US2402799A - Separation of sulphur and aromatic compounds from oil - Google Patents

Description

June 25, 1946. G. B. ARNOLD ETAL SEPARATION 0F SULPHUR AND AROMATIC COMPOUNDS FROM OIL Filed oct. 1e, 1942 N mehr-Smm fn Tmp-REE um GEORGE B ARNOLD HAnoLo V. A'rwsm.

INVENTORS THEIR ATTORNEY Patented June 25, 1946.

SEPARATION OF SULPHUR AND AROMATIC COMPOUNDS FROM OIL f George B. Arnold and Harold V. Atwell, Beacon, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application October 16, 1942, Serial No. 462,248

4 Claims. '1

This invention relates to the separation of sulphur and aromatic compounds from oil and particularly from hydrocarbon mixtures such as derived from petroleum and which contain sulphur-bearing compounds, aromatic hydrocarbons and non-aromatic hydrocarbons including aliphatic and alicycllc hydrocarbons,

' In accordance with the. invention sulphurbearing compounds and aromatic hydrocarbons are separated from hydrocarbon mixtures containing them by extraction with water or with a solvent consisting essentially of water at elevated temperature and pressure. The hydrocarbon mixture is thus separated `into extract and rafllnate phases. The extract phase comprises sulphur-bearing compounds or a mixture of sulphur-bearing compounds and aromatic hydrocarbons dissolved in the bulk of the solvent, while the ralnate phase comprises undissolved hydrocarbons mixed with a minor proportion of the solvent. The resulting phases are separated and separately subjected to cooling and settling, with or without substantial reduction in pressure, so

that separation between solvent and the associated hydrocarbon material occurs. Thus, reduction of temperature in the case of the extract phase results in separation of the solvent from the dissolved sulphur-bearing compounds or dissolved sulphur-bearing compounds and aromatic hydrocarbons, while reduction of temperature of the raflinate phase effects separation between solvent and rafllnate hydrocarbons.

The invention has application to the treatment of naphtha hydrocarbon mixtures and contemplates eflecting the extractive treatment at temperatures in the range about 400 to 600 F. and

under pressures which may range from 800 to 5500 pounds per square inch gauge, and sufficient to maintain the solvent and extract substantially in the liquid phase during the extractive treatment.

As disclosed in pending application, Serial No. 382,326, flled March 8, 1941, for Separation of aromatic hydrocarbons from hydrocarbon mixtures, it has been discovered that under substantially the foregoing conditions of temperature and pressure water or solvent consisting essentially of water exerts a substantial solvent action upon aromatic hydrocarbons such as benzol, toluol, xylol and also polynuclear aromatics such as naphthalene and anthracene so that these hydrocarbons may be selectively extracted from hydrocarbon mixtures containing them and other non-aromatic hydrocarbons including aliphatic, and alicyclic hydrocarbons.

It has also been discovered that under conditions of elevated temperature and pressure, water effects a high degree of solvent action upon sulphur-bearing constituents of hydrocarbon mixtures and particularly sulphur-bearing compounds of the non-mercaptan type which include thiophanes, thiophenes, disulphides, etc., and derivatives thereof.

By way of exam-ple a high boiling straight-run naphtha obtained from New Mexico crude is extracted at a temperature of about 525 F. and under a pressure of 2500 pounds with water employing a solvent dosage of 6 volumes of water to 1 volume of naphtha in one instance and a dosage of 12 volumes of water to 1 volume of naphtha in another instance. The charge naphtha in question has an A. P. I. gravity of about 47, an initial boiling point of about 20G-250 F., an end boiling point of about 400 F. and a total sulphur content of 0.232% by weight, as determined by the standard lamp method. Of this total sulphur content 0.056% comprises mercaptan sulphur, while the remainder, 0.176%, comprises nonmercaptan sulphur. A comparison of the volume of extract obtained with the different solvent dosages and also of the sulphur contents of the resulting extract and ralnate follows:

Solvent dosage, per cent by volume o( naptha.. Extract in volume per cent of naphtha Total sulphur content of extract, weight per cen Total sulphur content of rainate, weight per cent. 0.102 Mercaptan sulphur content of raffinate, weight per cent 0.057 0. 044 Non-mercaptan sulphur content of raliinate, weight per cent 0.045 0. 049 Ratio of mercaptan sulphur content ol rafnate to that of raw naphtha 1.0 0.79 Ratio ol non-mercaptan sulphur content oi raiiinate to that of raw naphtha 0. 25 0.28

tent, namely, of about 21%.

