Aldol Condensation

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Chun Cai - One of the best experts on this subject based on the ideXlab platform.

Tao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • kinetic study of retro Aldol Condensation of glucose to glycolaldehyde with ammonium metatungstate as the catalyst
    Aiche Journal, 2014
    Co-Authors: Junying Zhang, Baolin Hou, Aiqin Wang, Hua Wang, Tao Zhang
    Abstract:

    The kinetics of the retro-Aldol Condensation of glucose to glycolaldehyde was studied in a batch reactor at 423-453 k using ammonium metatungstate (amt) as the catalyst. three consecutive reactions were considered: retro-Aldol Condensation of glucose to erythrose and glycolaldehyde (r1), retro-Aldol Condensation of erythrose to two moles of glycolaldehyde (r2), and further conversion of glycolaldehyde to side products (r3). fitting of the experimental data showed that r1 was first-order reaction while r2 and r3 were 1.7th- and 2.5th-order reaction, respectively. conversely, the reaction rate of r1 was 0.257th-order dependence on the concentration of amt catalyst. the apparent activation energies for r1, r2, and r3 were 141.3, 79.9, and 52.7 kj/mol, respectively. the high activation energy of r1 suggests that a high temperature is favorable to the formation of glycolaldehyde. the experimental c-t curves at different temperatures and initial glucose concentrations were well predicted by the kinetic model. (c) 2014 american institute of chemical engineers

  • Kinetic study of retro‐Aldol Condensation of glucose to glycolaldehyde with ammonium metatungstate as the catalyst
    AIChE Journal, 2014
    Co-Authors: Junying Zhang, Baolin Hou, Aiqin Wang, Hua Wang, Tao Zhang
    Abstract:

    The kinetics of the retro-Aldol Condensation of glucose to glycolaldehyde was studied in a batch reactor at 423-453 k using ammonium metatungstate (amt) as the catalyst. three consecutive reactions were considered: retro-Aldol Condensation of glucose to erythrose and glycolaldehyde (r1), retro-Aldol Condensation of erythrose to two moles of glycolaldehyde (r2), and further conversion of glycolaldehyde to side products (r3). fitting of the experimental data showed that r1 was first-order reaction while r2 and r3 were 1.7th- and 2.5th-order reaction, respectively. conversely, the reaction rate of r1 was 0.257th-order dependence on the concentration of amt catalyst. the apparent activation energies for r1, r2, and r3 were 141.3, 79.9, and 52.7 kj/mol, respectively. the high activation energy of r1 suggests that a high temperature is favorable to the formation of glycolaldehyde. the experimental c-t curves at different temperatures and initial glucose concentrations were well predicted by the kinetic model. (c) 2014 american institute of chemical engineers

Yi-wei Zhu - One of the best experts on this subject based on the ideXlab platform.

Walter Leitner - One of the best experts on this subject based on the ideXlab platform.

  • recycling of two molecular catalysts in the hydroformylation Aldol Condensation tandem reaction using one multiphase system
    Green Chemistry, 2020
    Co-Authors: Marc Strohmann, Jeroen T Vossen, Andreas J Vorholt, Walter Leitner
    Abstract:

    Tandem reactions are of great importance to efficiently execute multiple conversions in one synthesis step. Herein we present a multiphase system for the hydroformylation/Aldol Condensation, which is able to recycle both optimized catalysts multiple times. The system consists of an organometallic rhodium/sulfoXantphos hydroformylation catalyst and basic NaOH as Aldol Condensation initiator, which are both immobilized in a polyethylene glycol phase. Under reaction conditions, NaOH is converted to sodium formate, which is still able to catalyse the Aldol Condensation. The reaction and recycling are demonstrated by the conversion of 1-pentene to the corresponding Aldol product in a recycling experiment. During nine consecutive runs, no significant loss of activity is found with an overall TON of 8700 in regard to the rhodium catalyst and an average rhodium leaching of only of 0.07% per run is observed.

James A. Dumesic - One of the best experts on this subject based on the ideXlab platform.

  • An overview of dehydration, Aldol-Condensation and hydrogenation processes for production of liquid alkanes from biomass-derived carbohydrates
    Catalysis Today, 2007
    Co-Authors: Juben Nemchand Chheda, James A. Dumesic
    Abstract:

    Abstract We present results for the conversion of carbohydrate feedstocks to liquid alkanes by the combination of dehydration, Aldol-Condensation/hydrogenation, and dehydration/hydrogenation processing. With respect to the first dehydration step, we demonstrate that HMF can be produced in good selectivity from abundantly available polysaccharides (such as inulin, sucrose) containing fructose monomer units using a biphasic batch reactor system. The reaction system can be optimized to achieve good yields to 5-hydroxymethylfurfural (HMF) from fructose by varying the contents of aqueous-phase modifiers such as dimethylsulfoxide (DMSO) and 1-methyl-2-pyrrolidinone (NMP). Regarding the Aldol-Condensation/hydrogenation step, we present the development of stable, solid base catalysts in aqueous environments. We address the effects of various reaction parameters such as the molar ratio of reactants and temperature on overall product yield for sequential Aldol-Condensation and hydrogenation steps. Overall, our results show that it is technically possible to convert carbohydrate feedstocks to produce liquid alkanes by the combination of dehydration, Aldol-Condensation/hydrogenation, and dehydration/hydrogenation processing; however, further optimization of these processes is required to decrease the overall number of separate steps (and reactors) required in this conversion.

  • Single-reactor process for sequential Aldol-Condensation and hydrogenation of biomass-derived compounds in water
    Applied Catalysis B-environmental, 2006
    Co-Authors: Christopher J. Barrett, Juben Nemchand Chheda, George W. Huber, James A. Dumesic
    Abstract:

    Abstract A bifunctional Pd/MgO-ZrO 2 catalyst was developed for the single-reactor, aqueous phase Aldol-Condensation and hydrogenation of carbohydrate-derived compounds, furfural and 5-hydroxymethylfurfural (HMF), leading to large water-soluble intermediates that can be converted to liquid alkanes. The cross Aldol-Condensation of these compounds with acetone results in formation of water-insoluble monomer (C 8 –C 9 ) and dimer (C 13 –C 15 ) product species, which are subsequently hydrogenated in the same batch reactor to form water-soluble products with high overall carbon yields (>80%). After a cycle of Aldol-Condensation followed by hydrogenation, the Pd/MgO-ZrO 2 catalyst undergoes a loss in selectivity by 18% towards heavier product (dimer) during subsequent runs. However, the catalytic activity and dimer selectivity are completely recovered when the catalyst is recycled with an intermediate calcination step at 873 K. The optimum temperatures for Aldol-Condensation of furfural with acetone and for Condensation of HMF with acetone are 353 and 326 K, respectively, representing a balance between dimer selectivity and overall carbon yield for the process. The product selectivity can be controlled by the molar ratio of reactants. When the molar ratio of furfural-acetone increases from 1:9 to 1:1, the selectivity for the formation of dimer species increases by 31% and this selectivity increases further by 12% when the ratio increases from 1:1 to 2:1. It is likely that this active, stable, and heterogeneous catalyst system can be applied to other base and/or metal catalyzed reactions in the aqueous phase.