TIChE International Conference 2011 November 10 – 11, 2011 at Hatyai, Songkhla THAILAND Paper Code: cr018
Effect of hydrochloric acid promoter and loading sequence on the properties of -alumina supported CuCl2 based catalysts for ethylene oxychlorination Churairat Wirotsakul*, Joongjai Panpranot 1, Piyasan Praserthdam1 1
Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand *e-mail:
[email protected]
Abstract – The effects of HCl addition and loading sequence of metal and HCl during the impregnation steps of the -alumina supported CuCl2 based catalysts have been studied. The amounts of CuCl2 which is the active species for the oxychlorination reaction were determined by solubility test using acetone extraction and electron spin resonance (ESR). The reduction behavior of copper species was investigated by H2-temperature program reduction (H2-TPR). The maximum amount of active CuCl2 on the catalyst was achieved with 2 wt% of HCl addition and co-impregnation metal loading. The catalyst also showed the highest reduction temperature of Cu(II) species. The catalyst activity was tested in the gas-phase oxychlorination of ethylene and was found to be stable during 5.5 hours time-on-stream. Keyword: Alumina, Hydrochloric acid, Copper Chloride, Ethylene Oxychlorination
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TIChE International Conference 2011 November 10 – 11, 2011 at Hatyai, Songkhla THAILAND
1.
2.2. Methods
Introduction
Polyvinylchloride (PVC) is one of the most important polymers currently used worldwide. PVC is formed by the polymerization of vinyl chloride monomer (VCM). VCM is produced by cracking of 1,2-dichloroethane (also called ethylene dichloride or EDC, C2H4Cl2), which is manufactured by either the direct chlorination or oxychlorination reaction of ethylene. In catalytic oxychlorination reaction, gaseous ethylene reacts with hydrochloric acid, and air (or oxygen) following reaction (1). C2H4 + 2HCl + 1/2O2 C2H4Cl2 + H2O
(1)
The reaction is performed at temperature 200-300C at atmospheric pressure in fluidized-bed reactors [1]. Commercial catalysts are produced by the impregnation of alumina with CuCl2 2H2O (4–8 wt% Cu). Other chlorides (mainly alkaline or alkaline earth chlorides) in a variable concentration are added to improve the catalytic performances, making the catalyst was more suitable for use in industrial reactors [2]. Vigue et al. have studied the activation γ-alumina with HCl. The studies have shown the disappearance of free OH groups. It concluded that addition of HCl consume the OH group on Al2O3 which decreased the formation of paratacamite and copper aluminate which are inactive species [3]. This work is further investigated from the previous thesis that studied effect of the different prometers and revealed that Mg is the best promoter. The purpose of this work is to study the effect of HCl addition and sequence of metals and HCl loading during impregnation step on the properties of Cu/γ-alumina catalyst. The catalysts are characterized by solubility test, TPR, ESR and ICP-OES. The study of catalytic activity is performed at 230C and 1 bar in packed bed reactor.
2.
Copper and Magnesium contents were determined by a Perkin Elmer Optima 2100DV AS93 PLUS inductive coupled plasma optical emission spectrometer. Solubility tests were carried out using acetone extraction to investigate the CuCl2 species and the copper aluminate species were determined by ESR spectrometer at STREC. The H2-TPR was used to study the reduction behavior of the catalysts using a Micrometritics Chemisorb 2750. The reaction was carried out with C2H4 : O2 : HCl molar ratios of 1 : 1.1 : 1.8 in packed bed reactor (I.D. 0.25 inch, length 1.5 inch).
Experimental
2.1. Preparation of catalyst The gamma-alumina was obtained from Sasol North America Inc. and pretreated at 1000oC in air for 1 hour. The catalysts composing of 4-8 wt% Cu and 0.05-4 wt% Mg on gamma alumina were prepared by impregnation method, in which of the volume of the solution of CuCl22H2O and promoters (MgCl26H2O and HCl 37 wt %) is equal to the pore volume of the alumina during impregnation. The sample was dried in an oven over night at 110oC and kept it in desiccators.
3.
Results and Discussion
3.1. Effect of HCl promoter on the formation of copper species. From the previous work, G. Leofanti et al. have evidenced that there are two different families of copper compounds on copper chloride-base catalyst. The first family is surface copper aluminate interacted with alumina support, which is non-soluble species with acetone. The second family is CuCl2, which is soluble species, precipitating directly from solution during the drying step of catalyst preparation and overlapping the surface aluminate. CuCl2 undergoes slow hydrolysis to form paratacamite, an insoluble copper species, depending on drying condition [2]. Solubility test using acetone extraction indicates the fraction of CuCl2 that has not been transformed into other inactive compounds after impregnation as shown in table 1. Table 1. Effect of HCl addition on the soluble copper species of CuMg/Al2O3 catalyst with 2wt%HCl
Sample
HCl composition (%wt)
Copper soluble ( % )
1
0
71
2
2
83
3 4
4 6
80 78
From ESR studies as shown in Fig.1, all ESR spectra reported the presence of Cupper (II) d9 paramagnetic species in the system while Cupper (I) d10 nonparamagnetic species cannot be observed. All of catalysts exhibited asymmetric signals ( in the range of 260 to 300 mT ) of surface aluminate species due to interaction between the unpaired electron and the copper nucleus [2],[5]. The presence of asymmetric signals decreased the intensity of ESR signals, lower copper aluminate as shown by lower ESR intensity resulted in higher CuCl2 on the catalyst surface and higher in soluble copper fraction. cr018-2
TIChE International Conference 2011 November 10 – 11, 2011 at Hatyai, Songkhla THAILAND The comparison of ESR intensity and solubility test was shown in Fig.2.
