Mineral oils: processes and products – Refining – Sulfur removal
Patent
1991-12-11
1994-03-08
Morris, Theodore
Mineral oils: processes and products
Refining
Sulfur removal
208209, 208210, 208213, C10G 4500, C10G 4504
Patent
active
052924289
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for hydrodesulphurisation of a hydrocarbon feedstock.
DESCRIPTION OF BACKGROUND ART
Crude oils, their straight-run and cracked fractions and other petroleum products contain sulphur in varying amounts, depending upon the source of the crude oil and any subsequent treatment that it may have undergone. Besides elemental sulphur, numerous sulphur compounds have been identified in crude oil including hydrogen sulphide (H.sub.2 S), C.sub.1 to C.sub.5 primary alkyl mercaptans, C.sub.3 to C.sub.8 secondary alkyl mercaptans, C.sub.4 to C.sub.6 tertiary alkyl mercaptans, cyclic mercaptans (such as cyclopentane thiol, cyclohexane thiol and cis-2-methylcyclopentane thiol), open chain sulphides of the formula R--S--R' where R and R' represent C.sub.1 to C.sub.4 alkyl groups, mono-, bi- and tri-cyclic sulphides, thiophene, alkyl substituted thiophenes, condensed thiophenes (such as benzo(b)thiophene, isothionaphthene, dibenzothiophene, and benzo(b)naphtho(2,1-d)thiophene), thienothiophenes, alkyl cycloalkyl sulphides, alkyl aryl sulphides, 1-thiaindans, aromatic thiols (such as thiophenol), and cyclic thiols such as cyclohexane thiol.
Generally speaking, low API gravity crude oils usually contain more sulphur than high API gravity crude oils, although there are some exceptions. Moreover the distribution of sulphur compounds in the different fractions of petroleum varies mainly with the boiling range of the fractions. Thus the lighter fractions such as naphtha contain fewer sulphur compounds, whilst the content of sulphur compounds also increases as the boiling point or API density or molecular weight of the fraction increases. Most of the sulphur compounds that have been positively identified as components of crude oil boil below about 200.degree. C. Many other sulphur compounds of high molecular weight and high boiling point remain unidentified in crude oil.
For a variety of reasons it is necessary to treat crude oil and petroleum fractions derived therefrom to remove the sulphur components present therein. Otherwise subsequent processing may be hindered, for example because the sulphur components may adversely affect the performance of a catalyst. If the hydrocarbon fraction is intended for fuel use, then burning of the fuel will result in any sulphur components present therein being converted to sulphur oxides which are environmentally damaging.
For these reasons it is necessary to remove as far as possible the sulphur content from hydrocarbon fractions derived from crude oil, such as gasoline fractions, diesel fuel, gas oils and the like. Typically such sulphur removal is carried out by a process known generally as hydrodesulphurisation. In such a process the hydrocarbon fraction is admixed with hydrogen and passed over a hydrodesulphurisation catalyst under appropriate temperature and pressure conditions. In such a process the aim is to rupture the carbon-sulphur bonds present in the feedstock and to saturate with hydrogen the resulting free valencies or olefinic double bonds formed in such a cleavage step. In this process the aim is to convert as much as possible of the organic sulphur content to hydrocarbons and to H.sub.2 S. Typical equations for major types of sulphur compounds to be hydrodesulphurised are shown below: ##STR1##
Generally the cyclic sulphur-containing compounds are harder to hydrogenate than the open chain compounds and, within the class of cyclic sulphur-containing compounds, the greater the number of rings that are present the greater is the difficulty in cleaving the carbon-sulphur bonds.
Besides the presence of sulphur oxides in the combustion gases from hydrocarbon fuels, other environmentally undesirable components of such combustion gases typically include aromatic hydrocarbons, which may be present because of incomplete combustion, and carbonaceous particulate matter often containing polycyclic aromatic hydrocarbons, metal compounds, oxygenated organic materials, and other potentially toxic materials.
Because of present conc
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Dennis Alan J.
Harrison George E.
McKinley Donald H.
Davy McKee (London) Ltd.
El-Arini Zeinab
Morris Theodore
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