Catalyst temperature-time

Within the last few decades many attempts for a most successful synthesis have been made. o-Fructose has proven to be the feed of choice. For the dehydration of D-fructose towards HMF, many variations in conditions (catalyst, temperature, time, concentration, and solvent) have been investigated and carefully balanced out. The aim was to overcome the by-product formation and thus an optimized HMF-yield [14, 23, 24]. 

Catalyst [Ph-T4-tetrol]/ [Catalyst] Temperature Time (h) Solvent Yield (%)... 

Then add a bit of NaHCOs (4 grams) and salt to saturate solution. Stir a bit more. Separate layers, Extract one more time and distill. Time depends on reaction speed. Reaction speed depends on the amount of catalyst and temperature. 60 C seems to be good, more catalyst, less time. More temperature May be more byproducts, this is what happen when acetic acid is the solvent. Probably a good way will be also acetic acid and 40-50 C, but dual phase is easy to extract ans uses less chemicals. 

Vanadium phosphoms oxide-based catalysts ate unstable in that they tend to lose phosphoms over time at reaction temperatures. Hot spots in fixed-bed reactors tend to accelerate this loss of phosphoms. This loss of phosphoms also produces a decrease in selectivity (70,136). Many steps have been taken, however, to aHeviate these problems and create an environment where the catalyst can operate at lower temperatures. For example, volatile organophosphoms compounds are fed to the reactor to mitigate the problem of phosphoms loss by the catalyst (137). The phosphoms feed also has the effect of controlling catalyst activity and thus improving catalyst selectivity in the reactor. The catalyst pack in the reactor may be stratified with an inert material (138,139). Stratification has the effect of reducing the extent of reaction pet unit volume and thus reducing the observed catalyst temperature (hot... 

Silicon Nitride. SiUcon nitride is manufactured either as a powder as a precursor for the production of hot-pressed parts or as self-bonded, reaction-sintered, siUcon nitride parts. a-SiUcon nitride, used in the manufacture of Si N intended for hot pressing, can be obtained by nitriding Si powder in an atmosphere of H2, N2, and NH. Reaction conditions, eg, temperature, time, and atmosphere, have to be controlled closely. Special additions, such as Fe202 to the precursor material, act as catalysts for the formation of predorninately a-Si N. SiUcon nitride is ball-milled to a very fine powder and is purified by acid leaching. SiUcon nitride can be hot pressed to full density by adding 1—5% MgO. 

Below is a table of asymmetric Diels-Alder reactions of a,/ -unsaturated aldehydes catalyzed by chiral Lewis acids 1-17 (Fig. 1.10, 1.11). The amount of catalyst, reaction conditions (temperature, time), chemical yield, endojexo selectivity, and optical purity are listed (Table 1.32). 

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

Fig. 1. Methyl ester concentration versus reaction time for solid bases and acids catalysts. Temperature 230 C, catalyst 2wt%, CH30H/oil= 12 1.

Fig. 16. Variation in a stationary cycling state of catalyst temperature, S03, and complex concentrations in the melt phase and the concentration of gas phase species with time in a half cycle in the forward flow portion of a reactor operating under periodic reversal of flow direction with r = 40 min, SV = 900 h (Csodo = 6 vol%, (Co2)o = 15 vol%, Ta = 50°C. Curves 1, just after switching flow direction 2,1 min 3, 6.6 min 4, 13.3 min, and 5, 20 min after a switch in flow direction. (Figure adapted from Bunimovich et at., 1995, with permission, 1995 Elsevier Science Ltd.)...

Catalyst precursor Time (h) Temperature (°C) P(H2) (bar) % Conversion % Selectivity References... 

The water-to-silicate molar ratio (R) is an another important technological parameter determining the final form of produced material. For example, fibers can be formed from hydrolysates with R l, for monodisperse spheres R 50 while bulk samples can be obtained from hydrolysates with R ranging broadly from 5 to 15. The hydrolysis process is also strongly influenced by such factors as temperature, time and character of the catalyst used. 

Dunker, A., Kumar, S., and Mulawa, P., Production of hydrogen by thermal decomposition of methane in a fluidized bed reactor—effect of catalyst, temperature and residence time, Int.. Hydrogen Energ., 31, 473, 2006. 

Run no. Catalyst Co-catalyst Temperature (°C) Run time (h) Epoxide Conv. of epoxide (mol%) TOF Selectivity for cyclic carbonate (mol%)... 

Fig. 1. Relationship between catalyst temperature and reaction time in methane partial oxidation catalyzed by Ni/Si02 (temperature of the gas phase (a) 1019 K, (b) 899 K, (c) 809 K, (d) 625 K). The reaction was carried out in a fixed-bed reactor (a quartz tube of 2 mm inside diameter) at atmospheric pressure. Before reaction, the feed gas was allowed to flow through the catalyst undergoing heating of the reactor from room temperature to 1073 K at a rate of 25 K min-1 to ignite the reaction, and then the reactant gas temperature was decreased to the selected value. Reaction conditions pressure, 1 atm catalyst mass, 0.04 g feed gas molar ratio, CH4/O2 = 2/1 GHSV, 90,000 mL (g catalyst)-1 h-1) (25).

The activity decline of a catalyst with time was iound at two temperatures,... 

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