-WP1 6.4 3.2 96.9 1.1 0.8 58.73

CE-WP2 6.9 3.7 96.8 3.2 0.6 32.91

CE-AWP 7.2 4.3 82.3 5.8 0.8 44.52

GAC 9.0 21.3 89 2.9 1.6 49.06

Batch Adsorption Testing – Material characteristics

pH of biochars range from 6 – 9; pH values for biochars from Chip Energy are around neutral

MC of sterilized biochars range from 0 – 6% d.w. except for AW & GAC

BS, CK AW & GAC have SG > 1; CE biochars have SG < 1

WHC refers to the amount of moisture the biochars can absorb; WHC of finer grained biochars are higher than coarse grained

biochars

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Batch Adsorption Testing – Material characteristics

Grain Size Distribution

Particle size (mm)

.01.1110100

Per

cent

pas

sing

0

10

20

30

40

50

60

70

80

90

100BSCKAWCE-WP1CE-WP2CE-AWPGAC

D50 of biochars range between 0.2 mm and 7

mm

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Batch Adsorption Testing – Protocol

Step 1:

Sterilization of biochars - 1210C (15 psi);30 min/cycle for 2 consecutive days

Step 2:

Evacuation of vials – 5 mm glass serum bottles crimped w/ butyl septa & aluminum caps

Biochar

Glass bottle

Rubber stopper

Syringe

Step 3:

5g material used; controls (no biochar); gas samples

stored in 5 ml vials & analyzed within 4 hr using HP 6890 GC w/ FID and GS

Carbon plot column

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Batch Adsorption Testing -Results

Adsorption Capacity of Biochars

Biochar Type

BS CK AW CE-WP1 CE-WP2 CE-AWP GAC

Qe,

mol

/Kg

0

1000

2000

3000

4000

10% CH4 v/v 8% CH4 v/v 5% CH4 v/v 2% CH4 v/v

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Effect of Moisture on Adsorption

Moisture Content (% WHC)

0 20 40 60 80 100 120

Qe,

mL/

Kg

900

1000

1100

1200

1300

1400

Moisture Content vs Qe, mL/Kg

Batch Adsorption Testing -Results

CE-WP2 tested at 10%

headspace CH4 (v/v)

MC was varied at 4 levels (25, 50, 75 & 100%

WHC)

WHC of Biochar ≈ 50% (d.w.)

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Batch Adsorption Testing -Results

Adsorption curves at different temperatures

Time, min

0 20 40 60 80 100 120 140

Qe,

mL/

Kg

0

200

400

600

800

1000

1200

1400

1600

Qe vs time, 24 oC

Qe vs time 35 oC

Qe vs time 41 oC

CE-WP2 tested at 10%

headspace CH4 (v/v)

Positive heat of adsorption; Qe decreases w/ increasing T

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Major Conclusions

Methane adsorption capacities of biochars are strongly dependent upon their physical-chemical characteristics

Generally, methane adsorption capacity of fresh biochars increases with decreasing particle size

Presence of moisture negatively affects the methane adsorption capacity of biochars

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Methane adsorption capacity decreases with increasing temperature

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Activated – pine & fur wood biochar showed the highest methane adsorption capacity (Qe ≈ 3500 mL/Kg)

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Future Goals and Objectives

Characterize more biochar types in the lab for their physical-chemical and geotechnical properties

Test the effects of biochar properties, MC, temperature & biochar amendment ratio on CH4 adsorption & oxidation capacity

Develop an effective design based on modeling the laboratory results and determine optimum biocover size for field implementation

Test the biochar in the field and monitor its performance for LFG mitigation

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16 Thank you!