Hydrogenation process condition

Table 5.4 Effects of changes in hydrogenation process conditions...

PVDE is not hazardous under typical processing conditions. If the polymer is accidentaky exposed to temperatures exceeding 350°C, thermal decomposition occurs with evolution of toxic hydrogen fluoride (HE). 

Calcium Pyrophosphates. As is typical of the pyrophosphate salts of multiple-charged or heavy-metal ions, the calcium pyrophosphates are extremely insoluble ia water. Calcium pyrophosphate exists ia three polymorphic modifications, each of which is metastable at room temperature. These are formed progressively upon thermal dehydration of calcium hydrogen phosphate dihydrate as shown below. Conversion temperatures indicated are those obtained from thermal analyses (22,23). The presence of impurities and actual processing conditions can change these values considerably, as is tme of commercial manufacture. 

Reforming Conditions. The main process variables are pressure, 450—3550 kPa (50—500 psig), temperature (470—530°C), space velocity, and the catalyst employed. An excess of hydrogen (2—8 moles per mole of feed) is usually employed. Depending on feed and processing conditions, net hydrogen production is usually in the range of 140—210 m /m feed (800—1200 SCF/bbl). The C —products are recovered and normally used as fuels. 

Regardless of detail, the experimental facts are clear process conditions that favor formation of hydrogen-poor catalysts favor migration and isomerization. Table 1 is a convenient summary of this concept. Hydrogen availability refers to hydrogen concentration at the catalyst surface. Additives that retard the rate of reduction increase hydrogen availability and retard isomerization they may also block sites with enhanced activity for migration (53). 

Dr. Woodward May I just make one comment to emphasize and to repeat what was said earlier Thermodynamics and kinetics. Yes, under the inlet conditions of several SNG processes, and also of methanation in ammonia and hydrogen processes, thermodynamically they are inside the carbon-forming region. At the exit they tend not to be. In practice, carbon is not formed. One could, therefore, conclude very simply that kinetics outweighs thermodynamics. 

A gas-liquid-particle process termed cold hydrogenation has been developed for this purpose. The hydrogenation is carried out in fixed-bed operation, the liquefied hydrocarbon feed trickling downwards in a hydrogen atmosphere over the solid catalyst, which may be a noble metal catalyst on an inert carrier. Typical process conditions are a temperature of 10°-20°C and a pressure of 2.5-7 atm gauge. The hourly throughput is as high as 20-kg hydrocarbon feed per liter of catalyst volume. 

Disproportionation of Pu(IV). There are several needs associated witn the occurrence, detection, and mitigation of the disproportionation of Pu(IV) in applied plutonium recovery/ purification procedures. First, there is a great need for much more detailed information concerning the effect of typical process conditions [e.g., temperature, concentration of plutonium, hydrogen ion, nitrate ion, nitrite ion, fluoride ion, other metal ions (e.g., A13+, Fe3+, etc.), etc.] on the occurrence and extent of the reaction ... 

The cyclohexene hydrogenation is a well-studied process especially in conventional trickle-bed reactors (see original citations in [11,12]) and thus serves well as a model reaction. In particular, flow-pattern maps were derived and kinetics were determined. In addition, mass transfer can be analysed quantitatively for new reactor concepts and processing conditions, as overall mass transfer coefficients were determined and energy dissipations are known. In lieu of benchmarking micro-reactor performance to that of conventional equipment such as trickle-bed reactors, such a knowledge base facilitates proper, reliable and detailed comparison. 

GL 18] [R 6a] ]P 17] About 100% selectivity was achieved for the hydrogenation of p-nitrotoluene [17], with conversions of 58-98%. The conversion for the electro-deposited catalyst was 58%, whereas the impregnated catalyst gave a 58-98% conversion, depending on the process conditions (see Table 5.1). 

A chemical reactor is an apparatus of any geometric configuration in which a chemical reaction takes place. Depending on the mode of operation, process conditions, and properties of the reaction mixture, reactors can differ from each other significantly. An apparatus for the continuous catalytic synthesis of ammonia from hydrogen and nitrogen, operated at 720 K and 300 bar is completely different from a batch fermenter for the manufacture of ethanol from starch operated at 300 K and 1 bar. The mode of operation, process conditions, and physicochemical properties of the reaction mixture will be decisive in the selection of the shape and size of the reactor. 

FIG. 33. The depletion of silane and the corresponding production of hydrogen for several process conditions, covering both the a- and the ) -regime. The solid line represents the case where all the consumed silane is converted into a-Si H() and 1.95H2. The dashed line represents the case where 30% of the consumed silane is converted into disilane instead of being deposited. (From E. A. G. Hamers, Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands, 1998. with permission.)... 

With the setup described, a series of depositions was carried out [531, 548], in which the substrate temperature was varied between 125 and 650°C. the pressure between 0.007 and 0.052 mbar. the gas flow rate between 15 and 120 seem, and the dilution of the silane gas with hydrogen ([SiHaj/flSiHa] + [Hi])) between 0.1 and 1. Under these conditions the deposition rate varied between 1 and 2.5 nm/s [531 ]. Molenbroek et al. [530] reported a variation of the deposition rate between 1 and 9 nm/s for similar process conditions, at a filament temperature of 2000°C. 

Hydrogenation of lactose to lactitol on sponge itickel and mtheitium catalysts was studied experimentally in a laboratory-scale slurry reactor to reveal the true reaction paths. Parameter estimation was carried out with rival and the final results suggest that sorbitol and galactitol are primarily formed from lactitol. The conversion of the reactant (lactose), as well as the yields of the main (lactitol) and by-products were described very well by the kinetic model developed. The model includes the effects of concentrations, hydrogen pressure and temperature on reaction rates and product distribution. The model can be used for optinuzation of the process conditions to obtain highest possible yields of lactitol and suppressing the amounts of by-products. 

Hydrogenation processes usually require standards and materials that may not be warranted in other operations of the petroleum industry. At certain combinations of elevated temperature and hydrogen partial pressure, both chemical and metallurgical changes occur in carbon steel, which in advanced stages can render it unsuitable for safe operation. Alloy steels containing chromium and molybdenum can be used under such conditions. 

The Ni/Re on carbon catalyst was also evaluated in a 1700 hour continuous reactor test to determine the stability of the catalyst. This test was performed with a different model compound than xylitol. Shown in Figure 5, the results from the lifetime test of the Ni/Re catalyst operated at constant process conditions sampled intermittently for 1700 hours. This shows that for a similar aqueous hydrogenation reaction deliberately operated to near completion, the catalyst retained its activity and product selectivity even in the face of multiple feed and H2 interruptions. We feel that this data readily suggests that the Ni/Re catalyst will retain its activity for xylitol hydrogenolysis. 

This study shows that the optimization of process conditions could be achieved rapidly by a judicious use of statistics and parallel reactors. A two-level factorial method with two center points was used to limit the total number of experiments to ten. Using two identical high-pressure reactors in parallel further shortened the time required to conduct these experiments. For the model reaction of phenol hydrogenation over a commercially available Pd/C, it was experimentally determined that the optimal yield was 73% at 135 °C, 22.5 bar, and 615 ppm w/w NaOH... 

Thermal stabilizers combat degradation by removing the hydrogen chloride that is generated. Additionally, we treat polyvinyl chloride more gently than we do polyolefins. We use milder processing conditions (lower temperatures and lower shear rates) and add lubricants to... 

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