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The direct on-site conversion of methane to methanol could provide a more cost-effective and less energy-intensive utilization of natural gas compared to the industrial two-step syngas based route. Despite the numerous approaches investigated for direct methane to methanol (DMTM) conversion in the last century such as homogeneous gas-phase, homogeneous liquid partial oxidation and heterogeneous catalytic partial oxidation, none of them were deemed successful for commercialization due to either the use of expensive reagents such as H2O2 and H2SO4, low yields and conversions, or inefficient system requirements. This has been mainly attributed to the thermodynamic challenge of breaking the strong C-H bond (bond dissociation energy of 435 kJ/mol) in the highly stable methane molecule and due to the higher reactivity of the product methanol leading to the formation of COx products. Based on density functional theory (DFT) calculations, it was postulated that the selective oxidation of methane to methanol was possible with weakly adsorbed oxygen species over transition metal surfaces such as Ag and Pt at high oxygen and water partial pressures. Recent experimental studies also indicated that the presence of water through site blocking action had beneficial effects on catalytic activity and methanol selectivity. Since the role of liquid water in a single continuous-flow reactor has not been well established, evaluating its effect on catalytic performance and product selectivity in the direct conversion of methane over platinum-based catalysts was the prime focus of this research. Therefore, a specifically designed trickle bed reactor (TBR) system capable of operating continuously and safely at high pressures was constructed to investigate the selective oxidation of methane over platinum-based catalysts in the presence of liquid water. Methane, oxygen and helium were pressurized and flow-metered prior to entering the reactor while the flow of deionized liquid water was controlled through a pump. The reactor assembly consisted of a quartz tube liner sealed at the top with a fluorocarbon O-ring in a stainless-steel shell (545 mm in length and 15.8 mm in inside diameter). A central thermowell fixed along the reactor tube which shielded an internal thermocouple was also quartz-sheathed to prevent undesired side reactions on the metal surface. Pelletized platinum catalyst supported on titania (ca. 1.5 g, dp = 150-250 µm) was packed in the isothermal region (ca. 100 mm) of the reactor with silicon carbide granules (dp ~ 1000 µm) filling the top and bottom void spaces. The reactor body was heated through a five-zone electric furnace. Pressure-controlled argon was allowed to flow between the annular region of the quartz liner and reactor shell at the same pressure as inside the quartz tube liner. The flowrate of argon was set approximately 2-3 times higher than the total gas flowrate through the catalyst bed to completely vaporize the effluent stream. The reactor effluent was throttled to atmospheric pressure and heated via heating cords to ensure no condensation of products prior to analysis via an existing online GC-Polyarc™-FID system. Long-term catalytic experiments were performed on platinum impregnated TiO2(P25) and TiO2(rutile) in the newly constructed trickle bed reactor at 220 °C and 30 bar. The inlet partial pressures of methane and oxygen were kept constant at 0.5 bar and 1.5 bar, respectively, while the feed rate of liquid water was varied from 0 - 0.3 ml/min with intermittent return to baseline condition (i.e., at PH₂O = 6.9 bar) to monitor catalyst activity. The results of this investigation indicated that co-feeding liquid water has beneficial effects on the activity of these catalysts as well as the selectivity towards C1 oxygenated products. Both catalysts were able to selectively convert methane to C1 oxidation products in the trickle bed reactor with the highest activity and selectivity obtained while operating in the flooding region whereby water exists in the liquid phase (PH₂O > 23.1 bar). Pt/TiO2(P25)selectively formed methanol and methoxy methanol with a maximum selectivity of ca. 10% at a methane conversion of 0.6%, corresponding to an average turnover frequency of 0.25 h-1. Carbon dioxide was the major product formed over Pt/TiO2(P25). Conversely, over Pt/TiO2(rutile), formaldehyde was the exclusive selective oxidation product formed with a remarkable selectivity of 90% at a methane conversion of 1%, corresponding to an average turnover frequency of 0.43 h-1. Carbon dioxide and carbon monoxide were also detected in the product spectrum. Thus, under similar operating conditions, Pt/TiO2(rutile) exhibited a significantly higher activity and improved selectivity, greatly favouring the formation of C1 oxygenates compared to Pt/TiO2(P25). The novel trickle bed reactor system has demonstrated great ability in operating continuously at steady state for long-term runs for the selective oxidation of methane in the presence of liquid water at high pressure (< 50 bar) and moderate temperature (< 400 °C). Although the findings in this research indicate that liquid water facilitates the direct conversion of methane to selective oxidation products such as methanol and formaldehyde, the role of liquid water is not still obvious and has not been explicitly studied. Therefore, it is recommended that more catalytic testing with optimised reactor conditions and/or addition of promoters (such as Ag, Ni, Pd, Mo, Co and Cu) should be done in order to improve methane conversion, as well as yield for C1 oxidation products. Furthermore, to enhance the performance of the reactor and better understand the interaction of liquid water with the solid catalysts in the tri-phasic system, hydrodynamics studies should be performed.

