Separators distillation towers

After cleavage the reaction mass is a mixture of phenol, acetone, and a variety of other products such as cumylphenols, acetophenone, dimethyl-phenylcarbinol, a-methylstyrene, and hydroxyacetone. It may be neutralised with a sodium phenoxide solution (20) or other suitable base or ion-exchange resins. Process water may be added to facilitate removal of any inorganic salts. The product may then go through a separation and a wash stage, or go direcdy to a distillation tower. 

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. 

Fig. 3. Separation and purification of butadiene A, first extraction distillation tower B, solvent stripper C, second extraction distillation tower D, topping...

In distillation towers, entrainment lowers the tray efficiency, and 1 pound of entrainment per 10 pounds of liquid is sometimes taken as the hmit for acceptable performance. However, the impact of entrainment on distiUation efficiency depends on the relative volatility of the component being considered. Entrainment has a minor impact on close separations when the difference between vapor and liquid concentration is smaU, but this factor can be dominant for systems where the liquid concentration is much higher than the vapor in equilibrium with it (i.e., when a component of the liquid has a very lowvolatiUty, as in an absorber). 

This chapter has only provided a brief overview of the technology of distillation. In part, to highlight some important engineering concepts and equipment, the following summary is given. As described, refinery main fractionators are distillation towers that separate very wide boiling fractions into a series of rough... 

Acetonitrile serves to greatly enlarge the spread of relative volatilities so that reasonably sized distillation equipment can be used to separate butadiene from the other components in the C4 fraction. The polar ACN acts as a very heavy component and is separated from the product without much difficulty.The feed stream is carefully hydrogenated to reduce the acetylene level rerun, and then fed to the single stage extractive distillation unit. Feed enters near the middle of the extractive distillation tower, while (lean) aqueous ACN is added near but not at the top. Butenes and butanes go overhead as distillate, with some being refluxed to the tower and the rest water washed for removal of entrained ACN. 

The first stage does the bulk of the separation, and the second is used to remove other dienes and acetylenes from the isoprene. In the extractive distillation tower of each stage, the ACN solvent is introduced near the top, and being the highest boiling component, travels downward. The effective relative volatility of the less unsaturated hydrocarbons is increased with respect to isoprene. Thus most of the impurities go overhead and the isoprene is carried down with the solvent. 

The primary process for separating the hydrocarbon components of crude oil is fractional distillation i.e. separation according to the boiling points of the components. These separated fractions are processed further by catalytic reformers, cracking units, alkylation units, or cokers which have there own fractional distillation towers for its products. 

The gas and liquid are separated in the cold separator, which is a three-phase separator. Water and glycol come off the bottom, hydrocarbon liquids are routed to the distillation tower and gas flows out the top. If it is desirable to recover ethane, this still is called a de-methanizer. If only propane and heavier components are to be recovered it is called a de-etha-nizer. Tiie gas is called plant residue and is the outlet gas from the plant. 

A fractional distillation tower is used to separate different compounds in petroleum. The fuels condense at different enfi efttures and produce different products. 

Petroleum distillation, (a) A distillation tower at a petroleum refinery, (b) A diagram showing the boiling points of the petroleum fractions separated by distillation. 

The catalytic performances obtained during transalkylation of toluene and 1,2,4-trimethylbenzene at 50 50 wt/wt composition over a single catalyst Pt/Z12 and a dualbed catalyst Pt/Z 121 HB are shown in Table 1. As expected, the presence of Pt tends to catalyze hydrogenation of coke precursors and aromatic species to yield undesirable naphthenes (N6 and N7) side products, such as cyclohexane (CH), methylcyclopentane (MCP), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP), which deteriorates the benzene product purity. The product purity of benzene separated in typical benzene distillation towers, commonly termed as simulated benzene purity , can be estimated from the compositions of reactor effluent, such that [3] ... 

In the atmospheric distillation process (Figure 2.1), heated crude oil is separated in a distillation column (distillation tower, fractionating tower, atmospheric pipe still) into streams which are then purified, transformed, adapted, and treated... 

