Distillation heterogeneous reactions

The SRC-II process, shown in Figure 2, was developed in order to minimise the production of soHds from the SRC-I coal processing scheme. The principal variation of the SRC-II process relative to SRC-I was incorporation of a recycle loop for the heavy ends of the primary Hquefaction process. It was quickly realized that minerals which were concentrated in this recycle stream served as heterogeneous hydrogenation catalysts which aided in the distillate production reactions. In particular, pyrrhotites, non stoichiometric iron sulfides, produced by reduction of iron pyrite were identified as being... 

In a 2-1. three-necked round-bottomed flask, fitted with an efficient sealed stirrer and a reflux condenser capped by a drying tube, are placed the dried anisyl chloride (Notes 2 and 3), 73.6 g. (1.5 moles) of finely powdered sodium cyanide, 10 g. of sodium iodide, and 500 ml. of dry acetone (Note 4). The heterogeneous reaction mixture is heated under reflux with -sngorous stirring for 16-20 hours, then cooled and filtered with suction. The solid on the filter is washed with 200 ml. of acetone and discarded (Note 5). The combined filtrates are distilled to remove the acetone. The residual oil is taken up in 300 ml. of benzene and washed with three 100-ml. portions of hot water. The benzene solution is dried over anhydrous sodium sulfate for about 15 minutes, and the solvent is removed by distillation at the reduced pressure of the water aspirator (Note 6). The residual -methoxyphenyl-acetonitrile is purified by distillation under reduced pressure through an 8-in. Vigreux column b.p. 94—97°/0.3 mm. 1.5285-1.5291. The yield is 109-119 g., or 74-81% based on anisyl alcohol (Notes 7 and 8). 

Riesenfeld and Bohnholtzer and Riesenfeld and Schumacher used ozone concentrated by liquefaction and distillation. From their kinetic measurements they conclude that a reaction of the second order and one of the first order take place simultaneously at quite low pressures, 6-60 mm. Hg the first order reaction predominates. The velocity constants of the second order reaction are not influenced by the total pressure, while those of the first order reaction appear to be inversely proportional to the total pressure. The figures given show that the first order reaction at the lower pressures is considerably influenced by the surface, and is quite probably a heterogeneous reaction, though the authors themselves do not consider this to be definitely shown. The decomposition appears to be rather sensitive to catalysts such as dust particles. 

The mathematical model comprises a set of partial differential equations of convective diffusion and heat conduction as well as the Navier-Stokes equations written for each phase separately. For the description of reactive separation processes (e.g. reactive absorption, reactive distillation), the reaction terms are introduced either as source terms in the convective diffusion and heat conduction equations or in the boundary condition at the channel wall, depending on whether the reaction is homogeneous or heterogeneous. The solution yields local concentration and temperature fields, which are used for calculation of the concentration and temperature profiles along the column. 

The use of reactive distillation for reactions that rely on a solid catalyst was developed in the early 1970s [4], Heterogeneously catalyzed reactive distillation poses the additional problem of how to place the solid cata-... 

Reactive distillation (RD) is a key opportunity for improving the structure of a process [1, 2]. The combination of distillation and reaction is possible, of course, only if the conditions of both operations can be combined. This means that the reactions have to show data for reasonable conversions at pressure and temperature levels that are compatible with distillation conditions. The type of catalysis is also important. Homogeneous catalysis is possible in most cases but needs a separation step to recycle the catalyst. This can be avoided in heterogeneous catalysis, but here special constructions are necessary to fix the catalyst in the reaction zone. If everything harmonizes, considerable advantages arise for the production of methyl acetate via RD, for example, only one column is needed instead of nine and a reactor (Fig. 2.1). 

Fig. 2.17 Equipment suitable for combining reaction and distillation (heterogeneous catalysis)...

Baur R., Taylor R. and Krishna R. (2003). Bifurcation analysis for TAME synthesis in a reactive distillation column Comparison of pseudo-homogeneous and heterogeneous reaction kinetics models. 

