Bio-Crude Production through Aqueous Phase Recycling of Hydrothermal Liquefaction of Sewage Sludge

Abstract

Hydrothermal liquefaction (HTL) is a promising technology for the production of bio-crude. However, some unresolved issues still exist within HTL, which need to be resolved before its promotion on a commercial scale. The management of the aqueous phase is one of the leading challenges related to HTL. In this study, the sewage sludge has been liquefied at 350 °C with and without catalyst (K2CO3). Subsequently, aqueous phase recycling was applied to investigate the effect of recycling on bio-crude properties. Obtained results showed that the energy recovery in the form of bio-crude increased by 50% via aqueous phase recirculation, whereas nitrogen content in the bio-crude was approximately doubled after eight rounds of recycling. GCMS characterization of the aqueous phase indicated acetic acid as a major water-soluble compound, which employed as a catalyst (0.56 M), and resulted in a negligible increase in bio-crude yield. ICP-AES highlighted that the majority of the inorganics were transferred to the solid phase, while the higher accumulation of potassium and sodium was found in the aqueous phase via successive rounds of recycling.

An In-Depth Process Model for Fuel Production via Hydrothermal Liquefaction and Catalytic Hydrotreating

“…Spirulina shows the highest initial TOC value in the AP, followed by wheat straw and sewage sludge. These values are in good agreement with literature data for Spirulina (6.7 g/L to 79.9 g/L) [34,40,41] and sewage sludge (8.3 g/L to 27.8 g/L) [36,40,42]. The TOC value of the modeled aqueous phase of wheat straw is higher than reported in literature (2.8 g/L to 27.8 g/L) [40,41].…”

Bio-Crude Production through Recycling of Pretreated Aqueous Phase via Activated Carbon

“…The reactor was allowed to heat up to 350 • C at the 3 • C/min with continuous stirring of 300 rpm. The temperature was selected following the previous SS studies [28,38]. After attaining the desired temperature, the reactor was maintained at a retention time of 15 min.…”

“…These hydrocarbons with long chains, such as hexadecane, originated from the decarboxylation of saturated fatty acids [48]. Phenolic compounds were found in smaller numbers, which were probably derived from the dehydration and cyclization of sugars [28]. It is concluded from the above observations that aqueous phase recirculation not only improves the energy recovery of the bio-crude but also increases the nitrogen content in the bio-crude that requires further upgrading via hydro-treatment to get in line with the quality of the fossil crude.…”

“…Daniel et al also examined the effect of water recycling on the properties of the bio-crude and reported higher bio-crude yields and lower solid yields with HHVs of 33 to 35 MJ/kg from blackcurrant pomace at 310 • C [27]. Recently, Shah et al carried out eight recycling experiments with the diluted aqueous phase with dried SS, and found a 50% increase in the energy recovery of the bio-crude with almost 2-fold increase of nitrogen [28]. Chen at al utilized the aqueous phase from spirulina platensis as a recirculating medium for the recirculation experiments of HTL of spirulina platensis, α-cellulose, and lignin.…”

Recovery and liquefaction of nitrogen-containing component and minerals from food processing wastes of vinegar using subcritical water

“…Pollution due to the environmental discharge of residual organics from food processing has become a social problem all over the world. In recent years, the concept of technical innovation which is converting conventional chemical processes to more sustainable and 'green' procedures [1], has been pursued in Japan. The depletion of energy resources can be minimized by efficient utilization and conversion of waste to energy.…”