Zeolite Adsorption Studies for Conditioning of High-Pressure Natural Gas Fluids

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Based on remote locations and capital cost, many current upstream gas processes use commercial desiccants (e.g. silica gel, activated alumina, alumina gel and molecular sieves) for deep dehydration of sour gases  (H2S+CO2+CH4+H2O) to avoid gas hydrates, mitigate corrosion and facilitate non-absorptive bulk separation.[1] The majority of reported adsorption studies involving sour gas species have been conducted at low pressures (p < 0.1 MPa) and a few at moderately high pressures (p < 6.9 MPa);[2,3] however, much higher pressures are applicable to industrial fluids, e.g., pipeline sour gas, producing shale gas and compressed CO2/H2S injectate for carbon capture and storage or sulfur management.

Among common desiccants, molecular sieve dehydration are often chosen over other dehydration materials for very low water dew point control, small pressure drop and the availability of high-quality bulk material.  Synthetic zeolites have received lot of attention from scientists in industry and academia due to well-controlled internal pore volumes, molecular-size pore apertures and regularity of crystal structures; however under high-pressure, their selectivity has not been studied on benchmarked materials for self consistency.

The goal of this work is to benchmark high-pressure sour gas adsorption for several microporous materials, beginning with zeolite 4A.  High-pressure adsorptions have been measured on several zeolite 4A samples using a home-built pVT adsorption apparatus (T = -30.00  to 150.00 °C; p = 0.00001 to 200 bar; sample size ca. 30 mg).  The advantages of this instrument are low volumes for sensitivity to multicomponent selectivity, good temperature control, broad pressure range and it is suitable for work with H2S, COS, and SO2 containing fluids.

High-purity zeolite 4A was hydrothermally synthesized using Rollma’s procedure.[4] The phase structure and crystal morphology of the zeolite were characterized by XRD and SEM image, respectively, while Si/Al ratio was measured by EDX microanalysis. The adsorption isotherms of CO2 and CH4 on this zeolite 4A sample were investigated at three different temperatures, T = 0.00, 25.00, and 50.00 °C, and at pressures up to 100 bar (H2S adsorption was measured up to p = 2 bar).  These measurements have been used to compare to low-pressure commercial instruments, assess semi-empirical isotherms and calculate isosteric adsorption enthalpies. In-situ CO2, H2S and CH4 adsorption using FT-IR and FT-RAMAN are briefly described as a tool to indicate the adsorbed species and possible extraneous reaction between adsorbates within future work.

(1)         Kohi, A.; R. Nielsen, R. Gas Purification, Gulf Publication: Houston, Texas, 2011; pp. 1049-1052

(2)         Fail, J. C.; W.D. Harris, W. D. Oil and Gas J. 1960, 58, 86

(3)         Himeno, S.; Komatsu, T.; Fujita, S. J. Chem. Eng. Data 2005, 50, 369

(4)         Rollma, L. D.; and Valyocsik, E. W. Inorg. Synth, 1983, 22, 61

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