Slurry reactions, catalytic

Figure 12 clearly shows the effect of iron sulfide content of the coal on total conversion and liquid product yield during hydrogenation. The conversion increased from about 52 per cent to 70 per cent using the hot-rod reactor with no added catalyst. The yield of toluene soluble product (oil plus asphaltene) increased from about 30 to 44 per cent with total sulfur increase from 1 to 6.5 per cent. Thus it would appear that iron sulfide can act catalytically in the dry hydrogenation reaction as well as in slurried reactions (15). 

Figure 6. Concentration profiles for mass transfer into a slurry with catalytic particles, with no enhancement at the gas-liquid interface (above) mass transfer and reaction at the interface (below) mass transfer and reaction in the porous particles.

The considerable differences in exponents for Npe and Nsc show that additional work is necessary to arrive at a broadly applicable relationship for k a as a function of system properties and operating parameters in stirred tanks. For recent system-specific studies on industrially important catalytic slurry reaction see Table 5. 

The above described reactor is useful for the measurements of heat of reaction as well as thermal behavior of gas-liquid or gas- liquid-solid, high-pressure, high-temperature reactions. Since the reactor can be operated under adiabatic conditions, it simulates the commercial operation. The reactor was successfully utilized by Bhattacharjee et al. (1986) for investigating thermal behavior of slurry phase, catalytic synthesis gas conversion. 

Pre-activation of the catalyst, heat-up, pressurization, and a period of thermal reaction are accomplished after the reactor is sealed, but before there is contact between catalyst and slurry. The catalytic period starts when the basket is dropped into the liquid and stops when the heater is removed from the autoclave. 

Bubble columns are convenient for catalytic slurry reactions also (67). It is therefore important to know how the hydrodynamic properties of the gas-in-liquid dispersion is influenced by the presence of suspended solid particles. In the slurry reactor absorption enhancement due to chemical reaction cannot be expected. However, if particle sizes are very small, say less than 5 yum, and if, in addition, the catalytic reaction rate is high a small absorption enhancement can occur ( 8). Usually the reaction is in the slow reaction regime of mass transfer theory. Hence, it is sufficient to know the volumetric mass transfer coefficient, kj a, and there is no need to separate k a into the individual values. 

The preparation and use of active catalysts coated on a structure packing was further studied as an attractive replacement for conventional catalysfs in randomly packed beds or slurry reactions. A method was developed in which catalytically active and selective BEA coatings could be prepared onto ceramic monoliths constituted either of pure silica or cordierite (Figure 4.7a) and mefallic wire gauze packings (Figure 4.7b). ... 

One of the earliest LHHW models to be developed for a slurry reaction was for the hydrogenation of glucose to sorbitol, considered in Example 17.1. Models for several other three-phase catalytic reactions have since been developed, many of which are listed in Table 17.3. 

The gas-liquid-sohd reactions are carried out in various types of reactors, such as packed beds, fluidized/slurry, and catalytic wall reactors (Figure 8.1). The advantages and limitations of these reactors are described in Table 8.1. Compared to fluid-sohd systems, an additional phase makes it difficult to predict flow patterns... 

Finally,in contrast to slurries containing soluble or catalytic fine particles(see 2.2.2 and 3.2),no consideration so far has been devoted to slurry reactions involving fine insoluble solid reactant.Indeed,in this case too,we may conceive situations.where the insoluble solid reactant size may be smaller than the liquid film next to the gas-liquid interface.We may then have steps in parallel and the gas absorption rate may well be enhanced by a sufficiently fast heterogeneous reaction. 

Figure 7.Concentration profile of dissolved gas A for catalytic slurry reaction(Catalyst particles are bigger than film thickness).

Stabilizers and pigments are normally slurried with macroglycol and added to the polymeric glycol charge, prior to diisocyanate addition. Therefore, care must be taken to avoid additives that react significantly with diisocyanates or diamines under processing conditions. Also, stabilizers should be chosen that have no adverse catalytic effect on the prepolymer or chain-extension reactions. 

