Mineral oils: processes and products – Chemical conversion of hydrocarbons – With preliminary treatment of feed
Patent
1987-11-13
1989-07-11
Sneed, H. M. S.
Mineral oils: processes and products
Chemical conversion of hydrocarbons
With preliminary treatment of feed
208 90, 208 40, 208 44, 208 45, 208309, 208179, 208180, C10C 300, C10C 308
Patent
active
048469572
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the separation of asphaltenes from oil.
The asphaltenes content of a petroleum product is the percentage by weight of wax-free material insoluble in n-heptane but soluble in hot benzene.
U.S. Pat. No. 3,321,394 discloses a process for separating asphalt and asphaltenes from hydrocarbon oils in which the oil is brought into contact with a solvent which may be a normal or isoparaffin having from 5 to 7 carbon atoms in the molecule to precipitate asphaltenes.
The solvent extraction process produces a mixture of precipitated asphaltenes and solvent. The mixture is then withdrawn from contact with the hydrocarbon oil originally containing the asphaltenes. It is then necessary to separate the asphaltenes from the liquid used to cause its separation. One method by which this may be done is by allowing the asphaltenes to settle by gravity. However we have found that the rate of sedimentation of the asphaltenes from the higher molecular weight solvents, e.g. C.sub.5 -C.sub.7 hydrocarbons is undesirably slow.
It will be desirable to find an improved method for separating asphaltenes from oils containing them.
According to the present invention the process for the separation of solid asphaltenes from hydrocarbon oil containing asphaltenes wherein the oil is brought into contact with an acid is characterised in that the acid is formic acid or a water soluble organic acid consisting of carbon hydrogen and oxygen and having at least two functional groups.
The preferred acid is formic acid. It has a low molecular weight and is therefore effective at low dosages. It is liquid over a range of temperatures useful for precipitating asphaltenes, but boils at a relatively low temperature (101.degree. C.) at atmospheric pressure so facilitating the use and recovery of the pure acid. Asphaltene precipitation can also be facilitated by a selected group of other organic acids namely those acids which are water-soluble, contain only carbon, hydrogen, and oxygen and which have a second functional group. The acidity of the acid may be due to a carboxyl group or a phenolic group. The second functional group may be a second carboxyl group or may be an aliphatic hydroxyl or phenolic group. Thus examples of acids which may be used are alkane dicarboxylic acids such as oxalic, malonic, succinic and glutaric, hydroxy alkane dicarboxylic acids e.g. citric acid, and phenols containing more than one phenolic group e.g. resorcinol. An extensive list of compounds identified as water soluble at room temperature is given in the table of physical constants of organic compounds in Handbook of Chemistry and Physics published by the Chemical Rubber Company (65th Edition). The acid is preferably substantially insoluble in heptane at 20.degree. C.
The acid must be brought into contact with the oil. Where the acid is not liquid at the temperature of the asphaltene precipitation step it may be necessary to use it as a solution. The solvent is preferably a relatively low boiling organic liquid e.g. methanol or acetone.
The introduction of excessive amounts of water with the acid is preferably avoided. Thus if aqueous formic acid is used as the acid, the formic acid concentration is preferably at least 50% wt/wt, more preferably at least 90% wt/wt. In order to provide adequate contact between the oil and the acid agitation is used. Excessive agitation, however, is undesirable as this may cause the precipitated asphaltene particles to break up. This will make it more difficult to separate them from the oil.
The viscosity of crude and residual oils tends to be very high. If the viscosity is very high it may be very difficult to separate the precipitated asphaltenes from the oil, particularly when the asphaltenes concentration is high (more than 10% wt/wt). The viscosity decreases as the temperature is increased and it is therefore often convenient to carry out the deasphalting step at moderately elevated temperatures e.g. 60.degree.-90.degree. C.
The viscosity of the oil may be reduced by the addition of a low viscosity misci
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Johnson Graham R.
Rutter Paul R.
Pak Chung K.
Sneed H. M. S.
The British Petroleum Company p.l.c.
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