Ethylene space-time yield

Even for the well-known ethylene oxide formation, improvements in space-time yield were reported. A value of 0.78 t/(h m ) using an oxidative modified silver was obtained, which exceeds considerably the industrial performance of 0.13-0.261 h m [159]. 

However, these investigations also point out that we need a proper definition of space-time yields for micro reactors. This refers to defining what essentially the reaction volume of a micro reactor is. Here, different definitions lead to varying values of the respective space-time yields. Following another definition of this parameter for ethylene oxide formation, a value of only 0.13 t h m is obtained -still within the industrial window [159, 162, 163]. 

An increase from 2 to 5 bar total pressure increases the space-time yield by about 20% (15 vol.-% ethylene, 85 vol.-% oxygen, 2-20 bar 0.235-3.350 s 11 h ) [4], At higher pressures, 10 and 20 bar, a decrease activity is observed. Since industrial processes occur at up to 30 bar, at first sight this result is surprising. The decreasing activity with pressure was partially explained by catalyst deactivation, probably as a consequence of the longer residence times applied. 

Quite new ideas for the reactor design of aqueous multiphase fluid/fluid reactions have been reported by researchers from Oxeno. In packed tubular reactors and under unconventional reaction conditions they observed very high space-time yields which increased the rate compared with conventional operation by a factor of 10 due to a combination of mass transfer area and kinetics [29]. Thus the old question of aqueous-biphase hydroformylation "Where does the reaction takes place " - i.e., at the interphase or the bulk of the liquid phase [23,56h] - is again questionable, at least under the conditions (packed tubular reactors, other hydrodynamic conditions, in mini plants, and in the unusual,and costly presence of ethylene glycol) and not in harsh industrial operation. The considerable reduction of the laminar boundary layer in highly loaded packed tubular reactors increases the mass transfer coefficients, thus Oxeno claim the successful hydroformylation of 1-octene [25a,26,29c,49a,49e,58d,58f], The search for a new reactor design may also include operation in microreactors [59]. 

By adding up to 36% ethylene glycol to the aqueous catalyst phase, the space-time yield could be boosted up to approx. 3 mt m-3 h-1 for propene hydroformylation, a factor of 20 in comparison to the conventional two-phase process without changing the reaction conditions. Because of this surprising speed-up, higher alpha-olefins up to 1-octene are converted with high to acceptable space-time yield (Fig. 22). Up to date this process is not commercialized, but has been tested in a continuous pilot plant. 

Symyx entered this competition in 1997 in collaboration with Hoechst with the goal of creating and validating primary and secondary synthesis and screening technologies and the use of this workflow to broadly explore mixed metal oxide compositions so as to discover and optimize new hits . The initial goal was a 10-fold increase in the space-time yield relative to the state-of-the-art MoVNb system for the ethane oxidative dehydrogenation reaction to ethylene. 

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

For the codimerization of ethylene and styrene, a pressure membrane reactor was developed and the reaction ran almost without any isomerization of the products or formation of side products. These undesired side reactions are often observed at high conversion. Nevertheless, the space-time yield dropped to zero within 15 residence times and low retention of the dendrimer as well as precipitation of palladium on the membrane were found. Larger dendritic catalysts with higher retentions did not show much improvement, indicating that catalyst deactivation was indeed the major problem. 

Reference [2] also indicates that the most economic route to vinyl acetate, when acetic acid is available, is to convert the raw materials to product in the vapor phase over a palladium catalyst. We therefore asked our research chemists to develop a catalyst suitable for the operation. They found a suitable catalyst by impregnating a silica base with 2% palladium along with some other proprietary chemicals. The chemists performed numerous experiments with the catalyst and found that it is quite selective towards vinyl acetate and quite active as measured in its space time yield (STY, grams of vinyl acetate/hr per liter of catalyst). The only significant side reaction we could notice is the combustion of ethylene to carbon dioxide and water... 

Increasing the steam to crude ratio from 0.5 to 2 results in a relatively small increase in olefin yield. As a result, the space time yield of olefins may be somewhat reduced by ratios of steam to crude greater than 1. The use of hydrogen as the diluent acts to effect increased yields of ethylene, but with the sacrifice of the yields of higher olefins such as propylene, butenes, and butadiene because of hydrogenolysis. 

The activated catalyst precursor was evaluated in a continuous, gas-phase fluid-bed reactor to produce a linear low-density ethylene/1-butene copolymer (LLDPE) with Melt Index (1215 ) of 2.9 and a density of 0.921 g/cc, utilizing a 1 -butene/ethylene and hydrogen/ethylene gas-phase molar ratio of 0.375 and 0.266, respectively, and a production rate (space time yield) of 5.3 lbs. PE/hr/ft of reactor volume. The granular polyethylene had a residual titanium level of 3-5 ppm and high bulk density of 26.2 Ibs./ft when the catalyst precursor was preactivated with Tri(n-hexyl) aluminiun at an Al/Ti molar ratio of 6.6. 

Last but not least, Tl-based MOFs were tried in the Zieglff-Natta polymerization of ethylene and propylene, though these systems were infaior to the well-known single-site metallocene polymerization catalysts with their trCTiendous turnover frequencies and space-time yields [107]. 

It is necessary, however, to maximize the intermediate olefin product at the expense of the aromatic/paraffin product which makes up the gasoline ( ). The olefin yield increases with increasing temperature and decreasing pressure and contact time. Judicious selection of process conditions result in high olefin selectivity and complete methanol conversion. The detailed effect of temperature, pressure, space velocity and catalyst silica/alumina ratio on conversion and selectivity has been reported earlier ( ). The distribution of products from a typical MTO experiment is compared to MTG in Figure 4. Propylene is the most abundant species produced at MTO conditions and greatly exceeds its equilibrium value as seen in the table below for 482 C. It is apparently the product of autocatalytic reaction (7) between ethylene and methanol (8). 

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