Solvent recovery xylene separation

Until late 1990s, purified m-xylene was produced predominantly by the HF/BF3 process developed by Mitsubishi Gas Chemical Co. The separation is based on the complex formation between m-xylene and solvent HF/BF3. However, concerns about the process operation, environment, metallurgy and safety render the process commercially unattractive due to its use of HF/BF3. These concerns led to many developments in the adsorptive separation process for m-xylene separation [3-8]. The UOP MX Sorbex process, developed by UOP and commercialized in 1998, already accounts for more than 70% of the world s m-xylene capacity. A 95% m-xylene recovery with 99.5% purity can be achieved by the MX Sorbex process. 

Research on solvent based polymer separation processes is by no means in its infancy. One of Ae first studies on mixed plastics was conducted by Sperber and Rosen [24,25] in the mid 1970 s. These investigators used a blend of xylene and cyclohexanone to separate a mixture of polystyrene (PS), poly(vinyl chloride) (PVC), high density polyethylene (HOPE), low density polyethylene (LDPE), and polypropylene (PP) into three separate phases. In adAtion, many United States and foreign patents dating from the 1970 s were granted for the solvent recovery of thermoplastic jwlymers [26-30]. The interest in solvent processes waned in the late 1970 s as the oil crisis eased, but the growing need to develop solutions to Ae solid waste problem has renewed Ae research effort [31-33]. 

Adsorptive solvent recovery with steam desorption and condensation units with gravity separator and a stripper have become a standard practice in modem production plants. The solvents-laden air (toluene, xylene) is collected from emission points, e.g., rotogravure printing machines, drying ducts by means of a blower and passed through the recovery plant. 

Another process that is sometimes used is extractive distillation [2,3]. The concept of extractive distillation is that a non-volatile polar solvent such as sulfolane is added, which has a different effect on the volatility of the components of the hydrocarbon mixture. Typically, the solvent decreases the volatility of the aromatic compounds, making them easier to separate from the aliphatics. The solvent is continuously added near the top of the extractive distillation column. Aliphatics are removed overhead and solvent and aromatics from the bottom of the column. The aromatics can be separated from the extractive solvent by distillation in a solvent recovery column. The boiling point of sulfolane (285 °C) is significantly higher than even o-xylene (144.4 C) enabling the isolation of the aromatic stream. Optionally, this can be further purified by a water wash. 

Acrylic Acid Recovery. The process flow sheet (Fig. 3) shows equipment and conditions for the separations step. The acryUc acid is extracted from the absorber effluent with a solvent, such as butyl acetate, xylene, diisobutyl ketone, or mixtures, chosen for high selectivity for acryUc acid and low solubihty for water and by-products. The extraction is performed using 5—10 theoretical stages in a tower or centrifiigal extractor (46,61—65). 

Unique adsorption selectivities are employed in the separation of Cg aromatic isomers, a classical problem that caimot be easily solved by distillation, crystallisation, or solvent extraction (10). Although -xylene [106-42-3] can be separated by crystallisation, its recovery is limited because of the formation of eutectic with / -xylene [108-58-3]. However, either -xylene, / -xylene, (9-xylene [95-47-6] or ethylbensene [100-41-4] can be extracted selectively by suitable modification of seoUtic adsorbents. 

Vapor-phase catalytic oxidation of dutene is a mote direct route to the dianhydtide. Hbls in Europe apparently uses this route, which eliminates the need for a separate dehydration step and for handling of any oxidants or solvents. Continuous operation is faciHtated, corrosion is minimized, and product recovery is simplified. The vapor-phase oxidation of dutene is similar to that of o-xylene to phthaHc anhydtide, and phthaHc anhydtide units can be... 

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

These solvents have high solubility for aromatics but not for nonaromatics. They also have high boiling points for later separation from the aromatics. Fractionation separates the benzene from the solvent and other aromatics. A typical Udex extraction starting with a reformed feed of 51.3% aromatic content gives 7.6% benzene, 21.5% toluene, 21%, xylenes, and 1.2% C9 aromatics. The recovery rate is 99.5% of the benzene, 98% of the toluene, 95% of the xylene, and 80% of the C9 aromatics. 

This case study involves the recovery of highly valued and high demand ethylbenzene (EB) and mixed-xylenes (comprising of p-xylene (PX), m-xylene (MX) and o-xylene (OX)) from a C8-aromatics mixture (C8A). As point out above, C8A is isomers mixture, so their separation (recovery) is not simple, that why there is only one commercial process of liquid-phase adsorptive separation available for EB recovery from C8A. [8] However, this process requires high investment cost and generates huge volume of waste adsorbent that may become an environmental problem. Therefore, another green process should be considered for the EB purification. The ratio of various properties of the key components (EB and PX) were tested to examine the possibly alternatives. The result showed, by vapor pressure ratio, the solvent-based extractive distillation can be employed for their purification. [7]... 

Removal of Aromatic Compounds. Because of the demand for high-purity aromatic compounds for petrochemical feedstocks, several processes have been developed for BTX (benzene, toluene, and xylenes) recovery from distillate streams. In these processes, aromatic compounds are separated from nonaromatic compounds by liquid—liquid extraction using polar solvents. The three major processes in use are the UOP—Dow UDEX process (di- or triethylene glycol solvent), the UOP sulfolane process (tetrahydrothiophene 1,1-dioxide), and the Union Carbide TETRA process (tetraethylene glycol). 

Water/hydrocarbon mixture Condensation, separation of the liquid water/ben-zine. The waste gas is ignited and the wastewater is fed to a treatment plant, e) Recovery of methanol and toluene [115]. During the production of a textile chemical a solution (mother liquor) is produced containing methanol and an aromatic solvent (toluene or xylene). An azeotrope containing methanol and toluene is produced by discontinuous ditillation. The toluene-containing phase separates out on addition of water. Methanol is recovered from the methanol-containing phase by continuous... 

The recovery of pure aromatics from hydrocarbon mixtures is not possible using distillation process because the boiling points of many non-aromatics are very close to benzene, toluene, etc. Also, azeotropes are formed between aromatics and aliphatics. Three principle methods are used for separation azeotropic distillation, liquid-liquid extraction, and extractive distillation. Three major commercial processes have been developed for separation Udex, Sulpholane, and Arosolvan. Over 90% plants now use one of these processes. Each use an addition of solvent such as a mixture of glycols, tetramethylene sulfone, or N-methyl-2-pyrrolidone to aid in the extraction of aromatics. This occurs with high precision and efficiency. Pure benzene, toluene, and xylene are produced by these processes. 

El. We have a liquid feed that is 48 wt % m-xylene and 52 wt % o-J lene, which are to be separated in a fractional extractor fFigure 13-51 at 25°C and 101.3 kPa. Solvent 1 is P,P -thiodipropionitrile, and solvent 2 is n-hexane. Equilibrium data are in Table 13-3. For each kilogram of feed, 200 kg of solvent 1 and 20 kg of solvent 2 are used. Both solvents are pure when they enter the cascade. We desire a 92% recovery of o-xylene in solvent 1 and a 94% recovery of m-j lene in n-hexane. Find outlet conposition, N, and Nf. Adjust the recovery of m-j lene if necessary to solve this problem,... 

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