US2100707A - Refining of mineral oils - Google Patents

Description

NOV. 30, 1937. I S, Q BHATNAGAR I 2,100,707v

REFINING OF MINERAL OILS Filed June l5, 1956 2 Sheets-Sheer, l

a 1 .Z-YJ w N m N s is gri-hlx.

I "f EXTRACT Nov. 30, 1937. s. s. BHATNAGAR REFINING r0.1 MINERAL oILs 2 Sheets-Sheet 2 Filed June l5, 1956 mmFM Immmm ozmss G .22E

Patented Nov. 30, 1937 'I PATENT OFFICE 2,100,107 REFIMNG or MINERAL oILs Shanti Swarupa signor to Steel London, England Application June 15,

In Great 9 Claims.y

Crude petroleum is separated by distillation into various fractions such as petrol, kerosene, gas oil, Diesel fuel oils, lubricating oils, etc., some of which require a refining treatment in order to render them suitable for use.

In the case, for instance, of the kerosene fraction, which usually distils between the approxi-- mate limits of 150 C. and 300 C., such a treatment is generally required for improving the 1mV burning qualities of the oil with respect to luminosity, tendency to smoke and incrustation of the Wick, and for reducing the tendency to discoloration during storage. The known treatmentwith strong or fuming sulphuric acid or with ad- 15- sorbents is not satisfactory in the case of kerosenes of inferior quality, containing a relatively high percentage of undesirable constituents, for example, aromatic and unsaturated hydrocarbons, etc., and such kerosenes are usually rened by treatment with certain selective solvents which extract the undesirable constituents of the oil; such solvents are, for instance, liquid sulphur dioxide, phenol, alcohol and acetone, of which only the iirst-named has found extensive commercial application.

The lubricating oil fraction (which may be a distillate or may constitute the distillation residue `according to its grade and to the nature of the crude petroleum) is in some cases treated 3owith a selective solvent in order to improve its viscosity index and resistance to oxidation and to Areduce its tendency towards the formation of gum and/or carbon deposits when used in inter` nal combustion engines. As such solvents,'fur 5- fural, nitrobenzene, a mixture of benzene and sulphur dioxide, and cresylic acid in conjunction with liquid propane, have been'- proposed among others. The use of selective solvents has also found oils, especially in the which the presence of as'large a proportion as possible of parainic constituents is desirable for used.for extracting the inferior constituents having poor ignition qualities, leaving a more highly paramnic reiined oil. According to this invention, mineral oils are 50 refined by subjecting them to extraction with glacial acetic acid. It has been found that this acid has a good selective solvent actionon the undesirable constituents of the oils furthermore, it is easily recovered unchanged and its use does g5 `no t necessitate operation under pressure orr at Bhatnagar, Lahore, In Brothers &`Company Limited,

application in the improvement of Diesel fuel satisfactory ignition qualities. Such solvents are y diane? 1936, Serial No. 85,409

Britain August 19, 1935 low temperatures. In the case of some oils it may be advantageous to dilute the oil under treatment with lighter hydrocarbons to'reduce its viscosity and permit a more eflicient separation of the undesirable constituents, and subsequently recover the diluent by distillation, or alternatively to carry out the process under temperatures or pressures other than atmospheric.

The invention is useful in its application to any petroleum fractions, in particular, burning oils, lubricating oils and Diesel fuel oils.

From a low grade kerosene it is possible to obtain .a refined product of excellent burning qualities and in good yield. It has been found that from certain kerosenes of only average burning qualities, it is possible to obtain yields of much improved oils as high as 92 per cent. of the original 011;' if only a smaller degree of improvement is desired, even higher yields may be obtained.

Crude lubricating oils are substantially improved in their viscosity index, their resistance to oxidation and their colour stability and may only require 'a nal treatment with an adsorbent earth in order to give products of high quality and good colour.

From low grade `Diesel fuel fractions it is possible to produce rened oils of much improved paraiiinicity and correspondingly improved, ignition qualities.

In carrying out the invention, the procedure may consist'in intimately mixing the oil with a suitable quantity of glacial acetic acid and then allowing the mixture to separate into layers. The quantity of glacial acetic acid. may vary from, say,one half to three times the volume of the oil depending on the nature of the oil and the degree of rening desired, although a larger quantity may be used: The upper layer (raflinate layer) constitutes the refined oil containing some lacetic acid, generally about per cent. at atmospheric temperatures of.26- 2'7 C. and a smaller quantity at lower temperatures. I'he lower layer constitutes the extract and consists of the balance of the acetic acid containing the undesirable portions extracted from the original oil.

