Co-pyrolysis of biomass and polyethylene over HZSM-5: effects of plastic addition on coke formation and catalyst deactivation

Charles A. Mullen, Christina Dorado, Akwasi A. Boateng

Agricultural Research Service – USDA – Wyndmoor, PA

TCS2016 – Symposium on Thermal and Catalytic Sciences for Biofuels and Biobased Products

Chapel Hill, NC

November 1, 20161

Biomass Fast Pyrolysis-oil

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Complex mixture of oxygenated hydrocarbons and water Acids, esters, ketones, aldehydes,

sugars, furans, phenols, 15-30% water

HHV: 20-30 MJ/kg, 50-75% that of petroleum fuels

Acidic: pH ~2

Thermally unstable

Like biomass : Rich in O; Deficient in H compared with petroleum

Bio-oil or Py-Vapor Upgrading

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CH1.5O0.65 0.7CH2 + 0.3CO2 + 0.05H2O

CH1.5O0.65 0.84CH + 0.16CO2 + 0.033H2O

Catalytic Fast Pyrolysis over HZSM-5

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CFP of biomass over HZSM-5 produces aromatic hydrocarbons with concurrent production of Coke and loss of H- low yields- rapid catalyst deactivation

• Agricultural Plastics

• Increase crop yields

• Reduce evaporation

• Control pests

• Transportation and preservation

• Waste

• 521 million lbs. U.S.A. per year

• ~70% Polyethylene

• Disposal Methods

• Incineration

• Burial

• Landfill

• Environmental concerns

• Recycling - limited

• Co-pyrolysis feedstock

Agricultural Plastic as a Co-Feedstock

Structure H/C O/C

Polyethylene 2 0

n n n

pyrolysis

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Co-catalytic pyrolysis of Biomass and Plastics

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• Hypothesis: Co-pyrolysis of plastic with biomass could increase the efficiency of biomass conversion• Increase the concentration of hydrocarbon pool intermediates

• Divert biomass carbon from coke producing pathways

• Increase yield

• Slow catalyst deactivation

• Provide alternative disposal method for agricultural plastics

Biomass & Plastic: Micro-Pyrolysis• Micro-Pyrolysis Coupled with GC/MS (Py-GC/MS)

• Experiment: Catalytic Pyrolysis of Biomass and Plastics with HZSM-5 (Catalyst/Biomass = 15/1)

• Result: The catalytic pyrolysis of plastics with switchgrass and its constituents, showed an increase in the carbon yields of specific aromatic hydrocarbons compared to the arithmetic sum of the catalytic pyrolysis of the feedstocks alone. The polyethylene plastics had the most instances in which this was the case.

• Dorado, C.; Mullen, C.A.; Boateng, A.A., ACS Sustainable Chem. Eng. 2014, 2, 301-311.

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Dorado, C.; Mullen, C.A.; Boateng, A.A., ACS Sustainable Chem. Eng. 2014, 2, 301-311.

CFP: Polyolefins and Biomass• Blending of Polyolefins with biomass have been found to be particularly

effective for increasing the yield of aromatics over HZSM-5

X. Li, H. Zhang, J. Li, L. Su, J. Zuo, S. Komarneni, Y. Wang,

Improving the aromatic production in catalytic fast pyrolysis of

cellulose by co-feeding low-density polyethylene, Applied

Catalysis A: General 2013, 455, 114-121.

Cellulose

Polypropylene

Experimental 1:1 Cellulose:PP

Additive 1:1 Cellulose:PP

13C Isotopic Labeling Study

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• Micro-Pyrolysis Coupled with GC/MS (Py-GC/MS)

• Experiment: Catalytic Pyrolysis of 13C Labelled Cellulose and Non-labeled Plastic with HZSM-5 (Catalysts:Biomass = 15:1)

• Result: Products from the catalytic co-pyrolysis of cellulose and plastic have carbon from both sources

Most olefins produced with mixtures of polyolefins -made up of mostly polyolefin carbon

Most aromatics produced from mixtures of polyolefins and polystyrene- even distribution of carbon

Proves plastic and biomass form aromatics and olefins through converging mechanism

• Dorado, C.; Mullen, C.A.; Boateng, A.A. Appl. Catal. B 2015, 162, 338-345. Isotopic Breakdown of Produced

Toluene (Cellulose + PE)

Catalyst Deactivation Study• Pyrolysis done at 650°C using CDS analytical Pyroprobe with either 30 sample or 60

sample runs (1 mg total sample each)• Switchgrass• HDPE• 1:1 w/w Switchgrass/PE

• Gases transferred to external reactor and passed over HZSM-5 bed with ~15mg of catalyst

