US2078468A - Treating hydrocarbon oils - Google Patents

Description

W. M. STRATFORD TREATING HYDROCARBON OILS Filed Nov. 16, 1932 11w NTOR I ll IL IL ll 8 QR RR April 27, 1937.

w A TTORNE V Patented Apr. 27, 1937 UNITED STATES PATENT OFFICE to The Texas Company,

. poration of Delaware New York, N. Y., a cor- Appllcaflon November 16, 1932, Serial No. 642,861

50lalml.

This invention relates to the treatment of hydrocarbon oils and more particularly to the treatment of distillates obtained by cracking petroleum hydrocarbons which may contain unstable, unsaturated compounds and undesirable organic sulfur derivatives.

The invention contemplates a method of treating and purifying hydrocarbon oils such as cracked naphtha containing either unstable, un-

10 saturated compounds having gum forming tend encies, or sulfur derivatives, or both, which includes subjecting the naptha to treatment with alkali metal or alkaline earth metal at elevated temperatures and pressures whereby the undesirable unsaturated compounds are polymerized to compounds of higher boiling point and the obnoxious sulfur derivatives are substantially decomposed. The treated naphtha is then separated from the polymers and residues and is 20 fractionated to yield a color and gum stable naphtha of the desired boiling point range.

The invention will be fully understood from the following description thereof considered with the drawing which representsin diagrammaticv sectional elevation an apparatus which may be used. for carrying out the process. The apparatus illustrated in the drawing isshown and described merely for the purpose of aiding and understanding the process, and it is to be understood 'that any other suitable apparatus may be substituted for that shown in the drawill In the drawing, the numeral 10 designates a suitable storage tank for the cracked naphtha to be treated. This storage tank is fitted with a drawofi line H controlled by the valve l2 which enters the intake side of the pumpl3. This pump discharges through the line l4 controlled bythe valve l5 which communicates with the coil l6 of the heater H. The numeral 20 indicates a mixing chamber which alsoserves as a storage for liquid sodium. This mixing cham- ,ber is provided with a mechanical stirrer 2| and a heating coil 22 through which a suitable heat- 45 ing medium may be circulated. The bottomof this mixer is fitted with a drawoff line 24 controlled by the valve 25 which communicates with the inlet side of a pump 26. This pump discharges through the line 28 and the valve 29 0 into the heating coil l6 of the preheater II at a point intermediate the ends of the heating coil.

' The discharge ofthe heating coil l6 communicates through the line ll and the valve 32 with the interior of the flash'chamber 34. The upper- 55 most point of the flash chamber is provided with a vapor line 35 while the bottom is fitted with a liquid drawofl line 36 controlled by the automatic valve 31. The interior of the' flash chamber 34 is advantageously fitted with a tray 39 of Raschig rings or similar refractory contact ma- 5 terials, as well as baflle plates 40 for preventing thecarrying over 01' liquid into the vapor line 35. The drawofl line 36 connects the bottom of the fiash chamber 34 with a separatory cham- The top of this separatory chamber is provided with a liquid drawofi line 42 controlled by the valve 43 while the bottom of the separatory chamber is fitted with a drawofi line 44 controlled by the valve 45 which connects the separatory chamber with the rotating retort 41. This retort is revolvable and is fitted with a vapor line 48 controlled by the valve 49 which enters the fractionating tower 50 at a lower point in the structure, while the bottom of the still is fitted with the drawofl. line 5i controlled by the valve 52.

The fractionating tower 50 is fitted at its uppermost point with a vapor drawofi line 54 controlled by the valve 55 which leads to a suitable condensing system (not shown). The bottom of the fractionating tower is provided with a drawoff line 56' controlled by the automatic valve 51 and the manually operated valve 58 which leads to a suitable storage. There is manifolded to the line 56 at a point intermediatethe valves 51 and 58 the line 59 controlled'by the valve 60 which connects with the intake of the pump Bl. This pump discharges through the line 62 into the mixing chamber 20.