- It is possible to conduct the process more economically by subjecting the oilto several successive extractions. Inthis case, the total quantity of glacial acetic acid is divided into several portions which are used successively for the extraction of a given quantity of oil; that is to say, the oil is rst mixed with onev portion of the acid and allowed to separate, the extract is removed and the partially refined oil -is -then treated in like manner with a further portion of the acid, 65

f be separated in a `centrifugal separator.

2 and sol on. In this manner, the proportion of acetic acid required for producing a desired result may be reduced and the yield of refined oil of a given quality increased. The most suitable number of stages depends in any given case on the total proportion of acetic acid to be used and on the available plant; generally va treatment with a volume of acetic acid varying from to 250 per cent. of the volume of the oil can be advantageously conducted in three or four stages.

The process may be conducted according to the counter-current system. rThe operation may be continuous, the glacial acetic acid and the oll to be treated passing in opposite directions through any suitable counter-current plant so that the fresh acetic acid first comes int contact with an oil from which the bulk of the undesirable constituents has already been removed, whilst the fresh oil rst comes into contact with acetic acid which has a of undesirable constituents extracted from a previous quantity of oil. Alternatively, the countercurrent system may be applied in the extraction of the oil in batches; in this case, each -batch of oil will be subjected to extraction in several successive stages, there being used for vthe final stage fresh glacial acetic acid and for each of the other stages the oil-containing acid constituting the extract from the next succeeding stage of the extraction of a previous batch of oil.

The glacial acetic acid and the oil may be mixed by means of a stirrer, a pump and orifice mixer, a homogenizer or anl orifice mixer fed by gravity. The ranate and extract maybe a1- lowed to separate in a settling vessel or they may Various methods are available for recovering the'acetic acid contained in the extract and in the raiiinate, such\ as washing with water, distillation, steam distillation, salting out or cooling to a suilciently low temperature to cause crystallization of the acid. Which method or combination of methods is most advantageous for treating the raffinate and the extract respectively will depend on the circumstances of each particular case.

For example, the refined oil may be substantially freed from acetic acid by washing with water, most advantageously applied in successive portions. 'Ihe washingwater containing the extracted acetic acid may then be used for washing an extract which has already been freed from Ehi: bulk of its acetic acid by washing or othere. According'to another procedure, the acid may be vrecovered from the-raffinate or extract, or from both, by distillation, with or without the assistance of reduced pressure. In the case of kerosene, however, distillation tends to cause a slight discoloration of the refined oil, so that a subsequent treatment with, for instance, sulphuric acid or an adsorbent earth may be necessary to restore the colour. Distillation may be conducted in any suitable type of plant, suchas a tube still having a flash tower in which the acetic acid vapour is released, or a climbing film or similar type of evaporator in which the vapour is released by centrifugal force. Heat may be economized byA heat exchange between the vapours or hot oil leaving the plant and the incoming mixture of oil and acetic acid. Whilst distillation may be conducted under reduced pressure, it is generally more convenient to operate under atmospheric pressure owing to the tendency to dilution of the acid if a steam ejector relatively high content is used for providing the reduced pressure, and to the danger of corrosion of working parts if a vacuum pump is used. Any oil carx'ied over with theacetic acid vapour during distillation is of good quality, even in the case of the extract, and its presence does not interfere with the re-use of the recovered acid in the process.

Yet another procedure for recovering acetic acid consists in salting out the bulk of the acid by means of anhydrous sodium acetate; the acid stili remaining in the oil may then be substantially removed by washing with water. The acetic acid salted out may be separated from the sodium acetate bydistillation.

Steam distillation will scarcely be an economical method for the recovery of acid from oils containing it in substantial proportions but may sometimes usefully be adopted for the treatment of oils from which the bulk of the acid has been removed by some other means, such asdistillation.

In all cases in which the treatment of the extract or raffinate leads to an aqueous solution of` acetic acid, glacial acetic acid may be recovered from the solution by azeotropic distillation and may be used again inA the process. Alternatively, the aqueous acid may be used for some other purpose, for example i'or the manufacture of esters.

In-some cases it may be desirable to subject the refined oil to distillation in order to improve its colour and to free it from the lastl traces of acetic acid. Or the last traces of acid may be removed by treatment with an alkali, such as sodium hydroxide or lime, followed by washing with water.

The invention permits the production of burning oils of very high quality from an unrefixied oil of the approximate distillation range of to 250 C.; in this case it is advisable to recover the acetic acid from the raiilnate by washing with water.

