Preparation Of Derivatized MIL-100 (Fe) And Its Catalysis Of Conversion Of Sugars To Lactic Acid

Over the past few years,with the rapidly increasing consumption of transportation fuels and the depleting amount of fossil fuels,the energy shortage and the deteriorated pollution of the environment was increasingly rigorous,and it has stimulated research on biofuels and biobased chemicals from lignocellulosic biomass.As a versatile biobased platform molecule,Lactic acid(LA)has been widely employed in food industries as well as the cosmetic industries especially in the production of biodegradable polylactic acid(PLA).It is also a remarkable chemical for the synthesis of a wide range of attractive intermediates.It has been concluded that Lewis acid sites play essential role in retro-aldol reaction,isomerization and 1,2-hydride shift for the whole catalytic LA production using sugars.So,it is necessary to seek new type of catalyst and explore its catalytic activity for the production of LA.Among the common catalytically active Lewis acid metal-organic framework matierals,MIL-100(Fe)is an attractive potential candidate for it is cheap and easy to get,environmentally friendly and the quality and structure properties of it are spectacular.Taking the above results into consideration,we have chosen MIL-100(Fe)just for its strong chemical,thermal stability and accessible coordinatively unsaturated metal centers that allow it very suitable to act as a solid Lewis acid in our reaction system.The results we obtained were as follows:(1)The crystalline porous iron carboxylate metal organic framework MIL-100(Fe)has been synthesized by hydrothermal reactions of three different iron source such as iron powder,ferric nitrate and ferric chloride with trimesic acid(H3BTC).The synthesized MIL-100(Fe)was systematically characterized by XRD,N2 Adsorption,TGA,FT-IR,and SEM.From the characterization results we could see that MIL-100(Fe)with iron powder as iron source possess better performance with a BET surface area of 1650 m2/g with a pore volume of 0.74 cm3/g.The pore size distribution of MIL-100(Fe)estimated by using the DFT method displays two different pore sizes centered at about 1.9 and 2.2 nm,respectively.It is octahedral in shape,and the particles is uniform in size.The therminal stability of it is excellent(stable up to 330 °C in the air).In addition,it showed satisfactory catalytic properties in the conversion of fructose into lactic acid(LA).It was the first time for MOFs materials to apply in the catalytic transformation from lignocellulosic biomass to LA in a “one-pot” process.The effects of reaction conditions,including temperature,reaction time,substrateloading on the conversions of fructose and the yields of LA were also investigated.The highest yields of LA was 32% obtained from 0.05 g fructose,0.05 g MIL-100(Fe)and 10 m L water at 190 °C for 2 h.The catalyst could be easily reused in 4 cycles.Activity evaluation revealed that the regenerated MIL-100(Fe)regained the catalytic activity(28% yield of LA).Even though this catalyst couldn’t kept completely stable,it still make MIL-100(Fe)an alternative catalyst for the conversion of fructose into LA.And its superior morphological and textural propeties especially for its more concentration of acid centers were demonstrated to contributed greatly to the pronounced catalytic performance in fructose-to-LA conversion as compared with other catalysts like Cu-BTC and MIL-100(Cr).(2)We also examined the activity of MIL-100(Fe)in the conversion of fructose to methyl lactate(MLA)and we got satisfactory results.The highest yields of MLA was 32% obtained from 0.05 g fructose,0.05 g MIL-100(Fe)and 10 m L MeOH at 180 °C for 28 h.Based on it,we also extended the types of substrates.(3)The effect of a post-synthetic acid treatment on the catalytic performance of MIL-100(Fe)was also evaluated.We Monitored the modification of the MIL-100(Fe)by reactions of which with different monocarboxylic acid such as trifluoroacetic acid,acetic acid and formic acid.The acid-treated frameworks of the catalyst are structurally robust as no differences have been found in XRD and FT-IR patterns after treatment.From the results of NH3-TPD characterization we could see that the acid amount of the acid-treated MOF was increased.A increase of the activity is found for the acid-treated MOFs when the reaction temperature was 150 oC and 170 oC,respectively.Although the yield of LA is not increased continuously when the reaction temperature was 190 oC,the total yields of products were increased by 12% and the conversion of fructose was increased by 13%.(4)For easier recycling of the catalyst,we synthesized magnetic Fe3O4@MIL-100(Fe)by a layer-by-layer method and explored its activity in the conversion of fructose to LA.Compare the XRD and FT-IR patterns with standard Fe3O4@MIL-100(Fe),the magnetic material was successfully prepared.Experimental results showed that yield of LA was 28% obtained from 0.05 g fructose,0.1 g MIL-100(Fe)and 10 mL water at 190 °C for 2 h,and the catalyst could be easily separated from the reaction system by adding an external magnetic field.(5)We synthesized bimetallic MIL-100(Fe-M)which containing two kinds of metal by adding different metal salts in the preparation of MIL-100(Fe),and researched its activity in the conversion of fructose to LA.Experimental results showed that yield of LA was 30% obtained under the optimal conditions with MIL-100(Fe-Cr)as catalyst.Taking the above results into consideration,it offered a commendable exemple that MOF compounds are very promising materials for various remarkable applications in biomass conversion,especially in lactic acid production.