Optimization of Solid Fuel Production by Co-Hydrothermal Carbonization of Polyvinyl Chloride and Pontederia Crassipes

Abstract

The chlorine content of Polyvinyl chloride (PVC) in municipal waste creates a major challenge in its disposal. Water hyacinth (WH), an invasive plant, disrupts aquatic life and impedes the movement of vessels on water bodies that they colonize. These two materials, PVC and WH however have high caloric value making them suitable to be used as a source of fuel. Hydrothermal carbonization (HTC), a method for producing solid fuel has been identified as a safe medium to remove chlorine from PVC. In this work, PVC, and WH were subjected to Co-HTC using water as the solvent. Response Surface Methodology (RSM) was used to optimize the hydrochar produced by varying the temperatures, residence time, and mixing ratios. 5 g of the feedstock was subjected to Co-HTC at temperatures 200 ℃, 230 ℃, and 260 ℃; residence time of 60 minutes, 90 minutes, and 120 minutes; and mixing ratio of PVC/WH 1:1 to 1:3. The result showed that increasing the temperature and resident time increased the dechlorination efficiency (DE) of the PVC with the highest DE at 94.3%. The mixing ratio had a minimal effect on the output variables. Increasing temperatures and residence time reduced the mass yield of hydrochar but increased their corresponding High Heating Values (HHV). The highest hydrochar yield, 70.33%, occurred at 200 ℃, the highest DE of 94.39% occurred at 260 ℃, and the highest HHV, 32.34 MJ/Kg occurred at 260 ℃. FTIR microscopy, TGA analysers, and Van Krevelen diagrams were used in analysing the thermal properties of the fuel produced. The optimal conditions predicted from the data using the RSM are temperature, 230 ℃, residence time, 86 minutes, and mixing ratio of 0.33. These parameters were used for the confirmation and validation and the HHV obtained was 27.32 MJ/Kg. The HHV is close to that of coal, implying that hydrochar produced from PVC and WH feedstocks can be a good source of fuel for domestic and industrial usage.