Distillation trains

Morari, M., and Faith, D. C., The Synthesis of Distillation Trains with Heat Integration, AlChEJ, 26 916, 1980. 

Most alkylphenols sold today require refinement. Distillation is by far the most common separation route. Multiple distillation tower separations are used to recover over 80% of the alkylphenol products in North America. Figure 4 shows a basic alkylphenol distillation train. Excess phenol is removed from the unrefined alkylphenol stream in the first tower. The by-products, which are less volatile than phenol but more volatile than the product, are removed in the second tower. The product comes off the third tower overhead while the heavy by-products come out the bottom. 

Monoalkylphenols are generally produced in specialized plants that have both continuous reactors and continuous vacuum distillation trains. 

Alkenes with between 4 and 24 carbon atoms react with phenol to produce an unrefined phenol—alkylphenol mixture. This mixture is fed to the distillation train where the phenol is removed for recycle and the product is isolated. The product is then stored in heated tanks made of stainless steel or phenoHc resin lined carbon steel. These tanks are blanketed with inert gas to avoid product discoloration associated with oxidation. 

Dialkylphenols are also produced in specialized plants. These plants combine complex batch reactors with vacuum distillation trains or other recovery systems. Alkenes with carbon numbers between 4 and 9 react with phenol to make an unrefined alkylphenol mixture, which is fed into the recovery section where very high purity product is isolated. The product is stored, handled, and shipped just as are the monoalkylphenols. 

Figure 5 illustrates a typical distillation train in a styrene plant. Benzene and toluene by-products are recovered in the overhead of the benzene—toluene column. The bottoms from the benzene—toluene column are distilled in the ethylbenzene recycle column, where the separation of ethylbenzene and styrene is effected. The ethylbenzene, containing up to 3% styrene, is taken overhead and recycled to the dehydrogenation section. The bottoms, which contain styrene, by-products heavier than styrene, polymers, inhibitor, and up to 1000 ppm ethylbenzene, are pumped to the styrene finishing column. The overhead product from this column is purified styrene. The bottoms are further processed in a residue-finishing system to recover additional styrene from the residue, which consists of heavy by-products, polymers, and inhibitor. The residue is used as fuel. The residue-finishing system can be a flash evaporator or a small distillation column. This distillation sequence is used in the Fina-Badger process and the Dow process. 

Because HCl is constandy present in most parts of the equipment, corrosion is always a potential problem. Chlorine and benzene, or any recycled material, must be free of water to trace amounts to prevent corrosion and deactivation of the catalyst. The reactor product contains HCl and iron. In some plants, the product is neutralized with aqueous NaOH before distillation. In others, it is handled in a suitably-designed distillation train, which includes a final residue from which FeCl can be removed with the high boiling tars. 

Chlorobenzene mixtures behave in distillation as ideal solutions. In a continuous distillation train, heat may be conserved by using the condensers from some units as the reboilers for others thereby, saving process energy. 

Figure 7-6. The PPG Industries Inc. Chloroethylene process for producing perchloro- and trichloroethylene (1) reactor, (2) graphite exchanger, (3) refrigerated condenser, (4) scrubber, (5) phase separation of perchlor from trichlor, (6, 7) azeotropic distillation, (8) distillation train, (9-11) crude trichlor separation—purification, (10-16) crude perchlor separation—purification.

In terms of downstream processes, the flow-rates, compositions, and so on, dictate the size and number of each unit operation for example, while a batch distillation may be used to separate a single feed into a number of different product streams, a continuous distillation train would in general require N columns for N different product streams. The fact that a high degree of modeling is used in the design of each MPI, results in the generally held belief that continuous processes... 

The second column in the distillation train of an aromatics plant is required to split toluene and ethylbenzene. The recovery of toluene in the overheads must be 95%, and 90% of the ethylbenzene must be recovered in the bottoms. In addition to toluene and ethylbenzene, the feed also contains benzene and xylene. The feed enters the column under saturated conditions at a temperature of 170°C, with component flowrates given in Table 9.10. Estimate the mass balance around the column using the Fenske Equation. Assume that the K-values can be correlated by Equation 9.68 with constants A , 5 and C, given in Table 9.10. 

For the safety comparison analysis the ISBL of acetic acid process was divided into two steps reaction section (reactor, separator, scrubber) and distillation train. Both steps were handled separately during the analysis. The analysis of the data and the results are presented in the Table 26 for reaction section and in the Table 27 for the distillation train. 

The total inherent safety index for reaction section is higher than for distillation train. Consequently the distillation train is inherently safer than the reaction section since ... 

In the distillation train there are no potential reactions, except potential interaction. 

Table 27. Safety analysis for the distillation train of the acetic acid process.

