Study On Cu-based Catalysts For Partial Hydrogenation Of Oils And Fats

Fatty acid methyl ester, as a derivative of natural oils and fats, is a renewable energy source, and is also an important raw material for chemical industry, while its application is limited because of the existence of polyunsaturated fatty acids. To reduce or even eliminate linolenic acid methyl ester（C18:3） and linoleic acid methyl ester（C18:2） by selective hydrogenation, increasing the amount of methyl oleate（C18:1）, is great significant to promote the application of fatty acid methyl ester.In this paper, the Cu/Si O₂ catalyst was prepared with Cu as the catalyst active component and self-made Si O₂ as the carrier. In order to overcome the shortcomings of Cu catalyst like low activity and poor thermal stability,the preparation method of the catalyst was developed, the dispersion degree of Cu on the Si O₂ carrier was increased, and the activity and thermal stability of the catalyst were improved. Secondly,the other metals were added to the Cu/Si O₂ catalyst to further improve the catalytic performance. The main results are as follows:（1） The porous Si O₂ was prepared by precipitation method, and its structure and morphology were characterized by XRD, SEM and N2 adsorption-desorption. Different Cu/Si O₂ catalysts were prepared by precipitation method,impregnation method, and the adsorption hydrolysis method, using self-made silica as the carrier. The dispersity of Cu species on Si O₂, and the interaction of Cu species and Si O₂ were analysised by means of XRD and TPR. It was found that the Cu species are highly dispersed on the Si O₂ carrier by adsorption hydrolysis method, and its catalystic activity is excellent for the hydrogenation reaction of methyl ester of fatty acid.（2） Firstly, copper source, p H, initial concentration of Cu（NO3）2, adsorption time, hydrolysis rate, calcination and reduction conditions and other factors were investigated during the process of preparing Cu/Si O₂ catalyst by adsorption hydrolysis method. Results showed that under the preparation condition of 0.25 mol/L Cu（NO3）2 solution as copper source, dropping ammonia until p H=9,Adding Si O₂ and adsorpting for 30 min, then diluting with water at a rate of 1.7-2.5 m L/min, firing at 350 ℃for 3 hours and reducting at 270 ℃ for 2 h, the Cu/Si O₂ catalyst showed the highest activity. Secondly, the Cu/Si O₂ catalyst prepared under optimal condition were characterized and analyzed by XRD, TEM, SEM and N2 adsorption-desorption.Found the average particle diameter of Cu loading on Si O₂ is about 3.6 nm, and the surface area of Cu/Si O₂ becomes smaller, with an average pore size becomes larger,compare to Si O₂. Finally, the effects of temperature, pressure, dosage of catalyst and reaction time on the composition of hydrogenated products were analyzed by single factor experiments. It was found that under the condition of temperature is 180 ℃, pressure is 0.8 MPa, reacting for 2 h, and with catalyst dosage is 2%, hydrogenated product is relative to the best, the content of linoleic acid methyl ester and methyl oleate are 8.97% and 62.48% respectively. The content of trans fatty acid methyl ester is 20.50%, and the amount of stearic acid methyl ester is not found to increase.（3） In order to improve the activity of the catalyst furtherly, reducing the content of linoleic acid methyl ester, a small amount of Ni（or Pd） was added to prepare Cu-M/Si O₂（M=Ni, Pd） catalyst. The selectivity of Cu-M/Si O₂ catalyst was improved by changing the order of metal loading and adjusting the reduction temperature. Performance of Cu-M/Si O₂ catalysts prepared under optimal conditions was compared to imported commercial catalysts. Found that oleic acid methyl ester yield is 90.26% and 85.93% respectively, with Cu-Pd/Si O₂ and Cu-Ni/Si O₂, are far higher than that of the imported commercial catalysts. Finally, the reuse of Cu-Pd/Si O₂ and Cu-Ni/Si O₂ was investigated, the result was that conversion rate of linoleic acid methyl ester can remain at more than 85% with Cu-Pd/Si O₂ reused 3 times, when Cu-Ni/Si O₂ was reused for 5 times, conversion rate of linoleic acid methyl ester can still be 77.41%.