Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process...
Reexamination Certificate
2002-03-20
2004-10-12
Wood, Elizabeth D. (Department: 1755)
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
C585S002000, C585S003000, C585S013000, C585S014000, C208S014000, C208S015000, C208S018000
Reexamination Certificate
active
06803492
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flow improver for crude and distillate oils which is recovered from crude oil by extraction by means of supercritical gases.
Crude oils, residue oils, oil distillates, such as, for example, diesel fuel, mineral oils, lubricating oils, hydraulic oils, etc., contain, depending on their origin or the nature of their processing, varying proportions of n-paraffins and asphaltenes, which represent particular problems since they crystallize out or agglomerate on a reduction in the temperature and can thus result in impairment of the flow properties of these oils. This impairment of the flow properties of the oils is known as “solidification” of the oil. The pour point is the standardized term for the temperature at which an oil, for example mineral oil, diesel fuel or hydraulic oil, just stops flowing on cooling. However, the pour point is not identical with the so-called flow point. The flow point is a non-specific term, not covered by standards, for the temperature at which a solid starts to flow under given measurement conditions. Due to the impairment in the flow properties, tanks, pipelines, valves or pumps may block, for example during transport, during storage and/or during processing of these oils, in particular in the case of paraffin-containing oils, which are difficult to inhibit. In addition, paraffin precipitations require increased pressures during re-start of pipelines (yield point).
Particular difficulties occur in practice if the wax appearance temperature (WAT) and in particular the inherent pour point of these oils is above the ambient temperature, in particular at 20° C. or above. In view of decreasing world oil reserves and increasing exploitation of deposits that yield crude oils with high inherent pour points, the recovery and transport of problem oils of this type is achieving ever-greater importance.
Flowability can be restored or maintained using a number of measures of a thermal or mechanical nature, for example scraping the crystallized paraffin off the inside wall of pipes by regular pigging, heating of entire pipelines, or flushing processes with solvents. It is undoubtedly more elegant to combat the causes of the phenomenon by addition of flow improvers, which are also known as pour point depressants or paraffin inhibitors. A lowering of the pour point to values below the respective ambient temperature, in particular to values of about 10° C. or below, is generally advantageous here.
The way in which these flow improvers work is generally explained as being that they inhibit crystallization of paraffins and asphaltenes or co-crystallize with the paraffins or paraffin/asphaltene adducts and thereby result in the formation of smaller paraffin crystals, which are no longer able to aggregate and form a network which impairs flowability. The consequence is a lowering of the pour point and maintenance of the flowability of the oil at low temperature. The effectiveness of the flow improvers is dependent both on their chemical structure (composition) and on their concentration.
The flow improvers disclosed in the prior art are generally synthetic polymers, which usually contain structural units of ethylene and structural units of unsaturated carboxylic acid esters.
The disadvantage of these flow improvers from the prior art consists in their expensive preparation and their lack of general applicability. Thus, it is generally necessary to re-formulate flow improvers for particular uses.
Besides the said synthetic polymers, the prior art also discloses attempts to prepare cold-flow improvers for oils directly from crude oil or oil products.
U.S. Pat. No. 3,523,071 discloses that the heavy products of a shale oil which has already been subjected to visbreaking are effective pour point depressants for hydrodenitrated shale oil. On the other hand, however, these products have no effect on crude shale oil.
U.S. Pat. No. 3,532,618 discloses the preparation of asphaltenes which act as pour point depressants in shale oil by hydrovisbreaking of shale oil followed by deasphalting of the hydrovisbreaker product stream.
U.S. Pat. No. 4,201,658 likewise discloses a process for lowering the pour point of shale oils. Here, the asphaltenes of a thermally treated shale oil were employed as pour point depressants in relatively high concentrations of up to 12% by weight.
U.S. Pat. No. 4,728,412 discloses the flow-improving action of tar sand bitumen which has been subjected to various treatments in crude oils having a high pour point. Here too, relatively high amounts of up to 60% by weight are used as pour point depressants.
It is evident from all these documents that high concentrations were necessary hitherto for paraffin inhibition using pour point depressants based on components present in petroleum. In addition, all pour point depressants disclosed in these processes first have to be produced by treatment of the crude oils (which are shale oils) at high temperatures.
K. Zosel, Angew. Chem. 90 (1978), pp. 748-755, discloses a process for the deasphalting of top oils. This process uses extraction with supercritical gases. However, the effectiveness of products obtained therefrom is not disclosed.
WO-00/52118 discloses a process for the refining of oils, including petroleum, which is characterized by supercritical extraction of the oils. A flow-improving action of extraction residues is not disclosed.
The object of the present invention is to provide a flow improver which represents an alternative to the synthetic polymers of the prior art. This flow improver should be inexpensive to produce with no additional use of resources compared with the prior art. It should also be effective in smaller amounts than the prior-art pour point depressants based on components present in petroleum and should be producible without heat treatment, including from crude oils.
SUMMARY OF THE INVENTION
Surprisingly, it has now been found that flow improvers based on components present in petroleum can be obtained by extraction of crude oils by means of supercritical gases.
The invention thus relates to an additive for improving the cold-flow properties of crude and distillate oils, where the additive is obtainable by extraction of crude oil with supercritical gas.
The invention furthermore relates to fuel oils which comprise the additives described above.
The invention furthermore relates to the use of an extraction residue obtainable by extraction of crude oil by means of supercritical gases as cold-flow improvers for crude and distillate oils.
The invention furthermore relates to a process for the preparation of an additive which improves the cold-flow properties of crude and distillate oils by subjecting crude oil to extraction by means of supercritical gases, and isolating the resultant extraction residue.
DETAILED DESCRIPTION OF THE INVENTION
Separation of substances by means of supercritical gases (supercritical fluid extraction, SFE) is a well known method in the prior art and its principles will not be discussed here. It is disclosed by way of example in “Angewandte Chemie, Volume 90 (1978), Issue 10, pages 747-761”, which is expressly incorporated herein by way of reference.
The additives according to the invention can be obtained from any desired crude oils. The crude oils are preferably conventional crude oils. A preferred embodiment uses resin-rich crude oils which have resin contents of at least 0.5% by weight, in particular at least 5%by weight. The resin contents of the crude oils may be, for example, up to 30% by weight, in particular cases even up to 50% by weight.
The extraction is preferably carried out with nonpolar or slightly polar, low-molecular-weight gases having molecular weights of up to 200, in particular up to 100 units, or mixtures thereof. Examples of suitable gases are carbon dioxide, C
1
-C
5
-alkanes, C
2
-C
5
-alkenes and C
1
-C
3
-fluoroalkanes. Preference is given to CO
2
, ethylene or propane.
The extraction is generally carried out at pressures of from 50 to 500 bar and at temperatures of from 30
Feustel Michael
Kentschke Utha
Oschmann Hans-Jörg
Clariant International Ltd.
Silverman Richard P.
Wood Elizabeth D.
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