545664 Co-Promoting Effects of Mg and K in Ethylene Oxychlorination

Tuesday, June 4, 2019: 2:33 PM
Republic ABC (Grand Hyatt San Antonio)
Hongfei Ma1, Endre Fenes1, Kumar R. Rout2, Terje Fuglerud3 and De Chen4, (1)Norwegian University of Science and Technology, Trondheim, Norway, (2)SINTEF, Trondheim, Norway, (3)INOVYN, Porsgrunn, Norway, (4)Chemical Engineering, Norwegian University of Science and Technology, Trondheim, Norway

Co-promoting effects of Mg and K in ethylene oxychlorination

Hongfei Ma1, Endre Fenes1, Kumar Ranjan Rout2, Terje Fuglerud3, De Chen1*

1 – Department of Chemical Engineering, NTNU, Trondheim, 7491, Norway

2 – SINTEF, Trondheim, 7491, Norway

3 – INOVYN Norway, Porsgrunn, 3936, Norway 

*Corresponding author: de.chen@ntnu.no

1. Introduction

Ethylene oxychlorination is an industrially important process to produce vinyl chloride monomer (VCM), where CuCl2/γ-Al2O3 based catalysts undergoes a reduction and oxidation process. [1] Alkali or alkali metals, such as K and Mg, are used as the promoters to improve the performance and stability of the catalysts in the industry, but the fundamental, exact mechanism details on how the promoters work in the reaction are still not clearly. In our previous works, [2, 3, 4] we have systematically researched the roles of dopants (K, Ce) on the ethylene oxychlorination CuCl2/γ-Al2O3 catalyst.

2CuCl2 → 2CuCl → Cu2OCl2→2CuCl2

In this work, we prepared the co promoted (K and Mg) catalysts to research the effect of the two promoters based on our previous reported methods. Reaction rate for reduction and oxidation were evaluated for the step transient reactions, and also for steady state. CuCl2 band gap energy with different promoters were also calculated to investigate the different influences of the promoters.

2. Experimental

The catalysts prepared from the chlorides salts with the incipient wetness method, containing 5 wt% Cu and e. g. 0.4 K have a K: Cu molar ratio of 0.4 and 5 wt% Cu. The reaction for both step transient and steady state experiments were conducted at 230 ˚C under atmospheric pressure, with the total gas flow of 3 ml/s. While the partial pressure of C2H4 for step transient was 10%, and 8% for steady state experiments. All the reactions were performed in our operando set up combining UV-Vis-NIR spectrometry and mass spectroscopy.

3. Results and discussion

From XRD patterns we can know that for all the catalysts copper chlorides remain undetectable by XRD due to a high dispersion of the copper metals. In order to fully active the catalysts, three cycles of redox, also called step transient reduction, oxidation and chlorination were proceeded. And the reaction rate of reduction and oxidation were obtained from MS. Since the third step chlorination is very fast, so it is difficult to get the reaction rate. We can know that different promoters had different influences to the reduction and oxidation steps. The rate determined step could be tuned. Figure 1 shows the C2H4 conversion of steady state reactions. We can know that catalysts promoted by Mg had higher C2H4 conversion. Looking deeply on the results, we can find that the initiation point of Mg promoted catalysts was very high, while the decreasing from starting point to steady state was also the most obvious. But it was the least for co promoted catalyst. Based on our previous researches [2, 3], the performance was closed related with the concentration of Cu2+, so we can see that the cooperation of K and Mg can keep the Cu2+, through tuning the reduction and oxidation rate.

In order to have a deeper understanding on the influence of the promoter to the active site of CuCl2, band gap energy was calculated by KMF function. The results are shown in Figure 2. We can see that the energy is much higher for Mg promoted than K promoted. It slightly increased from 0.4K to 0.1K0.3Mg and 0.4Mg. What the interesting thing is the tendency is similar with C2H4 conversion in steady state reactions. This means that band gap energy is a very important term in redox reactions. What’s more, compared with peak positon in TPR results the tendency was reverse.

4. Conclusion

As far as we have known, for the first time a CuCl2 based ethylene oxychlorination catalyst with two promoters were employed to understand the promoter effect. We utilized an operando method combined UV-Vis and MS to detect the oxychlorination cycles, including step transient and steady state conditions. Band gap energy was obtained to understand the difference of the catalysts. It also proved that UV-Vis spectroscopy is a useful method to evaluate the band gap energy in redox reactions. We can find the relation of band gap energy and the performance. More experiments and techniques will be employed to investigate deeper on the influence of co promoters to the active copper phase. Then the detailed difference will be thoroughly evaluated.

5. Reference

[1] N. B. Muddada, U. Olsbye, L. Caccialupi, F. Cavani, G. Leofanti, D. Gianolio, S. Bordiga, C. Lamberti, Phys. Chem. Chem. Phys. 12 (2010) 5605.

[2] K. R. Rout, E. Fenes, M. F. Baidoo, R. Abdollahi, T. Fuglerud, D. Chen, ACS Catal. 6 (2016) 7030.

[3] K. R. Rout, M. F. Baidoo, E. Fenes, J. Zhu, T. Fuglerud, D. Chen, Journal of Catalysis, 352 (2017) 218.

[4] M. F. Baidoo, E. Fenes, K. R. Rout, T. Fuglerud, D. Chen, Catalysis Today, 299 (2018) 164.


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