Where a very high quality is not the main desideratum, it may be found preferable to use an unreflned oil of somewhat higher distillation range, say about 200 to 310 C., and to mix the refined oil obtained therefrom with a fraction of the unrefined burning oil of lower distillation range (say N30-200 0.). This procedure leads to a burning oil which is of good quality and is distinctly superior to the unreflned fraction. It has the advantage that the larger interval between the boiling point of acetic acid and the initial distillation temperature of the oil facilitates the recovery of the acid by distillation, both from the raffinate and from the extract.

The oil obtained from the extract may be used for various purposes, according to its nature and source; thus it may be useful as a fuel oil, or as a parent material for the manufacture of petroleum resins, or it may be cracked to produce petrol or oxidized to produce asphaltic substances.

When an oil has been treated with a relatively large proportion ofacetic recover from the extract, by controlled addition of water, an oil whichis superior to the untreated the controlled addition of an anhydrous acetate,

acid, it is possible t0- such as sodiumacetate, instead of water, to the extract.

It has been found that the presence of even small quantities of water-in the acetic acid detracts appreciably from its value as an extracting agent. Generally, it'may'be said that the glacial acetic acid should be of at least the commei-cial concentration of 98.9 per cent. strength, although an appreciable degree of refining can still be obtained with an acid containing about 97 per cent. of acetic acid, especially when the unrened oil is a kerosene of relatively good quality. l When, as will frequently be the case, the unrefined oil contains small quantities 'of water in solution or suspension, repeated use of the acid will involve progressive dilution and loss .oflefiiciency unless steps are taken to counteract this. For this purpose,- the acid may be treated periodically to restore its concentration or a portion of the acidmay be withdrawn continuously and returned to the process after its concentration has-been restored.

It has been found, however, that moderately dilute acetic acid, containing about 85 per cent. of acetic acid, is still capable of extracting from the unrened oil a part of the' undesirable constituents which may be used for`other purposes. Hence it may be advantageous to subject unreiined oils containing water in solution or suspension to a -preliminary extraction with a diluted acetic acid of about 85 per cent. strength, thereby removing simultaneously the bulk of the water and a fraction of the undesirable constituents useful as a fuel oil, the remainder of the undesirable constituents being then removed by extraction with glacial acetic acid.

A suitable manner of carrying out the invention w'ill now be described by reference to the accompanying drawings, in which:-

Fig. 1 shows diagrammatically a four-stage counter-current plant for the extraction and Fig. 2 is a iiow sheet illustrating the recovery of the acetic acid from the raffinate and the extract by washingwith water.

Referring to Fig. l, M1, Mz, M3 and M4 are mixing tanks communicating through pumps P1, P2, P3 and P4. and orifice mixers O1, O2, Oa and Oi by way of pipes C1, C2, C3 and C1 with centrifugal separators CS1, CS2, CSa and CSi whose outlets are connected respectively by pipes F1, F2, F3 and F4 with a pipe line A and by pipes G1, G2, G3 and G4 with a pipe line B. The have branch pipes D1, D2, D3 and D4 and E1, E2, E3 and E4 respectively which discharge into the mixing tanks M1, M2, M3 and M4. The pipe lines A and B and the branch pipes D1, D2, Da, D4 and E1, E2, E3, E4, are provided with valves H and K, which are arranged so that any of the mixing tanks and its associated separator can be disconnected from the system. i

Unrened oil enters the plant 'at the right-hand end of the line A and glacial acetic acid at the left-hand end of the line B. The valves H being oil enters the tank Mi by closed and the valves K being open, the unreiined way of the branch pipe Di and glacial acetic acid enters the tank M1 by way of the branch pipe E1. The iiow of acid and oil through the apparatus is continuous and is regulated by level controls LCi, L02, LCs and LCi. In the tank M1 the fresh acetic acid meets partially refined oil delivered from the separator CS2 by way of pipe F2, pipe line A and branch pipe Di. The mixture is forwarded by the pump P1 to the separator CS1, which delivers the rened oil to the pipe line A and thence to the outlet from the plant. The acetic acid extract is delivered by way of pipe G1, pipe line B and branch pipey E2 to the tank M2, where it meets partially reiined oil from the separator CSa, and so on. The liquids in each of the tanks M1, M2, M3, M4, are mixed by means of the pumps P1, P2, P3, Pi, and orifice mixers O1, O2, Oa, O4; discharge of the mixture from the mixers is controlled by pressure regulators PRi PRz, PRa, PR4, so arranged that a portion of the mixture is returned continuously to the tanks M1, M2, M3, M4, and the Dumps Pi, P2, P3, P4, thus in creasing the time of contact of the acidand oil.

