Mineral oils: processes and products – Chemical conversion of hydrocarbons – Hydrogenation
Reexamination Certificate
2000-01-27
2002-11-26
Norton, Nadine G. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Hydrogenation
C208S113000, C208S131000, C208S143000, C208S125000, C585S921000, C585S922000
Reexamination Certificate
active
06485631
ABSTRACT:
The present invention is related to a process for upgrading of heavy hydrocarbons (petroleum—crude oils) with a low API grade to a higher API grade in a reactor system involving heat, mechanical shear forces, pressure and catalytic action whereby the oil in converted into lighter fractions and its viscosity reduced.
Oil refining and the development of the internal combustion engine have continued since the latter part of the nineteenth century. Each has influenced the other in the course of this development, but it is the oil industry and its effect on almost every part of modern living that has been the most spectacular.
Crude oil is a mixture of literally hundreds of hydrocarbon compounds ranging in size from the smallest, methane, with only one carbon atom, to large compounds containing 200 or more. A major portion of these compounds are paraffins or isomers of paraffins. These are straight-chain hydrocarbon compounds such as butane, C
4
H
10
which normally is denoted nC
4
. Isobutane on the other hand is denoted iC
4
.
The remaining hydrocarbon compounds are either cyclic paraffins called naphthenes or aromatics.
These families of hydrocarbons are called homologues, and because of the large quantity of these compounds which exist in crude oil, only the simplest of compounds in the homologues can be isolated to some degree of purity on a commercial scale. Generally, in refining projects, isolation of comparatively pure products are restricted to those compounds lighter than C7s. Most compounds, however, have been isolated and identified but only under strict and delicate laboratory conditions.
In the industry the products are restricted to groups of these hydrocarbons boiling between selective boiling ranges. Thus products are usually denoted by boiling points rather than by the compounds they contain.
Not all compounds contained in crude oil are pure hydrocarbons. The crude contains certain inorganic impurities such as sulphur, nitrogen and metals. By far the most common of these impurities are the organic sulphur compounds called mercaptans. These compounds are similar to hydrocarbons but with the addition of one or more sulphur atoms.
More complicated sulphur compounds also exist such as thiophenes in the high carbon number range homologues and disulphides in the middle distillate range. Because of the close relationship that exists between these sulphur compounds and neighbouring hydrocarbons in such characteristics as vapour pressures, the compounds can not be isolated by distillation processes on a commercial scale.
Organic chloride compounds are not usually removed from the crude as products but the corrosive effect attributed to these compounds on parts of refinery plants is always a source of concern. A considerable amount of investigation has been, and is still being, carried out on prevention of corrosion by HCI generated in the process from these organic chlorides.
The metals contained in crude are usually nickel, sodium and vanadium. Because these are not very volatile they are found in the heavier products of crude such as fuel oil. They only become a nuisance in certain cases when they can affect further processing of the oil, or if they exist in such large quantities in fuel oil as to limit the saleable value of the product. Their removal can be effected in such cases by an extraction process where they are removed as a part of a bituminous extract called asphaltenes.
Before leaving the subject of crude oil composition it is necessary to mention yet another series of organic compounds which, although not always present in the original crude, are often formed during the refining processes. These are unsaturated compounds. As mentioned earlier, most compounds contain carbon and hydrogen and are constituted in such a way that each carbon atom contains its full quota of four atoms, in the form of either hydrogen or carbon atoms. However, some of these molecules break down under conditions of high temperature and permanently lose one or more of those attached atoms. Such compounds are unstable and readily combine with themselves or other similar compounds to form polymers. They are called unsaturates while the stable hydrocarbons such as paraffins, cycloparaffins and aromatics are called saturated hydrocarbons. An example of such a compound is ethylene, which has the following formula C
2
H
4
.
Crude oil found in various parts of the world vary considerably in characteristics. This can readily be seen in the difference in specific gravity that exists between the crudes. For instance, Zelten crude (Libyan) has an API gravity of 39.0 while Bachequero crude has a gravity of 16.0. A Venezuela crude from the Orinoco basin has a gravity of 10 API. This difference is due to the fact that although each crude oil contains basically the same hydrocarbon compounds, the proportion of these hydrocarbons vary considerably from one crude to another. Thus some crudes are relatively rich in paraffins, and this is reflected by the waxy nature of the crude (most Middle East crudes fall into this group). Others contain more cycloparaffins and aromatics (such as Nigerian and some American West Coast crudes).
Although it is theoretically possible to produce any type of refined product from any crude, it is not usually economically feasible to do so. For instance, better yields of reformer stock for aromatics production is obtained from Nigerian crude than from Kuwait, while considerably more residium for fuel oil is obtained from Kuwait than Nigeria. To satisfy the demand of these two products, refineries often blend two such devious crudes, changing the proportion of the blend to satisfy the particular need. If product demands are seasonal, as in the case of many gas oils, imports of specifically selected crudes are scheduled to optimise the production of such cuts for the season.
Selectivity of crude type is comparatively easy to effect and is common practice in the refining industry where most oil companies have their own oil wells in various parts of the world. However, occasionally the demand for a particular product or the elimination of a low-value one becomes so persistent that major conversions of a chemical nature have to be adopted. Such processes as thermal and catalytic cracking and, more recently, hydrocracking are used to effect this.
In general, the products that are normally obtained from crude oil can be grouped as follows:
(1) Volatile products (these are the lightest products)
Propane LPG (liquefied petroleum gas)
Butane LPG
Light naphtha (C5s and nC6)
(2) Light distillates
Gasolines
Heavy naphtha (petrochem naphtha and base for paints)
Kerosene and jet fuels
(3) Middle distillates
Automotive diesel
Heating oils
Gas oils
(4) Fuels oils
Marine diesel
Bunker fuels (for ships)
(5) Lubricating oils
Motor
Spindle
Machine oils
(6) Waxes
Food and paper coating grade
Pharmaceutical grade
(7) Bitumen
Asphalt
Coke
Product form these groups are produced from distillation processes and treated to meet certain specifications. These specifications are the results of a compromise between desirable performance characteristics in the product and the ability to make such products from the crude and the processing facilities at hand. Wide rangs in physical properties are often tolerated in these specifications in order to cater for crude oil source, sales area and the product's ultimate use.
Thermal cracking processes are the true workhorses of the oil-refining industry. The processes are relatively cheap when compared to the fluid cracker and the hydrocracker, but go a long way to achieving the oil-cracking objective of converting low-quality material into more valuable oil products. The process family of thermal crackers has three members:
Thermal crackers
Visbreakers
Cokers
The term ‘thermal cracking’ is usually given to those processes that convert heavy oil (usually fuel oil or residues) into lighter product stock such as LPG, naphtha, and middle distillates by applying only heat to the feed over a prescribed element of time. When applied to a specific process the term re
Ellycrack AS
Norton Nadine G.
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