Table 2. Effect of loading sequence on %acetone extraction of CuMg/Al2O3 catalyst with 2wt%HCl
Sample
Loading Method
Copper soluble (%)
1
Co-impregnation with HCl
83
2
Cu and HCl last loading
82
3 4
Mg and HCl last loading HCl last loading
70 69
TPR profiles of copper species have been observed in two peaks that correspond to a two step reduction Cu(II) Cu(I) Cu(0) [2]. The solubility test results were supported by TPR results as shown in Fig.3. The coimpregnation catalyst exhibited the highest reduction temperature peaks, implying that the catalyst can maintain Cu(II) species in its active state because it was more difficult to reduce [4].
Fig. 1. Effect of HCl addition on CuMg/Al2O3 catalyst. HCl composition increases from bottom to top ( 0%wt to 6%wt )
Fig. 3. TPR profiles for studying of sequence loading effect
Fig. 2. Comparison of solubility test results and ESR results in various composition of HCl addition on CuMg/Al2O3 catalyst.
From Fig.2., the amount of soluble copper was maximized at 2 wt% HCl addition. Further increase of HCl addition did not increase the amount of CuCl 2 species, thus the optimum amount of HCl addition was 2 wt%.
3.2. Effect of loading sequence during the impregnation step Co-impregnation of CuCl2 and MgCl2 with 2 wt% HCl exhibited the highest soluble CuCl2 content as shown in table 2.
3.3. Activity test of catalyst in the oxychlorination reaction
The catalytic performance of CuMg/Al2O3 catalyst was carried out in the gas-phase oxychlorination reaction following three steps mechanism: (i) reduction of CuCl2 to CuCl, (ii) oxidation of CuCl to give an oxychloride and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 as shown in equation (2) to (4) respectively [6].
2CuCl2 + C2H4 C2H4Cl2 + 2CuCl
(2) cr018-3
TIChE International Conference 2011 November 10 – 11, 2011 at Hatyai, Songkhla THAILAND 2CuCl + 1/2O2 Cu2OCl2
(3)
Cu2OCl2 + 2HCl 2CuCl2 + H2O
(4)
The catalyst activity of CuMg/Al2O3 catalyst prepared by co-impregnation of CuCl2 and MgCl2 with 2 wt% HCl was studied in the gas-phase ethylene oxychlorination reaction. The conversion of ethylene to produce 1,2dichloroethane (EDC) was observed and shown in fig.4. The ethylene conversion achieved a stable value when the reaction time reached to 1 hour. The catalyst activity was stable during the 5.5 hours time-on-stream.
of catalysis 189 (2000): 105-116. [6]
G. Leofanti, M. Padovan, M. Garilli, D. Carmello, Alumina-supported Copper Chloride 4. Effect of Exposure to O2 and HCl. Journal of catalysis 205 (2002): 375-381.
Fig. 4. Activity of CuMg/Al2O3 catalyst in the oxychlorination reaction. ( Catalyst was activated by HCl and O2 mixture before reaction test. Reaction condition : reaction temperature 230C , pressure 1 atm , reaction time 5.5 hours , 0.3 g of catalyst , GHSV = 2856 hr-1 )
4.
Conclusions
The -alumina CuCl2 based catalyst prepared by coimpregnation with 2 wt% HCl addition resulted in the higher amount of CuCl2 active species and a shift of reduction peaks toward higher temperature. The catalyst showed good stability of ethylene conversion in the gasphase oxychlorination of ethylene.
References [1]
[2]
[3]
[4]
[5]
A. J. Rouco, Low temperature ethylene oxychlorination: effects of support and promoters on the mobilities of active species in CuCl2 catalysts. Journal of catalysis 157 (1995): 380-387. G. Leofanti, M. Padovan, M. Garilli, D. Carmello, Alumina-supported Copper Chloride 1.Characterization of Freshly Prepared Catalyst. Journal of catalysis 189 (2000): 91-104. Vigue, H., Quintard, P., Merle-Mejean, T., and Lorenzelli, V. An FTIR study of the chlorination of γ-alumina surface. Journal of the European Ceramic Society 18 (1998): 305-309. Liu, J., Lu, X., Zhou, G., Zhen, K., Zhang, W., and Cheng, T. Effect of KCl on CuCl2/ γ-Al2O3 catalyst for oxychlorination of ethane. Reaction kinetic and Catalysis Letters 88, 2 (2006): 315-323. G. Leofanti, M. Padovan, M. Garilli, D. Carmello, Alumina-supported Copper Chloride 2. Effect of Aging and Thermal Treatments. Journal
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