Propylene conversion over

Various polar and chemical compounds reportedly are capable of poisoning or deactivating disproportionation catalysts if present in the feed or allowed to contact the catalyst after activation. For example, propylene conversion over cobalt-molybdate catalyst was reduced when 300—2000 ppm of oxygen, water, carbon dioxide, hydrogen sulfide, ethyl sulfide, acetylene, or propadiene... 

The following reactor performance in recycle is the aim over 99.9% per/pass propylene conversion over 88% cumene selectivity, adiabatic temperature rise below 70 °C, but a maximum catalyst temperature of 250 °C. The inlet pressure should be sufficiently high to ensure only one liquid phase. Thermodynamic calculations at 35 bar indicate bubble temperatures of 198 and 213 °C for propylene/ benzene ratios of 1/4 and 1/7, respectively (Figure 6.5). The reactive mixture can be maintained as liquid up to about 250 °C, since the concentration of propylene diminishes gradually by reaction. 

In a first attempt, we simulate the reactor as an adiabatic PFR. We consider a diameter of 1.3 m and a total length of 7 m, which ensure propylene conversion over 99.9%. The feed consists of lOOkmol/h propylene at molar benzene/... 

Propylene conversion over three SAPO molecular sieves (SAPO-5, SAPO-11, and SAPO-34) was conducted at a variety of operating conditions. Catalyst behavior was correlated with the physical and chemical properties of the SAPO molecular sieves. The objective of this work was to determine the relative importance of kinetic and thermodynamic factors on the conversion of propylene and the distribution of products. The rate of olefin cracldng compared to the rate of olefin polymerization will be addressed to account for the observed trends in the product yields. The processes responsible for deactivation will also be addressed. 

THOMSON ETAL. Propylene Conversion over SAPO Moiecidar Sieves... 

Activity Studies. Propylene conversion over the specified catalysts was performed in a 9 mm o.d. quartz tubular reactor. The amount of catalyst charged into the reactor was 0.1 gram of SAPO-5, while only 0.05 gram of SAPO-11 and SAPO-34 was used to ensure constant contact time. The catalyst powders in the form of fine... 

Table n. Chromatographic Analysis of Major Hexene Products From Propylene Conversion Over SAPO Catalysts (Propylene Inlet Pressure= 16.2 KPa)... 

Figure 19 Propylene conversion over the poisoned catalyst. Curve 2 shows calculated conversion, curve 3 shows calculated conversion after adjusting the diffusion coefficient in zone 4 ...

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. 

Certain bacterial strains convert propylene glycol to pymvic acid in the presence of thiamine (15) other strains do the conversion without thiamine (16). Propylene oxide is the principal product of the reaction of propylene glycol over a cesium impregnated siHca gel at 360°C in the presence of methyl ethyl ketone and xylene (17). 

Conversions of ca 75% are obtained for propylene hydration over cation-exchange resins in a trickle-bed reactor (102). Excess Hquid water and gaseous propylene are fed concurrentiy into a downflow, fixed-bed reactor at 400 K and 3.0—10.0 MPa (30—100 atm). Selectivity to isopropanol is ca 92%, and the product alcohol is recovered by azeotropic distillation with benzene. 

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]. 

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. 

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. 

As part of the same study selectivity data were provided at 10-100 kPa partial pressures of n-butane at 0-17% conversion over HZSM-5 [90]. With increase in pressure and conversion secondary reactions started to occur. These results are also summarized in Table 13.6. The lowered selectivity to hydrogen, methane and ethane was attributed to increasingly less favorable conditions for monomolecular cracking. The dramatic increase in selectivity to propane which was absent at zero conversion, along with decrease in propylene was considered as signature for bimolecular cracking. More specifically, it was suggested that hydride transfer... 

Results for the cell with a Cu—molybdena—YSZ anode, shown in Figure 16b, were very different. Unlike ceria, which is a nonselective oxidation catalyst, molybdena is a selective catalyst for the partial oxidation of propylene to acrolein (CH2=CHCHO) and is used commercially for this process. The primary product at low conversion over the Cu— molybdena—YSZ electrode was acrolein, produced according to the reaction... 

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, ...

Further evidence supporting the bismuth center as a site of propylene activation comes from the analysis of the rates of formation and product distribution of propylene oxidation over bismuth oxide, bismuth molybdate, and molybdenum oxide. Bismuth molybdate is highly active and selective for the conversion of propylene to acrolein. However, the interaction of propylene with its component oxides yields very different results. Haber and Grzybowska (//. ), Swift et al. 114), and Solymosi and Bozso 115) showed that in the absence of oxygen, propylene is converted to 1,5-hexadiene over bismuth oxide with good selectivity and at a high rate, whereas molybdenum oxide is known to be a fairly selective but a nonactive catalyst for acrolein formation. The formation of 1,5-hexadiene over bismuth oxide can be explained if the adsorption of propylene on a bismuth site yields a ir-allylic species. Two of these allylic intermediates can then combine to give 1,5-hexadiene. 

The model describes, within the limits of measuring error, the experimental temperature and concentration profiles quite well over a wide temperature range (more than 100 C) and propylene conversion range (Table I), (Figures 2 - 4). But the reaction orders for propylene and oxygen have only a limited reliability since especially the oxygen concentration along the reactor varied only within narrow limits. Additionally, pressure and flow rate were, for the most part, held constant (Table I). 

---