Ion exchange temperature

Activity and selectivity of Pt/KL catalysts depend crucially on the method of their preparation. There seems to be a consensus that Pt/KL samples prepared by incipient wetness impregnation display a higher Pt dispersion and a higher aromatization yield than samples prepared by ion exchange. Temperature-programmed reduction shows that in samples prepared by impregnation, followed by calcination, a considerable fraction of the Pt is present as Pf ions, whereas Pt prevails in ion-exchanged samples after calcination (53). 

Catalysts Ion exchange Temperature(°C) Ion exchange steps Co(w/w%) Ion exchange level... 

Lean NOx-SCR with CH4 has been investigated on Co-modified synthetic ferrierite prepared in different conditions of ion exchange (temperature, time, precursor zeolite composition), A maximum NOx conversion (50% at 100% CH4 conversion) was obtained at 500°C. Activity and selectivity depend on the nature of Co species (from mononuclear to polynuclear cationic to oxidised phases) formed into ferrierite. The effect of side reactions such as uncatalysed and catalysed methane combustion on catalytic performance is discussed. 

No effects of ion exchange temperature on oy and K,. were observed when this treatment was carried out between 430 and 510°C (Figure 12), which corresponded to a range between 75 and 89% of the glass transition temperature (Tg) of UST porcelain. This temperature (Tg), determined by differential thermal analysis, DTA (404S, Netzsch), at a heating rate of 5°C/min in... 

Rosa V, Fredericci C, Moreira MF, Yoshimura HN, Cesar PF. Effect of ion exchange temperature on mechanical properties of a dental porcelain. Ceramics International 2010 36(6) 1977-1981. 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

The porous electrodes in PEFCs are bonded to the surface of the ion-exchange membranes which are 0.12- to 0.25-mm thick by pressure and at a temperature usually between the glass-transition temperature and the thermal degradation temperature of the membrane. These conditions provide the necessary environment to produce an intimate contact between the electrocatalyst and the membrane surface. The early PEFCs contained Nafton membranes and about 4 mg/cm of Pt black in both the cathode and anode. Such electrode/membrane combinations, using the appropriate current coUectors and supporting stmcture in PEFCs and water electrolysis ceUs, are capable of operating at pressures up to 20.7 MPa (3000 psi), differential pressures up to 3.5 MPa (500 psi), and current densities of 2000 m A/cm. ... 

The aqueous phase into which the monomer mix is dispersed is also prepared in a separate tank before transferring to the copolymerization ketde. It contains a catalyst, such as benzoyl peroxide [94-36-0], to initiate and sustain the polymerization reaction, and chemicals that aid in stabilizing the emulsion after the desired degree of dispersion is achieved. Careful adherence to predeterrnined reaction time and temperature profiles for each copolymer formulation is necessary to assure good physical durabiHty of the final ion-exchange product. 

Eor most polymer applications the removal of the inhibitors from the monomer is unnecessary. Should it be requited, the phenolic inhibitors can be removed by an alkaline wash or by treatment with a suitable ion-exchange resia. Uninhibited MMA is sufftcientiy stable to be shipped under carehiUy controlled temperature and time restrictions. Uninhibited monomers should be monitored carehiUy and used promptiy. 

The nitro alcohols available in commercial quantities are manufactured by the condensation of nitroparaffins with formaldehyde [50-00-0]. These condensations are equiUbrium reactions, and potential exists for the formation of polymeric materials. Therefore, reaction conditions, eg, reaction time, temperature, mole ratio of the reactants, catalyst level, and catalyst removal, must be carefully controlled in order to obtain the desired nitro alcohol in good yield (6). Paraformaldehyde can be used in place of aqueous formaldehyde. A wide variety of basic catalysts, including amines, quaternary ammonium hydroxides, and inorganic hydroxides and carbonates, can be used. After completion of the reaction, the reaction mixture must be made acidic, either by addition of mineral acid or by removal of base by an ion-exchange resin in order to prevent reversal of the reaction during the isolation of the nitro alcohol (see Ion exchange). 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

The 1990 Clean Air Act mandates for blended oxygenates ia gasoline created a potentially large new use for DIPE as a fuel oxygenate. Isopropyl alcohol can react with propylene over acidic ion-exchange (qv) catalysts at low temperatures, which favor high equiUbrium conversions per pass to produce DIPE (34). 

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