(369e) Conversion of Caffeine and Lipids in Catalytic Fast-Pyrolysis of Spent Coffee Grounds

Conversion of Caffeine, Lipids, and Fatty Acids in Catalytic
Fast-Pyrolysis of Spent Coffee Grounds.

Ari Fischer,
Shoucheng Du, George M. Bollas

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

Abstract

Fast
pyrolysis of spent coffee grounds is investigated as a means of valorizing
commercial coffee waste. Coffee is the second largest globally traded commodity
with imports reaching 6.7 million metric tons in 2013, as reported by the
international coffee organization.¹ Soluble coffee waste retains 65%
of the raw coffee mass and is regularly disposed of in landfills where its
environmental impact is experienced through oxygen intensive decomposition.²
In this work, spent coffee grounds are explored as a feedstock to engineer
alternative processes for the production of valuable chemicals, commodities, or
fuels. In particular, coffee隆炉s residual fibers, proteins, lipids, and other
organic species are chemically converted into fragmented products through
catalytic fast pyrolysis. Products include a gas phase containing ammonia;
hydrogen; methane; carbon monoxide; and carbon dioxide, liquid phase
characterized by condensed vapors and aerosols, and a solid char mainly
composed of fixed carbon with residual ash and inorganics. Pyrolysis conditions
are tuned to improve liquid quality with reduced oxygen content and increased
paraffins and olefins.³ Introduction of shape selective ZSM-5
catalyst promotes decarbonylation and decarboxylation to form aromatics.

Like
most biomass feedstocks, spent coffee grounds contain fibers in the form of
lignin and cellulose. In addition, proteins and lipids are abundant in spent
coffee grounds. Elemental analysis of spent coffee grounds is compared to that
of Aspen wood in Table 2.⁴ Coffee has a lower oxygen content and
higher carbon and hydrogen fraction than the wood counterpart. Unlike wood,
coffee has significant nitrogen content from caffeine, proteins, and other
nitrogen containing compounds, which form ammonia gas as a pyrolysis product.
Non-pyrolyzed nitrogen found in the char product was been shown to stimulate
plant growth.⁵ In this view, catalytic pyrolysis of spent coffee
grounds is posing a challenging process engineering problem, in which the char
product is best not to be burnt for the generation of the heat required for the
endothermic pyrolysis reactions; rather it is a useful product. Nonetheless, as
a first step towards advanced utilization of used coffee grounds, in-situ
catalytic upgrading is studied in this work.

Conventional
and catalytic pyrolysis of spent coffee grounds has been explored with fast and
slow heating rates. Bok et al.⁶ employed a fluidized bed reactor
with sand to study char, liquid, and gas yields for 673K to 873K generating a
maximum liquid product of 54.85 wt% at 823K. The liquid product contained a
range of ketones, alcohols, alkanes, aromatics, caffeine, and acids with a
water content between 23.96 to 32.93.⁶ Kan et al.⁷
performed slow pyrolysis in a TGA with NiCu-娄