Research on catalytic coal Hquefaction was also carried out using an emulsified molybdenum catalyst added to the slurry medium to enhance rates of coal conversion to distiUate (26). Reaction at 460°C, 13.7 MPa (1980 psi) in the presence of the dispersed catalyst was sufficient to greatiy enhance conversion of a Pittsburgh No. 8 biturninous coal to hexane-soluble oils ... 

The most common heterogeneous catalytic reaction is hydrogenation. Most laboratory hydrogenations are done on liquid or solid substrates and usually in solution with a slurried catalyst. Therefore the most common batch reactor is a stirred vessel, usually a stirred autoclave (see Figure 2.1.1 for a typical example). In this system a gaseous compound, like hydrogen, must react at elevated pressure to accelerate the process. 

The production of alcohols by the catalytic hydrogenation of carboxylic acids in gas-liquid-particle operation has been described. The process may be based on fixed-bed or on slurry-bed operation. It may be used, for example, for the production of hexane-1,6-diol by the reduction of an aqueous solution of adipic acid, and for the production of a mixture of hexane-1,6-diol, pentane-1,5-diol, and butane-1,4-diol by the reduction of a reaction mixture resulting from cyclohexane oxidation (CIO). 

In a later publication, Kolbel et al. (K16) have proposed a less empirical model based on the assumption that the rate-determining steps for a slurry process are the catalytic reaction and the mass transfer across the gas-liquid interface. When used for the hydrogenation of carbon monoxide to methane, the process rate is expressed as moles carbon monoxide consumed per hour and per cubic meter of slurry ... 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Catalytic hydrogenation is typically carried out in slurry reactors, where finely dispersed catalyst particles (<100 (tm) are immersed in a dispersion of gas and liquid. It has, however, been demonstrated that continuous operation is possible, either by using trickle bed [24] or monoHth technologies [37]. Elevated pressures and temperatures are needed to have a high enough reaction rate. On the other hand, too high a temperature impairs the selectivity of the desired product, as has been demonstrated by Kuusisto et al. [23]. An overview of some feasible processes and catalysts is shown in Table 8.1. 

Equation (1) consists of various resistance terms. l/Kj a is the gas absorption resistance, while 1/ K,a corresponds to the maleic anhydride diffusion resistance and l/i k represents the chemical reaction resistance. The reaction rate data obtained under the reaction conditions of 250°C and 70 atm were plotted according to equation (1). Although catalytic reaction data with respect to time on stream were not shown here, a linear correlation between reaction rate data and catalyst loading was observed as shown in Fig. 2. The gas absorption resistance (1/ a) was -1.26 h, while the combined reaction-diffusion resistance (lJK,a + 1 T]k) was determined to be 5.57 h. The small negative value of gas absorption resistance indicates that the gas-liquid diffusion resistance was very small and had several orders of magnitude less than the chanical reaction resistance, as similarly observed for the isobutene hydration over Amberlyst-15 in a slurry reactor [6]. This indicates that absorption of malei c anhydride in solvent was a rapid process compared to the reaction rate on the catalyst surface. 

In continuation of a previous work (1), catalytic hydrogenation of cinnamaldehyde has been studied in slurry phase using a high-pressure autoclave. A series of carbon powder (CP)-supported Pt catalysts with widely varying Pt dispersion and Pt location on the support has been used in the study. The purpose has been to find out how the location of the metal on the support and its dispersion affect the two parallel reaction paths, namely the hydrogenation of the C=0 and C=C bonds. 

The activated nickel powder is easily prepared by stirring a 1 2.3 mixture of NiL and lithium metal under argon with a catalytic amount of naphthalene (1(7 mole % based on nickel halide) at room temperature for 12 h in DME. The resulting black slurry slowly settles after stirring is stopped and the solvent can be removed via cannula if desired. Washing with fresh DME will remove the naphthalene as well as most of the lithium salts. For most of the nickel chemistry described below, these substances did not affect the reactions and hence they were not removed. The activated nickel slurries were found to undergo oxidative addition with a wide variety of aryl, vinyl, and many alkyl carbon halogen bonds. 

---