Mixed-base crude

Hybridrohbl, n. mixed-base crude oil. Hydantoinsaure,/. hydantoie acid. Hydnocarpussaure, /. hydnoearpie acid, hydrat, abbrev.. (hydratiert, hydratisiert) hydrated. 

The composition of crude oil may vary with the location and age of an oil field, and may even be depth dependent within an individual well or reservoir. Crudes are commonly classified according to their respective distillation residue, which reflects the relative contents of three basic hydrocarbon structural types paraffins, naphthenes, and aromatics. About 85% of all crude oils can be classified as either asphalt based, paraffin based, or mixed based. Asphalt-based crudes contain little paraffin wax and an asphaltic residue (predominantly condensed aromatics). Sulfur, oxygen, and nitrogen contents are often relatively higher in asphalt-based crude in comparison with paraffin-based crudes, which contain little to no asphaltic materials. Mixed-based crude contains considerable amounts of both wax and asphalt. Representative crude oils and their respective composition in respect to paraffins, naphthenes, and aromatics are shown in Figure 4.1. 

Figures 2 and 3 show the product distribution versus coke yield for a gas oil from mixed-base crude, and yields of gasoline versus coke for different types of charge stock.

Once-through cracking gas oil distillate from mixed-base crude... 

Petroleum crude oils, which are divided for the purposes of conventional classification into three main types—asphalt (or naphthenic)-base, paraffin-base, and mixed-base—contain varying amounts of hydrocarbons which readily solidify and are identified as wax. The asphalt-base crudes may contain only a trace of wax, while the wax content of the paraffin-base crudes and the mixed-base crudes may be as high as 15% or higher (73). Crude oils with a wax content as high as 35% are known. 

Because the paraffin and mixed-base crudes yield lubricating oil fractions of high quality, means had to be devised in the early days of the petroleum industry to separate the wax from the oil. The removal of wax from petroleum fractions is one of the most important phases in the production of lubricating oils and fuel oils of low pour point, and has received the attention of many investigators. 

Large amt of asphalt used in the US is artifical. It is obtained as the residue from distillation of asphaltic and mixed base crude petroleum oils... 

Wax distillate a neutral distillate containing a high percentage of crystallizable paraffin wax, obtained on the distillation of paraffin or mixed-base crude, and on reducing neutral lubricating stocks. 

Fig. 46. Composition of catalytically cracked gasoline produced by fixed-bed cracking of heavy gas oil from mixed-base crude. [Bates, ei ah, Ind. Eng. Chem. 34, 147 (1942) Ardern, Dart, and Lassiat, Advances in Chem. Ser. No. 6, 13 (1951). Reprinted by permission.]...

Motor Oils. Spark-ignition and diesel-engine oils differ primarily because the diesel oils must exhibit detergency properties to keep carbon from accumulating in the engine after a few hours of operation. Naphthene-base oils (low Viscosity Index) are somewhat satisfactory as diesel oils, but most heavy-duty oils are made by introducing a detergency additive to an oil manufactured from paraffin or mixed-base crude oils. 

Example 4-2. Use of Gravity Mid Per Cent Cuorve. Compute the specific gravity of a 41.4 API (0.8183 sp gr) mixed-base crude oil from the specific-gravity mid per cent curve. Figure 4-15 is the gravity mid per cent curve as determined in the laboratory. 

Pig. 6-1. Boiling range of refinery products (31.7 API Texas mixed-base crude oil). 

In general, paraffin-base raw products are the most easily treated, and the others follow in the order mixed-base and naphthene-base. This applies to the light distillates such as gasoline, as well as to the heavy lubricating oils. Many naphthene-base oils contain more sulfur than mixed-base oils, and paraffin-base oils may contain scarcely any sulfur. Paraffin- and mixed-base crude oils contain troublesome wax. The fact that a true naphthene-base oil contains no wax simplifies the manufacture of lubricants. 

Three broad classes of crude petroleum exist the paraffin types, the asphaltic types, and the mixed-base types. The paraffin types are composed of molecules in which the number of hydrogen atoms is always two more than twice the number of carbon atoms. The characteristic molecules in the asphaltic types are naphthenes, composed of twice as many hydrogen atoms as carbon atoms. In the mixed-base group are both paraffin hydrocarbons and naphthenes. 

The presence of paraffin wax is usually reflected in the paraffinic nature of the constituent fractions, and a high asphaltic content corresponds with the naphthenic properties of the fractions. As a result, the misconception has arisen that paraffin-base crude oils consist mainly of paraffins and asphalt-base crude oils mainly of cyclic (or naphthenic) hydrocarbons. In addition to paraffin- and asphalt-base oils, a mixed base had to be introduced for those oils that leave a mixture of bitumen and paraffin wax as a residue by nondestructive distillation. 

