Liquid-phase Hydrogenations

with coal utilization in mind, the hydrogenation of coal can be generally divided into two categories (1) the liquid-phase hydrogenation of coal and (2) the vapor-phase hydrogenation of coal. 

The liquid-phase hydrogenation of coal has been a topic of interest since the early 1900s (for example, see Bergius, 1912, 1913, 1925), leading to one of the first commercial developments for the production of liquid fuels from coal. Of late, research efforts have been directed toward cheaper sources of hydrogen, better catalysts, less severe operating conditions, and simpleroperating procedures. There has even been some emphasis on the elimination of the carrier liquid and more facile separation of the products (Chapters 18 and 19). 

The liqnid-phase hydrogenation of coal can occnr at 370°C-540°C (700°F-1000°F) and at pressures of 1500-7500 psi. The catalyst composition can also vary (Table 12.2) and the liquid vehicle may be a coal tar fraction or other coal product—the product type and the product distribution depend largely on the operating conditions bnt yields (conversion) of the order of 70%-95% have been reported. 

An increase in the process temperature usually leads to an increase in the yield of naphtha and gases and may even rednce the yield of middle distillates but only rarely appears to reduce the yield of the heavier products. The residence (or reaction) time may be of the order of 2 h and an increase in the residence time will not only increase the yield of gas, naphtha, and middle distillate but also serve to decrease the yield of the heavier oils. An increase in the pressure of the hydrogen (say, from 1200 to 1800 psi) can markedly affect the overall conversion and may even (under certain prime conditions) double the conversion yield there may, however, be other factors, such as the product distribution, which make the increased conversion unfavorable and, therefore, not a true benefit to the process. 

Kinetic studies using tetrahydronaphthalene (tetralin) as the hydrogen donor have shown that sufficient hydrogen is available for liquefaction of coal when the proportions of vehicle coal are of the order of 2 1 and that the conversion is quite rapid at temperatures on the order of 400°C (750°F). Thus, under these particnlar conditions (Fignres 12.6 and 12.7), coal becomes almost 100% solnble in pyridine within 10 min without any massive increase in hydrogen content of the product relative to the original coal. 

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Methods used in the reeyeling of plasties are deseribed, and details are given of a ehemieal reeyeling teehnique used by Veba Oel in its plant in Bottrop, Germany. This liquid phase hydrogenation proeess produees high quality synthetic oils, suitable for use as refinery feedstoeks, from mixtures of vaeuum distillation residues, serap plasties and other industrial wastes. 

Benchmarking to pure liquid-phase hydrogenation - use of hydrogen donors... 

Eodisch, R., Honicke, D., Xu, Y., Platzer, B., Liquid phase hydrogenation of p-nitrotoluene in microchannel reactors, in Matlosz, M., Ehrfeld, W., Baselt,... 

An example for a non-structure-sensitive reaction is provided by Davis et al. [102], who investigated the liquid-phase hydrogenation of glucose over carbon and silica based ruthenium catalysts with particle sizes between 1.1 and 2.4 run. Depending on catalyst loading which was between 0.56 wt.% and 5 wt.%, dispersion decreased from 91% to 43%. At the same time, TOFs varied only insignificantly in a range between 0.21 1/s and 0.32 1/s. 

The synthesis of Pd/ACF (0.42wt.% Pd) catalyst with monodispersed nanoparticles carried out at cuo = 3 is illustrated, as well as its catalytic performance in a liquid-phase hydrogenation of 1-hexyne in comparison with a traditional powdered Lindlar catalyst. 

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). 

T. Nomura, K. Murayama, and M. Matsushita, Sample Test Results of All Liquid Phase Hydrogen Attack, Japan Energy Corporation, presented to the API Task Group on Hydrogen Deterioration of Steels, May 1994. 

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. 

Figure 2 A typical concentration versus time profile for the liquid phase hydrogenation of MO [T=100°C, PH=6.2 MPa ro=300 RPM, W=lg 0.52 wt% Pd/Al203].

