Production of High Quality Bio-Oil Via Fast Co-Pyrolysis (FCP) of Cellulose and Polypropylene

Production of High Quality Bio-oil via Fast Co-Pyrolysis (FCP) of Cellulose and Polypropylene

Deepak Kumar Ojha and R. Vinu

Department of Chemical Engineering and National Center for Combustion Research and Development, Indian Institute of Technology Madras, Chennai- 600036, India

E-mail: deepakojha86@gmail.com, vinu@iitm.ac.in

Abstract

Fast pyrolysis has received a great attention for direct conversion of biomass into liquid fuels and valuable intermediates. The bio-oil produced from the process has high oxygen content and needs further upgradation to make it usable as a transportation fuel. Currently this is achieved via catalytic hydrodeoxygenation which is highly energy and hydrogen intensive. Co-processing of biomass with polymers is a novel strategy and this is expected to increase the product quality in terms of H/C ratio and heating value, thus reducing the upgradation cost. Detailed understanding of these reactions is prerequisite for the technological development and commercial implementation of the process. Fast co-pyrolysis (FCP) is thought to proceed via complex network of competing free radical and concerted reactions such as aldol condensation, retro-Diels-Alder reaction, β-scission and hydrogen abstraction between biomass and polymer free radicals.

In this study, fast co-pyrolysis of cellulose and polypropylene (PP) is investigated. The objectives of this work are two fold: firstly, the effects of cellulose: PP ratio on the yield of individual products and heating values were evaluated at different temperatures from 400 to 700 ^oC. Secondly, the evolution of major functional groups in a short time period of a few seconds is studied. Fast co-pyrolysis experiments were conducted in a Pyroprobe^® 5200 pyrolyzer (CDS Analytical Inc.) which was interfaced with multidimensional gas chromatograph/mass spectrometer (2D-GC/MS, Agilent Technologies). For the real time function group analysis, the Pyroprobe was interfaced with Cary 660 Fourier transform infrared spectrometer (FT-IR, Agilent Technologies). Table 1 depicts the yields of major products formed during fast co-pyrolysis of cellulose and PP of different compositions. Significant difference between calculated and experimental product yields shows that interactions between cellulose and PP are manifested in the form of alcohols. Importantly, the alcohols belonged to C10-C15 carbon number range. Specifically, long chain alcohols like (2,4,6-trimethylcyclohexyl) methanol, 2-isopropyl-5-methyl-1-heptanol and 11-methyldodecanol were obtained in significant amounts when PP content was high (50-75 wt.%) in the mixture. The heating values of the products were calculated using the empirical relation of Davenport, and interestingly, the heating values correlated well with the sum of yields of alcohols, hydrocarbons and monoaromatics. Overall, two fold improvement in heating value of the condensable products was observed.  Higher pyrolysis temperature led to the formation of mono and poly aromatic hydrocarbons. The real time functional group analysis indicated a reduction in reaction time with an increase in PP content in the feed. The time taken for the maximum yield of various products corresponded to 10 seconds, while pyrolysis was complete in less than a minute.

Table 1. Comparison between experimental and calculated composition of the major products formed in co-pyrolysis of cellulose and PP of different compositions at 500 ^oC.

Feed Composition	C:PP 100:0	C:PP 75:25		C:PP 50:50		C:PP 25:75		C:PP 0:100
Products	Expt.	Expt.	Calc.	Expt.	Calc.	Expt.	Calc.	Expt.
Alcohols	6.95	22.73	5.21	27.81	3.48	30.87	1.74	0
Hydrocarbons	0.67	28.23	23.56	40.21	46.44	43.65	69.33	92.21
Anhydrosugars	17.36	7.11	13.02	2.92	8.68	1.70	4.34	0
Aldehydes/Ketones	23.20	10.63	17.40	5.80	11.60	1.83	5.80	0
Furans	27.89	9.92	20.92	6.20	13.95	1.76	6.97	0
Char	5.67	11.29	6.20	14.32	6.73	13.28	7.27	7.8