US2941937A - Method of increasing the on-stream time of heat transfer units - Google Patents

Description

nite States METHOD OF INCREASING THE ON-STREAM TIME OF HEAT TRANSFER UNITS Italo V. De Chellis, Woodbury, NJ., assignor to Socony Mobil Oil Company, Inc., a corporation of New York No Drawing. Filed Nov. 5, 1956, Ser. No. 620,213 8 Claims. c1. zosso atent a increased octane rating from naphthas and gasolines of lower octane rating than that required for modern high compression, spark-ignited, internal combustion engines, the problem of tube fouling in heat exchangers and furnaces has come to the fore. It has been found that petroleum fractions which deposit no sediment at ambient temperatures precipitate deposits of unknown composition'on. tube surfaces when heated to temperatures of 350 to 1200 F. in heat exchangers and furnaces. These deposits are of such magnitude that designed on-stream periods of, for'example, 180 daysare reduced to as little as 30 to'90 days. a

The nature of the deposit varies with the nature of the fuel and does not appear to be correlated with the concentration of a particular type of material but results from a number of factors among which are the olefin, diolefin, nitrogen, sulfur and oxygen content of the petroleum fraction. V

For evaluating various methods of treating petroleum fractions of the class defined hereinbefore a tube-wall fraction is heated to 50 0 F.' during passage over the internally heated tube. The tube is weighed before and after contact with the selected amount of petroleum fraction being tested. The diiference between the weight before and after is a measure of the on-stream time which heat transfer surfaces in contact with the selected petroleum fraction can be expected to have.

The test is carried out under conditions such that the petroleum fraction being tested is heated to 500 F. during passage over the internally heated tube because during the course ofalarge number of tests it was observed that practically all of the deposits are laid down in the 350- 550 F. temperature range. It was also observed that pressure and flow rate have much smaller eifects upon the amount of deposit laid down than temperature. Therefore, in standard evaluation these two (pressure and rate of flow) were held constant to facilitate better control and reproducibility of results.

The present method of increasing the on-stream time of heat transfer surfaces in'contact with straight run or cracked petroleum fractions such as gasoline, naphtha, gas oil, heating oil, topped crudes and the like or mixtures of such straight and cracked fractions comprises contacting the petroleum fraction ofthe class defined hereinbefore with an aqueous'solution of alkali metal salts of organic acids which solution is substantially mutually immiscible with an aqueous solution of alkali metal hydroxide containing at least 29 weight percent alkali metal hydroxide. The petroleum fraction can be treated at any temperature above the temperature at which the alkali metal salt of the organic acid is a solid to temperatures' at which the vapor pressure of the constituents deposit testing method was developed. It has been established that the results so obtained arecorrela'ted with plant experience.

TUBE-WALL DEPOSIT TEST thereof make'the' operation impracticable; In general,

to an oxygen or sulfur' atom which hydrogenatom'is replaced by an'alkali metal atom supplied by-an alkali metalhydroxide atambientt'emperatures inaqiieous-s'olumaterial deposited on the internally heated tube determined.

Table I v J [Petroleum traction: straight run Wilmington, California gasoline. 40% California coker gasolineJi Treating Mg1ns. Deposit per Percent r Agent Liter ofOil Reduction Percent Treating Agent to Oil in'Tube' Increase "Ratio, 1; Wall Oil-Stream 1bs./b. Un- Treated Deposit Time treated 98 0 H 804 2:5 21 18 l4 16 Aque'ous15wt Percent; NaOH 1 1:5. .121 v 17. 19 24 Aqueous 45 wt. Percent NaOH 1:5. 21 .16 24 3 .32 Aqueous 50 wt. Percent KOH 115 21 16 24 32 50 wt. Percent KAP, 19 wt. Percent KOH, 31 wt. I V

Percent H20 1:10 I 7 9 3 5 8 138 l 'lreating temperature, -90" F 'water.

' Fresh blend.

.; KAPpotassiuJn alkyl phenols, KGB-potassium .hyd.ioxide,H,O-

Other petroleum fractions treated in a similar manner showed analogous improvement as the data in Table II establish.

