Study Of Anhydrous Catalyst In Acetylene Dimerization To Monovinylacetylene

Monovinylacetylene（MVA）, as an acetylene downstream product, is generally applied for the synthesis of chloroprene（CR）, styrene, butanedione and other important chemical products. CR has been identified as one of the seven synthetic rubbers in the world owing to its overall physical properties, such as its excellent mechanical strength, as well as high resistance to burning, light, and anti-oxidation, and it widely applied in the production of auto parts, machinery and industrial products and adhesive. Although acetylene method largely has been replaced in many developed countries by butadiene-based processes for CR production, acetylene method is still a primary process in locations where coal-based economies remain active like China. For the acetylene-based process, MVA as the key precursor is traditionally obtained by the dimerization of acetylene catalyzed by the Nieuwland catalyst, which is composed of Cu Cl and KCl or NH4 Cl in an acid aqueous solution. However,there are still many inescapable disadvantage,which is because of the low solubility of acetylene in the aqueous catalyst reducing contact and reaction time of the acetylene and catalytic system,one path conversion of the acetylene is just about 10 %,MVA selectivity is about 80 %. Meanwhile, the reaction of acetylene in the aqueous catalyst not only generates MVA,but also gives some side products, such as acetaldehyde by hydration of reaction of acetylene（CHoCH+H2O?CH3CHO） and divinylacetylene by trimerization reaction of acetylene(DVA, CHoC-CH=CH²⁺H2O?CH=C-CHoC-CH=CH2), which led to lower MVA selectivity. Therefore, the objective of this paper aims to study an anhydrous catalyst for acetylene dimerization to synthesis monovinylacetylene,further improve the activity, selectivity and stability of Nieuwland catalyst for the dimerization of acetylene, as follows:（1） In this paper, several high boiling point organic solvents were screened, such as DMF, DMSO, N-methyl-2-pyrrolidone and 1, 4-dioxane. The results proved that the DMF as solvent, conversion of the acetylene was significantly improved, but MVA selectivity was very low, and the catalyst stability was so poor, due to the formation of a dark red precipitate containing active Cu Cl component was caused in anhydrous organic solvents; therefore, we further explored effect of mixture solvent on catalytic performance in acetylene dimerization to monovinylacetylene, which included DMF and several other organic solvents. The mixture solvent of DMF and 1, 4-dioxane was used as solvent. while the volume ratio was 7/3（v/v）, the mixture solvent can effectively dissolve catalyst and inhibit solid polymer to be generated with reaction process, and then, which can decrease the loss of active component Cu Cl, maintaining stability of catalytic system. Then on this basis, the effect of adding cosolvent for acetylene dimerization was investigated, we explored the effect of adding four common organic amine salts for acetylene dimerization, which included Et NH2·HCl, Et2NH·HCl, Me2NH·HCl, Me3N·HCl, the ethylamine hydrochloride as the solubilizer, catalytic system become uniform and stable. The optimal catalytic system was determined, which was Cu Cl（7.92 g, 0.08 mol） as main catalyst, and CH3CH2NH2·HCl（3.83 g, 0.047 mol） as solubilizer; the mixture solvent of DMF and 1, 4-dioxane as solvent, reaction temperature, 80 ℃; space velocity, 200 h-1. The conversion of acetylene is 34.6 %, the selectivity of MVA reach 75.4 %,and the product yield can reach 26.1 %. Based on above results, collaborative bimetallic catalysis for acetylene dimerization can efficiently enhance the acetylene conversion and improved the stability of the catalytic system, which can promote the vinyl acetylene selectivity with the conversion of acetylene feeble changing. According to the different metals were screened, the results shown that the adding 10 % mol CuCl₂ can obviously promote activity and stability of catalyst, the conversion, the selectivity and product yield were 44.6 %, 67.4 % and 30.1 %, respectively.（2） In this works, with the integral molar quantity of Cu keeping invariable, the effect of changing mole ratio of Cu⁺ and Cu²⁺ for acetylene dimerization in the Cu Cl-CuCl₂ catalytic system were investigated. The results indicated that the integral molar quantity of Cu was 0.08 mol, with molar quantity of Cu⁺ increased, the conversion of acetylene increased at first and then decreased, while the selectivity of vinyl acetylene have no significant change. When the mole ratio of Cu⁺ and Cu²⁺ was 2∶1, the conversion of acetylene can reach 40 %, which demonstrated that the concentration of Cu⁺ and catalyst activity were not a linear relationship, meanwhile the concentration of Cu²⁺ have certain effect on acetylene dimerization. In addition, when the mole ratio of Cu⁺ and Cu²⁺ was 5.6∶1, a large number dark red precipitates will be generated after introducing C2H2 into reactor for 10 min, a little solution remained in the catalyst supported reaction process. The composition of dark red precipitates was characterized by FI-IR, XPS and TGA, the results implied that the composition of precipitates was 2C2H2·CH3CH2NH2·（2/3Cu Cl·1/3CuCl₂）, which was generated by interreaction of C2H2, CH3CH2NH2, Cu（I） and Cu（II） during the reaction. The mechanism of catalyst deactivation for acetylene dimerization was explored, the results indicated that the reasons for catalyst deactivation was the transform of Cu⁺ to Cu²⁺, therefore, the addition of Cu²⁺ is benefit for the catalytic activity and catalyst lifetime, which can be attributed to inhibit the oxidation of Cu⁺ to Cu²⁺ in the reaction process.（3） The weak reducing agents were introduced into catalytic system to inhibit the transform of Cu⁺ to Cu²⁺, and then enhance the content of effective active component, increase catalytic activity. We have screened several organic matters and sulfites, which contained hydroxyl and had weak reducibility, including Cu, glucose, ascorbic acid and sodium sulfite. The results demonstrated that ascorbic acid was optimal and promoted the conversion of acetylene, and the seclection of MVA had no significant change. After that,the dosage of ascorbic acid, reaction temperature, space velocity of C2H2 were optimized, the research results shown that optimal reaction condition was the dosage of ascorbic acid, 1.0g; temperature, 80 ℃; space velocity, 200 h-1. The conversion of acetylene can reach 40.1 %, product yield was 29.4 %.