Design Of Mg-based Solid Base For Isomerization Of Linoleic Acid And The Mechanism Studying

Conjugated linoleic acid,which has physiological function,is a collective term describing the positional and geometric conjugated dienoic isomers of polyunsaturated fatty acids(cis-9,cis-12-octadecadienoic acid).CLAs are generally found in ruminant animals and dairy products.CLA,predominantly c9,t11-18:2 isomer has been shown to be produced by the ruminant bacteria,as an intermediate on the process of biohydrogenation of linoleic acid into stearic acid.The three 9c,11t-,9t,11t-and 10t,12c-CLA have been indicated for good health,including reduces body fat,anticarcinogenic,antidiabetic,reduces atherosclerosis,reduces inflammation,beneficial for bone,enhances immune function.Hence,the CLAs in medicine and food have important research and application value.The main natural sources of CLAs in human diet are milk and meat from ruminants,dairy products and certain vegetable products,but the amount is basically very low.Even in western countries where dairy products are the staple food,CLAs's per capita intake is less than 1/3,therefore,as the interest in CLAs as supplement in current functional food products in enormous,its synthesis is of increasing importance.At present,the synthesis of CLAs mainly includes microbial production,alkali catalytic isomerization,oleic acid allyl alcohol dehydration,organometallic of homogeneous catalysis and heterogeneous catalytic isomerization method.Compared with these methods,the heterogeneous catalytic isomerization method has the advantages of easier to be taken apart and recycled,low environmental pollution.However,the catalytic efficiency of the heterogeneous catalytic isomerization method is still relatively low,and the hydrogenated products,especially trans fatty acids and other by-products are higher.The solid base catalysts due to the special surface basic sites easily extract proton from the linoleic acid substrate to form allyl anion which catalyst can be stabled by the adjacent metal ion of solid base.Hence,the solid base is a feasible catalyst for the preparation of cis conjugated linoleic acid by catalytic isomerization of linoleic acid.MgO is rich in alkaline sites,high specific surface area and low cost,therefore,in this paper,the Mg-solid base catalyst was designed for high catalytic activity,mild reaction conditions and less hydrogenated products.Meanwhile,the reaction mechanism of the catalytic reaction was revealed by the relationship between the catalyst structure and the catalytic activity.The main research work is as follows:1.The uniform pore size,high surface area of ordered mesoporous Ru-MgO-ZrO2 solid bases with different Mg content were synthesized using P123 as template and Zr(NO3)4 as Zr source through the evaporation-induced self-assembly sol-gel method.The effects of Mg content on the pore size and specific surface area of the catalyst were investigated,and then investigate the effect of Mg content on the catalyst surfaces,the alkali and the Ru form.As a catalyst for isomerization of linoleic acid,these properties on the catalytic isomerization of linoleic acid on conversion and selectivity.2.In order to reduce the influence of pore size on catalytic reaction and increase the contact opportunity between the reaction substrate linoleic acid and the active site of catalyst,the large pore mesoporous Ru-MgAl composite oxides with different Mg content were synthesized by adding N,N-Dimethyldodecylamine expanding agent of sol-gel method.The effect of pore size on the conversion and selectivity of the catalytic isomerization of linoleic acid was investigated,and the influence of pore size and catalyst surface basicity on the isomerization of linoleic acid was also studied.3.In order to improve the production efficiency of conjugated linoleic acid and giving full play to the role of basic sites in catalytic isomerization,the Ruthenium containing hydrotalcites were prepared by precipitation method.The Ru-MgAl composite oxides catalysts with different surface basicity were obtained by different calcination temperature.4.The Ru-MgAl hydrotalcite composite oxide catalysts with different Mg/Al molar ratios were synthesized to investigate the relation between basic sites,Ru active sites form with catalytic properties.It is revealed the three problems that the basic sites of Ru-MgAl composite oxide catalysts play a key role in the catalytic performance,the existence of Ru active sites form,and the interaction between the basic and Ru active sites.5.The Ru-MgAl composite oxide catalysts with different strong base sites were synthesized under different pH conditions by the method of co-precipitation.The effect on the catalysis performance by catalyst basicity of the strong base sites was investigated,it further reveals the role of the basic site and the Ru site of the catalyst and how the two active sites interact with each other.Through the above research,the following results are obtained:1.The amount of Zr/Mg in the catalyst has a significant effect on the order of the catalyst mesoporous structure.When Zr/Mg=3,the mesoporous structure of Ru-OMZM3 catalyst has good order and high specific surface area.The catalysis results showed that the content of Mg in the catalyst had an important effect on the performance of the catalyst.The results show that the surface basicity of the catalysts is more important than the surface areas for the catalytic isomerization of linoleic acid.For the Ru-OMZMr catalytic isomerization of linoleic acid into conjugated linoleic acid,the results indicated that the Ru-OMZM1 conjugated linoleic acid yield high reached 85%in 4h reaction time,the CLAs productivity reached 0.099 g(CLA)L-1(solvent)min-1,and the catalytic products were mainly 3 kinds of isomers with biological activity.2.The large pore of mesoporous Ru-MMAr composite oxide catalyst with different Mg content were successful synthesized by adding pore expanding agent,and the pore size increased to 5-6nm.The results show that the increase of the pore size of the catalyst can improve the catalytic activity to some extent,but the effect is not significant.It was found that the effect of Mg content on catalytic activity was more important.The yield of conjugated linoleic acid was 86%by Ru-MMA20 complex oxides and the CLAs productivity high reached 0.186 g(CLA)L-1(solvent)min-1 shown better catalytic performance.The catalytic products were also mainly the 3 kinds of isomers with biological activity.3.The synthesized RuMgAl hydrotalcite after the calcination of 450 ? has the highest activity for the isomerization of linoleic acid.Compared with the heterogeneous catalysts reported in the literature,the CLAs productivity of Ru-MgA1450 catalyst was improved significantly,high reaching 1.4g(CLA)L-1(solvent)min-1.Moreover,the CLAs productivity is even higher than that of the homogeneous KOH catalyst;the catalytic products are also mainly 3 kinds of conjugated linoleic acid isomers with biological activity.Preliminary catalytic reaction mechanism shown that the basic sites and high dispersion RuO2 of Ru-MgA1450 catalyst are the active sites for the catalytic reaction.The basic site plays a role of adsorption of linoleic acid and desorption of allylic hydrogen.The ruthenium activity site responded to migrate the double bond and steady allylic carbanion.And the basicity sites of Ru-MgAl catalyst and ruthenium activity site seem to have a synergic effect on the catalytic reaction.4.The catalytic results shown that the medium strength basicity and strong basicity is the base site of catalytic reaction,and highly dispersed RuO2 is another active site of catalytic isomerization.With the increase of Mg content in the catalyst,the dispersion of the active component Ru was increased,the interaction between Ru and the support strengthen,the oxidation state of RuO2 improved and the ability of RuO2 to activate C-H enhanced,which the catalytic activity was improved.5.The Ru-MgAl composite oxide catalysts with different strong base sites were successful synthesized under different pH conditions by the method of co-precipitation.There is relationship between strong basicity sites and catalytic activity.A catalyst with high catalytic activity of linoleic acid preparation of conjugated linoleic acid activity must have large surface area of Ru,proper SMSI action and high strong basicity,which three synergistic effects for isomerization of linoleic acid.The high content of Mg catalyst has high strong basicity;the Ru empty orbit can be easily combined with the allyl of linoleic acid.The two active sites transfer the H from allyl to the basic site by Ru-O-Mg bond,which makes the Ru-MgAl catalyst have high catalytic efficiency.