Propene conversions

Group C are catalysts that had high activity but low C.F. s. The NO conversions reached the maximum values at much lower temperatures of 623-643 K. The propene conversion was 100% at this point, and COj was the only deteaable oxidation product. In addition, significant amounts of NjO were detect. For some catalysts (such as catalyst B-1 OB), NjO was observed under the conditions used in Table 1. For others (such as catalyst B-15), it was observed at higher space velocities (see Table 2). 

Figures I and 2 show the NO and propene conversions of these three groups of catalysts as a function of temperature. For comparison, the NO conversion of a 3.2 wt.% Cu-ZSM-5 (Si/Al=70) catalyst is also shown, which was obtained at twice the space velocity as the Au catalysts. It can be seen that the NO conversions on Au/Al Oj of high C.F. s were comparable to those on Cu-ZSM-5 under these conditions.

Under the conditions used in this study, the catalytic activities were stable for NO reduction for all catalysts. However, in NOj reduction, deactivation was observed. For catalyst 1-7, there was a rapid, reversible deactivation that was more noticeable at lower temperatures. The activity could be restored by removing propene from the feed. Therefore, it was likely due to carbonaceous deposits on the catalyst. In addition, there was slow deactivation. For example, afto the experiment in Table 2 and cleaning in a flow ofN0/O2/H20 (0. l%/4.7%/1.5%, balance He) at SOOT, the catalyst showed an NO conversion of 33% and propene conversion of 42% at 450°C, versus 53 and 99%, respectively, before deactivation. For catalyst 1-5, only slow deactivation was observed. 

Figure 13.34 Skeletal distribution of the dimer fraction obtained at increasing propene conversion with ZSM-22 (TON). Test conditions 200-240°C 6.8 piPa with 12% propylene in propane feed [73].

Figure 13.35 Skeletal distribution of trimer fractions at 30% propene conversion, obtained on collidine-treated ZSM-22 (TON), ZSM-23 (MTT), ZSM-22 (TON), ZSM-48...

Acrolein is needed industrially on a great scale, and to obtain it selectively from propene and O2 various different heterogeneous catalysts have been investigated. In 1957-1962 Standard Oil of Ohio (SOHIO) developed the Mo03/Bi203-catalyst system [1,2], that did not lead to a high propene conversion but yielded a fairly good selectivity. Furthermore, acrylonitrile can be obtained instead of acrolein if NH3 is added to the system (ammonoxidation of propene, Eq. 1). 

Fig. 3. Acrolein yield and propene conversion as a function of catalyst composition.

Activities, expressed as the temperature at which propene conversions of 2 and 8% m-2 catalyst surface are obtained... 

The best per pass yield to C2 + C3 products (aldehydes plus acids with two and three C atoms) with the said catalyst was obtained at a propene conversion of 61.3% (selectivity to acrolein 83.7%), at the reaction temperature of 355 °C, with the following feed composition C3H6/H20/N2 11.6 10.0 78.4 (mol.%), with a gas contact time of 2.4 s. A decrease in solids circulation rate, while keeping gas residence time constant, led to a considerable decrease in propene conversion, while selectivity to C2 + C3 oxygenated products was not much affected by circulation rate. With a less concentrated feed, the amount of solid to be circulated for a defined olefin conversion is lower, but productivity also becomes lower. Other catalysts based on Bi/Mo/O or on V/Mo/W/Cu/O [72c] afforded conversions >70% and selectivity >90% industrial... 

Kim and Inui[54] have reported the synthesis of MCM-41 with incorporation of various metal components such as Al, Ga or Fe with different Si/metal ratio. These catalysts were used for the oligomerization of propene, and it was found that the order of activity was Al-MCM-41 > Fe-MCM-41 > Ga-MCM-41 with the optimum Si/metal ratio being equal to 200. The propene conversion increases with the temperature from 423 up to 523 K. The catalytic activity of mesoporous silicates was lower than zeolitic catalysts, such as MFI metallosilicates. However,... 

Run No. T w T Bax Composition of Reactor Feed (Mole Fraction) Overall propene conversion (%)... 

