Propylene conversions

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha Hquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the world market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthaUc acid and propylene conversion to acryflc acid, has also grown. Production from synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

The Reaction. Acrolein has been produced commercially since 1938. The first commercial processes were based on the vapor-phase condensation of acetaldehyde and formaldehyde (1). In the 1940s a series of catalyst developments based on cuprous oxide and cupric selenites led to a vapor-phase propylene oxidation route to acrolein (7,8). In 1959 Shell was the first to commercialize this propylene oxidation to acrolein process. These early propylene oxidation catalysts were capable of only low per pass propylene conversions (ca 15%) and therefore required significant recycle of unreacted propylene (9—11). 

In 1957 Standard Oil of Ohio (Sohio) discovered bismuth molybdate catalysts capable of producing high yields of acrolein at high propylene conversions (>90%) and at low pressures (12). Over the next 30 years much industrial and academic research and development was devoted to improving these catalysts, which are used in the production processes for acrolein, acryUc acid, and acrylonitrile. AH commercial acrolein manufacturing processes known today are based on propylene oxidation and use bismuth molybdate based catalysts. 

Today the most efficient catalysts are complex mixed metal oxides that consist of Bi, Mo, Fe, Ni, and/or Co, K, and either P, B, W, or Sb. Many additional combinations of metals have been patented, along with specific catalyst preparation methods. Most catalysts used commercially today are extmded neat metal oxides as opposed to supported impregnated metal oxides. Propylene conversions are generally better than 93%. Acrolein selectivities of 80 to 90% are typical. 

Rhodium Ca.ta.lysts. Rhodium carbonyl catalysts for olefin hydroformylation are more active than cobalt carbonyls and can be appHed at lower temperatures and pressures (14). Rhodium hydrocarbonyl [75506-18-2] HRh(CO)4, results in lower -butyraldehyde [123-72-8] to isobutyraldehyde [78-84-2] ratios from propylene [115-07-17, C H, than does cobalt hydrocarbonyl, ie, 50/50 vs 80/20. Ligand-modified rhodium catalysts, HRh(CO)2L2 or HRh(CO)L2, afford /iso-ratios as high as 92/8 the ligand is generally a tertiary phosphine. The rhodium catalyst process was developed joindy by Union Carbide Chemicals, Johnson-Matthey, and Davy Powergas and has been Hcensed to several companies. It is particulady suited to propylene conversion to -butyraldehyde for 2-ethylhexanol production in that by-product isobutyraldehyde is minimized. 

A Hquid-phase variation of the direct hydration was developed by Tokuyama Soda (78). The disadvantages of the gas-phase processes are largely avoided by employing a weakly acidic aqueous catalyst solution of a siHcotungstate (82). Preheated propylene, water, and recycled aqueous catalyst solution are pressurized and fed into a reaction chamber where they react in the Hquid state at 270°C and 20.3 MPa (200 atm) and form aqueous isopropyl alcohol. Propylene conversions of 60—70% per pass are obtained, and selectivity to isopropyl alcohol is 98—99 mol % of converted propylene. The catalyst is recycled and requites Htde replenishment compared to other processes. Corrosion and environmental problems are also minimized because the catalyst is a weak acid and because the system is completely closed. On account of the low gas recycle ratio, regular commercial propylene of 95% purity can be used as feedstock. 

Both fixed and fluid-bed reactors are used to produce acrylonitrile, but most modern processes use fluid-bed systems. The Montedison-UOP process (Figure 8-2) uses a highly active catalyst that gives 95.6% propylene conversion and a selectivity above 80% for acrylonitrile. The catalysts used in ammoxidation are similar to those used in propylene oxidation to acrolein. Oxidation of propylene occurs readily at... 

In the liquid-phase process, high pressures in the range of 80-100 atmospheres are used. A sulfonated polystyrene cation exchange resin is the catalyst commonly used at about 150°C. An isopropanol yield of 93.5% can be realized at 75% propylene conversion. The only important byproduct is diisopropyl ether (about 5%). Figure 8-4 is a flow diagram of the propylene hydration process. ... 

