US2131422A - Extraction process - Google Patents

Description

Sept. 27, 1938. A ANDERSON 2,131,422

EXTRACTION PROCES S Filed Feb. 20, 1937 Salve/7f Propane /nvcr7/0r:A/v/n R linderson By his A/f0rneg;

Patented Sept. 27, 1938 EXTRACTION PROCESS Alvin P. Anderson, Alton, IlL, assignor to Shell Development Company, San'Francisco, Calii'., a corporation of Delaware Application February 20, 1937, Serial No. 126,889

10 Claims. (Cl. 196-13) This invention relates to a' process for the treatment of hydrocarbon oils, such as petroleum fractions, with selective solvents comprising cresylic acid, and is particularly useful in the extraction of higher-boiling residual or distillate oils, such as cylinder oil, lubricating distillates, spindle oil, transformer oil, but may be applied also to the treatment of lower boiling fractions.

The types of hydrocarbons occurring in petroleum fractions and their relative concentration vary with the source and the boiling range of the fraction, and these variations in initial composition, as well as the quality of the desired extraction product, determine the exact nature of the separation eflected in the extraction processes. In general, however, the purpose of the process is to dissolve those components of the initial oil which are more aromatic, naphthenic, and/or olefinic in nature, i. e., those which have a relatively lower hydrogen-carbon ratio, while leav-v ing undissolved the relatively more paraflinic components. In the case of lubricating oils, the more paraffinio hydrocarbons present in crude lubricating oil fractions are more desirable because, as compared with themore soluble hydrocarbons, their viscosity is not so greatly affected by changes in temperature, are chemically more inert and stable, and exhibit less tendency towards the formation of undesirable resinous or sludge forming constituents on contact with air at elevated temperatures. This group of hydrocarbons, in the case of lubricating oils, does not include those compounds usually designated as wax" or petrolatum.

As a matter of convenience hereafter the component or group of components of the initial oil which it is desired to remove in the extraction process by preferential dissolution in the selective solvent as the extract will be designated as non-paraflinic constituents, and the component or group of components which it is desired to recover as the raftinate will be designated as paraffinic, it being understood that these terms are relative, and are to be interpreted with regard to the composition of the initial material and the extraction products produced, the non-paraffinic portion being in each case more readily soluble in the extract phase than the paraflinic portion.

According to one mode of carrying out such an extraction process, a selective solvent consisting of cresylic acid, or of a mixture of cresylic acid with a similar second solvent, such as phenol, is passed through a packed tower or a multi-stage treater countercurrently to an auxiliary solvent which is at least partially immiscible with the selective solvent in the presence of the oil, and the oil is subjected to the extracting action of these countercurrent streams by introducing it into the system either with the auxiliary solvent, or at a point intermediate to the points of introduction of the selective and auxiliary solvents respectively. Such a process is described in the Tuttle Patent No. 1,912,349. In certain processes the auxiliary solvent is introduced into the system at a plurality of points, as, for example, near the point of removal of the extract, at the point of introduction of the oil, and at a point lying between the points of introduction of the oil and the selective solvent, respectively.

Particularly useful as auxiliary solvents in such a process are liquid or liquefied hydrocarbon distillates boiling below about 45 0., although higher. boiling preferably 1 aromatic-free distillates I may be employed. Propane, either alone, or in process of the type described above, involving the flow of an oil and an auxiliary solvent countercurrently to a selective solventcomprising cresylic acid through several stages (which stages may be either real, as when a series of interconnected mixers and settlers or centrifuges is provided, or virtual, as when using one or more packed towers), the maximum rate of throughput of the oil is often undesirably limited by the slow or incomplete separation of the phases in one or more stages. Thus, when feeding too much of the initial oil into the system, whether or not the rate of flow of selective solvent is varied, the mixture in one or more stages becomes cloudy or emulsified, causing some of the extract phase to move in the wrong direction by being intermixed with the rafllnate; as a result the sharpness of the separation is lowered as indicated, for example, by a decrease in theviscosity index or paraflinicity of the raillnate oil,and anincrease in that of the extract oil, due to entrainment of railinate in the extract. This condition may progress so far as eventually to result in the coalescence of the two phases, with the result that the extraction zone is flooded with a solution of oil and solvents and the extraction ceases.

