Mechanistic Investigation of the Pyrolysis of Brown Grease

Mansour H Almatarneh,Reema A Omeir,Thi Xuan Thi Luu,Imarat Y Alnemrat,Lawrence M Pratt,Minh Bui,Dickens Saint Hilaire,Tianlong Deng

doi:10.1155/2020/8844225

Abstract

The conversion of brown grease using pyrolysis reactions represents a very promising option for the production of renewable fuels and chemicals. Brown grease forms a mixture of alkanes, alkenes, and ketones at a temperature above 300°C at atmospheric pressure. This work is a computational study of the detailed reaction mechanisms of brown grease pyrolysis using DFT methodology. Prior experimental investigations confirmed product formation consistent with a set of radical reactions with CO2 elimination, as well as ketone by product formation, CO forming reactions, and formation of alcohols and aldehydes as minor byproducts. In this work, computational quantum chemistry was used to explore these reactions in greater detail. Particularly, a nonradical pathway formed ketone byproducts via the ketene, which we refer to as Pathways A1 and A2. Radical formation by thermal decomposition of unsaturated fatty acids initiates a set of reactions which eliminate CO2, regenerating alkyl radicals leading to hydrocarbon products (Pathway B). A third pathway (Pathway C) is an alternative set of radical reactions, resulting in decarbonylation and formation of minor byproducts. The results of the calculations are in good agreement with recent experimental studies.

Highlights

Radical formation by thermal decomposition of unsaturated fatty acids initiates a set of reactions which eliminate CO2, regenerating alkyl radicals leading to hydrocarbon products (Pathway B)
Lipid feedstocks have been considered as one of the biomass sources with the most potential for producing renewable liquid hydrocarbon products, which can be used as petroleum alternatives. e primary reason for this is the higher energy density [4] and relatively simpler structure [5] compared to other biomass feedstock such as lignocellulose
Several lipid feedstocks are available for conversion to renewable liquid fuels including refined vegetable oils and animal fats, inedible plant oils, and waste oils and fats such as brown grease, yellow grease, and sewage sludge lipids. e ability to utilize nonfood lipid feedstocks is important for process economics and commercial viability as feedstock cost Journal of Chemistry accounts for anywhere between 40 and 80% of the production cost of renewable fuels [5,6,7,8]

Summary

Introduction

Radical formation by thermal decomposition of unsaturated fatty acids initiates a set of reactions which eliminate CO2, regenerating alkyl radicals leading to hydrocarbon products (Pathway B). E proposed reaction pathway for palmitic acid in the presence of unsaturated acid-derived radicals is illustrated in Scheme 2. A detailed computational study on the pyrolysis reactions in the absence of Fe(III) and in the presence of unsaturated fatty acid which is oleic acid was carried out.

Results

Conclusion