Study On Efficient Conversion Of Lactic Acid To Acrylic Acid

Many chemicals originated from petroleum industry have become the essentials in our daily life. Petroleum, as the non-renewable resource, its consumption is continuously increased in recent years. It is a common interest to find out new raw materials for chemicals production in view of sustainable development of economy. As a result, there is a strong trend to manufactory chemicals by using biomass resource.Acrylic acid is currently produced through two step oxidation of propylene, however, the process is complicated and different catalysts need to be used. One step partial oxidation of propane to acrylic acid is highly desirable and has derived numerous attentions in recent years, and the researches are focused on the VPO, MMO, and HPA types of catalysts. For the MMO type of catalyst, catalyst nature is very sensitive to preparing parameters and "window" of synthesizing active catalyst is rather narrow. Thus the reproducibility of catalyst structure/performance is poor. The route for acrylic acid production via bio-mass deriveable lactic acid is thus of great importance and has attracted extensive attentions.The research on dehydration of lactic acid to acrylic acid is currently performed in laboratory scale, and the yield and selectivity of acrylic acid as well as catalyst efficiency is not high enough. Many studies were focused on screening of catalysts and optimization of processes, but understanding of structure-performance correlation and reaction mechanism is not adequate. These aspects are the objective of the present thesis study.In the present thesis, we prepared various alkali phosphates and nitrates modified SAPO-5, SAPO-37, SBA-15, Fumed SiO2, and NaY as the catalysts for catalytic conversion of lactic acid. We systematically investigated the influence of fabrication methodology and support material on catalyst perporties. The catalytic performance was optimized in terms of the type and loading of alkali phosphates/nitrates, reaction temperature, liquid hourly space velocity, and lactic acid concentration. The results are summarized bellow:1. Use of SAPO-5,37 supported NaNO3 for dehydration of lactic acid to acrylic acidSAPO-5 and SAPO-37 were synthesized by hydro-thermal method. Origin of aluminum, type of template, and crystallization time showed significant effect on the formation and structure of SAPO-5 and SAPO-37 zeolites. Alkali (Li, Na, K) nitrates were introduced onto SAPO-5 and SAPO-37 by wetness impregnation. Physicochemical properties of the catalysts were characterized by various techniques. It was found that introduction of NaN03 to SAPO-n can efficiently decrease acid strength of zeolites. For NaNO3/SAPO-5, NaN03 loading first enhanced and then declined the surface acidity of samples. Change in catalyst performance is in accordance with the trend of acidity varation. Under the optimized conditions, lactic acid conversion of 75.2%, and acrylic acid selectivity of 38.6% were obtained over 23%NaNO3/SAPO-5. On the other hand, higher lactic acid conversion of 91.3% and lower acrylic acid selectivity of 28.6% were achieved on 23%NaNO3/SAPO-37. Over the unmodified SAPO-5 and SAPO-37, due to their strong surface acidity, the decarbonylation of lactic acid becomes a dominated reaction, and therefore, acetaldehyde is the major product.2. Efficient acrylic acid production through lactic acid dehydration over NaY zeolite modified by alkali phosphatesAlkali phosphates-modified NaY zeolites were developed as catalysts for efficient conversion of lactic acid to acrylic acid. The catalytic performance was optimized in terms of the type and loading of alkali phosphates, reaction temperature, liquid hourly space velocity, and lactic acid concentration. A high acrylic acid yield of 58.4% was achieved at 340°C over 14 wt% Na2HPO4/NaY. The physicochemical properties of the catalysts were investigated by various techniques including NH3-TPD, pyridine adsorption-FTIR, Raman, and MAS 31P NMR. Introduction of alkali phosphates to NaY zeolite results in a decline of surface acidity. The results of FTIR, Raman, and MAS 31P NMR investigations on the fresh and used catalysts suggest that sodium phosphate is largely transformed to sodium lactate during the reaction. The phosphates and the in situ generated sodium lactate function as highly active species for the target reaction. It is worth to note that the acrylic acid can be further considerably enhanced to～74% by changing the particle size of NaY (50-500 nm) and adopting suitable Na2HPO4 loading and reaction parameters. This is the highest acrylic acid yied known to date as compared to those reported in open literature.3. Sodium nitrate supported on SBA-15 and fumed silica for efficient production of acrylic acid and 2,3-pentanedione from lactic acidThe catalytic conversion of lactic acid to acrylic acid and 2,3-pentanedione over sodium nitrate that was supported on mesoporous SBA-15 and non-microporous fume silica was studied. Under optimized conditions, the yields of acrylic acid, 2,3-pentanedione, and acetaldehyde are 44.8%,25.1%, and 13.3%, respectively, over the 23%NaNO3/SBA-15 catalyst, giving a (acrylic acid+2,3-pentanedione+ acetaldehyde) yield of 83.2%. Such an excellent performance has never been reported before. It was observed that the performance of the catalysts is strongly affected by NaNO3 dispersion, catalyst texture and porosity, and product diffusion efficiency. A proper control of NaNO3 loading on NaNO3/SBA-15 can result in structure modification of the catalysts for improvement of 2,3-pentanedione selectivity. According to the results of IR investigation, we deduce that under certain reaction conditions, the surface NaNO3 species can readily transform to sodium lactate that functions as active component to catalyze the target reactions.