Aromatics recovery

So, Sulfolane and Carom, ca 1997, are two current rival processes. Sulfolane has a slight advantage over Carom ia energy consumption, while Carom has 6—8% less capital for the same capacity Sulfolane unit. In 1995, Exxon (37) commercialized the most recent technology for aromatics recovery when it used copolymer hoUow-fiber membrane ia concentration-driven processes, pervaporation and perstraction, for aromatic—paraffin separation. Once the non aromatic paraffins and cycloparaffins are removed, fractionation to separate the C to C aromatics is relatively simple. 

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

Superffex C t lytic Crocking. A new process called Superflex is being commercialized to produce predorninantiy propylene and butylenes from low valued hydrocarbon streams from an olefins complex (74). In this process, raffinates (from the aromatics recovery unit and the B—B stream after the recovery of isobutylene) and pyrolysis gasoline (after the removal of the C —Cg aromatics fraction) are catalyticaHy cracked to produce propylene, isobutylene, and a cmde C —Cg aromatics fraction. AH other by-products are recycled to extinction. 

The overhead temperatures of both the absorber and stripper are kept as low as possible to minimise solvent carryover. A temperature of about 311 K is typically used ia the high pressure absorber. The overhead temperature ia the stripper is set by the boiling poiat of the saturated complex solution and by the operating pressure of the stripper. At a stripping pressure of 0.166 MPa (1.7 atm), a temperature of 378 Kis used. The solvent-rich gas from the stripper is cooled to recover as much solvent as possible by condensation prior to the final aromatics-recovery section. Fiaal solvent recovery is accomphshed by adsorption on activated carbon (95). 

Extraction (discussed in Chapter 5) uses the selective adsorption of a component in a liquid to separate specific molecules from a stream. In application extraction may be coupled with its cousins, extractive distillation and azeotropic distillation, to improve extraction efficiency. Typical refinery extraction applications involve aromatics recovery (UDEX) and lubricants processing (furfural, NMP). Extractive distillation and azeotropic distillation are rarely employed in a refinery. The only... 

The forward reaction is extremely easy bevause of aromaticity recovery. These aspects of the intramolecular Diels-Alder reaction are generally very useful and able to provide polycyclic fused six-membered ring compounds which are otherwise difficult to realize. The controlling factors, geometry and mechanism of intramolecular Diels-Alder reactions have been comprehensively reviewed elsewhere i°4,106), and it is not our intention to discuss these in details. However, the synthetic utility of the reaction is demonstrated by the following examples107). 

Separation of toluene from the other components can be by solvent extraction or extractive distillation, just as described in the benzene chapter. The boiling points of benzene and toluene are far enough apart that the feed to separation unit of choice can be split (fractionated) rather easily into benzene concentrate and a toluene concentrate. Alternatively, the separation unit can be thought of as aromatics recovery unit. Then an aromatics concentrate stream is fed to the solvent extraction unit, and, the aromatics outturn can be split into benzene and toluene streams by fractionation. Both schemes are popular. 

Most of the toluene and xylenes have their origin in catalytic reforming or olefins plants. From there, the processing schemes vary widely from site to site. The schematic in Figure 3-6 captures most of the variations, although its hard to portray that some plants separate the BTXs from each other early in the scheme while others do it at varying places downstream of an aromatics recovery unit. 

Iso-plus Houdriforming a combination process using a conventional Houdri-former operated at moderate severity, in conjunction with one of three possible altematives-including the use of an aromatic recovery unit or a thermal reformer see Houdriforming. 

Han, S., Ferreira, F.C. and Livingston, A. (2001) Membrane aromatic recovery system (MARS) — a new membrane process for the recovery of phenols from wastewaters. Journal of Membrane Science, 188, 219. 

FIGURE 1 Toluene or aromatics recovery by sulfolane extraction. 

Aromatics recovery Ethylene oxide/Ethylene glycols Styrene (3)... 

References Emmrich, G., F. Ennenbach and U. Ranke, "Krupp Uhde Processes for Aromatics Recovery," European Petrochemical Technology Conference, June 21-22, 1999, London. 

Yields Overall aromatics recoveries are > 99% while solvent losses are extremely small, less than 0.006 Ib/bbl of feed. 

Reactor effluent is cooled in a series of exchangers (3) to recover waste heat and to condense (4) the hydrocarbons and steam. Uncondensed offgas—primarily hydrogen—is compressed (5) and then directed to an absorber system (6) for recovery of trace aromatics. Following aromatics recovery, the hydrogen-rich offgas is consumed as fuel by process heaters. Condensed hydrocarbons and crude styrene are sent to the distillation section, while process condensate is stripped (7) to remove dissolved aromatics and gases. The clean process condensate is returned as boiler feedwater to offsite steam boilers. 

Mars [Membrane aromatic recovery system] A membrane-based system for recovering aromatic compounds from aqueous waste streams. The membrane was initially made from a silicone rubber, but later versions used polypropylene glycol entrapped in a porous polypropylene sheet. Demonstrated first at a cresol-recovery plant in Knottingley, UK. 

A zeotropic and extractive distillations have been used through the years in the chemical industry to separate mixtures where the relative volatility of the key components is very close, or equal, to unity. Applications from the classical dehydration of alcohol with benzene (1) to more recent ones such as the propylene-propane separation (2) and aromatics recovery from hydrocarbon mixtures with N-methylpyrrolidone (3), indicate a continuous interest through the years in this area. 

Frederico CF, Ludmila PA, Boam SZ, and Andrew L. Pilot scale application of the membrane aromatic recovery system (MARS) for recovery of phenol from resin production condensates. J. Memb. Sci. 2005 257 120-133. 

If the required aromatics recovery is increased to 99 percent, what is the effect on solvent flow and stripper reboiler duty ... 

Aromatics concentrate in the solvent-rich stream that comes off the bottom of the extractive distillation column, while the nonaromatics concentrate in the column overhead. The main column bottoms are sent to a stripper column for solvent and aromatics recovery. Extensive heat exchange to recover energy... 

Section, which appears every month. It also has a special section on Patents which lists new patents according to their classification. The Process Issue of the Petroleum Refiner is now carrying a special section on Petrochemical Processes. In the September 1952 issue for example, Extractive Distillation for Aromatic Recovery, Modified SO2 Extraction for Aromatic Recovery, Udex Extraction, Ethylene Manufacture by Cracking, Ethylene Production, Hypersorption, Hydrocol, Dehydrogenation (for butadiene), and Butadiene Process, were described. These descriptions include the main essentials of the process, simplified flow diagrams, and the name of the company offering it. Formerly these processes were described under the Process Section. 

Dastgir, M. G., Peeva, L. G., Livingston, A. G. (2005). The performance of composite supported polymeric liquid membranes in the Membrane Aromatic Recovery System (MARS). Chem. Eng. Sci., 60, 7034-44. 

Overall yields of over 99% are achieved. Reaction is either in the liquid phase, using aluminum chloride catalyst, or in the vapor phase, using a boron trifluoride catalyst. Ethylbenzene can also be recovered by fractionation of some gasoline or naphtha fractions or some Cg fractions from aromatics recovery from pyrolysis gasoline (a by-product of ethylene production). Figure 6.8 shows U.S. production figures for both ethylbenzene and ethylene glycol. 

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