The vapor line which leaves the top of the 35 flash chamber 34 connects this chamber through the valve 64 with the treated naphtha fractionating tower 65. This fractionating tower is fitted at an upper point in its structure with a reflux cooling coil 66 and at a lower point in its structurewith a steam spray 68.

The bottom of the tower is fitted with a drawoff line 69 controlled by the automatic valve Ill and the valve II. This drawofl line leadsto a suitable storage tank not shown. There is manifolded to the line 69 at a point between the valve 10 and 1! the line [2 controlled by the valve 13 which connects through the pump 15 with the mixing chamber 20.

The top of the fractionating tower 85 is provided with the vapor line 'I I controlled by the valve I8 which communicates with the cooling coil 18 or the condenser 80. The cooling coil I8 discharges through theline 8! controlled bythe delivered to the pump I3 through the line H in controlled quantity. This pump may be of any type suitable for high pressure work and which is capable of delivering pressures up to 3000 lbs. per square inch. The naphtha is than charged into the heating coil l6 under a suitable pressure, for example, about 2000 lbs. per sq. in. which is sufllcient to maintain the naphtha substantially in the liquid phase under the conditions of temperature which obtain in the heating coil. A suitable temperature of 800 to 900 F. may be maintained at the outlet of the heating coil l6.

Metallic sodium, in finely divided form, is withdrawn from the mixing chamber 20 through the line 24 and the valve 25, and is injected by means of the pump 26 into the heating coil l6 at a point intermediate the ends of the coil. The finely divided sodium and the naphtha are intimately mixed in the coil of the preheater and, under the conditions of temperature and pressure prevailing therein, the sodium catalyzes the polymerization of the undesirable, unsaturated compounds present in the cracked naphtha. At the same time, some of the sodium combines chemically with the sulfur of the organic sulfur compounds present in the naphtha to yield sodium sulfide. The unsaturated organic compounds, which are formed by the decomposition of the organic sulfur compounds, tend to polymerize to form high boiling hydrocarbon compounds.

The quantities of sodium used in this operation may vary widely depending upon the quantities of unsaturates originally present inthe cracked naphtha, upon the quantity of sulfur present in the organic sulfur compounds and upon the quantity of unsaturates formed by the decomposition of the sulfur compounds. The time of reaction between the cracked naphtha and the sodium may be prolonged by increasing the length of the heating coil in the preheater.

By the proper control of the above mentioned variables affecting the reaction, substantially all of the undesirable, unsaturated compounds may be polymerized and a large proportion of the sulfur compounds decomposed. In such a case, the discharge from the heating coil IE will comprise a mixture of treated naphtha distillate, polymers, unreacted sodium, and sodium sulfide. This mixture is discharged through the line 3| and the valve 32 into the flash chamber 34 wherein the pressure may be reduced to a value determined by the type of naphtha used and the pressures and temperatures maintained in the heating coil l6. Within the flash chamber the treated naphtha is vaporized and passes upwardly through the chamber in the paths determined by the structure of the bailles 40. The

vapors are drawn off from the top of the flash chamber through the vapor line 35 and through the valve 64, and are discharged into a lower point of the fractionating tower 65.

The fractionating tower serves in the fractionation of the treated naphtha vapors. The temperatures within the tower may be regulated by the cooling supplied to the top of the tower by the cooling coil 66 and by the steam injected into the bottom of the tower through the steam spray 88. By the proper control of these factors ailecting the temperature difference within the tower, it is possible to fix the boiling point range of the vapors which are drawn oil. from the top of the tower, as well as of the residual oil, a pool of which of the tower.

In the operation of the fractionating tower 65, it is desirable that a certain quantity of steam be injected into the bottom thereof through the steam spray 68 for the purpose of decomposing any minute particles of metallic sodium that may be carried over from the flash chamber 34 through the vapor line 35. The use of steam in this way prevents the dangerous accumulations of sodium in the bottom of the tower 65 and in the storage tank to which the residual oil drawn off from the tower may be discharged.

