Aromatic extracts

In the manufacture of base oils, one of the refining operations is to extract with the aid of an appropriate solvent (furfural most often) the most aromatic fractions and the polar components. When free of solvent, the extracted aromatic fraction can eventually be refined, particularly to remove color or to thicken it, or still further, to fractionate it. The term, aromatic extract is used in every case. 

The aromatic extracts are black materials, composed essentially of condensed polynuclear aromatics and of heterocyclic nitrogen and/or sulfur compounds. Because of this highly aromatic structure, the extracts have good solvent power. 

The aromatic extracts have been used in the paint industry to partially replace linseed oil. They are still used for producing printer s ink. In addition, they are finding a variety of applications as plasticizers in the rubber industry or for the manufacture of plastics such as PVC. 

The aromaUc extracts are sought mainly tor their solvent power. They are characterized particularly by componential analyses such as the separation according to hydrocarbon family by liquid phase chromatography. 

All modern refineries have conversion units, designed to transform black effluent streams into lighter products gas, gasoline, diesel fuel. Among these conversion units, coking processes take place by pyrolysis and push the cracking reaction so far that the residue from the operation is very heavy it is called coke . 

---

Separation of Aromatic and Aliphatic Hydrocarbons. Aromatics extraction for aromatics production, treatment of jet fuel kerosene, and enrichment of gasoline fractions is one of the most important appHcations of solvent extraction. The various commercial processes are summarized in Table 4. 

Aromatics Extraction Process, pubhcation EM-9964, Adantic Richfield Co. 

Depending upon the refinery needs, the raw C5 plus steam cracked naphtha may be sent to isoprene extraction, treated to remove gum forming diolefins and sent to the refinery gasoline pool, or else completely hydrogenated and then fed to an aromatics extraction unit. 

Ethylbenzene is separated from mixed xylenes by fractionation using 360 trays and a high reflux ratio. Ethylbenzene is separated from the closest isomer paraxylene whose normal boiling point is only 3.90°F higher. The average relative volatility between ethylbenzene and paraxylene in the fractionation is about 1.06. The fractionator feed is entirely Cg aromatics which are prepared by the extraction of powerformate by the sulfolane process and by fractionation of the aromatic extract. 

Figure 2-2. The Union Carbide aromatics extraction process using tetraethylene glycol. ...

Ethylbenzene (C6H5CH2CH3) is one of the Cg aromatic constituents in reformates and pyrolysis gasolines. It can be obtained by intensive fractionation of the aromatic extract, but only a small quantity of the demanded ethylbenzene is produced by this route. Most ethylbenzene is obtained by the alkylation of benzene with ethylene. Chapter 10 discusses conditions for producing ethylbenzene with benzene chemicals. The U.S. production of ethylbenzene was approximately 12.7 billion pounds in 1997. Essentially, all of it was directed for the production of styrene. 

Steam cracking raffinate from aromatic extraction units is similar to naphtha cracking. However, because raffinates have more isoparaffins, relatively less ethylene and more propylene is produced. 

Mostly, 75% of the extender oils are used in the tread, sub tread, and shoulder regions of a tire. About 10%-15% are used in the sidewall, 5% are used in the inner finer, and less than 10% are used in the remaining parts. A typical tire can contain up to 700 g of oil. All types of mineral oils should be handled and used with care, but special care is required in the handling of aromatic oils. High aromatic oils also referred to as distillate aromatic extracts (DAEs) or simply extracts have been traditionally used as extender oils for elastomeric applications [27]. Their popularity is explained by their good... 

FIGURE 37.5 General refining techniques for production of distillate aromatic extract (DAE), mild extraction solvate (MES), and treated distillate aromatic extract (TDAE). (From Joona, M., High-aromatic tire extender oils implications and future, ITEC, OH, 2004.)... 

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... 

Rexforming A petroleum refining process which combines Platforming with an aromatics extraction process using ethylene glycol. Developed in the 1950s by Universal Oil Products. 

The carcinogenicity of polycyclic aromatic compound-rich tyre extender oils has lead to the proposal of a legislative ban on their use in Europe. The suitability of naphthenic oils as non-toxic plasticisers in tyre treads is discussed and results are presented of experimental studies of the use of these plasticisers in SBR, EPDM, sulphur-cured EPDM and peroxide-cured EPDM. Despite their low aromatic content, the naphthenic plasticisers are shown to give good results in SBR, probably as a result of the contribution to solvent characteristics of the naphthenic molecular structure. The use of naphthenic oils is expected to increase worldwide as they are said to be one of the best alternatives to aromatic extracts with regard to solvent properties, compatibility, performance and availability. 

Raffinate. In extraction processes, the stream that has had the extracted material removed from it is called raffinate, in contrast to the other produced stream, the extract. Usually associated with aromatics extraction from naphtha streams. 

The liquid phase adsorption processes for aromatics extraction are made economically relevant by the large world demand for aromatic petrochemicals. The global per annum production rates of the highest capacity aromatic petrochemicals derived from reformate or pygas for the recent past are shown in Table 7.1. 

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. 

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. 

Aromatic extraction removes benzene, toluene, and xylene (BTX) that are formed as byproducts in the reforming process. The reformed products are fractionated to give a BTX concentrate cut, which, in turn, is extracted from the napthalene and the paraffinics with a glycol base solvent. 

Extracts of aromatic plant or animal materials obtained using organic solvents or fluidised gasses are not considered as essential oils [1, 23, 25-28]. Concretes, absolutes, spice oleoresins, etc. which can be classified as aromatic extracts are not covered in this chapter. 

Aromatics Extraction Process, publication EM-9964, Atlantic Richfield Co. 

Rexforming a process combining platforming (q.v.) with aromatics extraction, wherein low octane raffinate is recycled to the platformer. 

---