Table 2 provides a comparison of the catalytic properties of the two oxides, M0O3 Y and (MoVW)5Oi4 (Dieterle, 2001 Mestl, 2002). M0O3 x was additionally preconditioned in 5 vol% H2/N2 at 450 °C to induce partial reduction. At identical propene conversions and space velocities, M0O3 Y produced much more C02 (Figure 14B) than partial oxidation products compared to (MoVW)5Oi4, which showed a high selectivity to partial oxidation products in accordance with the two-domains model (Petzodt et al., 2001). 

TABLE 2 Comparison of the Selectivity (%) of Oxygen-Deficient M0O3 x and (MoVW)5014 for a Propene Conversion of 20% (Dieterle, 2001 Mestl, 2002). 

In order to avoid these drawbacks and following RCH/RP s excellent experiences with liquid recycles, the gas recycle was replaced by the liquid recycle variant (Figure 14) which is used in most modem LPO plants. Combinations of gas and liquid recycle have also been described, claiming an increased propene conversion [203, 204]. 

The position of the double bond inside each structure depends on the catalyst composition. Formation of 2-methyl-2-pentene and 2,3-dimethyl-2-butene results from a consecutive isomerization reaction and thus depends not only on the catalyst composition but also on propene conversion. The relative reactivities of isomeric dimers for a double-bond shift are given in [6]. 

Nonaromatic HA is much more acidic if its conjugate base is aromatic (cf. cyclopentadiene with propene). Conversely, a substance is a very poor base if protonation results in loss of aromaticity (e.g., pyrrole). 

In contrast to the results obtained at higher conversions [11], the Initial coking rate during relative low propene conversion was about twenty times lower than during the... 

Yield of ethene (F ) Owing to the adsorption of both the reactants and the products, the yield of ethene, rather than propene conversion, is used ... 

Haruta and co-workers showed that silylation of the Au/Ti-MCM-48 catalysts prevents them from getting deactivated faster and also helps to improve PO selectivity and decrease H2 consumption [28,40,170,403]. Physical mixing of CsCl with Au supported on Ti-MCM-41 reduces H2 consumption by about 90% and improves propene oxide (PO) selectivity up to 97% at a propene conversion of 1.7% [205,403]. 

Microreaction technology allows for better temperature control, and a safer provision and handling of H P both within and outside the range of explosive mixtures with propene and PO. To minimize the decomposition of H P during the evaporation phase, a microstructured falling-film evaporator is used, placed below the mixing device and reaction zone. The reaction is carried out with an excess of propene, at temperatures below 160 °C and a pressure below 1.5 atm. Por a propene conversion of 5-20%, the selectivity for PO obtained is around 90%, but the selectivity with respect to HP is 25%. The catalyst is coated onto the reactor module, forming a layer several hundred micrometers thick. One problem encountered was the slow accumulation of deposits on the catalysts, which were derived from the formation of by-products. 

Besides hydrogen, other reductants for O2 in the liquid-phase epoxidation of propene include carbon monoxide, aldehydes, alcohols and other organic compounds. The reaction proceeds very efficiently with methanol as the reductant, in the presence of Pd and the Ti-Al-MCM-22 catalyst or Pd and peroxo-polyoxometalate catalysts the latter have been intercalated inside layered double hydroxides to make them heterogeneous [29e,h]. A propene conversion of 47%, with 91.5% selectivity for PO, was obtained at 80°C [29h]. 

This reaction has been studied in depth by ARGO Chem Tech, now Lyondell, which since 1996 has issued many patents on this subject [31]. The catalysts have analogies with those originally reported by Dow, which cited best values of 3.7% propene conversion and 47.2% selectivity for PO at 180 °C (catalyst Ag/Mg-Si02) [32a]. 

ARCO patents describe various approaches for the development of catalysts able to selectively epoxidize olefins other than ethene with oxygen. In all the catalyst formulations claimed, the main active component is supported silver, doped with various components [31a,b]. In the earlier patents, the best results reported were propene conversion 4.5%, selectivity for PO 59-61%, with a catalyst composition of 54% Ag, 2% K, 0.5% Mo, supported over calcium carbonate. Molybdenum was used to increase the selectivity (but the addition of Mo also caused a decrease in propene conversion). 

The best results reported are 0.090-0.120 gpo gcat productivity, at a propene conversion close to 8%, PO selectivity above 90% and selectivity based on hydrogen over 20%. Table 6.7 shows several results obtained from the literature. A commercially viable process would probably require a propene conversion >10%, PO selectivity >90% based on propene, and >50% based on hydrogen [36vj. 

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