Study On Ethane Oxychlorination To Ethylene Chloride Over γ-Al₂O₃ Supported CuCl₂ Based Catalysts

Because there has been a great demand for poly vinyl chloride (PVC), thevinyl chloride monomer (VCM) that is a raw material for producing PVC is animportant chemical product. There are three ways to produce VCM: acetyleneoxychlorination, ethylene oxychlorination and ethane oxychlorination.Acetylene oxychlorination is an old way to synthesize VCM, but it has beenused as a main route to manufacture VCM in our country. Now, ethyleneoxychlorination is used in most of foreign chemical companies. Ethyleneoxychlorination is a two-step way. In the first step ethylene is oxychlorinated to1, 2-dichloroethane. The dichloroethane is subsequently dehydrochlorinated atan elevated temperature to yield VCM and hydrogen chloride in the second step.The disadvantage of this way is its high cost. Ethane oxychlorination is thenewest way to produce VCM. European Vinyls Corporation has set upequipment producing 1000t VCM every year. However, in our country, no anyreport on this project is present. Because ethane can be obtained from naturegas, this route is a promising way to be used in chemical production and willcreate essential economical benefits. Firstly, we investigated theγ-Al2O3 supported CuCl2 based catalystsprepared by impregnation and their catalytic properties for the ethaneoxychlorination, which were influenced by some factors. The results show thatγ-Al2O3 (made in Zibo petrochemical group, Shandong province) is goodsupport, and high ethane conversion and ethylene chloride selectivity areobtained over the catalysts which were made with this support. Copper chlorideis an active component for the topic reaction and the catalytic activity isaffected by the amount of dispersed copper chloride. The most suitable amountof supported copper is 5wt%. The preparation condition can affect the state of the active site. Thecalcination temperature is very important for obtaining catalysts with highcatalytic properties. High temperature would lead to change of the structure ofsupport and active species. A favorable temperature is 550℃for this catalyticsystem. Short impregnation and calcination time are disadvantageous to theinteraction between the CuCl2 and γ-Al2O3 and catalytic stability.Impregnation for 12h and calination for 4h are favor for preparing catalystswith high catalytic properties. The results of the reaction showed that the conversion of ethane can reach96.9% and the selectivity to ethylene chloride can reach 48.8% overCuCl2-KCl-LaCl3/γ-Al2O3 catalyst (having a Cu, K ,La content of 5wt%,6wt%, 0.74wt%, respectively) under following reaction condition: reactiontemperature 500℃, atmosphere, 2160h-1( GHSV) , V(C2H6):V (HCl): V(air)=1:3:5. Secondly, we prepared and investigated the catalysts containing 5wt%copper with different K/Cu molar ration. The structure and the state of speciesover catalysts were studied by means of XRD, TPR, solubility test, UV-vis andTG-DTA. The results show that surface cupric chloride increases with additionof potassium chloride, and the ration of soluble copper to total copper increasesfrom 19.6% to 73%. The catalyst, in which molar ratio of K/Cu is 2, showedhigh ethane conversion and ethylene chloride selectivity. The potassiumchloride can promote dispersion of copper chloride and decrease the volatilityof copper chloride, so make the catalysts stable. The addition of potassiumchloride that makes catalysts molten at reaction temperature would increase thechlorine release from the CuCl2 particles owing to developing eutectic the saltmixture with CuCl2. The presence of KCl promotes the regeneration of cupricchloride by accelerating re-oxidation of Cu(Ⅰ) to Cu(Ⅱ). In addition, it wasfound that addition of KCl led to a decrease in apparent activation energy of thereaction. In a word, the addition of KCl not only enhanced the conversion ofethane and the selectivity of ethylene chloride but also decreased the volatilityof copper chloride. The catalyst CuCl2-KCl-LaCl3/ γ-Al2O3 shows a farther decreasingtendency to the volatility of CuCl2 and is more stable upon addition of LaCl3.We studied the catalytic stability change with the catalysts compose Cu content:5wt%, K content: 6wt%, La content: 0.74wt%, 3wt%, 5wt%, 7wt%, respectivelywhich are denoted as CuKXLa, where X represented weight percentage of La,for example, CuK3La stands for a catalyst containing 5wt% Cu, 6wt% K and3wt% La. The CuK5La catalyst shows the highest properties: ethane conversionwas 97.5% and ethylene chloride selectivity was 52.8%. Over the CuK7Lacatalyst used for 20h and CuK3La catalyst used for 10h carbon deposition was...