Referring to Fig. 2, from the extraction section which may be a plant of the kind shown in Fig.

1) refined oil containing, for instance, about 15 per cent of acetic acid passes to the reiined oil washing section 2, where it is washed with water containing a trace of acetic acid fromthe final extract washing section 3. AThe extract from`section I passes to the extract release section 5, in which the bulk of the extracted oilv is released from solution by treatment with water from the extract washing section 4, and the released oil then passes into the extract washing section 4 in which it is washed with water which has already been used for washing the refined oil in section 2 and contains some acetic acid. The washed extract from section 4 is then freed from the small quantity ofacetic acid still remaining in it by Washing with fresh water in the iinal extract washing section 3, the wash water thence passing to the rened oil washing section 2. 4The refined oil leaving section 2 and the extracted oil leaving section 3 may finally be freed from any residual trace of acid by washing with alkali. The aqueous Xacetic acid from section 5 passes to the recovery section 6 in which the acid is recovered by azeotropic distillation and a small quantity of extracted oil contained in it is separated. In each washing section, the washing may be conducted according to the counter-current system or `with successive portions of the washing liquid.

'I'he procedure illustrated in Fig. 2 provides an economical method of recovering acetic acid with use of a minimum quantity of water.

lThe following are examples of the application of the invention, the parts being by volume:-

Example 1.-10G parts of a kerosene oil of approximate boiling range 205"`290 C. and a smoke point 14.5 mm. (as determined by the smoke point method of the Institution of Petroleum Technologists) were treated with' 200 parts acid 'in counter-current in four stages. The rafnate layer containedabout 15 per cent. of acetic acid, from which it was nearly completely freed by washing with water in stages, leaving 68.5 parts of an oil having a smoke point 23 mm. Addition of the aqueous washings to the extract caused theseparation of a yellow oil having an acetic acid content of about 4.77 per cent.

A second batch of 100 parts of kerosene was treated in like manner, butthe Washings from the.

raflinate, instead of being used directly for releasing oil from the extract, were first used for washing the yellow oil previously released from Athe first extract, whereby its content of acid was reduced to less than' 0.2

for washing the rainate oil. The process can now of glacial acetic per cent. The washing water containing acetic acid was then used to requantity of fresh water- Q gravity exceeding unity at 4 be continued in as many stages as desired as illustrated in Fig. 2. I

Example 2.- parts of a kerosene oil of the approximate boiling range 205-310 C. and smoke point 15.5 mm. were treated with 250 parts of glacial acetic acid in four stages and the rafiinate and extract were freed from the bulk of the acid contained in them by distillation at atmospheric pressure. The ralnate layer contained about 0.5 per cent. of acetic acid and yielded after washing with water and alkali 6 8 parts of an oil having a'smoke point 24.5 mm. The extract yielded an oil residue having an acetic acid content of about 0.8-0.9 per cent. The combined acetic acid distillates contained about 3 per cent. of oil. n

When the distillations were conducted under reduced pressure (5-6 mm.) there was obtained a refined oil containing about 0.03 per cent. of acetic acid and an extract oil containing somewhat less than 0.07 per cent. of acetic acid. The acetic acid'distillates contained 1.6 per cent. of oil of very pale colour. g v

Example 3.-100 parts of kerosene having a smoke point 18 mm. yielded on treatment in one stage with 300 parts ofy glacial acetic acid 45 parts of reiined oil having a smoke point 29 mm. and an acetic acid extract from which by addition of sodium acetate there were'recovered 47v parts of oilhaving a smoke point i9 mm., representing a total yield of 92 per cent. oi oil of smoke point 24 mm.

Example 4.--100 parts of a normal kerosene fraction of approximate boiling C. and a smoke point 18 mm. yielded on treatment with a total quantity of 137 parts of glacial acetic acid applied in three successive stages, 73.2 parts of a rafnate having a smoke point 25.5 mm. The acetic acid was distilled from the extract and the distillate yielded on dilution with water, 9.3 parts of an oil of smoke point 19.5 representing a total yield of- 82.5 parts of an oil of smoke point 24.8 mm. The oil remaining as the distillation residue amounted to 16.3`parts and had a smoke point 9 mm.

