Fundamental Understanding of Co-(Fast)-Pyrolysis of Biomass and Polymers for Energy andResource Recovery
Tanumoy Ray, R. Vinu*
Department of Chemical Engineering, Indian Institute of Technology, Madras, Chennai 600036
E-mail: vinu@iitm.ac.in; Phone: +91-44-2257 4187, +91-9500158723

Abstract
The generation of drop-in fuels and intermediates from lignocellulosic biomass via fast pyrolysis is a promisingstrategy for large-scale production and utilization of biofuels. However, bio-oil produced via catalytic pyrolysis of biomass
contains significant oxygen that excess hydrogen is required for the upgradation of bio-oil in the downstream operation.
The main focus of this work is to investigate if the presence of thermoplastic polymers would improve the hydrogencontent in bio-oil. In this work, reaction kinetics of co-pyrolysis of cellulose and polypropylene (PP) of different
compositions under low (5 oC min-1) to medium heating rates (180 oC min-1) in a thermogravimetric analyzer, and very
high heating rates (> 2000 oC s-1) in a micropyrolyzer are studied. Weight loss profiles and differential thermograms wereanalyzed using various conventional techniques like Freidmann method, Chang method, Kissinger method, Flynn-WallOzawa technique and Coats-Redfern plots to evaluate the rate parameters, viz. activation energy (Ea) and frequency
factor (A), and reaction order (n) at various stages of conversion. The products of fast pyrolysis were analyzed in aGC/MS to understand the key interactions between cellulose and PP under rapid heating rate conditions. All theseinformation were utilized to develop a predictive kinetic model of decomposition of cellulose + PP involving the key
reaction steps like (i) formation of active cellulose, levoglucosan and char, (ii) formation of vapor phase species from PP,and (iii) interaction of PP vapors with char formed from cellulose. The model predictions and useful mechanistic insights
on the key interactions between cellulose and PP will be discussed in this presentation.

Keywords: Co-pyrolysis, fast pyrolysis, cellulose, polypropylene, kinetics
1. Introduction
Biomass is a precious resource for the production of
bio-oils and an efficient substituent of petroleum basedoils. First-generation biofuels were produced from starch
crops, but the usage of food crops and environmental
impacts were the cause of concern. The present
generation biofuel production focuses on utilizing highyielding non-food crops such as lignocellulosic biomass
for increasing the yield of bio-oils, reducing theirenvironmental impacts and economics involved.
Thermochemical processing employs application ofheat and catalyst to convert diverse biomass feedstocks
to fuel. (Fast) pyrolysis is a potential thermochemicalroute for the large scale production of bio-oils and usefulintermediates. It involves decomposition of organicmatter in the absence of oxygen at moderatetemperatures (400-600 oC) under very short time scales(milliseconds to a few seconds).[1]Bio-oils must be upgraded to reduce the oxygen andash content for its application as a fuel intermediate/blend-stock.
Conventional
upgradation
byhydrodeoxygenation requires significant amounts ofhydrogen to remove oxygen in bio-oil as H2O or CO2. In
this regard, co-pyrolysis of biomass with thermoplastic
polymers would be a cost effective solution. The
decomposition of cellulose, a major component ofbiomass, proceeds by a network of concerted

reactions,[2] while commercial PP degrades via a free
radical mechanism.[3] In the combined system, it is highly
probable that hydrogen abstraction reactions between
polypropylene and cellulose aid in improving the overall
H-content in bio-oil.[4] This significantly brings down thedownstream processing costs.
The key focus of this work is to understand thekinetics of slow and fast co-pyrolysis of cellulose andpolypropylene by thermogravimetric analysis (TGA) andmicropyrolysis experiments, respectively, and develop akinetic model to describe the key step of mass loss andrate limitations.
2. Materials and Methods
Microcrystalline cellulose (50 μm) and polypropylene(PP; Mn = 3,700, Mw = 14,000) were procured from
Sigma Aldrich. Individual and mixed samples of cellulose
and PP of c.a. 10 mg were heated from ambient to 900
oC in SDT Q600 TGA (TA Instruments) under N2 flow of
100 mL min-1. Fast pyrolysis of the samples was carriedout in a Frontier 3030 single-shot micropyrolyzer(Frontier-Lab, Japan) in the temperature range of 350 to500 oC. Rapid pyrolysis of c.a. 500 μg of the sample wasachieved at a rate of >2000 oC s-1 in a few seconds. The
pyrolyzed vapors were analyzed in a Shimadzu 2010 gas
chromatography/mass spectrometer (GC/MS). A HP-5ms
column was utilized to separate the components, whichwere quantified using a flame ionization detector.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

3.

