Propylene catalytic selectivity

Other industrial processes that have taken advantage of the process intensification deriving from the introduction of reactive (catalytic) distillation are (i) production of high purity isobutene, for aromatic alkylation (ii) production of isopropyl alcohol by hydration of propylene (iii) selective production of ethylene glycol, which involves a great number of competitive reactions and (iv) selective desulfurization of fluid catalytic cracker gasoline fractions as well as various selective hydrogenations. Extraction distillation is also used for the production of anhydrous ethanol. 

Table 26.2. Catalytic activity results in the absence or presence of 300 ppm of N2O, on NiM04. X = conversion of propane Y = yield in propylene S = selectivity in propylene. Temperature 723 K. (In parentheses, changes, in %, when compared to test in absence of N2O (test TR). Adapted from Ref. 30.

Schmidt and coworkers [551] have reported the effect of organoaluminum compounds on the catalytic properties of complex catalysts used in the oligomerization of propylene. The selectivity for the process depends strongly on temperature, pressure, and contact time. In a continuous process of oligomerization of propylene at 200 atm with AlEts activation it is observed that the yield of oligomers increases with temperature [552]. Studies on the oligomerization kinetics [553,5541 have shown that the reaction order with respect to propylene is close to unity. Activation energies of 11.7 and 14 kcal mol have been reported [553,554]. 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

This conceptual link extends to surfaces that are not so obviously similar in stmcture to molecular species. For example, the early Ziegler catalysts for polymerization of propylene were a-TiCl. Today, supported Ti complexes are used instead (26,57). These catalysts are selective for stereospecific polymerization, giving high yields of isotactic polypropylene from propylene. The catalytic sites are beheved to be located at the edges of TiCl crystals. The surface stmctures have been inferred to incorporate anion vacancies that is, sites where CL ions are not present and where TL" ions are exposed (66). These cations exist in octahedral surroundings, The polymerization has been explained by a mechanism whereby the growing polymer chain and an adsorbed propylene bonded cis to it on the surface undergo an insertion reaction (67). In this respect, there is no essential difference between the explanation of the surface catalyzed polymerization and that catalyzed in solution. 

Significant quantities of Cj and C, acetylenes are produced in cracking. They can be converted to olefins and paraffins. For the production of high purity ethylene and propylene, the contained Cj and C3 acetylenes and dienes are catalytically hydrogenated leaving only parts per million of acetylenes in the products. Careful operation is required to selectively hydrogenate the small concentrations of acetylenes only, and not downgrade too much of the wanted olefin products to saturates. 

Selectivity depends importantly on the catalytic metal. A number of selectivity series have been determined for simple olefins, and the presumption is that the sequence holds for more complex polyenes as well. Selectivity for the reduction of allene to propylene declined with metal in the order palladium... 

Deep catalytic cracking (DCC) is a catalytic cracking process which selectively cracks a wide variety of feedstocks into light olefins. The reactor and the regenerator systems are similar to FCC. However, innovation in the catalyst development, severity, and process variable selection enables DCC to produce more olefins than FCC. In this mode of operation, propylene plus ethylene yields could reach over 25%. In addition, a high yield of amylenes (C5 olefins) is possible. Figure 3-7 shows the DCC process and Table 3-10 compares olefins produced from DCC and FCC processes. ... 

Allyl alcohol is produced by the catalytic isomerization of propylene oxide at approximately 280°C. The reaction is catalyzed with lithium phosphate. A selectivity around 98% could be obtained at a propylene oxide conversion around 25% ... 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

In the case of selective oxidation catalysis, the use of spectroscopy has provided critical Information about surface and solid state mechanisms. As Is well known( ), some of the most effective catalysts for selective oxidation of olefins are those based on bismuth molybdates. The Industrial significance of these catalysts stems from their unique ability to oxidize propylene and ammonia to acrylonitrile at high selectivity. Several key features of the surface mechanism of this catalytic process have recently been descrlbed(3-A). However, an understanding of the solid state transformations which occur on the catalyst surface or within the catalyst bulk under reaction conditions can only be deduced Indirectly by traditional probe molecule approaches. Direct Insights Into catalyst dynamics require the use of techniques which can probe the solid directly, preferably under reaction conditions. We have, therefore, examined several catalytlcally Important surface and solid state processes of bismuth molybdate based catalysts using multiple spectroscopic techniques Including Raman and Infrared spectroscopies, x-ray and neutron diffraction, and photoelectron spectroscopy. 

The structure of the single phase bismuth-iron molybdate compound of composition Bl3FeMo20.2 related to the scheellte structure of Bi2Mo30-2( ). It is reported(, ) that the catalytic activity and selectivity of bismuth-iron molybdate for propylene oxidation and ammoxidatlon is not greater than that of bismuth molybdate. 

V-Sb-oxide based catalysts show interesting catal)dic properties in the direct synthesis of acrylonitrile from propane [1,2], a new alternative option to the commercial process starting from propylene. However, further improvement of the selectivity to acrylonitrile would strengthen interest in the process. Optimization of the behavior of Sb-V-oxide catalysts requires a thorough analysis of the relationship between structural/surface characteristics and catalytic properties. Various studies have been reported on the analysis of this relationship [3-8] and on the reaction kinetics [9,10], but little attention has been given to the study of the surface reactivity of V-Sb-oxide in the transformation of possible intermediates and on the identification of the sxirface mechanism of reaction. 

Figure 26 shows that trimethylamine (TMA), a strong Lewis base with a pAia value of 9.9, introduced to the reactant gas stream at a concentration of 10-20 ppm, appreciably improves the catalytic performances in every aspect of catalytic performance, propylene conversion, PO selectivity, H2 utilization efficiency, and catalyst life [88]. It is worth noting that TMA makes used catalysts... 

Figures 1 shows the catalytic performance of the Fe-BEA catalysts in the temperature range of 250-550 °C. It is clear from the figure that propylene yield depends on particle size of the parent BEA zeolite. Effect of the N20 concentration has been analyzed under reaction regimes RS-1 and RS-2. Increase in N20 concentration resulted in the same propene yields but increased the N20 conversion and decreased the selectivity toward propylene. At higher temperature has been obtained increases in the formation of the molecular oxygen which further accelerates production of the undesired carbon oxides. Thus, at lower feed concentration of N20, i.e. at 1 1 feed ratio of reactants (RS-1), formation of carbon oxides is suppressed and the selectivity of ODHP reaction is...

---