Yield per pass

The Aromax process was developed in the early 1970s by Toray Industries, Inc. in Japan (95—98). The adsorption column consists of a horizontal series of independent chambers containing fixed beds of adsorbent. Instead of a rotary valve, a sequence of specially designed on—off valves under computer control is used to move inlet and withdrawal ports around the bed. Adsorption is carried out in the Hquid phase at 140°C, 785—980 kPA, and 5—13 L/h. PX yields per pass is reported to exceed 90% with a typical purity of 99.5%. The first Aromax unit was installed at Toray s Kawasaki plant in March 1973. In 1994, IFP introduced the Eluxyl adsorption process (59,99). The proprietary adsorbent used is designated SPX 3000. Individual on-off valves controlled by a microprocessor are used. Raman spectroscopy to used to measure concentration profiles in the column. A 10,000 t/yr demonstration plant was started and successfully operated at Chevron s Pascagoula plant from 1995—96. IFP has Hcensed two hybrid units. 

A significant problem is the dehydrocoupling reaction, which proceeds only at low yields per pass and is accompanied by rapid deactivation of the catalyst. The metathesis step, although chemically feasible, requires that polar contaminants resulting from partial oxidation be removed so that they will not deactivate the metathesis catalyst. In addition, apparendy both cis- and /ra/ j -stilbenes are obtained consequendy, a means of converting the unreactive i j -stilbene to the more reactive trans isomer must also be provided, thus complicating the process. 

Eijuilibrium Constant. At the pressures used in commercial production of ethanol (6.1—7.1 MPa or 60—70 atm), alcohol yield per pass is significantly limited by equiHbrium considerations. This fact has focused attention on deterrnination of equiHbrium constants and equiHbrium yields (122—124). The results of these deterrninations are as follows ... 

The Stamicaibon process is described in Figures 3—7. The synthesis section of the plant consists of the reactor, stripper, high pressure carbamate condenser, and a high pressure reactor off-gas scmbber. In order to obtain a maximum urea yield per pass through the reactor, a pressure of 14 MPa (140 bar) and a 2.95/1 NH3—C02 molar ratio is maintained. The reactor effluent is distributed over the stripper tubes (falling-film type shell and tube exchanger) and contacted by the C02, countercurrendy. This causes the partial NH3 pressure to decrease and the carbamate to decompose. 

One needs to use the definitions of both the industrial conversion and the yield in order to determine how much of product B we can expect. This can be determined when having only the amount of starting A and the conversion and yield data for the process of interest. By multiplying the two fractions together, one obtains the fractional yield of product to be expected from a batch process, or the yield per pass (yield on one passage of the raw materials through the process) for a continuous process (Eq. 1.12). 

Molten salt mixtures of copper(II) chloride and copper(II) oxychloride have also been claimed to produce phosgene in a yield, per pass, of 10% from carbon monoxide at 460 C [174], Again, in this process, the depleted copper(II) salts are regenerated in a second reactor with a mixture of air and hydrogen chloride. 

In order to increase the driving force for crystallization or increase the yield per pass through the system, a continuous crystallization system can be intentionally operated as a cascade, as shown in Fig. 7-9. A significant number of these crystallizers in series become, in effect, a plug flow reactor. 

The second fact, linked to the first, is that a much lower srield in valuable products is obtained when paraffins are used instead of olefins or aromatics. The success of the butane-based MAA process occurred at the cost of a dramatic drop of molar selectivity (at most 65-67% compared to 75-77% when starting from benzene) and a drop of productivity by nearly 20% [3]. Compared to the benzene route, butane oxidation gives molar yields per pass of only about 55% instead of 75%. 

Although thermodynamic calculations show that the pressure has no effect on conversion at the reaction temperatures, operations are conducted at,I to 3.106 Pa absolute to facilitate the subsequent absorption of ethylene oxide in water. Yield per pass reaches a maximum with increased-residence time, but, to maintain high selectivity, this is limited to between 1 and 4 s in industrial plants.. 

In 1930-1932, Fischer and his coworkers (19, 20, 21) developed more active promoted nickel and cobalt catalysts, and increased the yield per pass to over 100 g. oil/cubic meter of 2 1 CO gas. In 1932, Fischer... 

The direct conversion of CH4 into methanol may have a high selectivity, but at a low conversion per pass. For example, Zhang et al. [537] reported a selectivity of 60% at a conversion of 12—13%. This corresponds to a yield of about 7.5%. This low yield per pass results in a large recycle ratio and a difficult separation associated with a low partial pressure of the product. This is illustrated by simple calculations in Figure 1.4 [410]. 

Oxidative dehydrogenation of butanes and butenes. Since dehydrogenation is endothermic the above process requires reduced pressure and high temperature to be effective. In order to drive the reaction towards completion an oxidative system is used to react with the hydrogen and yields per pass as high as 80% have been claimed. 

Yield per pass is also called gained rate, which has following relationship with... 

The narrower residence time distribution of horizontal stirred-bed reactors leads to higher yields per pass, formation of less off-specification material, and more uniform impact copolymers and reactors blends. 

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