Normal-Pentane

According to the nature of the solvent employed, the yields and constitutions of the asphaltenes are different. In the United States, asphaltenes are obtained by precipitation from normal pentane. 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

With the five-carbon alkane, pentane, there are three ways to draw the structural formula of this compound with five carbon atoms and twelve hydrogen atoms. The isomers of normal pentane are isopentane and neopentane. The structural formulas of these compounds are illustrated in Table 2, while typical properties are given in Table 1. 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

The analysis of variance for the model of Eq. (32), for example, for the data on the isomerization of normal pentane was shown in Table V we concluded that the model was marginally acceptable. However, the plot of the residuals of Fig. 15 indicates that this overall fit is achieved by balancing predictions that are too low against predictions that are too high. Hence the... 

An augmented central composite design was used in obtaining reaction-rate data in a flow differential reactor the reaction occurring was the isomerization of normal pentane to isopentane in the presence of hydrogen (Cl). Using the subscripts 1, 2, and 3 for hydrogen, normal pentane, and isopentane respectively, an empirical rate equation can be written... 

There are three forms of pentane the straight-chain normal pentane (a = 2), the branched isopentane (a = 1), and the doubly branched neopentane (a = 12) in the shape of a tetrahedron. Figure 4.37 shows that normal pentane has the highest density and boiling point, which can be attributed to the superior packing efficiency of linear molecules isopentane, in comparison, has lower density and lower melting and boiling points. Neopentane does not follow the usual rules it has the lowest... 

Napththa Isomerization. The only commercial isomerization of light naphtha was carried out in two plants employing the isomate process developed by the Standard Oil Co. (Indiana) (20). In this process, a feed containing normal pentane and low octane number hexanes is converted to isopentane and to hexanes of higher octane number. Pentanes and hexanes in any ratio may be processed. By recycle of selected fractions of the product, concentrates of isopentane or of neohexane and diisopropyl can be obtained as the ultimate products. 

The vapor pressure of a light component at a given temperature, divided by the vapor pressure of a heavier component at the same temperature, is called the relative volatility. For practice, calculate the relative volatility of isobutanes and normal pentane at 140°F (answer 4.0). Next, calculate their relative volatility at 110°F (answer 4.9).1... 

Isomerization—A refining process which alters the fundamental arrangement of atoms in the molecule, Used to convert normal butane into isobutane, as alkylation process feedstock, and normal pentane and hexane into isopentane and isohexane, high-octane gasoline components,... 

With all of the catalysts in this study, the ratio of isopentane to normal pentane varies directly as the ratio of isohexanes to n-hexane. (In this paper, the branched C6 paraffins are collectively referred to as isohexanes.) Therefore, the iso/normal ratio of the paraffins of either carbon number can be correlated with octane number for C5-l80°F product of a given cycloparaffin content and serve as a convenient indication of catalyst performance. 

Distillations. The upgraded coal liquids were distilled with a metal-mesh-spinning-band still under the conditions shown in Figure 1 to produce cuts at 200°, 325°, and 425° C. Asphaltenes were then precipitated from each >425° C residuum dissolved in benzene by addition of 50 volumes of normal pentane (15). Further distillations on the asphaltene-free materials, at 202° C and 4 micron pressure using a wiped-wall molecular still, produced 425° to 540° C distillate cuts and residua fractions. 

Example Isopentane (IC5), normal pentane (NC5), and cyclopentane (CC5) are to be separated by means of distillation. A 5000-bpd rich feed with these components is received. The mixed feed containing these and many other components—including ethane, propane, butane, through benzene—is received as a liquid. A three-column distillation train, in series, will be installed to produce IC5, NC5, and CC5 spec product liquid streams. Methane, ethane, propane, and butane have been removed in an upstream stabilizer column. Only trace ethane and propane are remaining in the feed stream feeding the first column, IC5. 

