Study on Catalytic Conversion of Lactic Acid to Acrylic Acid and2,3-pentanedion
|Course||Chemical Engineering and Technology|
|Keywords||Green chemistry lactic acid catalysis acrylic acid 2,3-pentanedione zeolite|
Acrylic acid is a very important chemical with a large demand, which is currently produced in industry via the oxidation of petroleum-based propylene.2,3-Pentanedione is a high value-added fine chemical and the current routes for its production are associated with a few disadvantages, such as, the employment of toxic and petroleum-dependent raw materials, the environmental pollution of by-products and the high cost of operation process. Thus, production of acrylic acid and2,3-pentanedione from biomass-based lactic acid, is receiving much attention, due to its low cost, less environmental pollution, and independent on petroleum. The exploration to develop more effective catalysts for this reaction is still highly desired.In this paper, vapor phase lactic acid conversion has been performed using a fixed-bed, down-flow reactor. Lactic acid conversion conducted over a series of metal salt catalysts supported on the different Si/Al ratio of the HZSM-5zeolites, Y zeolites and APO-5zeolites produces mainly acrylic acid,2,3-pentanedione. The dissertation focuses on the following four parts:(1) The standard enthalpy of formation, free energy and thermal capacity of lactic acid catalytic reaction were calculated by using the methods of Joback group contributions, modified RD and ABWY group contributions. The thermodynamic data of various reactions of lactic acid were compared at different temperature. The results showed that the reactions of lactic acid are thermodynamically feasible.(2) In our present work, a novel series of alkali-metal or alkaline-earth metal modified HZSM-5zeolites, Y zeolites and APO-5zeolites were prepared for lactic acid dehydrated to acrylic acid. The focus of our work is to identify strategies to improve selectivity to desired products. The skeleton structure, pore structure, surface area, pore size distribution, the concentration of ion exchange, surface defects and acidic property of the catalysts had been characterized by means of modern techniques such as X-ray powder diffraction (XRD), N2-adsorption at low temperature, atomic absorption (AAS), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), NH3temperature programmed desorption (NH3-TPD), quantitative determination of Bronsted acid sites method based on pyridine adsorption IR.(3) By using single-factor and the simplex optimization method to systematically examine the various factors affecting the reaction over various catalysts, including: the nature of zeolite catalyst carrier and the zeolite Si-Al ratio the catalyst active metal component in the load, the nature of catalyst activity and the activity of metal salts of anionic nature of the catalyst preparation method, lactic acid, lactic acid airspeed and inert carrier gas flow rate, temperature, reaction time, etc. The single factor and the simplex optimization method, formation of acrylic acid from lactic acid was optimum at88.05%acrylic acid yield over KBr/HZSM-5(30) at360℃,1.13g of catalyst amount and32ml/min carrier gas flow rate; This yield is relatively low as a result of acetaldehyde formation which is favored at high temperature. In optimizing experimental conditions, this catalyst can maintain the best catalytic lives for46hours.(4)In our work, a series of catalysts, constructed by loading alkali metal salts over porous materials such as zeolites, mesoporous and metal oxide materials had been employed as the catalysts for the conversion of lactic acid to2,3-pentanedione in a fixed-bed reactor. Influencing factors, such as, the concentration of lactic acid, the temperature, the nature of alkali metal salts and porous support and the loading of alkali metal salt, were systematically investigated. An as high as48%selectivity of2,3-pentanedione at a52.4%conversion of lactic acid was obtained at280℃over20wt%K/NaZSM-5(60) catalyst.(5)Based on structural properties of catalysts and catalytic experiments, the mechanism formation acrylic acid from lactic acid and condensation to2,3-pentanedione from lactic acid were studied. It required a certain amount of acid and the appropriate strength of weak acid for catalytic dehydration of lactic acid to acrylic acid. However, the acid-base properties of catalysts do not play a decisive effect for catalytic dehydration of lactic acid reaction. The active metal catalyst component (including the activity of metal ions and anions with matching) of the Tammam temperature is significantly influenced the catalytic performance. The catalytic activities for acrylic acid indicate that the selectivity of acrylic acid from the dehydration of lactic acid over the alkali salts catalyst is much more higher when the alkali salt has a suitable Tammam temperature, which the Tammam temperature of the salts modified the zeolites is closed to the optimum reaction temperature. Catalysts of alkali metal salts modified zeolites played the mainly catalytic activity on the catalytic dehydration of lactic acid to acrylic acid in the reaction process due to the pore structure and good thermal stability of zeolite, for storing and delivering the active alkali metal ions. It is advantage to form lactate with lactic acid for metal ions, and the lactate is an active reaction species dehydrated led directly to acrylic acid formation.