Extractive distillation was the basis of a process introduced commercially by the Shell Development Co. and put into operation in 1940 at the Houston refinery of the Shell Oil Co., Inc., for separating toluene from virgin stocks (6) subsequently it was used also on hydroformates and cracked naphthas. This process, shown diagrammatically in Figure 3, involves the production of a toluene concentrate by distillation to remove low and high boiling contaminants, which then is extractively distilled with phenol to separate the aromatics from the paraffin (5). The extract is obtained as a bottoms stream from the extractive distillation tower, and is further fractionated in a distillation tower to separate raw toluene from the phenol, after which the toluene is acid treated and redis-... 

In our example, we obtained a rather precise fixed-capital cost estimate from a private industry with high-pressure-technology experience. This estimate, updated to year 2000, was of 600,000 EUR for the plant sketched in Fig. 8.3-2, including all costs listed in the above paragraph. In case a distillation tower was needed to obtain pure CO2 for recycling, the chemical plant would be more expensive because a flash-type separator would be substituted with a distillation tower, with boiler and condenser. 

High vapor velocities, combined with high foam levels, will cause the spray height to hit the underside of the tray above. This causes mixing of the liquid from a lower tray, with the liquid on the upper tray. This backmixing of liquid reduces the separation, or tray efficiency, of a distillation tower. 

The very first continuous distillation column was the patent still used to produce Scotch whiskey in the 1830s. It had 12 bubble-cap trays with weirs, downcomers, tray decks, and bubble caps with internal risers. Current trayed towers are quite similar. As most distillation towers have always been trayed rather than packed, one would have to conclude that trayed towers must have some sort of inherent advantage over packed towers. And this is indeed true, in a practical sense even though, in theory, a packed tower has greater capacity and superior separation efficiency than a trayed column. 

Why do we usually want to separate water from the reflux stream, shown in Fig. 26.3 Some of the bad things that happen to the distillation tower, if water persistently entrains into the reflux are... 

In such a process an additive or solvent of low volatility is introduced in the separation of mixtures of low relative volatilities or for concentrating a mixture beyond the azeotropic point. From an extractive distillation tower, the overhead is a finished product and the bottoms is an extract which is separated down the line into a product and the additive for recycle. The key property of the additive is that it enhance the relative volatilities of the substances to be separated. From a practical point of view, the additive should be stable, of low cost, require moderate reboiler temperatures particularly for mixtures subject to polymerization or thermal degradation, effective in low to moderate concentrations, and easily recoverable from the extract. Some common additives have boiling points 50-100°C higher than those of the products. 

In the process (Figure 9-22), fresh vacuum residuum, microcatalyst, and hydrogen are fed to the hydroconversion reactor. Effluent is sent to a flash separation zone to recover hydrogen, gases, and liquid products, including naphtha, distillate, and gas oil. The liquid bottoms from the flash step is then fed to a vacuum distillation tower to obtain a 565°C (1050°F ) product oil and a 565°C + (1050°F+) bottoms fraction that contains unconverted feed, microcatalyst, and essentially all of the feed metals. 

A type of foam in which solid particles are also dispersed in the liquid (in addition to the gas bubbles), as in froth flotation. The solid particles can even be the stabilizing agent alternatively, the foam layer produced at the top of a separation vessel or distillation tower. The term sometimes refers simply to a concentrated foam, but this usage is not preferred. 

Extractive distillation, that is, fractional distillation in the presence of a solvent, is used to recover aromatic hydrocarbons from, say, reformate fractions in the following manner. By means of preliminary distillation in a 65-tray prefractionator, a fraction containing a single aromatic can be separated from the reformate, and this aromatic concentrate is then pumped to an extraction distillation tower near the top, and aromatic concentrate enters near the bottom. A reboiler in the extractive distillation tower induces the aromatic concentrate to ascend the tower, where it contacts the descending solvent. 

A separation process is sought that can satisfy both our present economic and enviromental constraints. It would also provide an alternative to present practice that relies on expensive azeotropic or extractive distillation processes used in the recovery of products from low relative volatility streams. As an example, virtually all industrial butadiene recovery processes now rely on extractive distillation using acetonitrile or other equivalent agent to enhance the relative volatility of the C4 components. The use of supercritical or near critical separation of these streams may satisfy these requirements provided certain pressure, temperature and recompression criteria can be met. Such a process would also reduce the need for a complex train of distillation towers. 

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