The treated fractionated vapors drawn 01f through the vapor line 11 are passed into the cooling coil 19 of the condenser 80 wherein they are substantially condensed. The treated condensate produced in this manner, which comprises a merchantable naphtha distillate is drawn off through the line 8| controlled by the valve 82 and passes to a suitable storage.

The residual oil, a controlled body of which is maintained in the bottom of the tower, may be withdrawn through the line 69 controlled by the automatic valve 10 and the manually operated valve H, and is discharged to a suitable storage tank. Under certain conditions of operation, it may be desirable to withdraw a certain quantity of this residual oil through the line 12 controlled by the valve 13 by means of the pump 15, which pump discharges the oil to the mixer 20.

The mixing chamber 20 serves as a storage for 2 sodium and such oil as is used in admixture with the sodium. The oil serves primarily to prevent the oxidation of the sodium and to assist in the proper subdivision of the sodium particles. It has been found that by using a heavy oil such as may be produced as a residual oil in the fractionating chamber 65, that extremely fine subdivision ofthe sodium is possible.

The residuum which collects as a pool in the bottom of the fiash chamber 34 and which consists of a. mixture ofpolymers comprising hydrocarbons of higher boiling point than the raw naphtha charge, sodium and sodium sulfide, is withdrawn through the line 36 and the automatic valve 31 and is delivered into the separatory chamber 4| wherein the mixture is allowed to stratify. The supernatant liquid polymers may be drawn off through the line 42 controlled by the valve 43 and delivered to suitable storage, while the lower layer of sodium, sodium sulfide and small quantities of polymers are drawn oil through the line 44 and the valve'45 and delivered to the rotating retort 41 which is maintained at a temperature preferably above the boiling point of sodium. The hydrocarbon polymers and sodium are vaporized and pass into the tower 50, which serves as a fractional condenser for condensing the vapors of the sodium which collects as a pool in the lower portion thereof. The vapors of the polymers, including vapors of hydrocarbon decomposition products thereof, pass upward and are drawn oif from the top of the tower through the vapor line 54 controlled by the valve 55, and passed to a condensing system (not shown) wherein the hydrocarbon vapors are substantially'condensed. The hydrocarbons so obtained are extremely unsaturated products and may serve as a potential source of resins and gumlike materials suitable for use in the arts.

is maintained in the bottom LII 50 is drawn off through the line 55 controlled by the automatic valve 51 and the valve 58 to a suitable storage In most. operations of the process, the sodium .may, with advantage, be 5 drawn off through the line 59 which is manifolded to the line 55 at a point intermediate the valves 51 and 58, passed through the valve 60 and the pump 6| into the line 52 which discharges into the mixing chamber 20.

The residue remaining in the still l1 may be drawn of! through the drawoff-line 5| controlled by the valve 52. In those cases where'this residue is extremely viscous or non-fluid, it may be necessary to operate the still on the batch principle. A scraper or the like may-be incorporated in the still structure to facilitate'the withdrawal of the bottoms.

The disposal of the residues which are formed as by-produets in the treatment of unsaturates with alkali metals has'always been attended by the difliculty of converting'any traces of sodium into inactive compounds. This is a necessary precaution since sodium will react with water with explosive violence and the liberation of great heat and therefore is a source of great danger. I have found that this difficulty may be overcome by exposing the sodium residues such as are drawn oil from the still 41 to the action of a limited amount of flue gas or carbon dioxide whereby some of the sodium sulfide is decomposed to yield hydrogen sulfide which then reacts with any free unreacted sodium to form the relatively inactive sodium sulfide.

