Hydrogenation selective liquid-phase

As catalytic semihydrogenation of alkynes to Cis-alkenes is not only a very important synthetic operation (ref. 1) but also of industrial interest, it is a challenging task for both synthetic and catalytic chemists. For instance, the importance of the problem is illustrated by numerous recent publications on different aspects of the selective hydrogenation of many compounds related to the propargyl alcohol structure (refs. 2-7). In this respect, 1,4-butenediol, obtained by the liquid-phase semihydrogenation of 1,4-butynediol, is a raw material for insecticides and Vitamin Bg (refs. 2,8,9). Furthermore, the total and selective liquid-phase hydrogenation of this compound is one of the procedure for making butanediol, the top 95 chemical produced in the United States (refs. 10,11), whose major use is in the manufacture of polyesters. 

The key to the success of the oxidation examples cited above is the ability of the catalysts used to exert proper kinetic control on the possible side reactions. Without it, thermodynamically favorable but undesired products such as CO2 and H2O are made instead. Controlling oxidation kinetics to stop at the desired oxygenated products is quite difficult, and has yet to be solved for many other systems. For instance, although many attempts have been made to develop a commercial process for the oxidation of propylene to propylene oxide, both the activity and the selectivity of the systems proposed to date, mostly based on silver catalysts, are still too low to be of industrial interest " propylene oxide is presently manufactured by processes based on chlorohydrin or hydrogen peroxide instead. In spite of these difficulties, though, recent advances in selective liquid phase oxidation of fine chemicals on supported metal catalysts have shown some promise, offering high yields (close to 100%) under mild reaction conditions." ... 

The selective liquid phase hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to the corresponding 2,4-nitroarylhydroxylamines has been studied over supported Pd, Pt, and Ru catalysts. Pt and Pd samples were found more active and selective than Ru. On the palladium catalysts the influence of metal particle size, temperature and nature of the support on the catalytic activity and selectivity has been also investigated. Both specific activity and selectivity were found to be dependent on the palladium particle size. Larger Pd particles were found more active and selective towards the formation of the nitroarylhydroxylamines The results reported have been interpreted on the basis of a different geometry and strength of adsorption of the substrate on the active sites. The products distribution is influenced also by the acid-base properties of the support used. 

Aramendia, MA Borau. V Jimenez, C Marina.s, JM Porra.s, A Urbano, FJ. Selective liquid-phase hydrogenation of citral over supported palladium. Journal of Catalysis, 1997 172,46-54. 

N. M. Bertero et al. Selective liquid-phase hydrogenation of citral over supported bimetallic Pt-Co catalysts, Appl Catal, A, 2009, 358(1), 32-41. 

Hydrogen peroxide is mostly produced on a large scale using the anthraquinone (AQ) autoxidation process. The key step is the selective liquid-phase hydrogenation of the AQs to their corresponding hydroquinones (Scheme 9.8). An industrial process has been designed at Chalmers University and developed and used by Akzo-Nobel on the pilot scale. It involves a three-phase monolith reactor but very few details... 

Rgure 9.12 Representative TEM Micrographs of the Pd/N-CNT Catalyst Used in the Selective Liquid-Phase Hydrogenation of Cinnamaldehyde. Adapted from Ref. [58], Copyright2008, Elsevier. 

Deviations from Raonlt s law in solution behavior have been attributed to many charac teristics such as molecular size and shape, but the strongest deviations appear to be due to hydrogen bonding and electron donor-acceptor interac tions. Robbins [Chem. Eng. Prog., 76(10), 58 (1980)] presented a table of these interactions. Table 15-4, that provides a qualitative guide to solvent selection for hqnid-hqnid extraction, extractive distillation, azeotropic distillation, or even solvent crystallization. The ac tivity coefficient in the liquid phase is common to all these separation processes. 

Chlorination of n-paraffins (C10-C14) in the liquid phase produces a mixture of chloroparaffins. Selectivity to monochlorination could be increased by limiting the reaction to a low conversion and by decreasing the chlorine to hydrocarbon ratio. Substitution of secondary hydrogen predominates. The reaction may be represented as ... 

TS-1-catalyzed processes are advantageous from the environmental point of view as the oxidant is aqueous hydrogen peroxide, which turns into water, and the reactions are operated in liquid phase under mild conditions, showing very high selectivity and yields, thus reducing problems and the costs of by-product treatments. Confinement of the metal species in the well-defined MFl pore system endows TS-1 with shape selectivity properties analogous to enzymes. For these features the application of the terms mineral enzyme or zeozyme to TS-1 is appropriate [42]. 

The reverse ME technique provides an easy route to obtain monodispersed metal nanoparticles of the defined size. To prepare supported catalyst, metal nanoparticles are first purified from the ME components (liquid phase and excess of surfactant) while retaining their size and monodispersity and then deposited on a structured support. Due to the size control, the synthesized material exhibits high catalytic activity and selectivity in alkyne hydrogenation. Structured support allows suitable catalyst handling and reuse. The method of the catalyst preparation is not difficult and is recommended for the... 

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

De Vos, R., Smedler, G., and Schoon, N.-H., Selectivity aspects of using the cross-flow catalyst reactor for liquid phase hydrogenations. Ind. Eng. Chem. Process Des. Dev. 25, 197-202 (1986). 

Vreactor=70 ml VCh=Vrcn=10 ml (0.045 mole) 111 1 =0.3 g PH2=80 bar (at RT) was not maintained during reaction NH3/RCN=0.25 without ammonia, selectivity of SB is higher at lower temperatures. The selectivity to RNH2 decreased with reaction time for the experiment performed without NH3. The apparent activation energy of the hydrogenation of RCN on RNi-L catalyst was 30.5 kJ/mol, which is close to the value 46 kJ/mol measured in the liquid phase hydrogenation of acetonitrile on CoB amorphous alloy catalyt [7], RNi-C is more active than RNi-L catalyst (compare Table 1 No 4 and 6 and Table 2 No 7 and 8). 

The present economic and environmental incentives for the development of a viable one-step process for MIBK production provide an excellent opportunity for the application of catalytic distillation (CD) technology. Here, the use of CD technology for the synthesis of MIBK from acetone is described and recent progress on this process development is reported. Specifically, the results of a study on the liquid phase kinetics of the liquid phase hydrogenation of mesityl oxide (MO) in acetone are presented. Our preliminary spectroscopic results suggest that MO exists as a diadsorbed species with both the carbonyl and olefin groups coordinated to the catalyst. An empirical kinetic model was developed which will be incorporated into our three-phase non-equilibrium rate-based model for the simulation of yield and selectivity for the one step synthesis of MIBK via CD. 

The liquid phase kinetics of the selective hydrogenation of mesityl oxide in acetone were studied for the purpose of developing a robust kinetic model to be integrated into an existing non-equilibrium rate-based model for the simulation of the CD process for MIBK production. A typical concentration versus time profde is illustrated in Figure 2. MIBK was produced with veiy high selectivity with essentially all of the MO converted to MIBK. Products from the... 

Table 1 illustrates the effect of hydrogen pressure on the selectivity to MIBK based on the initial rate of MIBK production and the rate of IPA production. Palladium gives very high selectivity to MIBK, typically in excess of 93% with the selectivity improving significantly with decreasing pressure. This result is of particular importance since the CD process for MIBK production is carried out at relatively low pressure (< IMPa). In contrast, alternative one-step processes for MIBK production are carried out in the liquid phase in trickle-bed reactors at pressures as high as 10 MPa. 

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