According to the present invention it was found thatthe speed of separation of the phases, whether effected in a settling tank, in a centrifuge, or in a tower, can be materially increased by employing, instead of anhydrous selective solvent, a mixture of a cresylic acid-containing selective solvent and a small amount of water. It was found that, when extracting viscous residual oils, at least 0.3% of water are necessary to effect an improvement in the settling rates, and that for safe uniform operation the water content should be maintained at above 0.4% by weight,

based on the selective solvent, while the best operation occurs when the water content is kept within the range from 0.5 to 0.7%. Other water miscible low-molecular oxygenated organic compounds, such as methyl alcohol, glycerol, glycol, acetone, etc., may be employed in place of or together with water to improve the settling rates. When such compounds are employed in addition to water, the quantity of water -may be as low as 0.2%.

It has, moreover, been found that it is essential that the water concentration be maintained below 1.0% and, preferably, below 0.8%. When more than this amount of water is employed, there is a decided shift in the solubility equilibria toward increases in the sizes of the raflinate layers, and towards decreased oil concentrations in the extract phases, causing larger quantities of hydrocarbons of intermediate solubility to be dissolved in the raillnate phase, thereby lowering the quality of the ultimate raflinate. Such a shift in equilibria upsets the extraction process and prevents the production of a raflinate of the desired quality in an apparatus of a fixed number of real or virtual stages. While it is sometimes possible partially to restore the equilibria by increasing the temperature, this is undesirable because an increase in temperature was found to cause slower rates of partition between the phases.

It should be noted that the water or other material is, in the present process, added merely to improve the rate of settling, the amount present in the system being insuflicient to cause a substantial lowering of the solvent power of the selective solvent for oil. This distinguishes the present invention from prior processes in which such substances have been employed in larger concentrations with the purpose of regulating the solvent power of the selective solvent. Thus, according to the present invention the quantity of water or other polar agent is sufllciently small not to cause the oil concentration in the extract phase in the stage at which the fresh solvent is introduced to be lowered by more than about 20%, as compared to and based on the concentration of oil in the corresponding extract phase when anhydrous selective solvent is employed.

The present invention, therefore, is based upon the discovery that there is a critical range of concentrations of water which materially improves the rate of separation of the rafiinate phase from the extract phase without causing so great a shift in the solubility equilibria as to upset the extraction process.

While the addition of small amounts of water is especially useful in extraction processes employing propane as the auxiliary solvent, other equivalent auxiliary solvents, as outlined above, may also be employed. The addition of water in rocesses operating without auxiliary solvents is,

however, undesirable because it was found that in the absence of an auxiliary solvent even the small quantities of water employed in the present process are detrimental to the selectivity of cresylic acid.

The expression cresylic acid, as employed in the present specification and claims, is intended to include o-, m-, and p-hydroxy toluene, mixtures of two or more of these as well as mixtures containing their higher homologues, such as ethyl hydroxy benzenes. The expression "cresylic acidcontaining, as applied to selective solvents, is intended to designate a selective solvent which may, save for the small amount of water specified according to the present invention, consist entirely of cresylic acid, as defined above, as well as selective solvents containing quantities (not over 65% by weight) of other aromatic and particularly phenolic solvents, such as phenol. By way of example, excellent results have been obtained by employing 0.6% of water in an extraction process employing as the selective solvent a mixture of 70% cresylic acid and 30% of phenol. It was, moreover, found that the settling rate can be increased by using a selective solvent which contains a concentration of phenol higher.

' ing water, described below, was found to be particularly useful in that it also improved the separation of dissolved solvent from the raflinate phase.

The process may, for example, be operated in an apparatus of the type illustrated schematically in the drawing, which is a flow diagram of one embodiment of the present invention. In the drawing, A and B represent cylindrical shells, filled with a plurality of partitions so as to provide settling chambers or stages I to 8. Each stage is equipped with a mixing device Ia. to 8a, which may be provided with means for distributing a liquid mixture or emulsion into the chambers with a minimum of turbulence. The chambers are interconnected by conduits, as shown.