Apart fr'om the reduction in sulphur content the lead susceptibility of the raffinate appears to be somewhat improved by removal of the foregoing sulphur compounds notwithstanding the fact that some valuable hydrocarbons were removed in the extract.

By employing a smaller solvent dosage, which may be even less than 600%, the volume of the extract removed in the` desulfurization step may be substantially decreased as is evident from the foregoing comparison, and still realize a high reduction in the non-mercaptan sulphur content of the feed. Reduction in the volume of the ex- -tract removed is advantageous from the standpoint oi decreasing the amount of aromatic hydrocarbons removed in the desulphurization step.

Under A the extract, amounting to 5.9% of the feed naphtha, comprises about 16% toluene or contains about 30% of the total toluene present in the feed naphtha. In the case of B the extract which amounts to 16.2% of the feed naphtha comprises about 9.4% toluene or about 44% of the total toluene present in the feed.

Therefore, according to a modification of the invention the feed hydrocarbon mixture is extracted in a countercurrent manner using a solvent dosage of about 2 to 6 volumes of solvent to 1 of feed mixture. The resulting primary extract and raiiinate phases are separated and the primary raiilnate phase is subjected to re-extraction with the solvent in larger proportion using a solvent dosage, for example, of 6 to 12 or more volumes of solvent per volume of solvent-free primary rafhnate. In this way secondary extract and railinate phases are obtained.

The solvent is removed from the primary extract phase and the secondary extract and both raflinate phases by reduction in temperature to about room temperature or to a temperature in the range'about 'I0 to 350 F. The solvent-free secondary extract thus comprises aromatic hydrocarbons of low sulphur content while the solvent-free secondary ramnate comprises non-aromatic hydrocarbons.

The solvent-free primary extract phase containing some aromatic hydrocarbons and rich in sulphur-bearing compounds may be subjected to further treatment so as to effect separation of sulphur-bearing compounds from valuable aromatic hydrocarbons and this further treatment may comprise desulphurization by contact with adsorbent earth or clay at elevated temperatures or desulphurization by treatment with mineral acid. After removal of sulphur from the primary extract by either of the above described procedures the sulphur-free material may be returned to the raillnate from the primary or secondary extractions.

It is also contemplated that the primary extract phase may, if desired, be subjected to re-extraction with water or solvent consisting essentially of water under different conditions of solvent dosage, temperature and pressure so as to e'ect a substantial separation between sulphur-bearing compounds and aromatic hydrocarbons.

In order to describe the invention further, reference will now be made to the flow diagram shown in the accompanying drawing.

As shown in the'drawing sulphur-bearing naphtha is drawn from a source not shown through a pipe I and a heat exchanger 2 and from there introduced to an extraction tower 3. Water is introduced to the upper portion of the extraction tower through a pipe I from a source to which reference will be made later. The water and naphtha are introduced to the tower in the proportion -of about 2 to 4 volumes of water per volume of naphtha. The temperature is maintained at about 500 F. or at a temperature in the range about 400 to 600 F. Suiiicient pressure is maintained so that the solvent and extract above the minimum, pressure required to maintain inthe liquid state at least the major portion of both the solvent and the primary extract constituents of thenaphtha. Thus, the pressure may be in the range about 800 to 2000 pounds per square inch gauge.

Countercurrent contact between the downwardly moving water and the upwardly moving naphtha results in formation of extract and rafnate phases.

