Synergy in the hydrothermal pyrolysis of oil shale/sawdust blends

• Effects of blend composition, water/blend ratio, water density, and pyrolysis duration on the yields of gas, consecutive extracts with hexane, benzene and tetrahydrofurane, and solid residue at hydrothermal co-pyrolysis of Kukersite oil shale (A) and pine sawdust (B) blends in a batch autoclave were studied.
• Synergy (Δ) in the yields of the co-pyrolysis products was described using the equimolar synergy model, Δ = δxAxB, where xA and xB were fractions of the components in the blends, and δ—a new characteristic, called synergy factor.
• The values of δ were estimated and compared at pyrolysis conditions studied.

Synergy (Δ) in a co-process is a difference between the actual result and the result calculated by proportional contributions of the components. In this work, Δ in the yields of hydrothermal pyrolysis products of Estonian oil shale (A) and pine sawdust (B) blends was studied. The effect of the sawdust organic matter fraction (xB) in the blend organic matter (0–1 g/g) on the yield of pyrolysis products (i): gas, consecutive extracts with hexane, benzene and tetrahydrofurane, and solid residue was estimated under various water/blend ratios (0–3 g/g), added water density (0–0.5 g/cm3), and durations (2–3 h) at nominal temperature 380 °C. Equimolar synergy reactions were proved basing on the proportionality between Δi and the product of the fractions of the components in the blend (xAxB). The coefficients of the proportionality (δ), called synergy factors, were estimated for the systems studied. As a rule, positive values of Δ and δ were found in the gas yield and negative in the yield of organic matter remaining in the solid residue. Lack of synergy was evident in the yields of benzene extract and tetrahydrofurane extract in the co-pyrolysis without water and when water density was below 0.3 g/cm3. An effective synergy was revealed in the yield of benzene extracts under insufficient durations when decomposition of the blend was not completed.