Cresylic acid enters mixer 8a from tank 9 via line H) by the action of pump 8e through valve l2. An auxiliary solvent, like propane, is fed into mixer la from storage tank l3 via line H, controlled by valve l5. Raw oil, such as a topped crude, is introduced into one of the intermediate stages, such as, for example, stage 3 from tank i6 via line I! and pump l8, at a rate controlled by valve l9.

As aresult of feeding the cresylic acid solvent, propane, and initial oil into mixers 8a, Ia, and 3a, respectively, the cresylic acid solvent and propane flow countercurrently to one another through the several sections in the following manner: The phase discharged from each of the mixers stratifies in the chambers l to 8 to form relatively lighter raflinate phases and relatively heavier extract phases. The extract phases settle and are withdrawn via lines lc to 80, while the rafiinate phases are withdrawn via lines Id to 8d. Extract phases from stages 2 to 8 are fed into mixers la to la, respectively, by pumps le to la, and raifinate phases from stages I to I are fed into mixers 2a to 8a, respectively, via valves U to 8!. The ultimate rafllnate phase is withdrawn through valve 20, and may be treated for the recovery of the propane and cresylic acid solvent in any desired manner. The ultimate extract phase is withdrawn through a valve 2| in line lc for a similar treatment.

The improvement according to the present invention resides in employing in the settling chambers a cresylic acid solvent containing small quantities of water, as described above. The solvent in the tank 9 may contain this water. When this solvent is anhydrous or substantially so, water may be introduced at one or more points in the process, as, for example, into the line l through a valve 22.

Instead of adding all of the water through the valve 22, I prefer to add the major portion of the water used in accordance with this invention to the ultimate rafilnate phase withdrawn from the chamber 8, either before or after this phase is freed of the auxiliary solvent. Thus, the raflinate phase may be flowed through a flashing stage 23' wherein propane is separated and withdrawn at 24. The residual portion of the ramnate phase is mixed with water fed via the valve 25, and the resulting mixture is stratified in settling tank 26. The addition of water causes separation of the mixture into two secondary liquid phases: one consists of a substantially oil-free concentrated aqueous solution of cresylic acid, which is withdrawn at the bottom and combined with substan-' tially anhydrous cresylic acid from the tank 9 via the line 2! and the valve 28; the other consists substantially of the refined rafilnate oil containing a very small amount of cresylic acid, and may be withdrawn at 29. The latter phase may be further treated, for instance, by vacuum distillation, to recover a solvent-free oil raflinate. The anhydrous cresylic acid in the tank 9 may be either the fresh make-up solvent or that recovered by distillation or by some other methodv from the extract phase produced in the same process. The proportions in which the anhydrous solvent and its aqueous solution are combined, either prior to or after being introduced into the extraction zone, are regulated to produce a solvent containing the desired concentration of water within the above specified range. Following is an illustrative example of this preferred form of the process:

The raifinate phase produced by a continuous method of countercurrent extraction in which initial oil was introduced at an intermediate point into counterflowing .streams of propane and cresylic acid was found to',contain about 16% of the total cresylic acid used in the process. It was subjected to the following treatment to separate the bulk of cresylic acid from the oil: propane was flashed off by reducing the pressure on the rafiinate phase. A small quantity of water (about 3% based on cresylic acid in this phase) was then added to the residual portion of the rafiinate phase, whereupon the oil-cresylic acid solution separated into an oil layer and an aqueous cresylic acid layer. The addition of such a large amount of water greatly improved the speed of separation between the oil and acid layers, as compared to prior processes in which small amounts of water (about 1%) were added. The layers were separated and the aqueous cresylic acid was combined with an anhydrous cresylic acid forming an aqueous cresylic acid solution with water content of about .6%; this solution was reused in the extraction of additional quantities of oil.

The degree of improvement obtainable by the addition of water may be seen from the following data. Employing a solvent mixture containing 30% phenol and 70% cresylic acid in a double countercurrent extraction system, a combination with. propane as the-auxiliary solvent, for the extraction of a residual oil having an initial viscosity index between 60 and '72, the phases withdrawn from the extraction stage nearest the point of introduction of the solvent were flowed through an eductor tube at the rate of 17 feet per second, .and the rate of settling determined by flowing the mixture through a 24 inch long gauge glass bomb. Without water the average rate of settling was about 0.3 foot per second, which was increased to 0.83 foot per second when 0.8% of water were added, employing the same temperature.