At the temperatures of reaction maintained in the operation of this process, the sodium does not react with the unsaturates to form the wellknown loosely bound sodium compounds insoluble in naphtha but appears to act catalytically on the unsaturates to form polymers without itself being consumed. This catalytic action of sodium is first noticed at temperatures of from 400 to 500 F. At temperatures lower than this,

the sodium does not appear to display this catalytic action but merely reactswith the un- 45 saturates to form the so-called sodium residues constituting sodium-hydrocarbon complex compounds insoluble in naphtha.

The polymerizing activity of the sodium appears to be paralleled by the desulfurizlng activ- 50 ity insofar as the temperature is concemed. At temperatures below 500- F. the sodium does not react energetically with the hydrocarbon-sulfur compounds and; as a result, a large proportion of the stable sulfur derivatives remain unreacted. 55 At temperatures above this, the desulfurizing action becomes more and more vigorous and at temperatures in the neighborhood of 900 F. the sodium actively decomposes all of the sulfur compounds. The mechanism of the reaction may be 60 as follows: The sodium unites with the sulfur to form sodium sulfide, simultaneously liberating unsaturated hydrocarbons. These unsaturated molecules are then polymerized in the presence of metallic sodium to form high molecular weight compounds such as gums or polymers of higher boiling point.

From the above consideration, it is apparent that the proper operating temperature for the process is determined in large measure by the reactivity of the unsaturated compounds present in the naphtha undergoing treatment, as well as by the stability of the sulfur derivatives and, although a temperature of 900 F. appears to be the most advantageous under ordinary conditions, the use of still higher temperatures, in certain specific cases, may be desirable for the most successful operation of the process.

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

I claim:

1. A method of treating and purifying a cracked naphtha distillate containing undesirable sulfur compounds and unsaturated hydrocarbons which comprises mixing the naphtha distillate with an alkali metal to form a mixture, i

heating the mixture to a temperature of the order of 800 to 900 F. and under superatmospheric pressure whereby the undesirable unsaturated compounds are polymerized and the sulfur compounds are decomposed to yield residues, separating the treated naphtha distillate from the polymers and residues and distilling it to yield a fraction of the proper boiling point range.

2. A continuous process of treating and purifying a cracked naphtha distillate containing undesirable unsaturated hydrocarbons which comprises continuously charging the cracked naphtha distillate to a heating coil, simultaneously commingling with the naphtha a measured quantity of sodium suspended in a hydrocarbon medium to form a mixture, heating the mixture to a temperature of the order of 800 to 900 F. under superatmospheric pressure whereby the unsaturated hydrocarbons are catalytically polymerized by the sodium, then continuously separating the treated naphtha from the polymers and subjecting it to a fractionation to produce a motor fuel of the proper boiling point range.

3. In the refining of a cracked naphtha distillate, the step which includes heating the cracked naphtha distillate to a temperature of from 800 to 1000 F. in the presence of a finely divided alkali metal polymerizing catalyst.

4. A method of treating and purifying a cracked naphtha distillate containing unstable unsaturated compounds and obnoxious sulfur derivatives which comprises heating the naphtha distillate with sodium to a temperature of the order of 800 to 900 F. and under a pressure of between 1000 and 2000 lbs. per sq. in. whereby the undesirable unsaturated compounds are polymerized to compounds of higher boiling point and the obnoxious sulfur compounds are decomposed to form residues, separating the treated naphtha from the polymers and residues and fractionating it to yield a color and gum stable naphtha oi. the desired boiling point range.

5. A method of treating and purifying a cracked naphtha distillate containing unstable unsaturated compounds and obnoxious sulfur derivatives which comprises heating the naphtha distillate with sodium to a temperature in the neighborhood of 900 F. and under a pressure of about 400 lbs. per sq. in. whereby the undesirable, unsaturated compounds are polymerized to compounds of higher boiling point and the obnoxious sulfur compounds are decomposed to form residues, separating the treated naphtha from the polymers and residues and fractionating it to yield a color and gum stable naphtha of the desired boiling point range.

WILLIAM M. STRA'I'FORD.

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