Over An deposited on 3-D mesoporous Ti-Si02 with pore diameter of 9nm, one of the best results was obtained. At an SV of 4000 h/mL/g-cat., propylene conversion above 8%, PO selectivity of 91% giving a steady STY of 80 g PO/h/kg-cat. [84]. The surfaces of 3-D mesoporous Ti-Si02 were trimethylsilylated for rendering hydro-phobicity, which enables higher temperature operation of reaction [86]. As a solid phase promoter, alkaline or alkaline earth metal chlorides are efficient, however, chloride anions markedly enhance the coagulation of An particles in a short period [87]. Finally, Ba(N03)2 was selected as the best promoter which might kill the steady acid sites as BaO (after calcination) on the catalyst surfaces [84,88]. 

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... 

Degussa-Huels AG, P25) could also produce PO in the gas phase composed of propylene, O2, H2, and N2 with selectivity above 90% at propylene conversion of 0.36% [93]. Soon after Guo reported that Ag deposited on TS-1 exhibited better performances (propylene conversion 1.4%, PO selectivity 93.5%), while he claimed that silver supported on Ti02 was not active for PO synthesis [94 96]. 

The catalysts which have been tested for the direct epoxidation include (i) supported metal catalysts, (ii) supported metal oxide catalysts (iii) lithium nitrate salt, and (iv) metal complexes (1-5). Rh/Al203 has been identified to be one of the most active supported metal catalysts for epoxidation (2). Although epoxidation over supported metal catalysts provides a desirable and simple approach for PO synthesis, PO selectivity generally decreases with propylene conversion and yield is generally below 50%. Further improvement of supported metal catalysts for propylene epoxidation relies not only on catalyst screening but also fundamental understanding of the epoxidation mechanism. 

The MS analysis shows that the C02 profile led that of the PO profile (results not shown). The step switch results further confirm that C02 formation is faster than PO formation and that both reactions take place in parallel. GC analysis of the steady state effluent stream from the reactor revealed that propylene conversion was 10.5% at 250 °C product formation rates were determined to be 1.33, 0.12, and 34.3 pmol/min, respectively, for acetone, PO,... 

In summary, the total oxidation of propylene to C02 occurred at a higher rate than partial oxidation to propylene oxide and acetone total and partial oxidations occurred in parallel pathways. The existence of the parallel reaction pathways over Rh/Al203 suggest that the selective poisoning of total oxidation sites could be a promising approach to obtain high selectivity toward PO under high propylene conversion. 

Figure 3-a shows the propylene conversion obtained on ITQ-21 and beta zeolites at space velocity of 18 h"1 and different temperatures. It can be seen that both zeolites, ITQ-21 and BETA, are initially highly active, but whereas ITQ-21 maintains full propylene conversion along the 8 hours of reaction at 125°C, zeolite BETA is completely deactivated at TOS=100 min. Increasing contact time (WHSV=12 h 1) results in a slight improvement for BETA (Figure 3-b), as conversion at 50 min TOS is in this case above 90%, but results are still far from those obtained with ITQ-21. 

Figure 3. Propylene conversion at 3.5 MPa, B/P=3.5 and (a) WHSV=18 h 1 (b) WHSV=12 h 1. Catalyst and temperature are given in the legends.

However, (Ph3P)2Rh(CO)Cl on alumina or activated carbon were effective hydroformylation catalysts under more severe conditions 108). At 148°C and a pressure of 49 atm (CO 37.5 mol%, H2 37.5, propylene 25), good activity was found. The propylene conversion was 30% at a contact time of 0.92 cm3 of reactor void space/cm3 of feed per minute. Isomer ratios of 1.3 to 1.9 1 n iso were realized. By-product formation was low, with <1% conversion to alcohols plus alkanes and 2.2% high-boiling materials. This system was stable for a 300 hour operating time, with no detectable loss of activity or selectivity. 

A 50-50 mixture of propylene and propane is charged at 100 lbmol/hr at 300 F and 365 psia. Propylene conversion of 80% is required. A 25 75 mixture of C6 and C9 is made. Find the volume of catalyst needed at constant temperature. 

Figure 16. Propylene conversion and product-selectivity results for the membrane-reactor measurements performed at 723 K with pure propylene as the feed. The results in panel a were for the SOFC with a Cu—ceria—YSZ anode, and the results in panel b were for the Cu-molybdena-YSZ anode. In panel a, the points are the rate of CO2 production, and the line was calculated from the current density and eq 8. In panel b, the points show the production of acrolein, and the line was calculated from eq 9. (Reprinted with permission from ref 165. Copyright 2002 Elsevier.)...