Environmental concerns, associated legislation, limited oil reserves and fluctuating crude oil prices are some of the factors that highlight the need for alternative and environmentally friendly routes to fuels. One alternative is to use Fischer-Tropsch Synthesis (FTS) as the major technology in conversion of carbon containing feedstock to transportation fuels. The FTS product, called syncrude, can be refined to high quality transportation fuels in Coal, Gas or Biomass to liquid plants (denoted as CTL, GTL, and BTL, respectively, and collectively referred to as XTL). The economic viability of XTL processes is generally subject to the present price of crude oil and past studies show that traditional refining is generally more economically viable. However, XTL processes have been shown to be more economical and in some cases more environmentally friendly than conventional options when legislative measures aiming to curb traditional fossil fuel usage are considered. This study explores XTL process configurations that can improve plant carbon efficiency to diesel and liquids. The configuration encompasses technologies used, operating conditions, and layout of unit operations. A basic GTL process configuration consists of an Air Separation Unit (ASU), Auto-Thermal Reforming (ATR), syngas cleaning, full conversion Low Temperature Fischer-Tropsch (LTFT) and wax hydrocracking (WHC). These operations are modeled individually and combined to produce a plant model for study with the aim of determining the effects of configurational alternatives on the process efficiency to liquids and diesel. Furthermore, given that the ASU is a major contributor to costs the effect of using oxygen-enriched or pure air is investigated. Since production of heavy wax is prioritized, FTS represents the use of cobalt catalyst in LTFT operation. Where air is used, FTS is run to high conversion in once through mode to avoid the unfavorable economics of recycling nitrogen. After separation of the syncrude, the light fraction is reformed back to syngas in order to maximize carbon efficiency. The heavy wax is hydrocracked to maximize distillate range material. The light products from the WHC are combined with the lights from FTS and the heavy wax is recycled. Carbon efficiency, liquid selectivity and diesel yield are the means of assessing performance. The Scilab programming language is used along with physical properties estimated using the COCO/ChemSep pure component database as a starting point. Estimation of properties for alkanes and olefins of carbon chain length up to C200 has been carried out. The presence of 25% nitrogen in the ATR was found to beneficial to the H2 : CO ratio in the resulting syngas. Furthermore, in FTS the presence of 10-20% nitrogen produced the lowest reduction in carbon monoxide conversion and _FTS. In general, the introduction of nitrogen resulted in decreased conversion of methane in the ATR and both decreased _FTS and conversion in FTS. WHC performance was found to benefit from alpha being as high as possible; however, when the heavy wax recycle was inactive the optimal value was 0.92. The OOT80 configuration was found to have the highest liquid selectivity, while the efficiency to diesel was maximized for the OIRC40 configuration.

