Flow Behavior and Aging of Pyrolysis Oils from Different Feedstocks

Abstract

This work focuses on the flow behavior and accelerated aging of pyrolysis oils produced in a screw reactor from different feedstocks. Beech wood, wheat straw, chicken manure, and sewage sludge were pyrolyzed at 350, 400, 450, and 500 °C, and the viscosity of the corresponding oils was measured at four different temperatures between 20 and 80 °C, with values up to 1 Pa s at 20 °C. Newtonian flow behavior was observed, except for wheat straw pyrolysis oils at temperatures below 50 °C. Absolute viscosity values as well as flow activation energies (E A ), covering a range from 38 to 57 kJ mol −1 , turned out to be independent of the pyrolysis temperature, except for beech wood oil. In this latter case, a peak in viscosity and activation energy was found at a pyrolysis temperature of 450 °C and is attributed to the low water content of the oil obtained at this temperature. Accelerated aging experiments were conducted for 24 h at 40 and 80 °C. For the latter temperature, the effect of a free surface and an inert gas atmosphere on aging was examined. This enabled us to separate the effect of polymerization and evaporation of volatiles on the change in viscosity. In both cases, beech wood pyrolysis oil showed the strongest aging (∼20-fold increase in viscosity). The lowest aging was found for wheat straw pyrolysis oil in a free surface sample cell, while almost no aging occurred under an inert gas atmosphere. Therefore, we conclude that aging of beech wood oil is mostly due to polymerization, whereas aging of wheat straw oil is essentially due to evaporation of volatiles. For chicken manure and sewage sludge oils, both polymerization and evaporation contribute almost equally to the increase of viscosity when an open sample cell is used. For beech wood pyrolysis oil, size-exclusion chromatography revealed a change in molecular weight upon aging from M w = 190 to 240 Da. A slight increase in M w could be detected for chicken manure and sewage sludge, but no indication for polymerization was found for wheat straw. Gas chromatography coupled with mass spectrometry was used to determine the concentration of characteristic oil components quantitatively, confirming the conclusions from viscosity measurements regarding aging mechanisms.

Intermediate pyrolysis of organic fraction of municipal solid waste and rheological study of the pyrolysis oil for potential use as bio-bitumen

“…It is also concluded that the two major factors that affected the pyrolysis oil viscosity were the temperature and the liquid moisture content. Jampolski [9] studied the viscosity of aged pyrolysis oils produced in a screw reactor from various feedstocks including beech wood, wheat straw, chicken manure, and sewage sludge. The viscosity measurement was taken between 20 and 80°C.…”

“…The shift factors were modelled by the WLF function and it was derived that ߙ ் = exp ቀ− The shifted viscosity data and the viscosity data at the reference temperature in Figure 8 were utilized to formulate the viscosity master curve of the OFMSW pyrolysis oil. Based on these data, the Carreau viscosity model was formulated as below: (9) The black and solid curve in Figure 8 shows the Carreau model predictions of the viscosity for the OFMSW pyrolysis liquid. The high R 2 (0.955 for the Carreau model) indicates that the Carreau master curve model is capable of capturing the viscosity characteristics at a wide range of shear rates.…”

Characterization of Heavy Products from Lignocellulosic Biomass Pyrolysis by Chromatography and Fourier Transform Mass Spectrometry: A Review

“…However, this fraction concerns only volatile and semivolatile species, which corresponds up to 30% of the bio-oil. , The other heavy and nonvolatile compounds are also of importance for the comprehensive bio-oil characterization and their valorization processes. Indeed, they are involved, most particularly phenolics, in aging reactions such as polymerization. , These condensation reactions increase viscosity and release water in the bio-oil, which is responsible for bio-oil storage issues and catalyst degradation . Therefore, their characterization is also of significant interest.…”

“…The sample was heated at 80 °C for 20 and 40 h. The achieved corresponding GPC-RI were slightly shifted to higher molecular weight values, compared to the nonheated bio-oil. In the work of Jampolski et al, GPC was performed on two pyrolysis oils of beech wood and wheat straw before and after accelerated aging conditions (at 80 °C for 24 h) . For the first bio-oil, an increase of the Mw, from 190 to 240 Da, was observed, indicating a polymerization process.…”

“…Indeed, they are involved, most particularly phenolics, in aging reactions such as polymerization. 69,127 These condensation reactions increase viscosity 128 and release water in the bio-oil, which is responsible for bio-oil storage issues and catalyst degradation. 129 Therefore, their characterization is also of significant interest.…”