(519g) Synthesis and Granulation of a Ca-X Zeolite-Based Molecular Sieve and Adsorption Equilibrium of Oxidative Coupling of Methane Gases

During last decades, some developments on the methane chemistry have brought the attention to its use as as feasible source of value-added chemicals [1]. In particular, the exploitation of methane from biogas is of interest for current biorefineries, and waste treatment plants. Nowadays, Biogas is mainly used as fuel for energy generation or in some other cases is just sent to the flares for final treatment [2], [3]. Developing of new products from biogas might help improving the overall economics of its production.

The Oxidative Coupling of Methane (OCM) allows the conversion of the methane contained in the natural gas into ethylene, which is a major building block for the chemicals and plastics industry. While significant efforts have been put into the development of new catalyst and reactors for the OCM, there is still a challenge to overcome in the separation of the reactor effluent gases. As reaction conversion is around 30%, it is expected a large amount of methane in the final product. The low concentration of ethylene and the large amount of byproducts, make the recovery process quite expensive[4].

Current industrial processes for isolation of high purity olefins generally involve high pressure cryogenic distillation in the olefin/paraffin separations[5]. This process is energy intensive and requires large capital and operating costs. In order to reduce the energy consumption, and to improve the economic potential of the process, novel separation techniques are required. Among different alternatives, selective adsorption and pressure swing can be used for selective removal of ethylene from the gas mixture. Despite the process is well known, the development of selective materials suitable for industrial operation is necesary. Most research efforts in this topic has been focused on the use of activated carbons and crystalline silicates (zeolites) [6].

Taking into account the aforementioned, A Na-X zeolite type was synthesized via hydrothermal treatment. The synthesis was carried out in stirred batch reactors at different gel composition (Varying Na₂O/Al₂O₃, H₂O/Al₂O₃ and SiO₂/Al₂O₃Ratios) and temperatures. Experimental design followed a simplex optimization method using as objective goal the crystallinity of the adsorbent material (characterized by XRD). Afterwards, the synthetized material was subjected to an Ion-exchange process with calcium, in order to improve the yield and selectivity for ethylene adsorption. Once obtained, the Ca-X zeolite, was put through an agglomeration process to obtain granulated molecular sieves (ca. 3 mm diameter). For this purpose an inorganic binding material was used. The obtained particles were characterized by measuring surface area, pore distribution, adsorption capacity and adsorption isotherms with OCM gases. Results indicate that the material is suitable to be used as adsorbent in pressure swing separation systems for OCM gases.

References:

[1] K. Skutil y M. Taniewski, “Some technological aspects of methane aromatization (direct and via oxidative coupling)”, Fuel Process. Technol., vol. 87, núm. 6, pp. 511–521, jun. 2006.

[2] British Petroleum Co, “Statistical Review of World Energy | Energy economics | BP Global”, bp.com. [En línea]. Disponible en: http://www.bp.com/en/global/corporate/energy-economics/statistical-revi…. [Consultado: 26-oct-2016].

[3] J. Tollefson, “‘Flaring’ wastes 3.5% of world’s natural gas”, Nature, ene. 2016.

[4] X. S. Nghiem, “Ethylene production by oxidative coupling of methane: New process fow diagram

[5] J. A. Hugill, F. W. A. Tillemans, J. W. Dijkstra, y S. Spoelstra, “Feasibility study on the co-generation of ethylene and electricity through oxidative coupling of methane”, Appl. Therm. Eng., vol. 25, núm. 8–9, pp. 1259–1271, jun. 2005.

[6] D. M. Ruthven, Principles of Adsorption and Adsorption Process, First. New York: Wiley-Interscience, 1984.