The direct conversion of methane to methanol can have great economic implications and have been under extensive research for the past century. It is speculated that platinum-based catalysts may achieve this due to its ability to adsorb molecular oxygen as reactive surface oxygen species that may react with methane to form methanol. The selective conversion to methanol over such a catalyst might be possible through site blocking action with in presence of steam and/or high oxygen partial pressures as well as the presence of a promoter. Thus, a packed bed reactor system capable of safely operating under high pressures (< 50 bar) is designed and constructed to investigate the performance of platinum-based catalysts in the direct oxidative conversion of methane to methanol whilst co-feeding steam. The design procedure is carried out from flowsheet development to the detailed design of individual units of the reactor system. The constructed reactor system is built around a quartz lined microreactor 200 mm long and 2.4 mm in diameter to minimize risks associated with the flammability of methane and oxygen mixtures. A method for complete product analysis of all carbon containing reaction products using gas chromatography with flame ionization detector in conjunction with an oxidizer-methanizer microreactor is developed which is capable of quantifying minor carbon containing reaction products formed at low conversions with yields greater than 10 μmol/mol. Flow, pressure and temperature controls are also developed for the reactor system to ensure steady state operation.

The increase in global population accompanied by depleting fossil fuel reserves and rising fuel demand is prompting the need to increase and diversify fuel production rates. In addition, increasing global pressure to reduce the contribution of greenhouse gas emissions to global warming and as well as rising oil prices are driving efforts to improve efficiency and environmental sustainability of fuel production. Low temperature Fischer-Tropsch synthesis is an attractive alternative to crude refining. During Fischer-Tropsch synthesis (FTS), synthesis gas, a mixture of H2 and CO is converted to a wide range of value-added long chain hydrocarbon products in a polymerisation reaction: (2n+1) H2 + n CO → CnH2n+2 + n H2O -∆H= 165 − 214 kJ ∙ mol!" 0-1 The benefit of Fischer-Tropsch synthesis is that any carbonaceous feedstock can be used to generate synthesis gas, including natural gas, coal and biomass. However, exploitation of biomass requires decentralised, small-scale units, to reduce the complexity of a variable feed supply. To make this feasible, small-scale FT reactors must be simple to operate and achieve high single-pass conversion. Multi-tubular fixed-bed reactors are ideal for realising this as they are relatively easy to scale-up and operate when compared to other reactor technologies. However, conventional catalyst packings for fixed-bed reactors result in high pressure drop. Structured packings offer an attractive solution as their high porosity (ca. 70%-90%) when compared to that of conventional pellet- or particle packed beds (ca. 40%) results in significant reductions in pressure drop, which lowers gas compression costs. Large pellets are typically used in fixed-bed reactors to reduce pressure drop, resulting in increased internal diffusion limitations which may result in increased CH4 selectivity and reduced C5+ selectivity, the desired product. In contrast, a thin layer of the catalytically active material applied on the surface of the structured substrate results in lower diffusion limitations, and thus maintaining a favourable product distribution. Furthermore, open-cell foams reactors have the potential to enhance external mass in fixed-bed reactors because of their tortuous flow channels and high geometric surface area. The aim of this study was to compare the performance of catalyst coated on a ceramic open cell foam with that of catalyst powder, pellets and catalyst coated on a ceramic honeycomb monolith in terms of CO conversion, CH4 and C5+ productivity per gram catalyst using an alumina-supported catalyst containing 22 wt.% Co and 0.05 wt.% Pt. Furthermore, the effect of catalyst layer thickness on catalyst performance was also evaluated. It was shown that the pellets performed poorly when compared to the catalyst powder due to its much higher CO2 and CH4 selectivity, which were attributed to poor temperature control, induced by large diffusion length (i.e., pellet diameter). The foams and monoliths also performed poorly when compared to the catalyst powder. For monoliths and foams wash coated with ca. 0.5 g of catalyst, it was seen that CO conversion achieved was on average ca. 40% lower than that achieved over the catalyst powder at similar space velocities. The product selectivity was also poor. Furthermore, it was seen that despite the tortuous flow channels of the foams, which were initially thought to produce better mass transfer than the flat-wall channels of the monoliths, the performance of the foams was not better than that of the monoliths. Thus, it is concluded that the use of monoliths and foams does not improve performance in Fischer-Tropsch synthesis. The poor performance may be attributed to poor heat and mass transfer properties in the reactor set-up, and possibly aggravated by catalyst deactivation incurred during reactor startup.