A typical configuration for a methanol carbonylation plant is shown in Fig. 1. The feedstocks (MeOH and CO) are fed to the reactor vessel on a continuous basis. In the initial product separation step, the reaction mixture is passed from the reactor into a flash-tank where the pressure is reduced to induce vapourisation of most of the volatiles. The catalyst remains dissolved in the liquid phase and is recycled back to the reactor vessel. The vapour from the flash-tank is directed into a distillation train which removes methyl iodide, water and heavier by-products (e.g. propionic acid) from the acetic acid product. 

Other than the reactor system, the distillation column that separates the unconverted ethylbenzene from the crude styrene is the most important and expensive equipment in a styrene plant. To minimize yield losses and to prevent equipment fouling by polymer formation, polymerization inhibitors are used in the distillation train, product storage, and in vent gas compressors. 

The qualities of the styrene product and toluene by-product depend primarily on three factors the impurities in the ethylbenzene feed-stock, the catalyst used, and the design and operation of the dehydrogenation and distillation units. Other than benzene and toluene, the presence of which is usually inconsequential, possible impurities in ethylbenzene are Cj-Cm nonaromatics and C Cm aromatics. The condensed reactor effluent is separated in the settling drum into vent gas (mostly hydrogen), process water, and organic phase. The organic phase with polymerization inhibitor added is pumped to file distillation train. 

M. A. Gomez and J. D. Seader. Synthesis of distillation trains by thermodynamic analysis. Comp. Chem. Eng., 9 311, 1985. 

M. A. Is la and J. Cerda. A general algorithmic approach to the optimal synthesis of energy-efficient distillation train designs. Chem. Eng. Comm., 54 353, 1987. 

M. Morari and C. D. Faith. The synthesis of distillation trains with heat integration. AlChE... 

Example Isopentane (IC5), normal pentane (NC5), and cyclopentane (CC5) are to be separated by means of distillation. A 5000-bpd rich feed with these components is received. The mixed feed containing these and many other components—including ethane, propane, butane, through benzene—is received as a liquid. A three-column distillation train, in series, will be installed to produce IC5, NC5, and CC5 spec product liquid streams. Methane, ethane, propane, and butane have been removed in an upstream stabilizer column. Only trace ethane and propane are remaining in the feed stream feeding the first column, IC5. 

A process simulation of this three-column distillation train has been made, finding and establishing the number of actual trays, column diame-... 

Alcohols are dried and sent to a distillation train where they are separated by conventional fractional distillation. Crude alcohols are separated into C2-C%, C6-C10, C12-Cu, C16-C18, and C20 + fractions. High purity, individual homologs are prepared by redistillation of the appropriate mixture. The product alcohols are marketed as ALFOL alcohols by Conoco Chemicals. 

The aluminum trialkoxides are then hydrolyzed with dilute sulfuric acid in the Ethyl process (23)- This forms free alcohol and an aqueous aluminum sulfate solution which are separated by phase split. The aqueous aluminum sulfate is sold. Product alcohols are washed with caustic to remove traces of acid, dried, and fed to conventional distillation train. The product alcohols are sold by Ethyl under the trade name of EPAL alcohols. 

Freshwater, D.C. and Henry, B.D., "The Optimal Configuration of Multicomponent Distillation Trains," Chemical Engineer, pp 533-536, September 1975. 

Close the urine in a glass vessel and let it putrefy for a month or more in a warm place. The odors involved with this process certainly class it as an outdoor activity. Filter the putrefied urine into a distillation train and slowly distil to dryness. Return the distillate to the solids that remain (the caput mortuum) and again digest for a month. Distil and repeat the cohobation of distillate on the solids a third time. 

As the Antimony Spirit enters the water you may perceive the liquid to be more viscous and soapy or foamy. This is a good sign the ore has opened. Now the flask of material is attached to a distillation train. Begin the distillation slowly at 80°C and slowly raise it to about 400°C over a period of three days. 

Overhead vapor from the CD column (1) is condensed and returned as reflux after removing propane and lights (P). The CD column bottom section strips benzene from cumene and heavies. The distillation train separates cumene product and recovers polyisopropylbenzenes (PIPB) and some heavy aromatics (H) from the net bottoms. PIPB reacts with benzene in the transalkylator (2) for maximum cumene yield. Operating conditions are mild and noncorrosive standard carbon steel can be used for all equipment. 

The polished product is passed to a distillation train (3) where a novel distillation arrangement allows the ethanol/ethyl acetate water azeotrope to be broken. Products from this distillation scheme are unreacted ethanol, which is recycled, and ethyl acetate product. 

The glycol plant feed along with any high aldehyde EO bleeds from the EO purification section are sent to the glycol reactor (9) and then to a multi-effect evaporation train (10, 11, 12) for removal of the bulk of the water from the glycols. The glycols are then dried (13) and sent to the glycol distillation train (14, 15, 16) where the MEG, DEG and TEG products are recovered and purified. 

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%. 

Figure 2.2 compares these two possible configurations for a simple plant. A fresh feed stream containing a mixture of chemical components A, B, and C is fed into a two-column distillation train. The relative volatilities are > aB > separation sequence A is taken out the top of the first column and B out the top of the second column. 

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