All types of crudes have been used in the production of spray oils. On the West Coast the asphaltic base crudes occurring locally have been generally used, while oils derived from mixed base stocks are now most commonly used east of the Rockies. 

The operation of the preprocessor is shown schematically in Figure 1. There are five basic steps o Select crude assay data o Build and report input tables o Generate crude data o Generate process data o Build and access LP data tables In the first step, the preprocessor accesses the disc file which contains all of Sun Petroleum Products Company s crude assays. The preprocessor extracts assay data for those crudes which the user has identified by card input as part of the base crude mix or to be made available to the LP model as an incremental refinery feed. The user can identify up to ten crudes any five of which can be designated as incremental. 

In the fourth step, the preprocessor generates plant performance data for the FCC, gas oil hydrocracker, motor reformer and BTX reformer. For each of these process units, the preprocessor calls the appropriate process simulator which computes the usage of equipment and utilities, product yields, and product properties for all base and alternate operations specified by the user. For all of the FCC operations, the feed properties are those of the atmospheric plus vacuum gas oil from the base crude mix blended with a specified fraction of deasphalter overhead. 

For all of the hydrocracker operations, the feed properties are those of the heavy naphtha from the base crude mix blended with a specified fraction of light cycle oil from the base FCC operation. For all of the motor reformer operations, the feed properties are those of the motor naphtha from the base crude mix blended with heavy hydrocrackate from the base hydrocracker operation. For all of the BTX reformer operations, the feed properties are those of the BTX naphtha from the base crude mix blended with light hydrocrackate from the base hydrocracker operation. Finally, for each process unit, the process simulator computes the change in plant performance associated with a fixed perturbation of each feed property about the base operation. 

The feed to the hydrocracker consists of the heavy naphtha cut from the base crude mix and light cycle oil from the base FCC operation. The hydrocracker simulator requires a description of each of these feeds in terms of the hydrocarbon components shown in Table I. Since these components are not directly measured in the crude assay nor are they predicted by the FCC simulator, special techniques were developed to estimate them from available data. 

For the heavy naphtha cut from the base crude mix, the following technique is used by the preprocessor ... 

For the motor and BTX naphthas from the base crude mix, the preprocessor (1) determines the amount of each component present in the crude, (2) computes the fraction distilled overhead for each component at the naphtha cutpoints specified for the crude distillation unit, (3) constructs for each naphtha the composition of the material remaining between the initial and final boiling points, and (4) computes the blended compositions of the motor and BTX naphthas from the base crude mix. 

Activities in the crude distillation unit submatrix represent the base crude mix operation and up to five incremental crude operations. 

Activities in the propane deasphalting (PDA) unit submatrix represent the operations on vacuum tower bottoms from the base crude mix and from the incremental crudes. The de-asphalter overhead streams from all activities enter one stream balance row with common properties. Each deasphalter bottoms enter a separate row for No. 6 fuel oil blending. 

Each material transfer activity enters a separate stream balance row with a +1 or -1 coefficient depending on whether the cutpoint change transfers material into or out of the unit. Each of these activities also enters the unit volume balance row and the feed property balance rows with appropriate sign. Feed properties for a material transfer activity are calculated by the preprocessor and represent base crude mix properties at the corresponding crude distillation cutpoint. 

A preprocessor case was developed with capability of running both Toledo s base crude mix and the incremental under consideration. This base prepared by the preprocessor was then run as an LP case. 

Alternative cases were developed by using a parametric LP approach to replace part of the base crude mix with incremental crude. This approach allowed the evaluation of the incremental crude, as a refinery charge, at a series of increasing rates to the refinery and gave some surprising results. The most important result was that optimum profitability of the crude occurred... 

If the residue which remains after distillation is a waxlike solid consisting largely of paraffin hydrocarbons the crude is designated as paraffin base. If the residue is a black pitchlike solid the crude is called asphalt base, Pennsylvania crude has a paraffin base whereas California oils are for the most part asphalt base. Often a clear-cut distinction cannot be made and the crude is described as being mixed base oil. Most Mid-Continent crudes are of this tyrpe. 

Crude oils are classified as paraffin-based, mixed-based, naphthene-based and the rather rare aromatic oils, depending on their paraffin, naphthene and aromatic hydrocarbon content (Figure 3.29). 

Minas Crude. Minas crude, which is classified as paraffinic, was subjected to pyrolysis to compare the results with those from Kuwait crude which is of mixed base. Some typical data are shown in Table IV. 

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