Recovery and Reuse of Valuable Chemicals Derived from Hydrothermal Carbonization Process Liquid

Abstract

Recovery and reuse of valuable chemicals from hydrothermal carbonization process liquid (HTC-PL) from tomato plant biomass (TPB) was conducted. Different HTC-PLs were characterized with FTIR and Py-GC-MS analyses revealing the presence of low molecular weight linear, cyclic, and aromatics compounds in the HTC-PL. Separation of these valuable chemicals by fractional distillation resulted in eutectic constrains. Solvent extraction separation followed by solvent recovery and reuse provided encouraging results. The non-polar portion of HTC-PLs were extracted by using n-hexane (C6H14), and diethyl ether (C2H5)2O solvents with 8.5 and 4.3% recoveries, respectively. Characterization by FTIR and Py-GC-MS revealed petrol fuel like materials in the extracts of C6H14 and (C2H5)2O, irrespective of higher boiling components. Blends of both non-polar extracts were flame tested revealing good burning characteristics with minimal smoke and residue. Bench scale spirit lamp tests showed the blend would be very useful for greenhouse winter heating. The polar extracts using methylene chloride (CH2Cl2) resulted in about 55% recovery. Py-GC-MS analysis revealed acetic acid and 5-Hydroxymethyl furfural (5HMF) majors in the extract along with related derivatives. 5HMF is a valued chemical and demonstrated to be a useful building block for many industrial applications, and flatform chemical for various synthesis. Other identified minor components of HTC-PL were vanillin, divinyl terephthalate, and syringol. After the extractions of polar and non-polar components in three steps, the HTC-PL residue was applied as nutrient source after maintaining pH (5.6) and concentration (TOC, 100–200 mg/L) to typical greenhouse plants. Plant growth was encouraging. The paper discusses all the potential valued reuse applications of HTC-PL in greenhouses without discharges, which contributes to environmental protection and economic benefits.