Carbon number distribution

The solvent is 28 CC-olefins recycled from the fractionation section. Effluent from the reactors includes product a-olefins, unreacted ethylene, aluminum alkyls of the same carbon number distribution as the product olefins, and polymer. The effluent is flashed to remove ethylene, filtered to remove polyethylene, and treated to reduce the aluminum alkyls in the stream. In the original plant operation, these aluminum alkyls were not removed, resulting in the formation of paraffins (- 1.4%) when the reactor effluent was treated with caustic to kill the catalyst. In the new plant, however, it is likely that these aluminum alkyls are transalkylated with ethylene by adding a catalyst such as 60 ppm of a nickel compound, eg, nickel octanoate (6). The new plant contains a caustic wash section and the product olefins still contain some paraffins ( 0.5%). After treatment with caustic, cmde olefins are sent to a water wash to remove sodium and aluminum salts. 

SASOL. SASOL, South Africa, has constmcted a plant to recover 50,000 tons each of 1-pentene and 1-hexene by extractive distillation from Fischer-Tropsch hydrocarbons produced from coal-based synthesis gas. The company is marketing both products primarily as comonomers for LLDPE and HDPE (see Olefin polymers). Although there is still no developed market for 1-pentene in the mid-1990s, the 1-hexene market is well estabhshed. The Fischer-Tropsch technology produces a geometric carbon-number distribution of various odd and even, linear, branched, and alpha and internal olefins however, with additional investment, other odd and even carbon numbers can also be recovered. The Fischer-Tropsch plants were originally constmcted to produce gasoline and other hydrocarbon fuels to fill the lack of petroleum resources in South Africa. 

The conversion of fatty alcohols is approximately 99%. The reaction product is then condensed and sent to a distillation column to remove water and high boilers. Typically, a-olefin carbon-number distribution is controlled by the alcohol composition of the reactor feed. The process is currentiy used to produce a-olefins from fatty alcohols. A typical product composition is at <5%, at 50—70%, C g at 30—50%, C2Q at <2%,... 

The carbon number distribution of technical secondary alkanesulfonates determined by pyrolysis gas chromatography and mass spectrometry (GC-MS) is shown in Fig. 13 together with the corresponding carbon number pattern of the raw material paraffins obtained by GC [16]. Pyrolysis was performed in a crucible-modified SGE pyrojector after covering the mixture with quartz wool. The presence of up to 10 wt % of disulfonates in technical alkanesulfonates is demonstrated by fast atom bombardment and mass spectrometry (FAB-MS) (Fig. 14) [24],... 

As alkanesulfonates are mixtures of homologs as well as isomers, high-performance liquid chromatography (HPLC) proves to be a general method for an exact analysis. For identifying the raw material basis (carbon number cut of normal paraffins used), the carbon number distribution of the homologs can be... 

FIG. 13 Carbon number distribution of alkanemonosulfonates by pyrolysis gas chromatography (GC)/mass spectrometry (paraffin raw material by GC). 

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... 

With the exception of methane and the C2 fraction, the carbon number distribution of Fischer-Tropsch products can be well represented by superposition of two ASF distributions ... 

For iron catalysts in general, the incorporation of 1-alkenes is negligible, and that of ethene is much lower than that of cobalt.1617 Therefore, for all published carbon number distributions for iron catalysts, a strict representation by two superimposed ASF distributions is obtained. Examples are given by Schliebs and Gaube,7 Dictor and Bell,8 and Huff and Satterfield.10 Also, the old experiments of the Schwarzheide tests are well represented by this model.7... 

The carbon number distribution of the synthesis run with co-fed 1-hexene shows an increased C selectivity of the C7 fraction (Figure 11.5). However, the increase of the following fractions strongly declines with increasing carbon number, so that the distribution approaches, within a few carbon numbers, the one obtained without co-feeding 1-hexene. This result suggests that readsorbed and... 

For an accurate representation of the carbon number distribution in the case of elevated pco and a high degree of syngas conversion, the bimodal model must... 

In Fischer-Tropsch synthesis the readsorption and incorporation of 1-alkenes, alcohols, and aldehydes and their subsequent chain growth play an important role on product distribution. Therefore, it is very useful to study these reactions in the presence of co-fed 13C- or 14 C-labeled compounds in an effort to obtain data helpful to elucidate the reaction mechanism. It has been shown that co-feeding of CF12N2, which dissociates toward CF12 and N2 on the catalyst surface, has led to the sound interpretation that the bimodal carbon number distribution is caused by superposition of two incompatible mechanisms. The distribution characterized by the lower growth probability is assigned to the CH2 insertion mechanism. 