Normally, aqueous solutions ( 50%) are sold. There are two synthetic routes for acetalization, a direct heterogeneous reaction of glucose with the alcohol (120 °C/2 x 10 Pa) or a two-step process in which a short-chain alcohol (e.g., butanol) is reacted first with either glucose (115 °C/no pressure) or starch (140 °C/4 x 10 Pa under depolymerization). The resulting glucoside is further reacted (120 °C/2 X 10 Pa) in homogeneous phase with the fatty alcohol. The reduced pressure enhances the removal of water. In both routes, acid catalysis is used. The excess alcohol is separated by - distillation. 

Benzoylpropionitrile. To a mixture of 21 4 g. of p dimethylamino propiophenone hydrochloride, 13 0 g. of potassium cyanide in a 500 ml. flask, add 260 ml. of boiling water heat the heterogeneous mixture under reflux for 30 minutes. Part of the dimethylamine, which is eliminated in the reaction, distils collect this in dilute hydrochloric acid. Cool the reaction mixture in ice the oil sohdifies and crystals form from the aqueous layer. Collect the solid (crude p benzoylpropiouitrile, 10-5 g.) by suction filtration and recrystallise it from benzene - light petroleum (b.p. 40-60°) it separates as almost colourless blades, m.p. 76°. 

Esterification. Extensive commercial use is made of primary amyl acetate, a mixture of 1-pentyl acetate [28-63-7] and 2-metliylbutyl acetate [53496-15-4]. Esterifications with acetic acid are generally conducted in the Hquid phase in the presence of a strong acid catalyst such as sulfuric acid (34). Increased reaction rates are reported when esterifications are carried out in the presence of heteropoly acids supported on macroreticular cation-exchange resins (35) and 2eohte (36) catalysts in a heterogeneous process. Judging from the many patents issued in recent years, there appears to be considerable effort underway to find an appropriate soHd catalyst for a reactive distillation esterification process to avoid the product removal difficulties of the conventional process. 

The principal commercial source of 1-butanol is -butyraldehyde [123-72-8] obtained from the Oxo reaction of propylene. A mixture of n- and isobutyraldehyde [78-84-2] is obtained in this process this mixture is either separated initially and the individual aldehyde isomers hydrogenated, or the mixture of isomeric aldehydes is hydrogenated direcdy and the n- and isobutyl alcohol product mix separated by distillation. Typically, the hydrogenation is carried out in the vapor phase over a heterogeneous catalyst. For example, passing a mixture of n- and isobutyraldehyde with 60 40 H2 N2 over a CuO—ZnO—NiO catalyst at 25—196°C and 0.7 MPa proceeds in 99.95% efficiency to the corresponding alcohols at 98.6% conversion (7,8) (see Butyraldehydes Oxo process). 

Heterogeneous catalytic systems offer the advantage that separation of the products from the catalyst is usually not a problem. The reacting fluid passes through a catalyst-filled reactor m the steady state, and the reaction products can be separated by standard methods. A recent innovation called catalytic distillation combines both the catalytic reaction and the separation process in the same vessel. This combination decreases the number of unit operations involved in a chemical process and has been used to make gasoline additives such as MTBE (methyl tertiai-y butyl ether). 

A low-pressure process has been developed by ICl operating at about 50 atm (700 psi) using a new active copper-based catalyst at 240°C. The synthesis reaction occurs over a bed of heterogeneous catalyst arranged in either sequential adiabatic beds or placed within heat transfer tubes. The reaction is limited by equilibrium, and methanol concentration at the converter s exit rarely exceeds 7%. The converter effluent is cooled to 40°C to condense product methanol, and the unreacted gases are recycled. Crude methanol from the separator contains water and low levels of by-products, which are removed using a two-column distillation system. Figure 5-5 shows the ICl methanol synthesis process. 

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