Figure 34 shows the NO and propylene conversions as fimctions of temperature in the case of Cu-Al-MCM-41-10-61 (Si/Al = 10 Cu exehange 61%). The maximum conversions observed for the formation of N2 and of NO2 are around 370 and 450 °C, respectively. The latter product appears only at temperatures higher than 370 °C. Propylene is essentially oxidized to carbon dioxide and water. 

Figure 34. Effect of temperature on NO conversion to N2 ( ), NO conversion to NO2 ( ) and propylene conversion (A) over Cu-Al-MCM-41-10-61 catalyst (reaction conditions GHSV = 100,000 h, ...

The organoactinide surface complexes exhibited catalytic activities comparable to Pt supported on sihca [at 100% propylene conversion at —63°C, >0.47s (U) and >0.40 s (Th)], despite there being only a few active sites (circa 4% for Th, as determined by CO poisoning experiments and NMR spectroscopy) [92]. Cationic organoactinide surface complexes [Cp An(CH3 ) ] were proposed as catalytic sites. This hypothesis could be corroborated by the use of alkoxo/hydrido instead of alkyl/hydrido surface ligands, which led to a marked decrease of the catalytic activity, owing to the oxophilic nature of the early actinides [203, 204]. Thermal activation of the immobihzed complexes, support effects, different metal/ligand environments and different olefins were also studied. The initial rate of propylene conversion was increased two-fold when the activation temperature of the surface complexes under H2 was raised from 0 to 150°C (for Th 0.58 0.92 s" ). 

In the absence of steam in the feed gas, Cu +Y has a high activity for deep oxidation of propylene to CO2 and H2O [12,14]. At low propylene/02 ratios, formaldehyde is formed with less than 10% selectivity. Selective oxidation of propylene is only possible at high propylene/02 ratios and low propylene conversions, acrolein being the main product formed [14]. 

At low steam/propylene ratios, acrolein is formed with 20-25% selectivity at propylene conversions of about 20% [13]. It is believed that the presence of steam suppresses deep oxidation of propylene and therefore allows higher... 

Some of the results obtained by Ben-Taarit et al. for propylene oxidation on Cu2+Y are similar to those reported by Mochida et al. when an excess of propylene is used in the feed [2]. The former authors stress that under these circumstances Cu+2 in Cu +Y is transformed to a Cu°/Cu20/Cu0 mixture. However, using optimized 02/propylene ratios, flow rates and temperatures, it seems that 70% selectivity for acrolein at 50% propylene conversion is achievable. Under those conditions there was no evidence for the formation of either a metallic or an oxide copper phase [2]. 

Fripiat et al. studied the oxidation of propylene dissolved in benzene at 150°C under a total pressure of 45 atm [20]. On Mo-X, 70% epoxide selectivity is obtained at propylene conversions of 7.5%. Side products are formed by further oxidation of the epoxide, by C-C cleavage in the olefin with formation of methanol, formic and acetic acid, and by fast esterification of the epoxide with these acids. 

Figure 2. Comparison of the catalytic behavior of VSil samples in propane oxidative dehydrogenation to propylene. Conversion of propane and selectivity to propylene at 470 C. Exp. conditions as in Fig. 1.

Lewis and protic acids, usually AICI3 and H2SO4, are used in the liquid phase at temperatures of 40-70°C and at pressures of 5-15 atm. Phosphoric acid on kieselguhr promoted with BF3 (UOP process)309 319 is used in gas-phase alkylation (175-225°C, 30-40 atm). In addition to the large excess of benzene, propane as diluent is also used to ensure high (better than 94%) propylene conversion. This solid phosphoric acid technology accounts for 80-90% of the world s cumene production. 

In the C4 coproduct route isobutane is oxidized with oxygen at 130-160°C and under pressure to tert-BuOOH, which is then used in epoxidation. In the styrene coproduct process ethylbenzene hydroperoxide is produced at 100-130°C and at lower pressure (a few atmospheres) and is then applied in isobutane oxidation. Epoxidations are carried out in high excess of propylene at about 100°C under high pressure (20-70 atm) in the presence of molybdenum naphthenate catalyst. About 95% epoxide selectivity can be achieved at near complete hydroperoxide and 10-15% propylene conversions. Shell developed an alternative, heterogeneous catalytic system (T1O2 on SiOi), which is employed in a styrene coproduct process.913 914... 

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