Service time of catalyst

It should be specially noted that the service time of catalyst is not equal to the life period of catalyst. The life period of catalyst is its own characteristic and does not change with the difference of using conditions. But the service time changes with the difference of the using conditions. So, if the catalyst is used in different plant or in different conditions in the same plant, its service time is different. At this time, we cannot say that its life period is different but can only affirm that its service time is different. The life period of the catalyst can generally be expressed as the output of ammonia produced per ton catalyst in its life period in the same condition, i.e., g-cat/tNUS-expended catalyst per ton ammonia (Table 9.23) it can also be expressed as the longest service time of the catalyst used in single furnace in its all industrial application. 

When the nominal service time is designed to be five years, the productivity is l,050t d within four years after running, then the output declines because the catalytic activity decreases. When the period reaches 6.8 years, the output decreases to rated output of 1,0001 d This potential increase production is shown as the sum of shade area I and II. As a result, if this design is adopted, the nominal service time of catalyst can prolong from five years designed to 6.8 years. 

Assuming that 5% safety factor of the compressor is used to increase output, the service time of catalyst can be prolonged to 3.3 years (for two years design) and 6.8 years (for five years design) respectively. 

It is clear that the increment of potential profit augments when the service time of catalyst is prolonged, but it does not mean that the longer the service time of the catalyst is, the better the result is. The reason is that, as mentioned above, a more significant benefit will be obtained only by increasing output, and in particular, the service time of synthesis catalyst can reach over 15 years. Similarly, a plant with capacity of 10001 d is taken as example, if the safety coefficient of the compressor as well as related equipments is 5%, the catalytic activity does not change during... 

Wenshan Wang et al. had discussed catalyst replacement. ° Zuxi Yu et al. took a chilled converter with four beds used in some ammonia plants with capacity of l,000t d as an example, applied REACTOR program to calculate the effect of catalytic activity on productivity, forecast the time to replace the catalyst in normal condition of production as well as forecast the economic benefits of output increment probably obtained after the replacement. Someone brought forward that the influence of the service time of catalyst on the economic benefits of the plant is appraised by the efficiency of converter (a), and a is token as a judgment of catalyst replacement. The efficiency of converter a is defined as ... 

Several factors will conceivably influence the retention. Not all poisons will be retained to the same extent. Retention of any given element might depend on its amount in the fuel and oil on the composition of fuel and oil on the operation variables of the engine on the design of the exhaust system on temperature, shape, size, position of the catalyst, and the atmosphere to which it is exposed the service time of the system etc. It may, or may not, vary linearly with any of these parameters. 

The first tests were carried out to evaluate the behavior of different catalysts under gas phase conditions (Table 15.1). It was observed that conversion of 18 decreased rapidly in the presence of various acidic zeolites H-B-ZSM-5, H-ZSM-5 and H-US-Y. This behavior was even more distinctive with BP04 and Nb205. The low service times of the catalysts are assumed to be caused by strongly adsorbed compounds as well as coke precursors blocking the acidic sites. Surprisingly, a silica catalyst having gentle acidity showed the best performance. With selectivity to 19 of about 40% there was no drop in conversion after 8 h TOS, even at 230 °C. 

The advantages of the new process for a-ketocarboxylic acid ester under gas phase conditions are high yields, high service time of the catalyst, and a one-step reaction using easily available starting materials. In contrast, the known processes are very complicated, costly and environmentally hazardous via Grignard reactions of oxalic acids. 

The transition metals, which are used as a catalyst, cannot be removed completely from the polymer. Residues of transition metals may cause problems with regard to service time of the final products. 

Life period and service time of ammonia catalyst... 

Types of devices (catalyst) Average service time/year Longest service time of single-loading/year... 

The unit consumption of the catalyst as its cost can determine its ratio accounting for the production cost. The frequency of replacement and regeneration of catalyst will affect the service time of the equipment, and then affect the reclaiming of investment of capital construction and maintenance expenditure. 

It is well known that the life period or service time of ammonia catalyst is the longest among eight catalysts in ammonia plant. It is seen from Table 9.23 that the unit consumption of novel Fei xO-based A301 and ZA-5 catalysts used in small devices is only 55.7g cat t... 

