Olefin propane-propene ratio

Since the measurement of on-line catalyst activity is difficult, we found it convenient to follow an on-line "reaction index" (RI), which is a selectivity ratio. The complex MTO reaction scheme can be presented schematically as A —> B —> C, where A represents methanol and DME, B - olefins, and C -aromatics and paraffins (Fig. 3). One particularly useful RI is the propane/propene ratio. Propene is the primary light olefin and propane represents paraffins. The propane/propene RI can be easily monitored by an on-line GC. We found that hydrocarbon selectivities correlate well with RI. For fixed hydrodynamics, it also correlates well with methanol conversion. 

The dependence of 100 B/D MTO product selectivity on propane/propene RI is shown in Fig. 5. Higher olefin yields were obtained at low propane/propene ratios. Olefins selectivity increased by about 7% when the reaction temperature was raised from 470°C to 515 C. Most of this increase was due to higher light olefin yields. 

Large-scale demonstration of the MTO process was carried out in same 100 bpd unit used for the MTG fluidized-bed demonstration (Fig. 19). Process conditions were 3252 psia, 470515°C, and methanol feed rate of 570620 k. Catafyst makeup rate was less than 0.5% of inventory per day. The demonstration unit accumulated 3600 h on-stream and processed 2130 ton methanol. Methanol conversion was 99.9+% throu out the run. Typical product distribution is shown in Figure 24 [49], which plots hydrocarbon yield versus propane to propene ratio, a reaction index that is a measure of severity. Higher olefins yields are reflected in lower values of the reaction index. The unit achieved a maximum of 60% olefin yield during the demonstration. Operation at lower pressure or with diluents, both known to increase olefin yield, was not implemented during this run. 

Note also that (1) d° Ta alkyhdene complexes are alkane metathesis catalyst precursors (2) the cross-metathesis products in the metathesis of propane on Ta are similar to those obtained in the metathesis of propene on Re they differ only by 2 protons and (3) their ratio is similar to that observed for the initiation products in the metathesis of propane on [(=SiO)Ta(= CHfBu)(CH2fBu)2]. Therefore, the key step in alkane metathesis could probably involve the same key step as in olefin metathesis (Scheme 27) [ 101 ]. 

More recently, it was demonstrated that 80 is a catalyst for the partial oxidation of olefins using dioxygen (230). For example, dry propene was oxidized to acetone when water vapor was present in the catalyst stream, some propanal could also be detected. Other reactions reported included the conversion of styrene to acetophenone and phenylacetaldehyde in an 80 20 product ratio, and 2-norbornene to 2-norbomanone and cyclohexene-4-carboxyaldehyde in a 70 30 product ratio. 

Above 300°C. the effective reaction of an alkyl radical with oxygen may be Reaction 3 rather than 2 because of the reversibility of Reaction 2. If it is assumed that Reaction 3 is important at about 450°C., its rate can be estimated from the competition between pyrolysis and oxidation of alkyl radicals. Falconer and Knox (21) observed that the ratio of (pro-pene)/(ethylene) from the oxidation of propane between 435° and 475°C. increased with oxygen concentration and decreased with temperature—the apparent activation energy difference for the two reactions forming the olefins being 27 =t 5 kcal. per mole. They interpreted this result in terms of a competition between Reactions 1 and 3. The observed ratio (propene)/(ethylene) was 3.5 at 435°C. and 10 mm. of Hg pressure. If log ki(propyl) = 13.2 — 30,000/2.30RT, the value for the n-propyl radical (34), then log k3 = 8.0. If the A factor is 109-3, we derive the Arrhenius equation... 

The validity of this new method was assured in the hydrogenation reaction of 1,3-butadiene on the two different types of catalysts, MoS2 and ZnO, so that it was extended to the hydrogenation of a-olefins, propene and 1-butene, on MoS2 and MoOx/TiOz catalysts. The ratios of alkane-2- to alkane-l-d, obtained in the reaction of propene and 1-butene with HD molecule on MoS2 catalyst at room temperature, and the isotope effect in the reaction with H2 and D2 are plotted in Fig. 26. In these experiments, the analysis of propane-1-d, and propane-2-dj was carried out by microwave spectroscopy... 

Scheme 23 also outlines a potential problem with the syjnthesis. The initial attack can occur at either end of the double bond of the 7r-complex, 28, to give the two isomers 29 and 30 in a ratio of 4 1. These two isomers are expected from Wacker chemistry since propene produces both acetone and propanal in about the same ratio from the two modes of addition. However, as shall be discussed below, this is not a serious problem with most a-olefins. The same catalyst oxidizes methyl vinylketone only to 4-chloro-3-hydroxy-2-butanone (29 R = C(=0)CH3). The optical purity was still only about 12%. 

Basset and his group have observed that propane and propene metathesis give similar Cn+i/Cn+2 ratios of cross-metathesis products on silica-supported tantalum-neopentylidene catalyst at 150°C. The olefin-metathesis activity of these Schrock-type supported complexes results from the presence of the silyloxy ligand (vide infra) - Organometallic complexes are bound to silica or alumina by reaction of soluble complexes and involve die formation of one or several bonds between the central metal and the oxygen atom of the oxide support. 

---