The primary product from Fischer-Tropsch synthesis is a complex multiphase mixture of hydrocarbons, oxygenates, and water. The composition of this mixture is dependent on the Fischer-Tropsch technology and considerable variation in carbon number distribution, as well as the relative abundance of different compound classes is possible. The primary Fischer-Tropsch product has to be refined to produce final products, and in this respect, it is comparable to crude oil. The primary product from Fischer-Tropsch synthesis can therefore be seen as a synthetic crude oil (syncrude). There are nevertheless significant differences between crude oil and Fischer-Tropsch syncrude, thus requiring a different refining approach.1... 

The Arge Fe-LTFT syncrude (Table 18.8)29 was much heavier than the syncrude of the two German Co-LTFT processes (Table 18.2). The Arge Fe-LTFT syncrude exemplified a high a-value Fischer-Tropsch product with a significant linear paraffinic wax fraction. The syncrude (Table 18.8) from the Kellogg Fe-HTFT synthesis was very similar in carbon number distribution to that of Hydrocol Fe-HTFT synthesis (Table 18.5). 

The separate stepwise condensation of the products from Fe-LTFT and Fe-HTFT synthesis produces streams of different carbon number distributions that serve as feeds to the oil refinery (Figure 18.4).30 It is consequently not necessary to employ an atmospheric distillation unit as the first step in the refinery. The stepwise condensation products from Fe-LTFT are reactor wax (liquid at LTFT conditions), hot condensate (>100°C), cold condensate (produced by condensation with the aqueous product and then phase separated), and tail gas (typically C4 and lighter). The stepwise condensation products from Fe-HTFT are decanted oil (liquid at 145°C 1.6 MPa), light oil (produced by condensation with the aqueous product and then phase separated), and tail gas. 

Acidic isomerization of the C5-C6 naphtha and some heavy alcohols from the aqueous product refinery (not shown in Figure 18.5) produced a reasonable-quality olefinic motor gasoline (Table 18.10). The octane value varied depending on the carbon number distribution of the feed, which could result in a product with an octane number up to ten units higher. 

The distributions of products within a certain carbon number fraction are far from equilibrium. In the Cg-fraction, for example, the dimethylhexanes would be thermodynamically favored over the trimethylpentanes, but the latter are predominant. The distribution within the trimethylpentanes is also not equilibrated. 2,2,4-TMP would prevail at equilibrium over the other TMPs, constituting 60-70% of the product, depending on the temperature. Furthermore, 2,2,3-TMP as the primary product is found in less than equilibrium amounts. Qualitatively, the same statement is valid for the other carbon number distributions. Products with a tertiary carbon atom in the 2-position dominate over other isomers in all fractions. 

Figure 5.34 shows the FT-NIR predictive models for total vol% paraffins, isoparaffins, naphthenes and aromatics and carbon number distribution for a typical naphtha dataset. Since NIRS can be demonstrated to have sufficient hydrocarbon speciation capability to reproduce the analyzis with the same precision as the GC method, but in a fraction of the time, then a useful process analytical goal has been achieved. 

Figure 10.26 Examples of H NMR predicted carbon number distributions for three light gas oil samples.

Various mechanisms have been proposed for the FT reaction (j ) (2) and (4- ). A generalized mechanism is illustrated in Figure T. Irrespective of which mechanism is correct, or is dominant, there is general agreement that stepwise chain growth is involved. This inevitably results in a wide carbon number distribution of products, the particular distribution being determined by the probability of chain growth (<1). The calculated effect of different values on... 

The n-paraffin carbon number distribution for a fuel is narrow. 

Characterize the carbon number, distribution, and concentration of fuel n-paraffins. 

Analytical Procedures. The chemical compositions of both liquid and gas products were determined by gas chromatography (GC). The normal paraffinic concentration in the liquid products and their carbon number distribution were determined by a GC method (5). The sample was analyzed first with a 2-ft silicone gum rubber (SE-30) column and then analyzed again with the same column attached behind a 3-inch Ca/A zeolite column which adsorbed all n-paraffins. 

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