545746 Oxygen Removal from NG By Methane Oxidation at Low Temperature

Wednesday, June 5, 2019
Texas Ballroom Prefunction Area (Grand Hyatt San Antonio)
Carla Queiroz1, Valéria Vicentini1, Holli Garrett2, Chandra Ratnasamy2 and Greg Cullen2, (1)BU Catalysts, Clariant SA, Suzano, Brazil, (2)BU Catalysts, Clariant Corporation, Louisville, KY

Oxygen removal from NG by methane oxidation at low temperature

NGCS 12 Abstract

Carla Queiroz1, Holli Garrett2, Valéria Vicentini1, Greg Cullen2, Chandra Ratnasamy2

1Clariant S.A., Avenue Jorge Bei Maluf, 2163, 08686-000 Suzano, São Paulo, Brazil

3Clariant Corporation, 1600 West Hill Street, Louisville, KY 40210, United States

1.     Introduction

Oxygen is a virulent contaminant in the natural gas processing, leading to several troubles even at low levels, including degradation of process chemicals, e.g. amine fluids, used to remove acid gases from the natural gas stream and the salts generated as a result eventually precipitate or cause foaming in the treaters of the gas plant. Furthermore, O2 promotes pipeline corrosion in the presence of a few amount of water and sulphur. In the regeneration of molecular sieves, oxygen can react with hydrocarbons and their residues to produce carbon, which coats the molecular sieves, reducing its life. For underground storage sites, bacterial activity that produces hydrogen sulphide is increased by oxygen. Pipeline specifications are normally set at 10 ppmv, but some practical examples show that this level is constantly reducing, achieving in some industrial plants levels below 2 ppmv. Natural gas customers recognize the problems associated with the presence of oxygen in natural gas and impose a penalty on the price they will pay for gas containing excessive amounts of oxygen. Therefore, it is imperative to employ a system for oxygen removal at low costs, wide oxygen removal range and at low temperature. Various technologies are applicable for oxygen removal, amongst them two general options offer the highest potential from a technical and economic point of view. The first is a continuous adsorption based process, commonly using copper as adsorption materials, which is placed in at least two or more fixed-bed adsorption columns, necessary for alternating operation of loading and regeneration, however, a reducing agent is required, as hydrogen, which is high cost and normally is not available at plants for this purpose. The second commercially and promising alternative for O2 removal in NG is a heterogeneously catalyzed oxidation reaction of methane to form H2O and CO2. Actually, methane acts as a reducing agent for oxygen. However, in this research, under certain operating conditions Pt offer benefits to the removal oxygen by oxidation. The influences of CO2 and H2S added separately to the reaction mixture as well as the stability and carbon formation on the catalytic activity were also examined.

2.     Results

Figure 1 presents the gas heating temperature for 100% of O2 conversion for the stream with pure methane for two space velocity studied (Fig.1a) and for the stream containing CO2 (Fig. 1b). The results indicated the ActiSorb GP 601 catalyst needs a very low temperature to complete removal of O2 from the NG, when compared to the typical methane combustion catalysts. Furthermore, the behaviour for methane oxidation in Fig 1 is expected, in which the increase the oxygen content in the feed gas requires a higher temperature, necessary for the complete O2 removal. Likewise, raising the GHSV a slight increase in the gas heating temperature, around 10 °C, was observed. These finding are agreed with the literature [1,2], since the Eley-Rideal mechanism, described for the oxidation of methane, assumes methane to have a limiting influence on reaction rate due to weak absorption interactions with the catalytic surface. On the other hand, O2 species to be sufficiently absorbed on the catalytic surface at any time and it is reduced easily by methane.

Figure 1: Gas heating temperature for 100 % of O2 conversion (O2 outlet > 10 ppmv): (a) O2 inlet and space velocity effect and (b) CO2 study.

When CO2 is contained in the feedgas in 25%vol, the difference in the gas heating temperature to achieve complete oxygen conversion is raised by 20 °C, probably due to a weak competition between the methane oxidation and CO2 reforming reactions. However, non-expressive effect was observed increasing the CO2 inlet to 50%, indicating there is no effect related to side reactions or low methane inlet content. Likewise, no-significant effect was found when the space velocity is raised in the conditions employed during the CO2 effect study.

The results for sulfur evaluation (not showed) revels a strong negative effect on catalytic activity with almost total loss of activity when H2S is on gas stream. Nevertheless, by performing in situ regeneration, under the same amount of O2 in the stream, the catalytic activity can be recovered in the same conditions of the fresh catalyst, achieving 100% of O2 conversion. Regarding to catalytic stability, the results demonstrate high stability for O2 removal under constant gas heating temperature at low GHSV, with full conversion. Furthermore, it was not identified carbon formation at conditions employed, where we have the same amount of carbon for both, fresh and spent catalyst.

3.     Conclusion

The ActiSorb GP 601 Pt-based catalyst operate at low temperature for oxygen removal from natural gas (as function O2 inlet content), is able to take away oxygen at specified levels and has high thermal stability and low carbon build-up. The investigation showed a strong negative effect of sulfur (as H2S) on O2 removal process, but a simple in situ regeneration procedure allows to recover the catalytic activity in the same conditions of the fresh catalyst.  

4.     Reference

[1] F. Ortloff, F. Graf, T. Kolb. Removal of Oxygen from Biogas via Catalytic Oxidation of Methane International Gas Union Research Conference, WP5-26, Copenhagen (2014)

[2] P. Gélin, L. Urfels, M. Primet, E. Tena. Catalysis Today 83, 45-57 (2003)

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