Enhanced Acid/Base Catalysis in High Temperature Liquid Water

Chinese Chemical Letters Vol. 17, No.6, pp 841-844, 2006841http://www.imm.ac.cn/journalccl.htmlEnhanced Acid/Base Catalysis in High Temperature Liquid WaterXiu Yang LU*, Qi JING, Zhun LI, Lei YUAN, Fei GAO, Xin LIUDepartment of Chemical and Biochemical Engineering, Zhejiang University, Hangzhou 310027Abstract: Two novel and environmentally benign solvent systems, organic acids- enriched hightemperature liquid water (HTLW) and NHg-enriched HTLW, were developed, which can enhancethe reaction rate of acid/base catalyzed organic reactions in HTLW. We investigated thedecomposition of fructose in organic acids-enriched HTLW, hydrolysis of cinnamaldehyde andaldol condensation of phenylaldehyde with acetaldehyde in NHz- enriched HTLW. Theexperimental results demonstrated that organic acids-enriched or NH3-enriched HTLW can greatlyaccelerate acid/base-catalyzed organic reactions in HTLW.Keywords: High temperature liquid water, acid/base-catalysis, organic reactions.High temperature liquid water (HTLW), as an environmentally benign medium, hasdrawn increasing attention for organic chemical reactions and biomass conversion- .HTLW has a strong tendency to ionize and can act as an acid and/or base catalyst. Inaddition, HTLW can dissolve organic compounds to some extent allowing for ahomogenous reaction within an aqueous phase. Extensive researcheshave beenpursued on acid/base- catalysis reactions in HTLW without addition of acid or base.However, slow reaction rate and poor selectivity are the problems for thesenon-catalyzed organic syntheses or biomass conversion in HTLW, which greatly limitedthe applications of this attractive technique in industry.Savage et al. studied CO2 enriched HTLW to accelerate dehydration of cyclo-hexanol to form cyclohexene and the alkylation of p-cresol with tert-butyl alcohol toform 2-tert-butyl-4 methylphenol in HTLW". Torry et al. explored the effects of saltson hydrolysis of di-benzyl ether and benzyl phenyl amine in supercritical andnear-critical water'2. Here, we propose organic acids-enriched HTLW and NH3-enriched HTLW (ammonia can be easily recycled by heating) as new environmentalbenign reaction media, and report its applications in the decomposition of fructose,hydrolysis of cinnamaldehyde and aldol condensation of phenylaldehyde withacetaldehyde.A 500 mL high pressure batch reactor with a mechanical impeller and a samplingline was employed. First, the system was degassed with vacuum pump, and then flledwith high purity nitrogen. Reactants were quickly中国煤化工after thetemperature of deionized water inside reached thally, theTYHCNMHG' E- mail: luxiuyang@ zju.edu.cn842Xiu Yang LU et al.samples (2-3 mL) were collected at certain reaction time, filtrated and analyzed withHPLC (Agilent 1100) or GC (Agilent 1790F). Prior to the sampling, 2-3 mL solutionwas vented to wash the sampling line.The identification was made by comparison thepeak of retention times of the sample with that of the pure compounds, and conformedwith GCIMS (Agilent 6890/5973).Decomposition of fructose in organic acids-enriched HTLWThe effects of different organic acids (formic acid, acetic acid) on the decompositionkinetics of fructose in HTLW were determined at temperatures from 180°C to 220°C andpressure of 10 MPa. The initial concentration of fructose and the organic acid wereboth 10.8 mg/mL. The rate constant was calculated based on first-order reactionassumption. Comparison of the rate constants for fructose decormposition underdifferent conditions is ilustrated in Figure 1, showing that the reaction rates are greatlyenhanced with the addition of organic acids. At the same concentration, formic aciddemonstrated stronger ability to accelerate the fructose decomposition than acetic acid.Figure 1 Comparison of the rate constants for fructose decomposition with formic acid andacetic acid (P= 10 MPa)0.冒0.e-←- without catalyst-X- with acetic acid0.5一个with formic acidX0.4p力170180 190200210220230T emperature /CThe effects of formic acid concentration and residence time on the fructoseconversion are shown in Figure 2. The fructose conversion increased with increase ofthe concentration formic acid.Hydrolysis of cinnamaldehyde in NH3-enriched HTLWThe effects of ammonia concentration and residence time on the cinnamaldehydeconversion are shown in Figure 3.The results showed that with the increasingammonia concentration, the reaction rate of the cinnamaldehyde hydrolysis was greatlyenhanced.中国煤化工YHCNMHGEnhanced Acid/Base Catalysis in High Temperature Liquid WaterFigure 2 Effects of formic acid concentration and residence time on fructose conversion(T=200°C, P=10 MPa, and the initial concentration of fructose 10.8 mg/mL)100%80%0 mg/mL60%-2.5 mg/mL40%5.7 mg/mL0 - 8.0 mg/mL20%-* 1.2 m/mL一+ 13.8 mg/mL0%030Residence timc/minFigure 3 Effects of ammonia concentration and residence time on cinnamaldehyde conversion(T=240°C, P= 15 MPa)860%ar0 mg/L6.6 mg/L.13.2 mg/L.26.4 mg/L.52.8 mg/L10015020025300Residence time /minAldol condensation of phenylaldehyde with acetaldehyde in NH3-enriched HTLWFigure 4 depicts the effects of ammonia concentration and the residence time onbenzaldehyde conversion.The results showed that the reaction rate of aldolcondensation of benzaldehyde with acetaldehyde increased significantly with increasingamount of ammonia added.In summary, two novel and environmentally benign solvent systems, organicacids- enriched HTLW and NHa-enriched HTLW, were investigated to enhance thereaction rate of acidbase catalyzed organic reactions in HTLW. The experimentalstudies of the decomposition of fructose, hydrolysis of cinnamaldehyde and the aldolcondensation of phenylaldehyde with acetaldehyde suggested that organic acids enrichedHTLW and NH3 -enriched HTLW can greatly accelerorganic中国煤化工reactions.TYHCNMHGXiu Yang LU et al. .Figure 4 Effects of ammonia concentration and residence time on benzaldehyde conversion(T=260°C, P=15 MPa, and the molar ratio of benzaldehyde to acetaldehyde at 1:5.7)80%60%日er40%- 8-26.3 mg/L0 mg/L52.5 mg/L20%口105.0 mg/L- 0- 157.5 mg/L0%0200400600Residence time /minAcknowledgmentsThe authors are grateful for the financial support of the National Natural Science Foundation ofChina (20476089, 20176054), Project of the Ministry of Science and Technology of China (No.2004CCA05500 ) and Zhejiang Provincial Natural Science Foundation of China (ZE0214). Welike to thank Dr. Jie Lu of Georgia Institute of Technology for valuable suggestions and revision ofthe paper.ReferencesC. A. Eckert, C. L. Liotta, J. S. 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