Synergy in co-pyrolysis of oil shale and pine sawdust in autoclaves

Synergistic effects (Δ) in low temperature co-pyrolysis of Kukersite oil shale and pine (Pinus sylvestris) sawdust were studied in autoclaves in the ranges of blend composition xi = 0–1 g/g, nominal temperature 360–400 °C and duration 2–4 h. The value of Δ was estimated as the difference between the actual yield of pyrolysis products (gas, pyrogenetic water, subsequent extracts into hexane, benzene and tetrahydrofurane, and organic solid residue) and the additive value calculated as linearly proportional to the contributions of the individual components. The amplitude of Δ was explained based on the stability of a new cross-compound AnB formed between the liquid and solid decomposition products of the components. An equimolar synergy reaction (n = 1) was proved to result synergies in the yields of the co-pyrolysis products. The extent of synergy was quantitatively evaluated by means of positive and negative values of a new characteristic, synergy factor (δ) expressing proportionality between the synergy and product of the shares of the components in the blend (Δ = δxAxB). The maximum synergistic increase in the yield of total oil (sum of hexane and benzene extracts), by 21.6%, was revealed for xi = 0.5 g/g when the primary thermal decomposition of kerogen was not completed (360 °C, 2 h). Lack of synergy prevailed under the optimum conditions for thermobituminization (380 °C, 2–4 h). A decrease in the oil yield from the additive value by 9% was evident when the secondary coke formation from thermobitumen and oil took place (400 °C, 2–3 h).