Composition of naphtha

Table 8. Composition of Naphthas from Various Sources...

Naphtha is also obtained from other refinery processing units such as catalytic cracking, hydrocracking, and coking units. The composition of naphtha, which varies appreciably, depends mainly on the cmde type and whether it is obtained from atmospheric distillation or other processing units. 

The typical change in the.composition of naphtha as it passes through the reformer is shown in Table 2—1. 

The cracking of naphtha produces most of the world s ethylene. Naphtha is the crude oil fraction boiling Irom about 32°C to 192°C. The composition of naphtha made from crude oil comprises four basic components linear paraffins, branched paraffins, naphthenes (cyclo-paraffins) and aromatics. The relative amount of these in naphtha is dependent on the source crude oil and varies widely. 

The composition of naphtha from fluid catalytic cracking has been reported by Melpolder, Brown, Young, and Readington (55). 

Because the end use dictates the required composition of naphtha, most grades are available in both high- and low-solvency categories and the various text methods can have major significance in some applications and lesser significance in others. Hence the application and significance of tests must be considered in the light of the proposed end use. 

The composition of naphtha varies, but cracking yields for ethylene are about 30%, with a wide variety of co-products such as methane, propylene, butadienes, butane and a mixture of other fuel oils accounting for the remaining 70%. With ethane as feedstock, ethylene yield is very high at about 80% with few byproducts. 

Step 6 Input compositional analyses and flow rates of light ends. These are important to calculate the composition of naphtha cuts. 

Composition of fraction / in the product Composition of fraction / in the feed Composition of middles distillates Composition of gases Composition of naphtha Composition of VGO Composition of VR... 

The composition of the cracked gas with methane and naphtha and the plant feed and energy requirements are given in Table 9. The overall yield of acetylene based on methane is about 24% (14). A single burner with methane produces 25 t/d and with naphtha or LPG produces 30 t/d. The acetylene is purified by means of /V-methy1pyrro1idinone. 

The cracked gas composition is shown ia Table 10 for the water queach operatioa (16). Oae thousand cubic meters of methane and 600 m of oxygen produce 1800 m of cracked gas. If a naphtha quench is used, additional yields are produced, consuming 130 kg of naphtha/1000 of methane... 

A few industrial catalysts have simple compositions, but the typical catalyst is a complex composite made up of several components, illustrated schematically in Figure 9 by a catalyst for ethylene oxidation. Often it consists largely of a porous support or carrier, with the catalyticaHy active components dispersed on the support surface. For example, petroleum refining catalysts used for reforming of naphtha have about 1 wt% Pt and Re on the surface of a transition alumina such as y-Al203 that has a surface area of several hundred square meters per gram. The expensive metal is dispersed as minute particles or clusters so that a large fraction of the atoms are exposed at the surface and accessible to reactants (see Catalysts, supported). 

Gum turpentine is obtained from wounding living trees to get an exudate containing turpentine and rosin. Turpentine is separated from the rosin by continuous steam distillation and further fractionation. Wood turpentine comes from the extraction of stumps of pine trees using naphtha, and subsequent separation of rosin and turpentine by fractional distillation. Tail-oil turpentine is a byproduct of the Kraft sulphate paper manufacture. Terpenes are isolated from the sulphate terpentine and separated from the black digestion liquor. The composition of turpentine oils depends on its source, although a-pinene and p-pinene are the major components. 

This reaction is endothermic and is favored by low pressure. In practice, however, the process is conducted at a pressure of 1-3 MPa (because of a concurrent hydrocracking reaction) and a temperature of 300-450°C using Pt-based catalysts [7]. The feedstock for the reforming process must be carefully purified from S- and N-compounds (below 1 ppm), which may use up a significant portion of hydrogen produced. The typical composition of the off-gas from the catalytic reforming of naphtha is as follows (vol%) H2—82, CH4—7, C2—5, C3—4, and C4—2 [7]. 