I claim as my invention:

1. A process for the separation of parafi'lni'c and non-paramnio portions of a petroleum lubricating oil fraction containing the same, comprising the steps of flowing concurrent streams of said oil and a liquid auxiliary solvent for the parafiinic portion of the oil, consisting predominantly of one or more liquid or liquefied hydrocarbons containing lessthan six carbon atoms in the molecule through an extraction zone counter-currently to a stream of a cresylic acid-containing selective solvent containing between about 0.3% and 1.0% water under conditions to cause the formation of counterfiowing rafflnate and extract phases, separating said phases, and removing the separated phases at spaced points in the extraction zone.

2. The process according to claim 1 in which the water concentration in the selective solvent is between about 0.5 and 0.7%.

3. The process according to claim 1 in which the auxiliary solvent consists predominantly of propane.

4. The process according to claim 1 in which the liquid phases are separated by settling.

5. A process for 'the separation of paraflinic and non-parafllnic portions of hydrocarbon oil containing the same which comprises flowing said oil through an extraction zone countercurrently to -a cresylic acid-containing selective solvent containing between about 0.3% and 1.0% water in the presence of a liquid auxiliary solvent for the paraifinic portion of the oil which, when mixed with said selective solvent in the presence of the oil, is capable of forming two liquid phases, thereby producing liquid extract and rafllnate phases, separating said phases and withdrawing the separated phases at difierent points in the extraction zone.

6. A continuous process for the separation of parafiinic and non-paraflinic portions of hydrocarbon oil containing the same, which comprises continuously flowing said oil through a countercurrent extraction apparatus countercurrently to a cresylic-acid containing selective solvent in the presence of a liquid auxiliary solvent for parafiinic portions of the oil which, when mixed with said selective solvent in the presence of the oil is capable of causing the formationof liquid raftinate and extract phases, continuously separating and withdrawing raffinate and extract phases from said apparatus at spaced points thereof, adding a quantity of water to the withdrawn rafiinate phase to cause the formation of a liquid aqueous solvent phase and a liquid oil phase, separating said aqueous solvent phase from the oil phase, mixing said separated aqueous solvent with substantially anhydrous cresylic acidcontaining selective solvent, and continuously introducing the resulting mixture of anhydrous and aqueous solvents into the apparatus for the extraction of oil, said quantity 01' water being such as to cause said resulting mixture of anhydrous and aqueous solvents to have a water concentration of between 0.3% and 1.0%.

'7. The process according to claim 6 in which the said quantity of water is such that the water concentration in said resulting mixture of anhydrous and aqueous solvents is between about 0.5% and 0.7%.

8. A process for the separation of parafllnic and non-parafilnic portions of hydrocarbon 011 containing the same which comprises contacting said oil with a cresylic acid-containing selective solvent containing between about 0.3% and 1.0% of a separating aid of the class consisting of water, methyl alcohol, glycerol, and glycol in the presence of a liquid auxiliary solvent for the parafflnic portion of the oil which, when mixed with said selective solvent in the presence of the oil, is capable of forming two liquid phases, and separating said phases.

9. A process for the separation of parafllnic and non-parafllnic portions of hydrocarbon oil containing the same which comprises contacting said oil with a cresylic acid-containing selective solvent containing between 0.2% and 1.0% of water and in addition a small quantity of a low molecular oxygenated water-miscible organic compound in the presence of a liquid auxiliary solvent for the parafllnic portion of the oil which, when mixed with said selective solvent in the presence of the oil, is capable of forming two liquid phases, and separating said phases.

10. A process for the separation of parafflnic and non-paramnic portions of hydrocarbon 011 containing the same which comprises contacting said oil with a cresylic acid-containing selective solvent containing between about 0.3% and 1.0% of a separating aid of the class consisting of water, methyl alcohol, glycerol, and glycol in the presence of a liquid auxiliary solvent consisting predominantly of hydrocarbons normally boiling below C. which, when mixed with said selective solvent in the presence of the oil, is capable of forming two liquid phases, and separating said phases.

ALVIN P. ANDERSON.

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