Example 5.-100 parts of a petroleum fraction suitable as a base for making lubricating oil were treated with 250 parts of glacial acetic acid and the' raiiinate, after separation from the extract, was treated with further 250 parts of glacial acetic acid. The raiiinate from this second treatment was washed with water until free from acid and yielded 82 parts of an oil having the characteristics shown in the following. table, those parisonzuntreated oil Treated oil o. i 0 que.

Red

Red-green b1oom It wm be seen that the treatment has remiten in an improvement in the viscosity temperature coefilcient and in the colour and ln a reduction of the specic gravity.

-The extract was a sticky 15 C./ 15 C. Example 6.11100 partsof unreilned kerosene of approximate boiling range 205f290. C. and

75 smoke point 14.5 mm. were treated in one stage range 180-290 diluting the of the untreated oil being given for com-i B ue-blsck tions which consists in black oil of specific with 200 parts of glacial acetic acid. After separation of the ramnate, the extract was diluted with water until 10 parts of oil had separated; this was removed and water was again added until further 10 parts of oil had separated. After removal of this oil, the residue was diluted with an excess of water.

The oils separated at each stage of the dilution were progressively darker and of diminishing burning properties. The fraction iirst separated was superior to the original unreilned oil having a smoke point 16.5 mm. and being nearly colourless. The second fraction had a smoke point 8.5-9 mm. and was darker in colour, whilst the finalfractlon, amounting to 4.5 parts had a smoke point 5 mm. and was deep brown.

Example 7.-100 parts of a gas oil fraction of smoke point' 14 mm. and specic gravity 0:8675 (15 C./15 C.) were treatedin one stage with 300 parts of glacial acetic acid. There were obtained 'l2 parts of a raffinate having an improved paramnicity, as is shown by its increased smoke point (19.5 mm.) and decreased specic gravity (0.8555). The acetic acid was distilled from the extract, leaving a residue of smoke point 'l min.

Having thus described the nature of the said invention and thebest means I know of carrying the same into. practical effect, I claim:-

1. Aprocess for refining liquid'peti'oleum oil fractions which comprises subjecting the fraction-to extraction with a quantity of acetic acid of at least 97 per cent. strength amounting to at least about half the volume of the fraction and separating from one another the layers of reilned oil and extract thus formed.

2. A process for refining liquid petroleum oil first to extraction with acetic acid of about 85 per cent. strength, separating from one another the layers of oil and extract thu's formed, subjecting the separated loil to extraction with a. quantity of acetic acid of at least 97 per cent. strength amounting to at least about half the volume of the oil and separating from. one another the la ers of refined oil and extract thus formed.

3. A process for rening liquidpetroleum oil fractions which consists in-mixing the fraction with a quantity of acetic acid of at least 97 per cent. strength amounting to at least about half the volume ofthe fraction, separating from one another the layers of rened oil and extract thus formed, washing the rened oil layer with water, extract layer with the water which has already beenA used for washing the refinedl oil layer and contains some acetic acid and separating the oil thus released.-

4. A process for refining liquidpetroleum oil fractions which consists in mixing the fraction with a quantity of acetic' acid of at least 9'? per cent. strength amounting to at least about half the volume of the fraction, another the layers of rened oil and extract thus formed, diluting the extract layer and separating the oil thus released, washing the separated oil the aqueous washings nrst for washing the refined olllayer and subsequently for diluting a further quantity of the extract layer to release extracted oil therefrom.

5. A process for refining liquid petroleum fracmixing the fraction witha. 4quantity of acetic acid of at least 97 per cent. strength amounting to at least about^half the volume of the fraction, separating Vfrom one another the layers of renned oil and extract thus formed, mixing the extract layer in stages with separating from one' successive quantities of water and separating the y8. A process for obtaining a Diesel fuel oil. oil released in each stage. which comprises subjecting a. Diesel fuel oil 6. A process for producing a burning oil, which fraction of petroleum to extraction with a quantiacetic acid amountingto at least about half the arating from one another the lagers of rened volume of the fraction, and separating from one oil and extract thus' formed.

another the layers of rened oil and extract thus 9. A process for obtaining a burning oil, which formed., comprises subjecting the higher boiling portion w 7. A process for obtaining a lubricating oil, ofakerosene oil fraction of petroleum to extrac- 10 which comprises subjecting a Iubricatingoil fraction with a quantity of glacial acetic/ acid H011 0f PetrOlellm t0 extraction with 8 quantity amounting to at least about half the volume oi.'

15 from one another the layers of refined oil and exsene oil fraction. 15.

tract thus formed. S. S. BHA'I'NAGAR.

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