I heated cotton in a sealed container (with a small hole) over a natural gas flame. Some gases and smoke were produced. What would they probably be? I can come up with some guesses based on the composition of cellulose: COX2, CHX4 or possibly other hydrocarbons, CO, HX2, HX2O, however I do not know which of those they are. Obviously, soot (C) was also formed, due to the visible smoke particles.
Answer
During pyrolysis, organic compounds are thermally decomposed in the absence of oxygen. The pyrolysis products are classified into categories based on their physical state of existence: char (solid), bio-oil (liquid) and non-condensable gases (gas). The relative proportions of these three product fractions significantly vary depending upon the process conditions, as is shown in the table below.
Pyrolosis TechnologyResidence TimeHeating RateTemperatureCharBio-OilGasesConventional5-30 min<50∘C min−1400-600∘C<35%<30%<40%Fast Pyrolysis<5 s~1000∘C s−1400-600∘C<25%<75%<20%Flash Pyrolosis<0.1 s~1000∘C s−1650-900∘C<20%<20%<70%[1]
The exact compositions of the products of cellulose pyrolysis at different temperatures can be seen below.
ProductsPeak Temp, 500∘CHolding Temp, 400∘CPeak Temp, 750∘CPeak Temp, 1000∘CCO0.99%0.25%15.82%22.57%COX20.3%1.45%2.38%3.36%HX2O3.55%6.49%8.72%9.22%CHX40%0%1.11%2.62%CX2HX40%0%1.05%2.18%CX2HX60%0%0.17%0.28%CX3HX60%0%0.70%0.80%HX20%0%0.36%1.18%CHX3OH0.25%0.21%1.03%0.98%CHX3CHO0.01%0.05%1.58%1.7%tar16.37%83.35%59.92%49.12%char83.63%6.17%3.32%3.91%other0.19%0.16%2.14%1.78%total105.25%98.36%98.8%99.86%
The holding time for each of these reactions was 30 s[2]. As shown in the table, CO, HX2O, and COX2 are the major gaseous products, with HX2 and hydrocarbons being produced in considerably smaller proportion.
[1] Patwardhan, Pushkaraj Ramchandra, "Understanding the product distribution from biomass fast pyrolysis" (2010). Graduate Theses and Dissertations. Paper 11767.
[2] Hajaligol, M. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Product Compositions and Kinetics for Rapid Pyrolysis of Cellulose. Industrial & Engineering Chemistry Process Design and Development Ind. Eng. Chem. Proc. Des. Dev. 1982, 21, 457–465.
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