Recycle Split Vapor

Recycle Split-Vapor with Enrichment process (RSVE)... 

If a vapor from the phase split is either predominantly product or predominantly byproduct, then it is removed from the process. If the vapor contains predominantly unconverted feed material, it is normally recycled to the reactor. In these cases, there is no need to carry out any separation on the vapor. 

Determine the relation between the fraction of vapor from the phase split sent to purge (a) and the fraction of methane in the recycle and purge (y). 

If the vapor from the phase split is either predominantly product or predominantly byproduct, then it can be removed from the process. If the vapor contains predominantly unconverted feed material, it is normally recycled to the reactor. If the vapor stream consists of a mixture of unconverted feed material, products and byproducts, then some separation of the vapor may be needed. The vapor from the phase split will be difficult to condense if the feed to the phase split has been cooled to cooling water temperature. If separation of the vapor is needed in such circumstances, one of the following methods can be used ... 

The liquid stream can readily be separated into relatively pure components by distillation, the benzene taken off as product, diphenyl as an unwanted byproduct and the toluene recycled. It is possible to recycle the diphenyl to improve selectivity, but it will be assumed that is not done here. The hydrogen feed contains methane as an impurity at a mole fraction of 0.05. The production rate of benzene required is 265 kmol-lr1. Assume initially that a phase split can separate the reactor effluent into a vapor stream containing only hydrogen and methane, and a liquid containing only benzene, toluene and diphenyl, and that it can be separated to produce essentially pure products. For a conversion in the reactor of 0.75,... 

The new EO planes are as simple as any you will read about in this book. The feeds are mixed, reacted, then split into recycle and finished product streams, as shown in Figure 10—3. The oxidation reaction takes place in the vapor phase. 

One way to utilize a stabilizer Is illustrated In Figure 5, which is simply the Figure 4 process with the liquids from K and 4 diverted to a stabilizer. The stabilizer could be either refluxed or cold-feed, as a further variation. This process reduces the recycle load significantly in the two lower compression stages, as compared to the previous processes. This process also provides an additional control for the crude oil vapor pressure which can be independently varied, since the fractionator split can be controlled and the fractionator bottom product is blended with the crude stream. It may be desirable to blend this stream into separator 1... 

It is economic to cool the compressed methane for liquefaction by the gas that does not liquefy in the throttling process. In the Claude process, the gas at an intermediate temperature splits into two parts. One of them enters the expander and exhausts as a saturated or slightly superheated vapor, and produces work. The remaining gas is further cooled in the second heat exchanger and throttled to liquefy. The portion that is not liquefied is combined with the output vapor of the expander and recycled into the compressor. 

The effluent from the adiabatic reactor is quenched with liquid from the separator. This quenched stream is the hot-side feed to the process-to-process heat exchanger, where the cold stream is the reactor feed stream prior to the furnace. The reactor effluent is then cooled with cooling water, and the vapor (hydrogen, methane) and liquid ( benzene, toluene, diphenyl) are separated. The vapor stream from the separator is split. Part is purged from the process to remove the methane byproduct and the remainder is sent to the compressor for recycle back to the reactor. 

Inside the column a liquid stream flows downward and a vapor stream rises. At each point in the column some of the liquid vaporizes and some of the vapor condenses. The vapor leaving the top of the column, which contains 97 mole% benzene, is completely condensed and split into two equal fractions one is taken off as the overhead product stream, and the other (the reflux) is recycled to the top of the column. The overhead product stream contains 89.2% of the benzene fed to the column. The liquid leaving the bottom of the column is fed to a partial reboiler in which 45% of it is vaporized. The vapor generated in the reboiler (the boilnp) is recycled to become the rising vapor stream in the column, and the residual reboiler liquid is taken off as the bottom product stream. The compositions of the streams leaving the reboiler are governed by the relation... 

Design studies had shown that to recover the high heat content in the reactor effluent stream efficiently, it is desirable to split the effluent streams from each reactor into two parts, with the major part going to preheat the recycle gas to that reactor. A small fuel-fired heater is provided in each reactor train to trim the temperature of the recycle gas to that reactor. The excess hot effluent streams from all the reactors are combined and used to preheat and vaporize the methanol feed to the dehydration reactor. Although the process design is nearly in heat balance, a discrete quantity of... 

Most producers operate with a molar ratio of alcohol-to-oil of at least 6 1. This is 100% more than is consumed in the transesterification reaction so the excess must be removed and recycled. The excess methanol splits 60%/40% between the methyl esters and glycerin, so methanol must be removed from both streams (Ma et al., 1998a 1998b 1999). Methanol recovery is frequently accomplished by flash vaporization, which yields the methanol plus any water that may have been present in the reaction mixture. Excessive water is removed by a distillation column. 

A + C + D—>G, A + C + E— //, A + E- F, 3D — 2F. Four gas fresh feed streams enter the process. One of these is fed into the bottom of the stripper. The vapor stream leaving the reactor is cooled before entering a separator. Liquid from the separator is fed into a stripper, which produces a bottoms product stream. Vapor from the separator is split between a gas purge and a recycle stream back to the reactor. The vapor from the stripper is also fed into the reactor. The reactor is cooled by manipulating cooling-water flow rate to cooling coils. 

The liquid streams from the separator and the bottom of the absorber are combined and fed into a distillation column. The bottoms from the column is split into two streams absorber lean oil and recycle acetic acid. The overhead vapor condenses into two liquid phases because of the nonideality of the phase equilibrium. The aqueous phase from the decanter is removed as product and sent to further processing, which we do not consider here. Some of the organic phase (mostly vinyl acetate) is refluxed back to the column, and some is removed for further processing. 

The ICI process is an example of neutralization at atmospheric pressure. Nitric acid feed is preheated by part of the vapors produced in the neutralizer and is then split into two streams. Recycled, undersized product is dissolved in one stream, conditioning material in the other. The recombined streams are added to a two stage neutralizer along with ammonia and recirculated solution to give 87 to 89% ammonium nitrate feed for evaporation. The C I—Girdler-Cominco process is similar in principle the Pintsch-Bamag (23) process uses a two-stage neutralizer without recirculation. 

In specific cases when the vapor-liquid equilibrium favors distillation at the side of the organic component of an azeotrope and a high purity of the organic component is specified the membrane system may be used just to split the azeotrope. For the separation of the system acetonitrile-water a hybrid system as shown in Fig. 3.19 may be economically advantageous. Here the membrane system is used to cross the azeotropic point the partially dehydrated vapor enters the second column in which final dehydration is effected. Again it is necessary to determine the economical optimum between the size of both columns, the energy consumption of the first one and the volume of the recycle stream from the second column at one side, and the size of the membrane system and its outlet concentration on the other side. 

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