Benzene-toluene feed, distillation

Figure 2. Simple distillation system for the separation of a 45%-55% benzene-toluene feed into 92% benzene distillate and a 95% toluene bottoms product. Available-energy flows and destructions are given in 10° Btu/hr.

For the rectification in Example 11.4-1, where a benzene-toluene feed is being distilled to give a distillate composition of xp = 0.95 and a bottoms composition oix = 0.10, calculate the following. 

Distillation of Benzene-Toluene Feed Using Enthalpy-Concentration Method. A... 

Example 8.1.13 Consider the problem of benzene-toluene distillation illustrated in Example 8.1.8. It is to be carried out in a packed tower at 1 atm with a reflux ratio of 2 using a SOSO benzene-toluene feed mixmre coming in at 3 kgmol/min Xiid = 0.9S, XiM = O.OS, where i = 1 is for benzene. The HTU values in these flow rate ranges are given in Table 8.1.4 (Seader and Henley, 1998). 

Hquid—Hquid-phase spHt the compositions of these two feed streams He oa either side of the azeotrope. Therefore, column 1 produces pure A as a bottoms product and the azeotrope as distillate, whereas column 2 produces pure B as a bottoms product and the azeotrope as distillate. The two distillate streams are fed to the decanter along with the process feed to give an overall decanter composition partway between the azeotropic composition and the process feed composition according to the lever rule. This arrangement is weU suited to purifying water—hydrocarbon mixtures, such as a C —C q hydrocarbon, benzene, toluene, xylene, etc water—alcohol mixtures, such as butanol, pentanol, etc as weU as other immiscible systems. 

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

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 distillation train first separates the benzene/toluene byproduct from main crude styrene stream (8). Unconverted EB is separated from styrene (9) and recycled to the reaction section. Various heat recovery schemes are used to conserve energy from the EB/SM column system. In the final purification step (10), trace C9 components and heavies are separated from the finished SM. To minimize polymerization in distillation equipment, a dinitrophenolic type inhibitor is co-fed with the crude feed from the reaction section. Typical SM purity ranges between 99.90% and 99.95%. 

Optimize the design of a distillation column to separate 225 metric tons per hour of an equimolar mixture of benzene, toluene, ethylbenzene, paraxylene, and orthoxylene with minimum total annualized cost. The feed is a saturated liquid at 330 kPa. The recovery of toluene in the distillate should be greater than 99%, and the recovery of ethylbenzene in the bottoms should be greater than 99%. 

A column is to be designed to separate 1000 moles/hr of a binary mixture of benzene (QH ) and toluene ( 7 ). The feed will contain 40% benzene and 60% toluene. A distillate that is 99% benzene and a bottoms that is 1% benzene are desired at a reflux ratio of 3 to 1. For this mixture, the average value of relative volatility (a) is 2.50. Estimate the number of equilibrium stages at this reflux ratio and the optimum feed stage location. 

A feed stream made up of 40% mole benzene and 60% mole toluene is to be separated into benzene-rich and toluene-rich products using a distillation column. The column has ten equilibrium stages including a partial condenser and a partial reboiler and is operated at 172 kPa. The feed stream, with a flow rate of 100 kmol/h, is at its bubble point at 172 kPa and is placed in the fourth stage from the top. It is required to determine the compositions of the two products at different reflux ratios. Vapor-liquid equilibrium data for the benzene-toluene system are provided in Table 5.1 at 172 kPa. 

The benzene-toluene mixture of Example 6.1 is to be separated into approximately 50 kmol/h distillate and 50 kmol/h bottoms products. The column is to be operated at a reflux ratio of one. Determine the effect of the number of stages and feed location on the purity of the products. 

It is required to separate the benzene-toluene mixture of Example 6.1 into a benzene-rich distillate with 0.80 mole fraction benzene and a toluene-rich bottoms with 0.05 mole fraction benzene. The separation is to be made using a distillation column with 15 theoretical stages that include a partial condenser and a partial reboiler. Calculate the reflux ratio required to achieve the specified separation and determine the optimum feed location. What effect would lowering the number of stages to ten have on the reflux ratio and the optimum feed location ... 

