Preparation Of Methyl Oleate From C18 Methyl Ester By Selective Hydrogenation

Fatty acid methyl esters?FAMEs?are obtained by transesterification of natural animal and vegetable fats.FAMEs are also known as biodiesel and are good substitutes for petrochemical diesel.The presence of polyunsaturated components limits the use and performance of diesel.Elimination or reduction of methyl linolenate?C18:3?and methyl linoleate?C18:2?and convert them to methyl oleate?C18:1?by selective hydrogenation,at the same time avoid the production of methyl stearate?C18:0?can improve the combustion and emission performance,oxidation stability while maintaining acceptable cold flow performance.In chemical industrial applications,the single C=C of methyl oleate can also effectively avoid messy reactions,lower reaction rates and worse product performance.This paper selects the SBA-15 molecular sieve which has been widely used in the catalyst carrier field and the three most used active metals Ni,Cu and Pd in hydrogenation for catalyst preparation.First of all,compare the methyl oleate selectivity of the three catalysts and select the metal with the highest selectivity and then optimize the preparation method and process in order to prepare a highly active and highly selective hydrogenation catalyst.Finally explore the hydrogenation process and test stability,the results are as follows.?1?Prepare SBA-15 molecular sieve by hydrothermal synthesis and then prepare10%Ni/SBA-15,10%Cu/SBA-15 and 0.5%Pd/SBA-15 by wetness impregnation?WI?,use XRD,N₂ adsorption-desorption,SEM and TEM to characterize the morphology,pore structure and metal dispersion of the molecular sieves and catalysts.The characterization results show that the molecular sieve has a typical two-dimensional hexagonal pore structure and large specific surface area?SSA?,pore volume and pore diameter The SSA,pore volume and pore size of the three catalysts have been reduced to varying degrees but still remained at a high level.The crystal particles formed in the respective catalysts are large due to the large loading of Ni and Cu.the low loading Pd catalyst has small crystal particles and they are uniformly dispersed.Select a suitable weight hourly space velocity?WHSV?to optimize the temperature according to respective hydrogenation activity of catalyst.Compare the C18:1 content of the three catalytic products at their respective optimal temperature,the C18:1 mass fractions of the three products are 76.48%for NiSi-WI,86.91%for CuSi-WI and 78.32%for PdSi-WI,Cu was determined as the active metal for futher study.?2?The Cu/SBA-15 catalysts with 10%loading of copper were prepared by wetness impregnation?WI?,deposition precipitation?DP?and ammonia evaporation?AE?methods respectively.Characterization results showed that the pore structure of the catalysts prepared by WI is better but there are poor copper species distributions and larger crystal particles;DP and AE methods can effectively disperse the copper species and the copper crystal particles are so small that they can enter inside the molecular sieve channel.The silica pore wall of CuSi-AE catalyst were partially dissolved and destroyed so that the SSA of CuSi-AE drops a lot,however it has larger pore volume and diameter.The key point is that the layered sheet of copper silicate is produced in the catalyst.The same hydrogenation process was used to investigate and compare the hydrogenation activity of the three catalysts and results showed that the order of activity was CuSi-AE>>CuSi-DP>CuSi-WI.The activity of CuSi-AE was significantly higher than that of WI method and iodine value?IV?of its product is80.51.The conversion rate of C18:2 and C18:3 was high and the mass fraction of C18:1 reached 90.12%.The effect of the DP method to enhance the activity is not obvious compared with WI method.The reason why the activity of the CuSi-AE catalyst got improved is not only the dispersion of copper species and the expansion of pores but also the generation of copper silicate in the evaporation progress of ammonia,as a result more hydrogenation activity centers are produced after reduction.Therefore the AE method is the best choice for the preparation of the catalysts.?3?To investigate and optimize the influence of the amount of ammonia added,ammonia evaporation temperature and calcination temperature on Cu/SBA-15prepared by AE method.As a result,maintain the amount of ammonia added at 2.5mL,optimize the ammonia evaporation temperature and calcination temperature at90?and 350?respectively.Characterization results show that after optimization of the catalyst preparation process The characterization results of the catalysts show that after optimization of the preparation process,the damage of the support pore structure is reduced and more copper silicate is produced.The optimized catalyst was used to investigate the hydrogenation process conditions and compared with the hydrogenation process of the Ni,Cu and Pd catalysts by the WI method.It was found that not only the catalytic activity but also the C18:1 selectivity have been significantly improved when prepared Cu/SBA-15 by AE method,and it caused production efficiency get significantly improved while costs get effectively reduced.The hydrogenated product of optimized CuSi-AE contains more cis-C18:1 and has better cold flow performance.The effects of temperature,pressure,weight hourly space velocity?WHSV?and volume ratio of hydrogen to ester were then investigated,results showed the content of methyl oleate increased from 45.45%to 90%and91.06%at most under the conditions of 150?,0.5 Mpa,WHSV 3 h^-1,V_?Hydrogen?:V_?Ester?1200,with the polyene component was less than 2%and C18:0 slightly increased.The catalyst stability was investigated using the above hydrogenation process conditions and it was found that the catalyst can be continuously,efficiently and stably operated for 28 hours with the product contains C18:1more than 90%.