Study On Optimization Of Acetylene Dimerization For Preparation Of Monovinylacetylene

Chloroprene rubber (CR) is one of the earliest production of the world’s importantvariety of synthetic rubber. Compared with natural rubber and other synthetic rubber,chloroprene rubber is light resistance, aging resistance,bending resistance, acid andalkali resistance, heat resistance, flame resistance,oil resistance, ozone resistance, wearresistance,chemical resistance, and other excellent comprehensive performance,furthermore it has a wide temperature range, high resilience, high strength and goodphysical and mechanical properties. So it is widely used in transportation, construction,light industry, national defense and military and other fields.There are two methods to synthesis chloroprene,including acetylene method and1,3-butadiene method. Now many foreign use1,3-butadiene method to producechloroprene rubber, while the acetylene method is still adopted in china. Acetylenedimerization for preparation of monovinylacetylene is an important unit operation ofchloroprene rubber production by acetylene method, the production efficiency of thisoperation unit directly affects the benefit of the entire chloroprene rubber industry.Nieuwland catalytic technology has been used for acetylene dimerization in China sinceimported from the former Soviet Union50’s last century,although after years ofimprovement, the technology still exists many shortcomings such as low acetyleneconversion rate, low yield and selectivity of target product MVA, many side reactions.Inaddition, there will produce a lot of tarry non-volatile polymeric by-products during theproduction process, the polymer can plug the pipeline effectting production, but alsoaccumulated in the reactor wall and other positions, weaken the efficiency of heattransfer process gradually. Therefore, it is necessary to make further optimization andimprovement of Nieuwland technology of acetylene dimerization to preparemonovinylacetylene. For the disadvantage of low yield and poor selectivity of MVA,high generation of polymer during the process of acetylene dimerization, a series ofoptimization research were carried out. First, proper amount of rare earthchloride(REC1or REC2) was added to the traditional Nieuwland system of acetylenedimerization, it is found that:1）Adding appropriate amount of earth chloride totraditional Nieuwland catalyst system of acetylene dimerization can effectively inhibitthe formation of polymers;2) Adding earth chloride at80℃can inhibit the generationof target product MVA and divinylacetylene(DVA) by-product both, but the degree of inhibition of DVA is much stronger than the MVA, so MVA/DVA value was improvedgreatly, increased from6to10~60;3）Adding earth chloride REC1can promote thegeneration of MVA at60℃and40℃, MVA%increased from9%to10%at60℃,andMVA%increased from5.5%to6.5%at40℃;4) Adding REC2doesn’t affect theformation of MVA at60℃, the MVA%is same as Nieuwland catalytic system, is about9%.Adding REC2at40℃can promote the formation of MVA, MVA%also canimproved to6.5%.Secondly, pyridine,2-chloropyridine,2,6-two chlorine pyridine,4-methylpyridine,2-amino-5-chloropyridine five ligands were added to the traditionalNieuwland catalytic system respectively, it is found that:1)Adding five ligand caninhibit the formation of MVA at different degrees, MVA%decreased from10%to4%~6%range, which the MVA%is minimum when add2-chloropyridine, its4%;2）Adding five ligand can also inhibit the formation of DVA at different degrees, DVAcontent decreased from about1.7%to0.1%~0.5%, which its only about0.1%when add2-chloropyridine;3)The degree of inhibition on DVA is greater than MVA when add thefive ligands, so the selectivity of MVA is improved, increased from80%to80%~90%,and it reaches90%when add2-chloropyridine.Then, different amount of urea was added to Nieuwland catalytic system(15.67gNH4Cl+30.75g CuCl+45mL distilled water+0.3mL hydrochloric acid), it is found that:1) Adding different amount of urea can improve the selectivity of target product MVA;2）Different amount of urea has different effects on the conversion of acetylene, onlywhen the amount of urea is0.1mol the acetylene conversion rate will not drop, toomuch or too little both inhibit the transformation of acetylene, and the conversion rate ofacetylene decline;3) When adding0.1mol urea to the Nieuwland catalytic system,acetylene conversion rate remained unchanged, while the selectivity of MVA improved,so the yield of MVA increases, MVA%increases from10%to13%;4)Adding0.05mol,0.15mol,0.2mol urea, the MVA selectively improves while the acetylene conversiondecreases, finally the yield of MVA decreases.Finally, we studied the effect of various acid on the dimerization of acetylene, wereplaced the hydrochloric acid of the traditional Nieuwland catalyst with sulfuric acid,phosphoric acid, boric acid, it is found that:1）Replaced hydrochloric acid with boricacid, MVA%remained unchanged, is still about10%, when replaced with sulfuric acidand phosphoric acid MVA%decreases both, decreases to6%,8%respectively;2)Replaced with phosphoric acid the production of by-product DVA greatly enhanced, its content is close to MVA, so the value of MVA/DVA decreases, at the end of the reactionMVA/DVA value is only1.2;3) Replaced with phosphoric acid, the conversion rate ofthe acetylene improves greatly, it improves from21%of the conventional Nieuwlandcatalytic system to30%.