Hydrocarbons adsorptive separation

Kulprathipanja, S. (2001) Process for monomethyl acyclic hydrocarbon adsorptive separation. U.S. Patent 5,252,127. 

Aromatic and Nonaromatic Hydrocarbon Separation. Aromatics are partially removed from kerosines and jet fuels to improve smoke point and burning characteristics. This removal is commonly accompHshed by hydroprocessing, but can also be achieved by Hquid-Hquid extraction with solvents, such as furfural, or by adsorptive separation. Table 7 shows the results of a simulated moving-bed pilot-plant test using siHca gel adsorbent and feedstock components mainly in the C q—range. The extent of extraction does not vary gready for each of the various species of aromatics present. SiHca gel tends to extract all aromatics from nonaromatics (89). 

Kulprathipanja, S. (1995) Process for the adsorptive separation of metaxylene from aromatic hydrocarbons. U.S. 

Kulprathipanja, S. (1991) Adsorptive separation process for the purification of heavy normal paraffins with non-normal hydrocarbon pre-pulse stream. U.S. Patent 4,992,618. 

This chapter reviews the adsorptive separations of various classes of non-aromatic hydrocarbons. It covers three different normal paraffin molecular weight separations from feedstocks that range from naphtha to kerosene, the separation of mono-methyl paraffins from kerosene and the separation of mono-olefins both from a mixed C4 stream and from a kerosene stream. In addition, we also review the separation of olefins from a C10-16 stream and review simple carbohydrate separations and various acid separations. 

The second part of the book covers zeolite adsorptive separation, adsorption mechanisms, zeolite membranes and mixed matrix membranes in Chapters 5-11. Chapter 5 summarizes the literature and reports adsorptive separation work on specific separation applications organized around the types of molecular species being separated. A series of tables provide groupings for (i) aromatics and derivatives, (ii) non-aromatic hydrocarbons, (iii) carbohydrates and organic acids, (iv) fine chemical and pharmaceuticals, (v) trace impurities removed from bulk materials. Zeolite adsorptive separation mechanisms are theorized in Chapter 6. 

Chapter 7 gives a review of the technology and applications of zeolites in liquid adsorptive separation of petrochemical aromatic hydrocarbons. The application of zeolites to petrochemical aromatic production may be the area where zeolites have had their largest positive economic impact, accounting for the production of tens of millions of tonnes of high-value aromatic petrochemicals annually. The nonaromatic hydrocarbon liquid phase adsorption review in Chapter 8 contains both general process concepts as well as sufficient individual process details for one to understand both commercially practiced and academic non-aromatic separations. 

The use of specialized procedures, such as azeotropic and extractive distillation as well as absorptive and adsorptive separations, is another important trend in hydrocarbon fractionation. These processes are discussed in the following section. 

Saturated and aromatic hydrocarbons were separated from the acid-, base-, and neutral nitrogen-free bitumen by adsorption chromatography using silica gel, grade 12, as the adsorbent and cyclohexane as the eluting solvent. The column was dry packed, and the cutpoint was made at two void volumes. At the cut points, the UV absorbance was measured at 270 nm to determine the overlap of aromatics in the saturates. Aromatics were desorbed with 60% benzene-40 % methanol. 

The primary requirement for an economic adsorption separation process is an adsorbent with sufficient selectivity, capacity, and life. Adsorption selectivity may depend either on a difference in adsorption equilibrium or, less commonly, on a difference in kinetics. Kinetic selectivity is generally possible only with microporous adsorbents such as zeolites or carbon molecular sieves. One can consider processes such as the separation of linear from branched hydrocarbons on a 5A zeolite sieve to be an extreme example of a kinetic separation. The critical molecular diameter of a branched or cyclic hydrocarbon is too large to allow penetration of the 5A zeolite crystal, whereas the linear species are just small enough to enter. The ratio of intracrystalline diffusivities is therefore effectively infinite, and a very clean separation is possible. 

Generally speaking, thin-layer chromatography (TLC) has a large number of applications. The first problem with which the analyst is confronted concerns gathering information regarding the mixture to be separated, in terms of mixture polarity and the range of molecular masses. In the case of hydrocarbons that have one no-polar character, an adsorption separation technique is... 

In a study of selective adsorption of sulfur compounds and aromatic compounds in a hexadecane on commercial zeolites, NaY, USy, HY, and 13X by adsorption at 55 °C and flow calorimetry techniques at 30 °C, Ng et al. found that a linear correlation between the heat of adsorption and the amount of S adsorbed for NaY.162 Competitive adsorption using a mixture of anthracene, DBT, and quinoline indicates that NaY selectively adsorbs quinoline, while anthracene and DBT have similar affinity to NaY, indicating that NaY is difficult to adsorptively separate sulfur compounds from aromatic hydrocarbons with the same number of the aromatic rings. 

Shcherbakova, Petrova, and co-workers (258-263) studied the chemical modification of silica for applications in gas chromatography (for example, in the adsorption separation of hydrocarbons by gas chromatographic methods). The adsorption properties are investigated as a function of the degree of surface modification with ClSi(CH3)3. A number of silica samples were chemically modified so that they would have the desired adsorption properties (17). Chemical modification is an effective means of changing the shape of adsorption isotherms. 

Separation and Sub-fractionation of Alkanes Saturated hydrocarbons were separated from the neutral oil by silica-gel (60-120 mesh, dehydrated at 150°C for 5 h) chromatography in a 1 m X 30 mm i.d. column eluted with distilled n-hexane. n-Alkanes were separated from iso-octane solutions of total alkanes by adsorption for one week on 5 X molecular sieve (freshly dehydrated for 2h h at U00°C). Washing with iso-octane, followed by Soxhlet extraction, freed the molecular sieve from inwanted non-adsorbed compo mds n-alkanes were recovered by desorption after refluxing the molecular sieve for several hours with n-hexane. For the Kuwait crude and fluidized-bed tar, the molecular-sieve treatment was preceded by urea-adduction of n-alkanes and thiourea-adduction of branched-chain alkanes. 

In the Parex process, the p-xylene is separated at 120 to 175 °C by selective adsorption. Separation of the Cg-aromatics is effected by an adsorbing solid material (adsorbant) and a suitable liquid. The process is based on the fact that the various components, adsorbed to a different degree, are recovered from the active surface of the adsorbant. A synthetic zeolite is used as the adsorption agent, the active centres of which are formed by cations from the first and second group (K, Ca) of the periodic table. A hydrocarbon with a low adsorption capacity, such as toluene or p-diethylbenzene is used for desoiption, and can easily be separated from p-xylene by distillation. In this process, the liquid phases are fed through a... 

When high-purity linear internal olefins are desired, as would be the case for the production of detergent alcohols or synthetic lubes, one takes the dehydrogenation product after the removal of light-cracked hydrocarbon fraction to an adsorptive separation process. In this case, olefins are... 

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