The extract phase containing sulphur-bearing compounds and some aromatic hydrocarbons is continuously drawn off from the bottom of the tower through a pipe 5. The withdrawn extract phase is passed through a cooler B to a separating vessel 1 wherein separation between water and dissolved material occurs as a result of reduction to a temperature in the range about '10 to 350 F. The pressure in the vessel 1 may be substantially the same as that prevailing within the extraction tower-3 or may be substantially lower. Reduction in the temperature of the extract phase material entering the vessel 1 permits maintaining substantially lower pressures in the vessel 1 without having the liquid flash into vapor.

The separated water accumulates in the bottom of the vessel 1 and is withdrawn therefrom through a pipe 8 to a receiver 9. From this receiver it flows all or in part through a pipe I0 and heater Il which discharges into the previously mentioned pipe 4, any make-up water being added through a pipe I2.

The sulphur-bearing compounds and hydrocarbon materials separated from the extract phase are withdrawn from the upper portion of the vessel 1 through a pipe I3 and may be conducted through a branch pipe l3a leading to a desulphurization unit I4, wherein separation of the sulphur-bearing compounds from the aromatic hydrocarbons may be effected by the action of a solid adsorbent material or by the action of av mineral acid as already intimated.

The raffinate phase formed in the extraction tower 3 is continuously withdrawn from the upper portion thereof through a pipe I5 leading to a second extraction tower I8 which may be substantially similar in design and operation to the tower 3. lAs in the case of tower 3 a stream of water is introduced to the upper portion of the tower I6 through a pipe I1 and to which reference will be made later.

The water and hydrocarbon material is introduced to the tower I6 in the proportion of about 6 to 20 volumes of water to 1 volume of hydrocarbon mixture. The temperature is maintained in the range 400 to 600 F. and preferably about 525 to 575 F., while the pressure is also maintained sufcient to keep the solvent and extract substantially entirely in the liquid phase. Under these conditions the water exerts a high solvent action upon toluene and a relatively low solvent action upon aliphatic, naphthenic and paramnic constituents of the hydrocarbon feed mixture.

As in the case of thel primary stage, the pressure is just above the minimum, or not more than about 200 pounds above the minimum, required to maintain in the liquid state at least the major portion of both the solvent and the secondary extract constituents of the naphtha. 'I'his pressure may be in the range about 800 to 2000 pounds per square inch gauge, or about 1600 to 1800 pounds for an extraction temperature of about 525 to 575' F. i

The hydrocarbon mixture is thus separated into extract and raffinate phases. The raflinate phase is continuously withdrawn through a pipe il and a cooler I9 to a separating vessel 20 wherein water separates from the substantially non-aromatic hydrocarbons as a result of reduction in temperature to about 'I0 to 350 F. The substantially non-aromatil: raffinate hydrocarbons are drawn off from the separating vessel through a pipe 2| while the water is drawn of! from the bottom of the separator through a pipe 22 communieating with a tank 23.

The extractphase is continuously withdrawn from the bottom of the tower I6 through a pipe 24 and a cooler 25 to a separating vessel 26 wherein phase separation occurs as a result of the reduction of the temperature.

The aromatic extract separated in the separator 26 is drawn oif through a pipe 21 while the water is drawn of! through a pipe 20 likewise communicating with the previously mentioned tank Allor a portion of the water accumulating in the tank 2l is conducted through pipe 30 leading to a heater 3l which discharges into the previously mentioned pipe I1 through which the water is returned to the extraction tower I6.

Preferably the solvent used in the two stages is kept separate and not allowed to intermingle. However, it is contemplated that provision may be made for conducting a portion of the solvent from tank 23 to the tower 3. The presence of aromatcs in the water may provide a useful solvent in the desulphurization step in some instances.

When operating a two-stage process as illustrated and charging straight-run naphtha containing about 3 to 4% by volume of toluene, the volume of solvent-free primary extract phase may not exceed about 5% of the naphtha, such extract containing about 5 to 20% of the total toluene content of the naphtha.

