Continuous hydrothermal co-liquefaction of aspen wood and glycerol with water phase recirculation

Abstract

Hydrothermal liquefaction is a promising technology for the conversion of a wide range of bio-feedstock into a biocrude; a mixture of chemical compounds that holds the potential for a renewable production of chemicals and fuels. Most research in hydrothermal liquefaction is performed in batch type reactors, although a continuous and energy-efficient operation is paramount for such process to be feasible. In this work an experimental campaign in a continuous bench scale unit is presented. The campaign is based on glycerol-assisted hydrothermal liquefaction of aspen wood carried out with the presence of a homogeneous catalyst at supercritical water conditions, 400 • C and 300 bar. Furthermore, in the experimental campaign a water phase recirculation step is incorporated to evaluate the technical feasibility of such procedure. In total, four batches of approximately 100 kg of feed each were processed successfully at steady state conditions without any observation of system malfunctioning. The biocrude obtained was characterized using several analytical methods to evaluate the feasibility of the process and the quality of the product. Results showed that a high quality biocrude was obtained having a higher heating value of 34.3 MJ/kg. The volatile fraction of the biocrude consisted mostly of compounds having number of carbon atoms in the C 6 -C 12 range similar to gasoline. In terms of process feasibility, it was revealed that total organic carbon (TOC) and ash significantly accumulated in the water phase when such is recirculated for the proceeding batch. After four batches the TOC and the ash mass fraction of the water phase were 136.2 [g/L] and 12.6 [%], respectively. Water phase recirculation showed a slight increase in the biocrude quality in terms on an effective hydrogen-to-carbon ratio, but it showed no effects on the product gas composition or the pH of the water phase. The successful operation demonstrated the technical feasibility of a continuous production of high quality biocrude.

Hydrothermal co-liquefaction of microalgae, wood, and sugar beet pulp

“…Co-liquefaction of wood with glycerol was demonstrated in a continuous liquefaction setup by Pedersen et al [8]. Their product analysis did not reveal to what extent glycerol was converted during processing and contributed to the biocrude.…”

Application of Algae as Cosubstrate To Enhance the Processability of Willow Wood for Continuous Hydrothermal Liquefaction

“…The ability of algae to develop viscosity, change the slurry texture and prevent dewatering might be related to the presence of hydrocolloids in algae. Hydrocolloids are long chain hydrophilic 10 polysaccharides that form dispersions and have a common property: thickening. Some hydrocolloids are also able to provide stickiness or to form gels 44 .…”

“…Comparative studies showed that there is a high probability for successful feedstock pumpability if both the syringe and the centrifugation tests are passed. The comparison between the laboratory scale pumpability tests and the performance of a high pressure piston pump is based on the experience gained from operating the continuous bench scale HTL plant installed at Aalborg University, described elsewhere 10 . The continuous HTL system includes a high pressure piston pump that delivers the feedstock at 30 MPa.…”

“…The phase separation represents a major obstacle to pump aqueous slurries at pressures of 20 MPa to 30 MPa. Previous works show that fine milling, chemical pretreatment or slurry make-up with various additives is compulsory for continuous processing of wood in HTL systems where slurries with maximum wood concentration of 17 wt% were processed 8,9,10 . While wood and other lignocellulosic materials require special treatment to obtain pumpable aqueous slurries, continuous liquefaction of algae pastes can be implemented quite easily 11,12,13 .…”

The Effect of Particle Size on the Quality and Yield of Batch and Continuous Hydrothermal Liquefaction Products

“…Prapaiwatcharapan et al [6] investigated the effect of operating conditions on the yield and characteristics of the biocrude that is obtained in a semi-continuous system through single-step and two-step sequential HTL using microalgae as feedstock. Pedersen et al [16] investigated glycerol-assisted HTL of aspen wood in the presence of a homogenous catalyst with a water-phase recirculation at supercritical water conditions. In this study the focus was on the effect of biomass particle size on the yield and quality of the HTL products in both batch and continuous HTL systems.…”