Results and Discussion

3.1 Co-pyrolysis in TGA
Cellulose and PP in weight ratios of 100:0, 80:20,60:40, 40:60, 20:80 and 0:100 were pyrolyzed in TGA atvarious heating rates, viz., 5, 10, 20, 50, 100 and 180 oC
min-1. The thermogram exhibited two distinct peaks
corresponding to the decomposition of cellulose and PP.
Cellulose and PP decomposed in the temperature rangesof 300 – 380 oC and 400 – 500 oC, respectively. A
detailed kinetic analysis of weight loss profiles wereperformed using the conventional techniques ofFriedmann, Kissinger, Chang, Flynn-Wall-Ozawa andCoats-Redfern.[5] The apparent activation energies (Ea) ofthermal decomposition of the mixtures were evaluatedand it was found that Ea of cellulose decomposition wasunaffected by the presence of PP (< 3 kcal mol-1variation), while the presence of cellulose greatly
enhanced the degradation of PP. Figure 1 depicts thevariation of Ea evaluated by the first Kissinger technique,which is based on maximum rate of weight loss of thesample at various heating rates.

initially formed as a result of cellulose pyrolysis, aids incracking the primary pyrolysis vapors from PP to form
secondary gas phase species. All these information wereutilized in building a combined kinetic and transportmodel of co-pyrolysis of cellulose and PP, that caneventually be extended to biomass + polymer system.
Currently, a completely segregated model is found tosatisfactorily describe the experimental weight loss
profiles. However, the inclusion of key interactions in themodel are underway to comprehensively describe themechanism.
3.2. Co-pyrolysis in Micropyrolyzer
Fast co-pyrolysis of cellulose and PP is currently
being investigated in a micropyrolyzer-GC/MS system tounderstand the nature of interactions under high heating
rate conditions. In this regard we are monitoring thechange in product composition as result of inclusion ofpolymer in biomass. Apart from individual product yields,
we are also studying various properties of bio-oil likeelemental composition, acid value, molecular weight andhigh heating value. The interesting features of this part ofthe study and a comparison of the mechanism of copyrolysis under slow and fast pyrolysis conditions will be
discussed in the presentation.
4.

Figure 1. Variation of Ea of cellulose and PP withcomposition according to first Kissinger technique.

Conclusions

In this work, we have studied the co-pyrolysis
behavior of cellulose and PP as a mimic to understandthe behavior of biomass and thermoplastic polymers
under such reaction conditions. The TGA analysis showsa clear interaction between cellulose and PP, which isreflected in lower Ea of PP decomposition in presence ofcellulose. Currently, micropyrolyzer studies under fastpyrolysis conditions and modeling activity are underway
to understand the product distribution in bio-oil and thecontrolling mechanism under various reaction conditions.
References[1] Brown, R.C. (Ed). In: Thermochemical Processing of
Biomass Conversion into Fuels, Chemicals and Power,1st Ed.; UK (2011) Wiley.
[2] Vinu, R.; Broadbelt, L. J. Energy Environ. Sci. 5(2012), 9808-9826.
[3] Kruse, T. M.; Wong, H.-W.; Broadbelt, L. J.;
Macromolecules. 36 (2003) 9594-9607.
[4] Pérez, M.G.; Chaala, A.; Yang, J.; Roy, C. Fuel 80(2001) 1245-1258.
[5] Wang, X.-S.; Li, X.-G.; Yan, D. J. Appl. Polym. Sci.
78 (2000) 2025-2036.

Figure 2. Variation of Ea with conversion according toFlynn-Wall-Ozawa method.
Flynn-Wall-Ozawa method was utilized toinvestigate the variation of Ea with conversion at heating
rates, and as shown in Figure 2, it is clear that there is asignificant increase in Ea of almost all the mixtures after a
total conversion of 30 wt.%. This shows that char, that is
7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013