In order to follow the catalytic recovering produced by the burning of coke, partially regenerated catalyst samples were submitted to standard reaction tests for benzene hydrogenation (metallic function) and normal pentane isomerization (acid function). Benzene hydrogenation was done at 423 K, 0.1 MPa, WHSV = 2 h 1, and molar ratio H2/Bz = 20. 200 mg of catalyst were loaded, which was reduced at 533 K with H2 for 2 h before the test. The isomerization of n-pentane was performed at 773 K, 0.1 MPa, WHSV = 2 h 1 and molar ratio H n = 6. 200 mg of catalyst were loaded, and were reduced with hydrogen at 773 K for 2 h before the test. 

Isomerization of C5 and Q paraffins is a refinery process that generates high octane for the gasoline pool, while contributing no olefins or aromatics (11). Branched C5 and C6 paraffins have much higher octanes than normal pentane and normal hexane, as shown in Table 4.9 (5). Furthermore, C5 and C6 isomers can be separated by distillation, and flow schemes can be employed to recycle lower-octane isomers to the isomerization reactor. 

The temperature of isomerization controls equilibrium isomer composition, and thereby product octane. Figure 4.8 is a plot of isopentane in the C5 product as a function of temperature. The data are from pilot plant runs with three types of commercial UOP isomerization catalysts. The feedstock was a 50/50 mixture of normal pentane and normal hexane, containing about 6% cyclics. The 1-8 and I-80 catalysts are very active at a low temperature, where equilibrium isopentane content is highest. The acid functions in 1-8 and 1-80 are chlorided aluminas. The zeolitic catalyst, HS-10 , requires relatively high temperatures of operation. The LPI-100 catalyst contains sulfated zirconia as the acid function and falls in the middle of the temperature range (12). Due to the equilibrium constraints, a lower temperature operation yields a higher octane product. The 1-8 and 1-80 catalysts yielded Research Octane Numbers of 82-84, as compared to 80-82 for LPI-100 catalyst and 78-80 for HS-10. 

The results shown in Fig. 6.10 were generated for a 20-tray, 2-ft-diame-ter column, with a feed on tray 11 of 100 lb-mol/h at 90°F. The feed composition is 5 mol % propane, 40 mol % normal butane, 45 mol % normal pentane, and 10 mol % normal octane. Product purity specifications are 0.5 mol % butane in the bottoms and 0.5 mol pentane in the distillate. The operating pressure of the column is 73 psia, and the reflux ratio is 1.76. The temperature on tray 6 is 179.9CF and on tray 14 is 130.6°F. Figure 6.13 gives the composition profiles in the column. Note the buildup of the HHK component near the bottom of the column... 

A dynamic simulation of this column using HYSYS was used to explore the dynamics of the process for the two cases where different tray temperatures are controlled. Either tray 6 or tray 14 temperature is controlled by manipulating reboiler heat input. Reflux flowTate is held constant. Disturbances are step changes at time equals 5 minutes in feed flowrate (25 percent increase) or feed composition. The feed composition disturbance is a drop in the HHK component in the feed (normal octane changed from 10 mol % to 0 mol % while normal pentane changed from 45 mol % to 55 mol %). 

The first structure, with all of the carbon atoms in a straight line, is called normal pentane, or n-pentane. The second structure, clearly different from the first, is called isopentane, and the third, different still, is called neopentane (named after the guy who saved the universe ). That s not too complicated, but remember that organic molecules can contain many, many carbon atoms. With 10 carbon atoms, decane (Cj H ) has 75 different possible structures. Using a different prefix for each structure would be a bit cumbersome. So, chemists came up with a different way of naming organic molecules besides using prefixes. This system, known as the IlIPAC system (lUPAC stands for International Union of Pure and Applied Chemistry), uses names for basic structures and then numbers to explain the different orientations. For example, the molecule CH3 is known as the methyl group. Pentane is the molecule The isomer of... 

Reagents. Normal pentane (99%), heptane (99%), and decane (99%) were further purified by distillation and by percolation through activated silica gel. Reagent-grade benzene, methanol, and trichloroethylene (TCE) were redistilled. Isopropylamine (IPA) was used as received. 

Nomenclature. The question arises as to how the various isomers of a hydrocarbon can be named and distinguished. When the number of poffiible isomers is small this offers no problem. The two isomers of butane are named normal butane and isobutane. The three isomers of pentane are known as normal pentane, isopentane, and neopentane. 

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