• Products then analyzed by GC/MS

• Catalyst analyzed for coke yield post-run

Switchgrass Pyrolysis over HZSM-5: Chromatograms

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Sample 60

HDPE Pyrolysis over HZSM-5: Chromatograms

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Breakthrough Straight Chain HC

SWG/HDPE Co-Pyrolysis over HZSM-5

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Trend in the Production of Aromatic Hydrocarbons: Samples 1-30

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• Catalyst to Feed Ratio 15:1 (w/w)

• Catalyst to Total Feed Processed 15:1 to 1:2

• Catalyst to Total Switchgrass Processed 7.5:1 to 1:1

• Aromatic Hydrocarbons = Benzene, Toluene, Ethylbenzene, Xylenes, C3-benzenes, indenes, naphthalenes

• Production of Aromatic Hydrocarbons decreases ~1.3 times slower for mix than additive prediction

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.07

1:1 SWG:HDPE 0.40

Predicted 1:1 0.53

Trend in the Production of Aromatic Hydrocarbons: Samples 1-30

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• Catalyst to Feed Ratio 15:1 (w/w)

• Catalyst to Total Feed Processed 15:1 to 1:2

• Catalyst to Total Switchgrass Processed 7.5:1 to 1:1 in mixture

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.03

1:1 SWG:HDPE 0.28

Predicted 1:1 0.38

Trend in the Production of Aromatic Hydrocarbons: Samples 1-60

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• Catalyst to Feed Ratio 15:1 (w/w)

• Catalyst to Total Feed Processed 15:1 to 1:4

• Catalyst to Total Switchgrass Processed 7.5:1 to 1:2 in mixture

• Observed and predicted deactivation rates are similar

• Results are ambiguous due to scatter in data

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.22

1:1 SWG:HDPE 0.58

Predicted 1:1 0.57

Trend in the Production of Aromatic Hydrocarbons: Samples 1-60

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• Catalyst to Feed Ratio 15:1 (w/w)

• Catalyst to Total Feed Processed 15:1 to 1:4

• Catalyst to Total Switchgrass Processed 7.5:1 to 1:2 in mixture

• Observed and predicted deactivation rates are similar

• Results are ambiguous due to scatter in data increasing as number of pulses increases

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.12

1:1 SWG:HDPE 0.40

Predicted 1:1 0.41

Trend in Production of Alkyl Benzenes

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• Alkyl Benzenes = Benzene, Toluene, Ethylbenzene, Xylenes, 1, 2, 3-trimethylbeznene, 1-ethyl-3-methyl benzene

• Trends in Deactivation Rates are similar to those for total aromatics

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.29

1:1 SWG:HDPE 0.53

Predicted 1:1 0.59

Trend in Production Naphthalenes

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• Naphthalenes = Naphthalene, 1-methylnapthalene, 2-methylnapthalene, 2,6-dimethylnapthalene

• CFP over HZSM-5 of HDPE alone produces a very small amount of naphthalenes

• Yields for switchgrass and 1:1 SWG:HDPE are similar

Feed Relative DeactivationRate

Switchgrass 1

HDPE 0.07

1:1 SWG:HDPE 0.64

Predicted 1:1 0.53

Aromatic Selectivity

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Selectivity Trends

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Selectivity in aromatics production does not change as catalyst is used

Biomass Breakthrough Products: Acetic Acid

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• Acetic acid production increases until catalyst to biomass reaches ~ 0.375

• Complexity of chromatogram did not allow for analysis of acetic acid for biomass/plastic mixture runs

Biomass Breakthrough Products: Phenol

23Mukarakate, C. et. al. Green Chem., 2015, 17, 4217

• For Switchgrass phenol production is maximized at about catalyst: total biomass of ~1:2

• For 1:1 switchgrass :HDPE, phenol increases slightly until catalyst: feed of 1:1.5 and then remains steady

Coke Yields

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Conclusions

• Blending polyethylene with biomass leads to an increase in yield of aromatic hydrocarbons over fresh HZSM-5 during catalytic fast pyrolysis

• This study aimed to learn about the effect of HDPE blending with switchgrass on catalyst deactivation rates

• 1:1 Mixture of Switchgrass:HDPE reduced the rate of deactivation compared with calculated prediction up to catalyst: total biomass 1:2

• Scatter in data increases at pulses at catalyst: total biomass > 2:1 • Difference in rate of deactivation between observed in calculated is smaller than for early in the catalyst lifetime

• Blend results in slightly higher selectivity for benzene compared with alkylated benzenes. Selectivity is stable over catalyst lifetime.

• Higher concentration of hydrocarbon pool intermediates can reduce coke formation from cellulosic portion of biomass but may not effect coke formed from lignin.

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Acknowledgments

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• Frankie Lazauskas – Drexel University Co-op

• Tom Coleman

• Christina Dorado

• Akwasi Boateng