In addition, a method of petroleum classification based on other properties as well as the density of selective fractions has been developed. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C (295°F), as well as that of the asphaltene content, followed by a more detailed examination of the chemical composition of the naphtha (bp < 200°C < 390°F). For this examination a graph is nsed that is a composite of cnrves expressing the relation among the percentage distillate from the naphtha. 

The data from the density (specific gravity) test method (ASTM D1298 IP 160) provides a means of identification of a grade of naphtha but is not a guarantee of composition and can only be used to indicate evaluate product composition or quality when used in conjunction with the data from other test methods. Density data are used primarily to convert naphtha volume to a weight basis, a requirement in many of the industries concerned. For the necessary temperature corrections and also for volume corrections, the appropriate sections of the petroleum measurement tables (ASTM D1250 IP 200) are used. 

Hydrocarbon composition is also determined by mass spectrometry, a technique that has seen wide use for hydrocarbon-type analysis of naphtha and gasoline (ASTM D2789) as well as for the identification of hydrocarbon constituents in higher-boiling naphtha fractions (ASTM D2425). 

Introduction of zeolites into catalytic cracking improved the quality of the product and the efficiency of the process. It was estimated that this modification in catalyst composition in the United States alone saved over 200 million barrels of crude oil in 1977. The use of bimetallic catalysts in reforming of naphthas, a basic process for the production of high-octane gasoline and petrochemicals, resulted in great improvement in the catalytic performance of the process, and in considerable extension of catalyst life. New catalytic approaches to the development of synthetic fuels are being unveiled. 

The amount of benzene produced in a reformer will depend on the composition of the feed. Every crude oil has naphtha with different PNA (paraffin, naphthene, aromatics) content. In commercial naphtha trading, the PNA content is often an important specification. High naphthene and aromatic content would indicate a good reformer feed. High paraffin content would indicate a good olefin plant feed. 

Besides ethylene and propylene, the steam cracking of naphtha and catalytic cracking in the refinery produce appreciable amounts of C4 compounds. This C4 stream includes butane, isobutane, 1-butene (butylene), cis- and trans-2-hutene, isobutene (isobutylene), and butadiene. The C4 hydrocarbons can be used to alkylate gasoline. Of these, only butadiene and isobutylene appear in the top 50 chemicals as separate pure chemicals. The other C4 hydrocarbons have specific uses but are not as important as butadiene and isobutylene. A typical composition of a C4 stream from steam cracking of naphtha is given in Table 8.3. 

Depending on the nature of the raw material (coal, natural gas, naphtha), both the reaction conditions of gasification, and the employment of reforming (shift conversion) will determine the composition of the syngas. For instance, synthesis gas produced from coal normally has a H2 C0 ratio of unity and therefore the ratio has to be adjusted to 2.0 prior to the use of the gas for methanol synthesis. Accordingly, syngas derived from CH4 bears a cost advantage for the needed ratio of 2.0. 

Jet fuels are typically prepared from either straight-run kerosene or from wide-cut kerosene/naphtha blends off of the atmospheric distillation unit. TABLE 3-10 briefly describes the composition of some typical jet fuel grades. 

The model is user friendly and the input requirements are simple. An example of typical user input is shown in Table XIV, which contains all necessary information to run the model. In the example, charge stock information for a blend of two naphthas is produced by means of naphtha library codes the detailed composition developed by the module INPUT for the specified naphtha codes is shown in Table XV. Optional output of yields, temperature, and octane at six points through each reactor can also be generated. The process and reactor conditions are summarized in Table XVI, and complete yields along with the product properties are shown in Table XVII. 

Cady, Marschner, and Cropper (9) in 1951, relating to the composition of the light naphtha fraction of mid-continent petroleum... 

In setting the prices for the premium cases, we have incorporated a sliding price scale on some by-products hence, a range of prices appears in some rows of Table V. These price variations reflect differences in the composition of a particular by-product which result from cracking different feedstocks. By way of example, the aromatics content of a pyrolysis naphtha depends on the specific feedstock from which it is derived. The premium price of the particular pyrolysis naphtha thus depends on its BTX concentration. The nonaromatic content of the pyrolysis naphtha is valued the same as naphtha. Further details can be found in Table VI. 

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