Solvent refining processes aromatic extraction

The major solvent refining processes include solvent deasphalting, solvent dewaxing, lube oil solvent refining, aromatic extraction, and butadiene extraction. These processes are briefly described below. 

An ExxonMobil extraction process used to extract aromatics from lube feedstocks to improve the viscosity index and quality of lubricating oil base stocks, integrated with HYDROFINING In solvent refining processes, that portion of the oil which is dissolved in and removed by the selective solvent the solvent rich phase. Contains a low percentage of oil which is typically high in aromatic content. 

The separation of organic mixtures into groups of components of similar chemical type was one of the earliest applications of solvent extraction. In this chapter the term solvent is used to define the extractant phase that may contain either an extractant in a diluent or an organic compound that can itself act as an extractant. Using this technique, a solvent that preferentially dissolves aromatic compounds can be used to remove aromatics from kerosene to produce a better quality fuel. In the same way, solvent extraction can be used to produce high-purity aromatic extracts from catalytic reformates, aromatics that are essentially raw materials in the production of products such as polystyrene, nylon, and Terylene. These features have made solvent extraction a standard technique in the oil-refining and petrochemical industries. The extraction of organic compounds, however, is not confined to these industries. Other examples in this chapter include the production of pharmaceuticals and environmental processes. 

Phenol An aromatic hydrocarbon (C6H50H) used in the manufacture of phenolic resins, weed killers, plastics and disinfectants as well as in solvent extraction, a petroleum refining process. 

Carom [Carbide aromatics extraction] A two-stage process for removing aromatic hydrocarbons from petroleum refining streams. In the first stage, the aromatics are removed by liquid-liquid extraction with a proprietary solvent (a mixture of polyalkylene glycols and a glycol ether) at ambient temperature. In the second stage, the aromatics are stripped from the solvent by steam distillation. Developed by Union Carbide Corporation first commercialized in 1986, and now licensed by UOP. Seven units had been licensed by 2002. 

Process oils are not typical lubricants and are mostly used as processing aids in manufacture. They are generally additive-free mixtures of crude oil hydrocarbons and include products such as (i) medicinal white oils, (ii) technical white oils, (iii) bright process oils and (iv) dark process oils. Medicinal white oils are composed exclusively of isoparaffins and alkylnaphthenes. Technical white oils are less refined products than medicinal white oils and are composed of saturated hydrocarbons, though they may also contain a slight amount of aromatic compounds. Bright process oils include both yellow raffinates and brown distillates. Dark process oils are extracts from solvent refining of mineral base oils. 

One of Sun s objectives for the new plant was that the base stocks be at least of the same quality as those from solvent refining, therefore this hurdle had to be overcome. Their solution was to give the total dewaxed hydrocrackate product a light furfural extraction (about 97% raffinate) to remove the tri+ aromatics which appeared to be at the root of the problem.1516 Thus their process involved two solvent extraction steps, one before the hydrocracker and one afterwards. This route gave stable base stocks, but with some residual color. An example of the improvement obtained can be seen in Table 7.10, where 100, 200, and 500 SUS base stocks ( 1, 2, and 3 in Table 7.10) of approximately 110 VI from hydrocracking a distillate/DAO blend were tested for stability before and after furfural extraction. The results show that the extraction improves color relative to unextracted samples for the immediate hydrocracker products and that their performance in the stability test was improved as well by extraction. 

As we have seen, reduction of aromatics levels in lubricating oil base stocks relative to the feed has always been a significant part of their overall processing. The extraction step in the traditional solvent refining technology removes some aromatics, particularly the low VI polycyclic aromatics that contribute to oxidation instability and deposit formation. Hydrofinishing further reduces the levels of polynuclear aromatics, since conditions are generally too mild to reduce mono and... 

As in the traditional acid extraction process, the feedstock is generally dewaxed solvent refined base stock, since levels of the aromatics, polynuclear aromatics, and nitrogen and sulfur compounds are already reduced relative to a straight-run gas oil. This facilitates hydroprocessing by lightening the load on the catalysts and extending their lives. Equally important is that this is an already dewaxed feed, so the white oil producer does not have to bear the capital costs of crude fractionation and dewax units. 

Applications of Solvent to Aromatics Separation. There are two distinct techniques for using solvents in separation processes (2) extractive distillation and liquid-liquid extraction. Frequently these techniques or special variants can be combined in specified sequences to give a separation unobtainable by either method alone. Such has been the case for many of the solvents used or suggested in aromatics separation. The remainder of this discussion demonstrates the applicability and advantage of using dicyanobutane as a solvent for aromatics separation in petroleum refining. 

Edeleanu Process. The first commercially successful application of extraction of petroleum-refining processes was established by Edeleanu (38, 39), who extracted aromatic hydrocarbons from kerosenes with liquid sulfur dioxide to improve their burning qualities. The solvent is extremely selective for this purpose and acts without chemical reaction. 

In the wood rosin process, rosin is isolated from aged pine stumps that have been left in fields cleared for farming or lumbering operations. The stumps are cut and shredded to pieces the size of matchsticks. The wood chips are then extracted with an appropriate solvent, eg, aUphatic or aromatic petroleum hydrocarbons or ketones. The extract is fractionally separated into nonvolatile cmde rosin, volatile extractibles, and recovered solvent. The dark rosin is usually refined further to lighter-colored products using selective solvents or absorption. 

Another sulfur dioxide appHcation in oil refining is as a selective extraction solvent in the Edeleanu process (323), wherein aromatic components are extracted from a kerosene stream by sulfur dioxide, leaving a purified stream of saturated aHphatic hydrocarbons which are relatively insoluble in sulfur dioxide. Sulfur dioxide acts as a cocatalyst or catalyst modifier in certain processes for oxidation of o-xylene or naphthalene to phthaHc anhydride (324,325). 

Liquid extraction is utilized by a wide variety of industries. Applications include the recovery of aromatics, decaffeination of coffee, recovery of homogeneous catalysts, manufacture of penicillin, recovery of uranium and plutonium, lubricating oil extraction, phenol removal from aqueous wastewater, and extraction of acids from aqueous streams. New applications or refinements of solvent extraction processes continue to be developed. 

Solvent extraction is successful as a refining procedure only with stocks of paraffinic character. Raw stocks which have too much naphthenic character do not respond to solvent extraction. For some purposes the properties of naphthenic oils are desirable and there are procedures used specifically to obtain these special stocks from naphthenic crudes. Figure 16-2 is a schematic diagram of the refining of naphthenic oils. The final step in the modern process is hydrofinishing the older process used a sulfuric acid treatment instead to reduce the content of aromatic compounds. 

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