The secondary extract phase will amount to about to 20% by volume and this extract will contain from about 40 to 50% or higher of the total toluene content of the naphtha.

The process may be operated as a single stage obtaining a single extract phase containing sulphur-bearing compounds and aromatic hydrocarbons amounting to from about 10 to 30% by volume of the solvent-free extract. Thus, the solvent desage employed may be about 12 to 16 volumes of water per volume of naphtha feed, with an extraction temperature of about 525 F., an operating pressure of about 1100 to 1600 pounds and preferably about 1200 to 1400 pounds, while maintaining a total throughput of 500 to 1000 gallons of naphtha and solvent per hour per square foot of tower cross-sectional area. The solvent-free extract will amount to about 13 to 13% by volume, the toluene content amounting to about 50% of the total toluene present in the feed naphtha.

This extract may be separately treated by extraction with a smaller dosage of water, for example, about 2 to 4 volumes of water per volume of solvent-free extract at about 500 F. so as to extract therefrom a fraction rich in non-mercaptan sulphur compounds.

While treatment of naphtha has been described it is also contemplated that feed to the extraction process may be any desired fraction of the naphtha. Thus, where it is desired to obtain 6 toluene, the naphtha may be fractionated to segregate a fraction rich in the desired aromatic I constituents, namely, toluene, for example, a fraction consisting essentially of hydrocarbons havm8 a boiling range of about 200 to 250 F. This fraction is then subjected to extraction with water in a manner already described.

It is contemplated that the naphtha or naphtha fraction may be subjected to preliminary treatment to remove gum-forming bodies and some of the easily removable sulphur compounds such as the mercaptan sulphur. This preliminary treatment may involve removal of dioleflns or gumforming bodies by contact with adsorbent earth or clay. The clay treatment may be carried out at elevated temperatures.

Preliminary removal of the mercaptan sulphur compounds may be effected by chemical treatment involving treatment with mineral acid and/or caustic solution.

While the invention has been described in connection with desulphurizatlon and the recovery of aromatic hydrocarbons from straight-run naphtha, it is contemplated that the invention may be applied to other hydrocarbon mixtures including cracked and reformed gasolines and also to kerosene, Diesel fuel oil and lubricating oils. It is also contemplated that the treatment may be applied to hydrocarbon mixtures derived from other than petroleum sources, such as tar distillates, and other natural or synthetic oils where it is desired to effect desulphurization and also the removal of nitrogen compounds.

For example, the invention may be employed to effect separation between sulphurized and unsulphurized components of vegetable, animal or sh oils which have been subjected to sulphurizing treatments.

If desired, raifinates obtained by Water extraction may be subjected to further extractive treatments, as with other selective solvents such as furfural and the like for the purpose of obtaining fractions of desired characteristics.

In the operation of the extraction towers referred to above provision may be made for recycling any suitable proportion of the extract and raffinate phase material for the purpose of controlling or modifying the extraction operation. Thus, the hydrocarbon feed mixture is advantageously introduced to an intermediate section of the extraction tower and a portion of the extract phase drawn off from the bottom of the tower, while a portion of the solvent-free extract is returned to the tower at a point intermediate the point of feed introduction and the point of extract phase removal. In this way the lower portion of the extraction tower operates as an enriching section.

Advantageously the extraction tower or towers may be operated with the water in the continuous phase and the hydrocarbons in the dispersed phase. In such case, the interface between extract and rafiinate phases is maintained near the top of the tower. However, this interface may be maintained at any desired point in the tower.

Any number of extraction towers may be employed in series or in parallel` Instead of extraction towers the operation may be carried out with stage countercurrent apparatus.

Also, while countercurrent extraction has been mentioned, it is also contemplated that concurrent flowv of solvent and feed through the extraction zone may be employed, the eliluent mixture being discharged to a phase separting veshydrocarbon such as benzene, employing a temperature in the range about 300 to 600 F. and a pressure in the range 500 to 2500 pounds per square inch.