A stream containing benzene, toluene, and biphenyl is to be separated in a distillation column to produce purified benzene in the distillate. The separation will take place in an existing column with a total condenser, a partial reboiler, and several optional feed locations. The feed stream is of fixed flow rate, composition, and thermal conditions. The entire feed may be introduced at any one of the available feed trays, but may not be split and introduced at more than one feed tray. The condenser pressure is controlled by an inert gas flowing in and out of the reflux drum. Using column modules representation, determine the degrees of freedom for this operation, and recommend a set of specifications to define the column performance. 

A distillation column is designed for the separation of a mixture of benzene, toluene, and biphenyl into a distillate (mostly benzene), a side draw (mostly toluene), and a bottoms product (mostly biphenyl). The column will operate at a pressure of about 175 kPa and a temperature ranging from about 90°C in the condenser to about 240°C in the reboiler. The three products define two column sections, and in each section a A -value for biphenyl, designated as the reference component, and relative volatilities for the other components are estimated based on the average temperature and pressure in the section. The feed stream component flow rates, relative volatilities, reference K-values, and product rates are given below ... 

Eollowing are two examples (16.1 and 16.2) of a distillation column that demonstrate the effect of applying different pairing strategies. In both examples the control loops for the column pressure and the liquid levels in the condenser accumulator and the column bottom are determined independently based on practical considerations. Thus, the column pressure is controlled by various techniques that may involve the condenser coolant rate, and the liquid levels are controlled by the product flow rates. What remains to be decided is how to pair the distillate and bottoms compositions with the reflux rate and the reboiler heat duty. The same distillation column is used in both examples, having a total condenser and a reboiler, one feed and two products. The column is designed to separate a benzene-toluene mixture into benzene and toluene products with specified purities. 

The dehydrator is a column with-about 30 trays, designed to separate the water from the phenol by heteroazeotropic distillation in the presence of benzene and feed-and make-up toluene. The benzene/water azeotrope (bplJ>13 69 C, water content 8.8 per cent weight) and toluene/water azeotrope (bpl013 = 84 Q water content 13.5 per cent weight) leaving at the top are cooled rod condensed to yiddjwo phases ... 

A distillation column with a partial reboiler and a total condenser is being used to separate a mixture of benzene, toluene, and 1,2,3-trimethylbenzene. The feed, 40 mol% benzene, 30 mol% toluene, and 30 mol% 1,2,3-trimethylbenzene, enters the column as a saturated vapor. We desire 95% recovery of the toluene in the distillate and 95% of the 1,2,3-trimethylbenzene in the bottoms. The reflux is returned as a saturated liquid, and constant molar overflow can be assumed. The column operates at a pressure of 1 atm. Find the number of equilibrium stages required at total reflux, and the recovery fraction of benzene in the distillate. Solutions of benzene, toluene, and 1,2,3-trimethylbenzene are ideal. 

There is no short-cut method for stabiliser, but this can be easily simulated as a distillation column with vapour distillate. The feed should be sent close to the top. For the separation benzene/toluene and toluene/di-phenyl a short-cut method as Fenske-Underwood-Gilliland can be used. R/Rmin=1.2 or N/Nmin=2 may be taken in a preliminary design. Note that the use of design models in preliminary simulation makes converge easier the recycles by guarantying the specifications. Obviously, the short-cut design must be reliable in order to fulfil later the specifications in rating mode. 

Axens/Uhde Benzene, Toluene Reformate and/or hydrotreated Pyrolysis gasoline BT cuts In extractive distillation, the addition of a selective solvent modifies the vapor pressures of the hydrocarbons in the feed in such a way that paraffinic and naphthenic components can be separated from the aromatics by distillation. 65 2009... 

Initial consideration is usually given to a sequence of ordinary distillation columns, where a single feed is sent to each column and the products from each column number just two, the distillate and the bottoms. For example, consider a mixture of benzene, toluene, and biphenyl. Because the normal boiling points of the three components (80.1, 110.8, and 254.9°C, respectively) are widely separated, the mixture can be conveniently separated into three nearly pure components by ordinary distillation. A common process for separating this mixture is the sequence of two ordinary distillation columns shown in Figure 7.10a. In the first column, the most volatile component, benzene, is taken overhead as a distillate final product. The bottoms is a mixture of toluene and biphenyl, which is sent to the second column for separation into the two other final products a distillate of toluene and a bottoms of biphenyl, the least volatile component. 

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