349985 Chemicals and Commodities from Waste Coffee: Analysis of Fast Pyrolysis Product with Respect to Experimental Design

Monday, November 4, 2013
Grand Ballroom B (Hilton)
Ari Fischer and George M. Bollas, Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, CT

Chemicals and Commodities from Waste Coffee: Analysis of Fast Pyrolysis Product with Respect to Experimental Design

Ari F. Fischer and George M. Bollas

Department of Chemical & Biomolecular Engineering,
University of Connecticut, Storrs, CT 06269 USA

Email: ari.fischer@uconn.edu, george.bollas@uconn.edu

Coffee is the world's second largest traded commodity (surpassed only by petroleum products) underscoring its global relevance.  In consequence of brewed coffee consumption, appreciable quantities of spent coffee grounds (SCG) are produced with little utility aside from compost.  The commercial brewing process produces 650 kg of SCG to 1000kg of raw material, providing excessive and presently useless biomass rich in fixed carbon [1].  In this investigation, SCG collected from local coffee brewing institutions are used as feed for biomass fast-pyrolysis to convert solid raw material into gas, oil, and solid char residue.  SCG is the chosen feedstock for this study due to its high carbon content, waste product nature, and immense supply globally as a byproduct of commercial usage.  Recycling SCG into liquid and gas commodities is a fruitful pursuit because it can eliminate harmful environmental impacts from disposal and can potentially contribute to future energy production needs. 

Pyrolysis is defined as the thermal decomposition of organic matter in an oxygen free environment.  The raw material is rapidly heated and converted into gas, liquid, and solid fragments of the initial matter.  The main benefit of biomass pyrolysis is the ability to convert solid carbon sources into dense and transportable liquids with better and more flexible applicability than the cumbersome feedstock starting material.  Pyrolysis product varies with heating rates, feed composition, pyrolysis temperature, and other experimental factors.  Liquid yield from fast pyrolysis can be as high as 80% [2].

Goals for this investigation include determining the quality of the bio-oil produced from fast pyrolysis as a fuel for heating or power generation, transport fuel precursor, and specialty chemical synthesis.  Factors considered in this investigation include reactor type, presence of catalyst, and pyrolysis temperature.  Experiments were conducted using a Spouted-Bed reactor design along with a Packed-Bed drop down reactor design (Figure 1).  Spouted-Bed reactor is favorable due to enhanced particle contact and heating rates, but is less consistent in feeding rates.  Fixed-bed reactor is favorable due to exact feed size and controllability, but is limited by slower heating rates and gas-solid interaction.  ZSM-5 catalyst was utilized to study vapor cracking on liquid quality and yield.  Oil and char output was measured in all experiments, and oil content was analyzed using GC-MS. 

Results show that SCG is effectively depolymerized and deconstructed through the pyrolysis process.  Initial feed is clearly decomposed as appreciable liquid is produced at selectivity up to 55wt%.  Char residues are consistently low at 15-25wt%, while gas products make up 20-30wt%.  Product liquid and initial feedstock dissolved in methanol are compared through GC/MS analysis (figure 2 shows chemicals in drop down reactor liquid product). Figure 3 exhibits the notable components found in the spouted bed catalytic liquid product and compares with that of pine biomass in figure 4 (woody biomass has received significant attention in relevant literature as a feedstock for fast pyrolysis).

Current work focuses on studying liquid composition of major components hexadecanoic acid (palmitic acid), caffeine, and 9,12-octadienoic acid (linoleic acid), and comparing the decomposition of these at different experimental conditions.  One notable observation is the resistance of palmitic acid to cracking even when ZSM-5 is used to enhance deoxygenation reactions.  This presentation will discuss project motivation, experimental design, reactor set up, and liquid analysis.  This is an independent undergraduate research project funded by the UConn IDEA Grant. The integration of undergraduate research experience into the chemical engineering curriculum, from the student's perspective, will be briefly discussed.


[1] Mussatto, S. I., Machado, E. M. S., Martins, S., & Teixeira, J. A. (2011). Production, composition, and application of coffee and its industrial residues. Food and Bioprocess Technology, 4(5), 661-672.

[2] Bridgwater, A. V., & Peacocke, G. V. C. (2000). Fast pyrolysis processes for biomass. Renewable & Sustainable Energy Reviews, 4(1), 1-73.

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