Service time of ammonia synthesis catalyst/year... 

Note (1) Area I shows the output over l,000t/d for two-years service time of the catalyst when increased capacity of compressor is 5%. (2) Sum of area I and II show the increasing capacity of catalyst having five years service time, when increased capacity of compressor is 5%. 

It is known from Table 9.25 that for the plant whose service time of the catalyst is 7.5 years, although the catalyst should be replaced once (but the replacement can be arranged during temporary stoppages at the plant, which does not occupy the production time), the cost of catalyst increases by one time, and part output will be lost during the catalyst reduction. However, in the view of running period of 15 years, potential profit increment of the enterprise with the service time of... 

Hydrocarbon oxidation on base metal catalysts is also susceptible to lead poisoning, especially if the catalysts are exposed to relatively high temperatures, for at least part of their service time. It was noted above that lead retention, especially on base metal catalysts, also increases with temperature up to a certain point. This behavior is shown by the results of Yao and Kummer (81) in Fig. 18. One should note that the hydrocarbon used for testing catalyst activity, namely propylene, was quite reactive. With a less reactive test hydrocarbon one could expect a still sharper effect. The comparison with a reference production noble metal catalyst, given in Fig. 18, is quite instructive. 

In the isomerization of styrene oxides in a fixed bed reactor under gas phase conditions, the catalytic performance of various catalysts on the activity, selectivity and service time was screened at 300°C and WHSV = 2-3h" . As shown in Fig. 15.1, zeolites with MFI-structure are superior to other zeolite types and non zeolitic molecular sieves, as well as greatly superior to amorphous metal oxides. 

Smaller reactor size reduces the cost, improves control, and isolates process variables, however, effects of catalyst aging/deac-tivation as a function of time are not similarly reduced. These effects can be accelerated in the laboratory environment by increased temperature, water partial pressure, contaminant gas partial pressure, and various contaminant metals. As with scaled down equipment, these efforts are not without problems, however, when some catalyst lifetimes are measured in years, this is the only viable solution to meaningful catalyst research and development. This type of testing, coupled with characterization, has resulted in FCC catalysts with less resistance to coking and thus longer service life. 

The implications of being able to increase the conversion of an equilibrium reaction by using a permselective membrane are several. First, a given reaction conversion may be attained at a lower operating temperature or with a lower mean residence time in a membrane reactor. This could also prolong the service life of the reactor system materials or catalysts. Second, a thermodynamically unfavorable reaction could be driven closer to completion. Thus, the consumption of the feedstock can be reduced. A further potential advantage is that, by being able to conduct the reaction at a lower temperature due to the use of a membrane reactor system, some temperature-sensitive catalysts may find new applications [Matsuda et al., 1993]. 

Figure 7. Effect of catalyst service time on gas production rates. Test conditions temperature, 750°C flow, 2000 std cc/hr N2 and 1.16 grams/hr water.

Figure 12 shows the variation of catalytic performance during time-on-stream (equilibration time) for the catalyst prepared by precipitation at pH 4.0. In this case the conversion is constant during service time (around 7%), and the selectivity to methacrylic acid exhibits a lower increase (from the initial 21% up to 40% for the equilibrated catalyst after approximately 50 hours time-on-stream) than for the compound prepared at strongly acid pH (see Figure 9). In this case, the only chemical-physical features which are modified during the equilibration time are i) the extent of POM reduction, which progressively increases, as demonstrated by the electronic spectrum of the unloaded catalyst as compared to...

All these data indicate that the progressive increase in activity during service time observed for the catalyst prepared at strongly acid pH (Figure 9) is due to the development of an active species during equilibration, which occurs as a consequence of partial structural decomposition of the POM and redistribution of molybdenum in the framework. This active species can be hypothesized to include Mo ions located in the cationic position of the framework. An additional phenomenon is the increase in the extent of reduction of the POM, which is in part responsible for the progressive increase in selectivity. 

The heterogeneous catalysts used in the past had some drawbacks such as incomplete conversion in most cases, low selectivity because of consecutive aldol condensation to form preferably trimers and low service time [i.e. catalyst time on stream (TOS)]. 

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