Carbon type distributions

The n-d-M method is an empirical method for determining the carbon type distribution (%CP %CN, %CA) by simple measurement of the refractive index ( ), density (d), and molecular weight (M) of the sample. It also provides the mean number of naphthenic (RN) and aromatic (RA) rings per molecule. The method was developed by researchers at Koninklijke/Shell in Holland after World War II. Its application includes lube feedstocks and raffinates.2 Nearly all applications have been to solvent refined stocks. The current American Society for Testing and Materials (ASTM) method is D3238. ASTM D2140 is applicable to insulating oils. 

FIGURE 4.3 Viscosity-gravity constant in relation to carbon-type distribution. 

Source S. S. Kurtz, Jr., R. W. King, W. J. Stout, D. G. Parkikian, and E. A. Skrabek, Relationship Between Carbon-Type Distribution, Viscosity-Gravity Constant, and Refrac-tivity Intercept of Viscous Fractions of Petroleum, Anal. Chem., vol. 28, pp. 1928-1936 (1956). With permission. 

Figure 7.2 C DPMAS NMR spectra of the three humic fractions isolated from a peat soil using the procedure outlined in Figure 7.1. Carbon-type distributions generally used to describe samples are aliphatic (0-50 ppm), carbohydrate (50-110 ppm), aromatic (110-190 ppm) and carboxyl (190-220 ppm). Elemental data [6] are average elemental compositions for each humic fraction. Functional group analyses are for these specific samples [7]. There is considerable variation in these chemical characteristics among samples, and between environments, for each fraction. For descriptions of compositional variations in humic materials from different environments the reader is referred to the references [1-5].

In formulating liquid detergent products with LAS, the carbon chain distribution, phenyl isomer distribution, and DATS level can all contribute to the solubility and viscosity characteristics. Hydrotrope requirements for isotropic liquid detergents can vary widely for different types of commercial LAS. 

The carbon number distribution of Fischer-Tropsch products on both cobalt and iron catalysts can be clearly represented by superposition of two Anderson-Schulz-Flory (ASF) distributions characterized by two chain growth probabilities and the mass or molar fraction of products assigned to one of these distributions.7 10 In particular, this bimodal-type distribution is pronounced for iron catalysts promoted with alkali (e.g., K2C03). Comparing product distributions obtained on alkali-promoted and -unpromoted iron catalysts has shown that the distribution characterized by the lower growth probability a, is not affected by the promoter, while the growth probability a2 and the mass fraction f2 are considerably increased by addition of alkali.9 This is... 

From a study of gasoline cver-cracking with either ZSM-5 or REHY, the resulting total hydrocarbon distributions by carbon number are grossly similar. In both cases, predominantly C2 - C5 products are formed from C6+ components. However, there are significant differences in detail, notably in hydrocarbon-type distributions. 

The carbon-number distributions (35) for the CnH2n+zO compounds in the oil neutrals are relatively short and exhibit maxima near the center of each Z(O) series. In contrast, the carbon-number distributions for the asphaltene-neutral Z(O) compounds are characterized by the occurrence of maximums in the beginning of each distribution. The origin of the differences in these Z(O) distributions is not clear. Furthermore, the former result contrasts with the result obtained for the oil aromatic hydrocarbons and the latter parallels the distribution of weight percents in each Z(H) series for the asphaltene neutrals. It is tempting to ascribe the difference in the distribution of weight percents of the various Z(O) compound types in the oil and asphaltene neutrals to the chemistry associated with the COED process. However, the fact that considerable overlap exists in the neutral-aromatic Z(O) compounds between the oils and asphaltenes precludes this conclusion because the results could reflect phenomena associated with solvent extraction. 

Z(Oz) series. It is not obvious how this result, which is opposite to that observed for the aromatic neutral fractions, is reconciled with a separation of acids based upon their physical properties, such as solubilities, in pentane and benzene. Similar to the result attained for the aromatic hydrocarbons, the carbon-number distributions for the acid fractions are characterized by the occurrence of maxima early in the distributions of weight percents in the various specific-Z series. However, for corresponding compound types (i.e., the same basic ring structure) the range in carbon number is significantly shorter for the acids than for the aromatic hydrocarbons. 

Figure 6.22 shows the typical carbon number distribution of products obtained using Ni-REY in steam at 400°C and with a time factor W/F of 1 h. The results obtained with MFI-type (ZSM-5) and REY zeolites in N2 are also shown for comparison. Although steam was used as a carrier gas, Ni-REY gave the largest amount of fuel, e.g. gasoline, kerosene, and gas oil, thus suggesting the potential use of steam as a carrier gas. 

CO reactants and the H2O product of the synthesis step inhibit many of these secondary reactions. As a result, their rates are often higher near the reactor inlet, near the exit of high conversion reactors, and within transport-limited pellets. On the other hand, larger olefins that are selectively retained within transport-limited pellets preferentially react in secondary steps, whether these merely reverse chain termination or lead to products not usually formed in the FT synthesis. In later sections, we discuss the effects of olefin hydrogenation, oligomerization, and acid-type cracking on the carbon number distribution and on the functionality of Fischer-Tropsch synthesis products. We also show the dramatic effects of CO depletion and of low water concentrations on the rate and selectivity of secondary reactions during FT synthesis. 

Iron has 6 electrons in the 3d orbital, 2 in the 45, and none in the 4p orbital. The inert gas configuration requires 18 electrons—ten 3d, two 45, and six 4p electrons. Iron pentacarbonyl enters this configuration by accepting two electrons from each of the five carbonyl groups, a total of 18 electrons. Back-bonding of the d-rr type distributes the excess electrons among the five carbon monoxide molecules. 

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