Expressions for 9 SM and H2 can be derived and related to rate (k) and equilibrium constants (K). The SI and S2 site balances are 9SM +9a + S, = 1 and //2 + S2 = 1 respectively 9sx, S2 are empty sites). Based on Henry s law, the gas-phase hydrogen pressure and the liquid-phase hydrogen concentration may be used interchangeably. The rate expression can be written as follows ... 

The object of the present study was to use in the above mentioned hydrogenations improved carbon supported catalysts, which could compete with the Pd black catalyst. Carbon materials are common supports, their surface properties can be modified easily and it is possible to prepare carbons with different proportion of micro-, meso- and macropores, which can be key factors influencing their performances. A highly mesoporous carbon was synthesised and used as support of Pd catalysts in the enantioselective hydrogenations. To our knowledge this is the first report on the use of highly mesoporous carbon for the preparation of Pd catalysts for liquid-phase hydrogenation. 

The ratio of double bond isomerization and addition occurring during the liquid-phase hydrogenation of both (+)- and (-)-apopinene has been mea-... 

Yet another way to detect mass transport problems is with a newly developed poisoning technique.24,26,49,50 This technique works for liquid-phase hydrogenations and possibly for other reactions that are poisoned by CS2. It takes advantage of the fact that CS2 poisons Pd and Pt linearly until all reaction stops. If mass transfer problems exist, the initial linear decrease in rate occurs at a slope less steep than the slope of the chemically controlled rate (Fig. 1.7). If no mass transport problems exist, the rate decreases linearly from the start with no change in slope. Therefore a plot of rate versus amount of CS2 reveals the existence or absence of mass transport problems 49... 

The solvent is very important for the hydrogenation of ketones. One of the most important factors in the liquid-phase hydrogenation of ketones is whether the medium is acidic, neutral, or basic, and a great deal of work has gone into attempting to understand chemoselectivity and stereoselectivity based on combinations of the metal catalyst and the reaction medium. 

Price and Schiewetz Ind Eng. Chem. 49 (807), 1957] have studied the catalytic liquid phase hydrogenation of cyclohexene in a laboratory scale semibatch reactor. A supported platinum catalyst was suspended in a cyclohexene solution of the reactant by mechanical... 

Coalcon A coal gasification process using a fluidized bed operated with hydrogen. Developed by Union Carbide Corporation and the Chemical Construction Company, based on work on liquid-phase hydrogenation completed by Union Carbide in the 1950s. A 20-ton per day pilot plant was operated in the 1960s, but a planned larger demonstration plant was abandoned because of cost. 

The liquid-phase hydrogenation of various terminal and internal alkynes under mild conditions was largely described with metal nanoparticles deposited/in-corporated in inorganic materials [83, 84], although several examples of selective reduction achieved by stabilized palladium, platinum or rhodium colloids have been reported in the literature. 

Case 1 in Figure 45.2 refers to a case where the reaction between S and H2 is very slow. In that case, the rate of hydrogen consumed by the reaction (i.e., the rate of the reaction) is small compared to the maximum rate of mass transfer. Thus, mass transfer feeds the liquid phase easily with dissolved hydrogen. The liquid-phase hydrogen concentration is very close to that at equilibrium given by the Henry s law ... 

Furfural is obtained industrially (200000 t a-1) by dehydration of pentoses produced from hemicelluloses. Furfurylic alcohol is obtained by selective hydrogenation of the C=0 bond of furfural, avoiding the hydrogenation of the furan ring. Liquid phase hydrogenation at 80 °C in ethanol on Raney nickel modified by heteropolyacid salts resulted in a 98% yield of furfuryl alcohol [31]. 

From liquid-phase hydrogenation studies56, we can derive the enthalpy of formation of the perhydro-tris[l,2-a 3,4-c 5,6-e]pyrrolo-l,3,5-triazine and of perhydro-tris[l,2-a 3,4-c 5,6-e]pyrido-l,3,5-triazine (35 with n = 5 and 6, respectively). Correcting for medium effects in directly measured enthalpies of solution, hydrogenolysis reaction 43... 

The liquid-phase hydrogenation of dienes and polyenes is also an extensively studied topic. The behavior of metals in such reactions is similar to that in the gas-phase reactions, i.e., Pd is the most selective catalyst. 

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