Oxidation Pretreatment Of Activated Carbon Carrier Support Bismuth Catalyst For Acetylene Hydrochlorination

Polyvinyl chloride（PVC） is important in national economy, widely used in construction, agriculture, industry, science and technology and other walks. Vinyl chloride monomer（VCM） is irreplaceable raw materials for PVC. Due to the present “deficient oil rich coal” energy situation of China, calcium carbide acetylene method that hydrochlorination of acetylene to produce vinyl chloride in domestic production has been occupied a dominant position. In this method, activated carbon supported HgCl2 as catalyst. Because mercury emissions caused serious environmental pollution, PVC industry is facing a severe test. Therefore, it has important practical significance to study the green mercury free catalyst to replace the mercury catalyst. Activated carbon supported metal catalysts are one of the important objects in the research of mercury free catalysts, as an important part of mercury-free catalyst, the structure and properties of the carrier directly affect the catalytic performance of the catalyst. The pretreatment of the carrier is an important means to improve the properties of the carrier. Physical properties and chemical properties of active carbon can be changed by pretreatment, so as to improve the performance of catalyst. The paper take activated carbon load nonnoble Bi metal catalyst as objects, studied the effect of the oxidation pretreatment of activated carbon and metal additive load non-noble Bi metal catalyst performance for acetylene hydrochlorination. Carrier and catalyst are analyzed by the characterization methods of N₂ adsorption/desorption（BET）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, X-ray powder diffraction analysis（XRD）, temperature programmed reduction（H₂-TPR）, thermo-gravimetric（TG）, Fourier infrared（FT-IR）, Boehm titration and X-ray photoelectron spectroscopy（XPS）, explained the structure activity relationship between the structure of activated carbon and the catalytic performance of the catalyst. Mainly work and results are as follows:（1） Explores the impacts of HNO₃, H₂SO₄, H₂O₂ and KMnO₄ oxidation pretreatment of active carbon on bismuth catalyst catalytic performance of the acetylene hydrochlorination. The results found that different oxidizing reagents pretreatment catalyst activity are improved, order for H₂O₂ > HNO₃ ≈ H₂SO₄ > KMnO₄. Oxygen containing functional groups of the activated carbon surface after pretreatment with KMnO₄, H₂SO₄ and HNO₃ were increased, but the specific surface area of activated carbon had different degree of reduce, influenced the activity of catalyst. The catalytic activity of the catalyst is better after H₂O₂ pretreatment, and the catalytic activity was related to the concentration: the activity of the catalyst increased larger with H₂O₂ concentration increased, while catalyst activity reduced when the H₂O₂ concentration was too high. Catalytic activity of catalysts have the best catalytic performance when active carbon pretreatment with 15% H₂O₂. Characterization results show that appropriate concentration of H₂O₂ can increase the surface oxygen groups and the specific surface area and pore volume of activated carbon, which promoted the loading and dispersion of the active components, active component species and the carrier to form a strong interaction and a better crystalline, therefore the catalyst activity increased. However when the H₂O₂ concentration is too high, can cause damage to catalyst pore structure, results in the decrease of specific surface area activated carbon carrier and pore volume, reduce the activity of catalysts.（2） Examines the effects of HNO₃, H₃PO₄, CH3 COOH and B2O₃ solution treat with AC-H₂O₂ activated carbon on the bismuth catalyst performance of the acetylene hydrochlorination. The catalytic performance of catalyst after different acid treatmented by order was CH3COOH>HNO₃>H₃PO₄>B2O₃. Results showed that the activity of the catalyst increased after HNO₃ treatment, but the catalyst stability is poorer; H₃PO₄ processing has little influence on the catalytic performance; catalytic performance decreased by B2O₃ treatment; the best performance of catalyst was revealed when CH3 COOH treatment. Characterization results showed that the physical structure of activated carbon after acetic acid treatment did not change significantly, activated carbon surface acidic groups（mainly hydroxyl and carboxyl groups） increased, the carrier surface polarity increased, promoted to the adsorption and metal dispersion of active components, the number of surface active sites of the catalyst increased. The interaction between active component and support of catalyst was enhanced. So the catalytic ability of the catalyst was improved.（3） Investigate the metal additives（Fe, Mg, Zn, K, La and Ce） impact on performance of bismuth catalyst of the acetylene hydrochlorination. The results showed that the activated carbon after additives treatment effects on the catalytic activity by order was Zn>Bi>Fe>La>Mg≈Ce>K. The addition of Zn can improve the activity of Bi/AC-H₂O₂-A, while the addition of K additives can reduce the catalytic activity of catalysts. Characterization results showed that the active components dispersion of catalyst surface and the activity center of the catalyst were increased after adding Zn additives, therefore Zn-Bi/AC-H₂O₂-A catalyst showed higher catalytic activity of acetylene hydrochlorination. While carbon deposit in the reaction process is easy to make the catalyst deactivation. The amount of carbon deposit in reaction process increased by adding K additive, blocked a part of the channel of the catalyst, reduce the active sites of the catalyst, which leads to catalytic activity decline, is not conducive to improving the catalytic performance of Bi/AC-H₂O₂-A catalyst.