Recovery of Valuable Chemicals from Agricultural Waste Through Pyrolysis

Agricultural crop residues are a source of inexpensive biomass to convert into bioproducts. The recovery of valuable chemicals from plant waste would partly solve the disposal issue and offer a more environmentally friendly alternative to synthetic chemical production. One approach to separate and concentrate valuable chemicals from biomass is pyrolysis using a batch reactor process. A mechanically fluidized reactor (MFR) was developed to pyrolyze biomass from ambient to temperatures near 600 °C, forming gases that are then condensed in an ice-chilled condenser to form a bio-oil. The bio-oil produced by the MFR can be separated within temperature ranges, termed one-dimensional or 1-D pyrolysis. Further separation of bio-oil can be achieved by two condensers, one set at a high and one at a low temperature, to isolate the gases by boiling point, termed two-dimensional or 2-D pyrolysis. Char is a by-product of pyrolysis and can be converted into a value-added product, activated carbon, by heating using a jiggled bed reactor (JBR). The biomass investigated, tobacco leaf, tomato plant, spent coffee ground, and hydrolysis and organosolv lignin, were chosen based on availability and the valuable products previously identified in the bio-oil. The thesis objectives were: 1) optimize the 1-D and 2-D MFR for chemical recovery; 2) to isolate bio-oil fractions containing pesticide and antioxidant activity with the 2-D MFR and 3) to compare the activated carbon produced by the JBR from char. After 2-D MFR pyrolysis, a total nicotine recovery of 90% from tobacco bio-oil compared to solvent extraction was obtained when the nicotine concentration was 20%. Both the tobacco and tomato bio-oils could be separated through the 2-D MFR to isolate fractions with high insecticide activity, and the antioxidant concentration in the tomato and organosolv lignin bio-oil was 97 and 91%, respectively. The tomato char produced the activated carbon with the highest adsorption capacity, comparable to commercial coconut shell. In summary, valuable products including pesticides, antioxidants and activated carbon can be recovered from crop waste by MFR pyrolysis demonstrating a successful example of a biorefinery, a sustainable process for converting biomass into a range of bio-based products