Obviously many modifications and variations of the invention as above set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated by the appended claims.

We claim'.

1. A continuous process for extracting sulphurbearing and aromatic constituents from a naphtha hydrocarbon mixture comprising aliphatic, alicyclic, aromatic hydrocarbons and sulphurbearing compounds which comprises subjecting the hydrocarbon mixture to countercurrent and intimate contact during passage through an extraction zone with a solvent consisting essentially of water at a temperature in the range about 400 to 600 F., effecting the contact under pressure sufilcient to maintain at least the major portion of the solvent and the extract hydrocarbons in the liquid state, maintaining a ratio of solvent to hydrocarbons of about 2 to 4 volurnes of solvent per volume of naphtha such that a primary extract phase is formed rich in nonmercaptan sulphur-bearing compounds and a primary raiilnate phase is formed comprising aliphatic, alicyclic and the major proportion of the aromatic hydrocarbons present in the naphtha -feed mixture,l separately removing said primary phases, subjecting the removed primary ranate phase to further extraction with said solvent in larger proportion suilicient to form a secondary extract phase comprising aromatic hydrocarbons dissolved in the bulk of the solvent and a secondary railinate phase comprising non-aromatic hydrocarbons mixed with a small amount of the solvent, separately removing said secondary phases and separating the solvent therefrom.

2. The process according to claim 1 in which the primary extraction is eiected at a temperfeed to extraction with a solvent consisting essentiallyof water in the proportion of from about 2 to 4 volumes of solvent per volume oi' naphtha, effecting said extraction at a temperature in the range about 400 to 600 F. and under a pressure in the range 800 to 2000 pounds per square inch gauge such that at least the maior portion oi' both solvent and extract are maintained in liquid phase, forming a primary extract phase rich in non-mercaptan sulphur compounds dissolved in water and a primary ramnate phase comprising aromatic and non-aromatic hydrocarbons, said raiiinate phase containing the major portion of I the aromatic hydrocarbons present. in the feed.'

separating said phases, subjecting the primary ramnate phase to further extraction with fresh solvent in the proportion oi about 6 to 20 volumes of water per volume or hydrocarbons, eilecting said extraction at a temperature of about 525 to 575 F. under a pressure oi about 1600 to 1800 pounds suiicient to maintain the solvent and extract substantially entirely in the liquid phase, forming a secondary extract phase comprising aromatic hydrocarbons dissolved in the solvent and a secondary raiilnate phase comprising nonaromatic hydrocarbons and separating said phases.

4. A continuous process for extracting sulphurbearing and aromatic constituents from a naphtha hydrocarbon mixture comprising aliphatic, alicyclic, aromatic hydrocarbons and sulphur-bearing compounds which comprises subjecting the hydrocarbon mixture to countercurrent and intimate contact during passage through an extraction zone with a solvent consisting essentially of water at a temperature in the range about 400 to 600 F., effecting the contact under pressure suiilcient to maintain at least the major portion of the solvent and the extract hydrocarbons in the liquid state, maintaining a ratio of solvent to hydrocarbons of about 2 to 4 volumes of solvent per volume of naphtha such that a primary extract phase is formed rich in nonmercaptan sulphur-bearing compounds and a primary rainate phase is formed comprising aliphatic, alicyclic and the major proportion of the aromatic hydrocarbons present in the naphtha feed mixture, separately removing said primary phases, subjecting the removed primary rafiinate phase to further extraction with fresh solvent in larger proportion at a temperature in the range 400 to 600 F. and under pressures suiilcient to maintain the solvent and extract substantially entirely in the liquid phase, forming a secondary extract phase comprising aromatic hydrocarbons dissolved in the solvent and a secondary railinate phase comprising non-aromatic hydrocarbons, separating said secondary phases, removing solvent from the secondary extract phase and recycling the so recovered solvent to the primary extraction.

GEORGE B. ARNOLD. HAROLD V. ATWELL.

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