Dry reforming of associated natural gas using catalytic membrane reactors.

Temimi, Ali Ramadan

Abstract

The mitigation and utilization of greenhouse gases, such as carbon dioxide (CO2), are among the most important challenges in the area of energy research. Dry reforming of propane (C3H8) (DRP), which uses both CO2 and C3H8 as reactants, is a potential method to utilize the previously-mentioned gases in the atmosphere. Associated natural gas containing high concentrations of CO2 and C3H8 could therefore be utilized for hydrogen and synthesis gas (syngas) production in the near future, without need for the removal of CO2 from the source gas. Thus, the DRP reaction is a suitable process to convert C3H8 and CO2 to more useful raw materials. The reforming of (CO2) with associated natural gas can be adapted to generate a synthetic gas having 1:1 hydrogen to carbon monoxide (CO) ratio. This type of gas synthesis may be used during the production of a large number of industrially-important chemicals. From an environmental point of view, this reaction can also be used to mitigate the so-called "greenhouse effect", since the conversion of these gases into valuable chemical(s) and feed stocks could alleviate and significantly reduce the emissions of CO2 and associated natural gas into the atmosphere. In this thesis, a catalytic membrane reactor has been used to carry out experiments on the conversion of reactants, product selectivity and distribution, catalyst selection and activity. Interpretation of the reaction mechanism and kinetics of this important reaction are also presented. Previous experimental research has been centered on the reactor development, catalyst impregnation and the feasible applications in industry. The Group VIII metals of the periodic table of elements, supported on oxides, have been found to be effective for this reaction. Carbon deposition causing catalyst deactivation was found to be one of the major challenges inhibiting the large-scale application of the reaction. Nickel (Ni)-based catalysts impregnated on an alumina wash-coated tubular membrane support showed carbon-free operation and was thus used to generate important data regarding the performance of membrane reactors for this reaction. In this work, the membrane reactor investigated for CO2 reforming with associated natural gas operated in pore-flow through mode, using a catalyst-impregnated porous membrane that had no separating functions, but which acted as a support for the catalyst. The catalyst was therefore immobilized as highly-dispersed nanoparticles in the pore of the membrane structure. CO2 and associated natural gas were forced through the pores of the membrane where the catalytic reaction took place. The membrane, in effect, worked as a contact zone for the reactants and the catalyst. Because of fast convective flow, internal diffusion limitations were reduced as the products were immediately removed from the membrane pore, avoiding product accumulation within the membrane and therefore eliminating consecutive reactions. As a consequence, the effective product yield was not influenced by mass transfer limitations and selectivity for the desired product could be increased. The reverse water-gas-shift reaction was a possible cause for the reduced yield of hydrogen. The reduction or elimination of the mass transfer limitation is particulary important for CO2 reforming with associated natural gas, where there is a high propensity for consecutive reactions. This research investigated the catalytic dry reforming of propane over Zr/Ni/Pd/Cu/-Al2O3 catalysts under the temperature range 600ºC/873.15ºK to 700ºC/973.15 ºK. These catalysts (supported on alpha-Al2O3) were chosen for this study because primary studies showed better selectivity and activity, and smaller deactivation resistance than for other catalysts. The thermal structure, pore size distribution, gas permeability and chemical structure of such Hybrid Ceramic Membranes (HCMs) were characterised using various methods, including gas permeability measurement, Scanning Electronic Microscopy (SEM), Accelerated Surface Area and Porosimetry analysis (ASAP), nitrogen Adsorption, Energy Dispersive X-ray Analysis (EDXA) and gas permeation mechanisms through the catalytic porous membrane. The initial experimental results from the HCMs exhibited good thermal stability, gas permeability and hydrophilic properties, as the accompanied water vapour that was formed could permeate through membranes better than the gases that resulted from the dry reforming of propane with CO2 (C3H6, C2H6, C2H4, CH4 and CO). Preliminary experiments were conducted to check the working condition of the catalyst testing unit. The results were quantitatively analysed and a typical productive reactive run was selected as a representative sample. The experimental reactive runs were conducted using three different sets of ceramic membrane supports under various operating conditions, including pressure at 1.0, 2.0 and 3.0 bars, temperature at 600ºC/873.15ºK, 650ºC/923.15ºK and 700ºC/973.15ºK, and overall inlet premixed reactant fed gas flow rates of 100ml/min, 200ml/min and 300ml/min, fed at a flow ratio of 1:1, 1:2 and 2:1. The best experimental reactant fed gas conversion results of 34%, and 58% of CO2 and C3H8 respectively were obtained at a pressure of 2 bar, a temperature of 650ºC/923.15ºK and a flow rate of 200ml/min that was fed at ratio of 2:1. The production gas selectivities were of 68%, 25%, 28%, 26%, and 55% for C3H6, C2H6, C2H4, CH4, and CO respectively and liquid yield namely water. Thus a catalytic membrane reactor (CMR) for the dry reforming of CO2 and propane was presented along with its typical performance characteristics. This reactor structure was implemented here to achieve an efficient integration not only on the reactor section but also in the process scale as recommended in this study.

Citation

TEMIMI, A.R. 2015. Dry reforming of associated natural gas using catalytic membrane reactors. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-1987973

• Thesis Type: Thesis
• Deposit Date: Jun 15, 2023
• Publicly Available Date: Jun 15, 2023
• DOI: https://doi.org/10.48526/rgu-wt-1987973
• Keywords: Greenhouse gases; Membranes; CO2 repurposing; Carbon dioxide repurposing
• Public URL: https://rgu-repository.worktribe.com/output/1987973
• Award Date: Dec 31, 2015