Study On Pd Based Catalyst For Hydrogenation Of Calcium Carbide Acetylene To Ethylene

The downstream derivatives of ethylene,such as plastics and fibers,are related to all aspects of human life,leading to the market demand for ethylene in China is increasing year by year.The domestic ethylene market is mainly satisfied by domestic production and foreign imports.Most domestic ethylene in China is cracked through naphtha,but this process is not suitable for China’s national conditions.Coal is the most basic and long-term energy source in China.The vigorous development of coal chemical industry in rich coal areas drives the development of calcium carbide acetylene industry.Therefore,it is of great significance to study the selective ethylene production of high concentration acetylene by using acetylene as the raw material of calcium carbide.Pd catalyst is considered to be an excellent catalyst for acetylene hydrogenation.The research on Pd catalyst mainly focuses on the trace acetylene hydrogenation process in petroleum routes,but little on the high concentration acetylene hydrogenation catalyst.The difference of reaction conditions will lead to the difference of catalytic activity and catalytic phenomena.So this paper takes Pd based catalysts as the research object to study the process conditions for selective hydrogenation of acetylene to ethylene with high concentration.Considering the limited catalytic performance of single metal Pd,the catalytic performance of Pd based catalysts can be further improved by adding metal promoters or changing the metal morphology of the catalyst.Different preparation methods can obtain catalysts with different metal dispersion.So we used NaBH₄,EG and H₂ as reduction to prepare catalysts,and explored the influence of different preparation methods.The results of TEM and activity test showed that Pd particles on the catalyst prepared by EG reduction method were uniformly dispersed,smaller particle size and the best catalytic activity performance.Then,a series of Pd catalysts with different supports（MCM-41,AC,Al2O3,Si O₂,Ti O₂）were prepared by EG reduction method,and their catalytic performance were investigated.XRD,TEM and other characterizations showed that 1% Pd/MCM-41 catalyst supports have rich weak acidity and suitable pore environment,resulting in nearly 100% acetylene conversion and 62.09% ethylene yield compared with other supported catalysts.Then a series of catalysts were prepared with MCM-41 as support,and the reaction condition was optimized.Then life test was carried out under the optimum conditions.It was found that the life of 0.1% Pd/MCM-41 catalyst was stable at ³2 h,and the catalyst was eventually deactivated after 47 h.The C2H₂ conversion rate decreased from 99.37% to 13%,and the C2H₄ yield decreased from 82.74% to 13%.Previous studies found that the stability of Pd/MCM-41 catalyst was poor.Therefore,we tried to improve the stability by introducing second metal into Pd catalyst.Five commonly non-noble metals were selected as additives.It was found that the introduction of Cu metal had the highest catalytic activity but the activity was not different from that without additives.Then we optimized the amount of Cu introduced,and found that when the molar ratio of metal was 1:1,the catalytic activity was the best.The characterization results showed that when n Pd:n Cu=1:1,the alloying degree was the highest,leading to its excellent catalytic performance.After the introduction of copper,the C2H₄ yield remained about 78% at 47 h,the C2H₂ conversion decreased from 99.59% to 25% and the C2H₄ yield decreased from 90% to 22% at 100 h.It can be seen that the addition of Cu not only improves the catalytic activity,but also enhances the stability of the catalyst.On the basis of previous experiments,we investigated the effect of morphological differences on the catalytic activity of high-concentration acetylene hydrogenation.Pd decahedral and Pd Cu hexagonal nanosheet alloys were synthesized by hydrothermal method in the ratio of n Pd:n Cu=1:1 and loaded on MCM-41 as compared with spherical catalysts.It was found that under the conditions of same metal ratio,the C2H₄ selectivity of the Pd decahedral catalyst was about 15% higher than that of the spherical Pd/MCM-41 catalyst at 100% C2H₂ conversion.Secondly,the selectivity of C2H₄ of Pd Cu hexagonal nanoplate alloy catalyst is up to 95.83%,which is significantly higher than the ethylene selectivity of the spherical Pd Cu/MCM-41 catalyst（80%）under the same conditions.The catalytic activity of the Pd decahedral and Pd Cu hexagonal nanoplate alloy catalysts with improved morphology is higher than that of the ordinary spherical catalyst under the same conditions.