(323d) Upgrading Methane to Olefins Using Oxidative Coupling of Methane in a Chemical Looping System

Methane is viewed as a fuel or an energy source, with limited applications in its direct use as a feedstock for chemicals manufacturing. The high molecular stability of methane requires an indirect approach where it is first converted to an intermediate chemical like syngas, which can then be used for producing commodity chemicals. This method of methane conversion requires multiple processing steps and are highly energy intensive. The direct approach for methane conversion to value-added products, on the other hand, allows for process intensification, which makes it competitive both in terms of cost and energy. Oxidative Coupling of Methane (OCM) has the highest per pass yields towards products among all existing direct methane conversion technologies. It also provides a one-step process towards manufacturing olefins (C₂₊ hydrocarbons) from methane. Traditionally, methane oxidation in OCM has been carried out by co-feeding molecular oxygen with methane over an activated catalyst. The chemical looping method, however, utilizes the lattice oxygen in a metal oxide catalyst for methane oxidation, which results in a higher selectivity towards C₂₊as compared to the results from the traditional co-feed process. The intended use of the olefinic product stream could be to separate it into different components and integrate it with existing refinery operations. In another approach the product stream can be sent to an oligomerization reactor to convert the unsaturated hydrocarbons to gasoline over a ZSM-5 catalyst. Such a process shows flexibility in its utilization as a commercial technology.

A manganese-based oxide was synthesized and used as the metal oxide catalyst for this study. Gases other than pure methane like shale gas and biogas were also used to demonstrate the versatility of the catalyst. Parameters such as reaction pressure, steam flow rate and gas-hourly space velocities were varied to observe their effect on the amount of C₂₊ products produced. These experiments were performed in a fixed bed condition, cycling between oxidation and reduction steps. The results obtained were coupled with Thermogravimetric Analysis (TGA) of the metal oxide catalyst to investigate recyclability of the catalyst when subjected to multiple cycles. The effects of these parameters was also analyzed by nitrogen physisorption (BET) for pore volume and surface area changes from the original metal oxide catalyst. The studies performed were directed towards the application of the manganese based catalyst in a co-current moving bed reactor.