Abstract:
The effects of reaction temperature on hydrothermal liquefaction (HTL) process of municipal sewage sludge (MSS) and on liquefied products characteristics were investigated. The results showed that the bio-crude yield and asphaltene yield reached the highest level at 370 ℃, which were 26.82% and 27.73%, respectively. The water recovery ratio and volume reduction ratio were also increased to the maximum value of 94.81% and 80.16%, respectively, indicating that improved effects on volume reduction of MSS were obtained after HTL process. The mass concentration of water-soluble organics dropped to 29.47 g/L, which demonstrated that higher reaction temperature would promote the decomposition of these water-soluble organics. The bio-crude was mainly composed of aliphatic acids, amines and aliphatic hydrocarbons, and the carbon chain length of aliphatic acids was located in between 16 and 18, which indicated that the properties of bio-crude were similar to those of diesel oil. The water-soluble organics were mainly composed of carboxylic acids, esters, amides and phenols while the existence of carboxylic acids would have detrimental influences on the growth of plants, the availability of soil nutrient and the biodiversity of environment. The gaseous products were mainly consisted of CO
2 which could be explained by the decarboxylation taking place on the surface of MSS particles. The ash content of residual solids reached the highest level (79.72%) at 370 ℃, which showed that a better extraction rate of organic matters in residual solids could be obtained by HTL process. During the HTL process, the energy recovery ratio of liquid bio-fuels was between 53.23% and 98.20% at 270 ℃ to 370 ℃, indicating that more than half heating value of the MSS could be recovered to be liquid bio-fuels upon a HTL treatment.