Multifunctional and multi-staged reactors for liquid fuel generation from renewable feedstocks

Abstract

With fast depletion of fossil fuel, finding alternative and sustainable energy sources is one of the largest problems we currently face. Alternative energy sources, such as biomass and plastic waste, are good starting materials to potentially reduce our dependence on fossil fuel. Biomass is a sustainable feed stock, but it requires densification due to lower energy density. Biomass is also a distributed energy source; hence processing biomass continuously in a small-scale reactor with short residence time may be highly profitable. Plastic wastes derived from petroleum products are also a good replacement, since they can be recovered or processed to synthetic crude oil for use in transportation. Catalytic partial oxidation (CPO) of biomass or plastics over a noble metal catalyst which convert the solids (or liquids) into syngas and then to light hydrocarbons, is a promising technique to generate suitable liquid fuels. The CPO product, syngas, can be used to produce methanol over a Cu/ZnO/Al2O3 catalyst under elevated pressure. Alternatively, the CPO technique could be integrated with a dehydration reaction to produce densified liquid fuel (DME and butene) from biomass-derived alcohols. Methanol, one important product generated from biomass-derived syngas, is a platform for production of higher hydrocarbons. Chapter 2 describes small-scale methanol synthesis in a multifunctional reactor over a Cu/ZnO/Al2O3 catalyst. Conversion is increased by using in situ condensation with water as a coolant. Parallel hydrogenation of CO, CO2 produces the largest amount of methanol in the shortest period of time, and is closest to equilibrium in a fixed-bed reactor. A multifunctional reactor with water coolant is able to increase the conversion by a factor of two. Chapter 3 discusses methanol synthesis with in situ adsorption using nanocomposites (salt inside a porous matrix). CaCl2 inside silica gel has high capacity to uptake a significant amount of methanol at the synthesis operating conditions, resulting in equilibrium shift towards the product (methanol) and increase in the single-pass conversion of the reactants (CO). Multiple multifunctional reactors were built and their single-pass conversions were investigated. An integration of in situ condensation and in situ adsorption is proposed to further increase conversion. Chapter 4 and 5 describe the combination the CPO reaction and the dehydration reaction in an autothermal staged reactor to deoxygenate biomass-derived alcohols. The novelty of this reactor is that it integrates exothermic and endothermic reactions in a single reactor tube. Chapter 4 investigates the integration of the CPO reaction and methanol dehydration reaction to produce dimethyl ether (DME). Reactor configurations were compared, showing that a side feed of methanol between the two stages have the similar performance as those in an isothermal reactor with the dehydration reaction. Top feed methanol to the CPO stage results in decreasing in DME yield since part of the methanol consumed in the top stage is used to generate heat and drive the second stage endothermic reaction. Chapter 5 describes the use of a similar concept and reactor configuration with butanol as feed, since butanol is a next generation transportation fuel derived from biomass. The effect of isomers (n-butanol, 2-butanol, iso-butanol, and tert-butanol) and catalysts ( HZSM-5, HFER, and y-Al2O3) were studied in a systematic way. Butenes are the desirable dehydration product, which is the intermediate to produce transportation fuel or other chemicals. The integration of the CPO reaction and alcohol dehydration reaction also provides a potential way to reduce the capital cost of the process since it is not necessary to employ a fired heater or combustion chamber to preheat the butanol. The fast oxidative pyrolysis of polystyrene (PS) waste in an autothermal fixed-bed reactor is discussed in chapter 6. The PS particle is fed in the reactor by an auger, which then reacted on the catalyst particle surface, and converted into styrene monomers and other minor products. The temperature of oxidative pyrolysis was varied from 600 oC to 900 oC. Production of styrene dimers and trimers was not observed. The styrene yield was 75% at high C/O ratio (2.2-2.4) and was 85% with H2 as sacrificial fuel. The results of oxidative prolysis of PS provide valuable insights regarding the capabilities of catalyst for oxidative pyrolysis of other plastic wastes, e.g. polypropylene (PP), polymethyl methacrylate (PMMA), and etc. In chapter 7, several experiments are proposed to explore more efficient ways to generate liquid fuel from biomass-derived syngas, including a multifunctional reactor with baffles and spinning catalyst baskets, one-step DME synthesis and one-step gasoline ranged hydrocarbon synthesis from syngas. Additionally, process integrations are also proposed to generate long chain hydrocarbons for transportation purposes. Methanol (generated from syngas) can be reacted with hyoxymethylfurfural (HMF) to obtain an acetal or hemiacetal product. A CPO reaction on the top stage with Guerbet reaction on the second stage is proposed to generate butanol from ethanol. Finally, more oxidative pyrolysis of plastic wastes is proposed with more complex feedstocks, such as PE, PP, and PMMA. The diversity of applications suggests that biomass (or plastic waste) upgradation; involving reactor design, process integration and CPO reactions; are an important area of research. This thesis offers preliminary insights to understand the production of liquid fuel from sustainable energy sources with multifunctional or multi-staged reactors.