Remained catalyst life

H2-to-OII Ratio vs. Product Distribution, Remained Catalyst Life, and Hydrogen Consumption... 

For commercial appHcation, catalyst activity is only one of the factors to be considered. Equally important is catalyst life, but Htde has been pubHshed on this aspect. Partly because of entrainment losses and partly through loss of acid as volatile triethyl phosphate, the catalyst loses activity unless compensating steps are taken. This decline in activity can be counteracted by the periodic or continuous addition of phosphoric acid to the catalyst during use, a fact that seems to have been disclosed as early as 1940 (94). A catalyst subjected periodically to acid addition could remain in service indefinitely, according to a report by Shell (91). A later Shell patent (85) states that complete reimpregnation with acid is required every 200 mn-days. 

If a solvent is used as part of the catalyst solution, then it also must be separated from the product. Finally, the buildup of various byproducts from ligand degradation, from raw material side reactions and from subsequent reaction of the desired product must be addressed so that the catalyst solution remains fully functional to achieve an economic catalyst life. 

Fig. 6 Schematic drawing of ZSM5 catalyst bed deactivation. View of the fused silica reaction tube at about 40 % of catalyst life time. Black zone (I) of deactivated catalyst particles covered with coke ("methanol coke"). Small dark reaction zone (II) in which methanol conversion to 100 % occurs. Blue/grey zone (III) of active catalyst on which a small amount of "olefin coke" produced by the olefinic hydrocarbon product mixture has been deposited on the crystallite surfaces. The quartz particles before and behind the catalyst bed (zones 0) remain essentially white.

By 1939 a Midget chamber-type polymerization process (20) had been developed that economically employed feed rates as low as 250,000 cubic feet per day, whereas the older units were uneconomical at feed rates below about 2,000,000 to 3,000,000 cubic feet per day. Midget units proved successful because it was found that when operating the polymerization reaction at pressures of 500 pounds per square inch a sufficient amount of feed remained in a dense phase to wash the catalyst clear of most of the heavy polymer, thus extending catalyst life and eliminating catalyst regeneration. 

Since the hardening is carried out at a lower temperature compared to the conventional processes, the acid value of the fatty acids (as a measure for the selectivity of the reaction) remains at a very high level. In catalyst life time tests we observed a 3 times higher catalyst productivity when using a DELOXAN supported 1 wt. % palladium fixed bed catalyst compared to the same catalyst in a trickle bed hardening process. 

The process reported here uses a clever combination of the factors that promote catalyst life and efficiency. The soluble phosphine or its phosphonium salt, used in a molar excess of about 50 over palladium, stabilizes the palladium complex in aqueous solution the sulfolane-water solution ensures the solubility of the reactants, while extraction with hexane under CO2 pressure recovers the product with only small contamination by palladium, phosphorus or nitrogen. The phosphine or its phosphonium salt and the ammonium bicarbonate remain in the aqueous solution. Since the TON is good and the solution can be recycled, consumption of palladium is very low. 

In both the liquid-phase and the gas-phase reactions, the STYs of PO have reached a level of 100 gpo kgcaJ, h which is comparable to that of ethylene oxide synthesis in industrial processes. However, there still remain some barriers against commercialization, namely catalyst life and hydrogen utilization efficiency. 

The precious metal content of a typical threeway catalyst in the USA currently is 20gr/cu ft (Ref. 6). To maintain a catalyst life similar to the US standard of a minimum 50,000 miles at the anticipated much higher remaining lead content (max. 13 mg/1) of European lead free gasolines, the precious metal content will have to be higher. 

The practical applicability on an industrial scale of this rather exotic two-phase system remains to be demonstrated. Doing so will require a clarification of such basic issues as activity, cost, catalyst lifetimes (and thus catalyst life and economic feasibility), toxicity, concerns regarding the ozone depletion potential (ODP) and greenhouse warming potential (GWP) values of the corresponding fluorinated compounds, etc. There is also the possibility of competitive extraction of fluorinated hydrocarbons by the aldehyde phase in the 0X0 reaction (leading to potential problems in subsequent hydrogenation to the plasticizer... 

Patents claiming specific catalysts and processes for thek use in each of the two reactions have been assigned to Japan Catalytic (45,47—49), Sohio (50), Toyo Soda (51), Rohm and Haas (52), Sumitomo (53), BASF (54), Mitsubishi Petrochemical (56,57), Celanese (55), and others. The catalysts used for these reactions remain based on bismuth molybdate for the first stage and molybdenum vanadium oxides for the second stage, but improvements in minor component composition and catalyst preparation have resulted in yields that can reach the 85—90% range and lifetimes of several years under optimum conditions. Since plants operate under more productive conditions than those optimum for yield and life, the economically most attractive yields and productive lifetimes maybe somewhat lower. 

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