. Table II Treating agent: a

50 wt. percent KAP 19 wt. percent KOH 31 wt. percent H2O Treating temperature F. 80-90 Trfeating ratio: 1 vol. treating agent; 10,vol. or petroleum rac ron Briefly, the present invention provides for contacting the petroleum fraction to be heated in contact with heat transfer surfaces, i.e., containing a deposit precursor or precursors. with an aqueous treating solution comprising an alkali metal salt of an organic acid as hereinbefore defined in one ormore stages at a treating agent to oil ratio of about 1 to about 100 volumes of treating agent per volume of oil to be treated at a temperature above the solidification point of the treating agent and below the temperature at which the vapor pressure .of the constituents of the treating agent make the treatment impractical. The treated oil is separated from the treating agent, washed with water to remove entrained treating 4 nitrogen. As a consequence, it is frequently necessary to pretreat naphthas containing amounts of nitrogen in excess of 0.0001 percent. Present practice is to hydrodesulfurize the naphtha to reduce the danger of sulfur poisoning the platinum catalyst and to reduce corrosion in the reformer hot transfer lines and heat exchangers. To remove nitrogen it is necessary that the severity of the conditions in the pretreater be increased appreciably. However, treatment of a naphtha containing 0.0001 percent or more of nitrogen in the manner disclosed herein reduces the load on the pretreater or eliminates the need for a pretreater as well as increasing the on-stream time for heat exchangers, furnaces and the'like.

Similarly, in the hydrocracking of petroleum fractions having an initial boiling point above about 500 F. wherein a petroleum fraction having an initial boiling point above about 500 F. is heated to a temperature above 300 R, and wherein the heated petroleum fraction is 300 F. with a treating agent comprising an aqueous agent solution, and passedto the heating units, i.e., heat V to; the regenerated treating solution'or, preferably, ,by

intimatelymixing the regenerated treating solution with an-aqueons fortifying solution of alkali metal hydroxide having a concentration of alkali metal hydroxide such thatfthe regenerated treating solution and the fortifying solution are substantially immiscible. After fortification, the fortified, regenerated treating. solution is separated from the fortifying alkali metal hydroxide solution. The separated fortified, regenerated treating solution is returned to the treating stage.

Particularly effective, and presently preferred, treating agent is an aqueous mixture of alkali metal hydroxide, alkali metal salt of alkyl phenols, i.e., alkali metal alkyl phenolates and water which at temperatures above about 60 F. is substantially immiscible with aqueous solutions containing at least 29 weight percent alkali metal hydroxide. A suitable aqueous treating agent is one containing about 1 to about 68 weight percent alkyl phenols, about 33 to about 39 weight percent potassium hydroxide and the balance water to make 100 weight-percent. An

alkaline solution containing at least one alkali metal salt of an organic acid having ahydrogen atom attached to an atom selected from the group consisting of, oxygen and sulfur atoms replaceable by an atom of alkali metal,

said treating agent being substantially immiscible at tempera-tures below about 120 F with an aqueous solution consisting of at least 29 weight percent alkali metal hydroxide, to obtain treated petroleum fraction and fouled treating agent, separating said treated petroleum fraction from fouled treating agent, and water washing said treated petroleum fraction. v

I claim:

1. In the conversion ofa petroleum fraction boiling above 100 F. and containing substances'which tend to precipitate and form deposits on heat transfer surfaces when said fraction is heated to temperatures above 300 attached to an atom selected from the group consisting additional,-exemplary treating agent contains at least about 27 weightpercent alkali metal isobutyrate, and alkali metal alkyl phenolat'e, at least about 25 weight percent alkali metal hydroxide, and the balance water to make l00'wcight percent in which the ratio of isobutyrate to alkylphenolate is up to 0.67., t

.. It is interesting to note that extraction of the naphtha to be reformed overnitrogen and olefin sensitive catalysts 1 of oxygen and sulfur which hydrogen atom is replaced by an alkali metal atom supplied by an alkali metal hydroxide at ambient temperatures in aqueous solution, to obtain a treated petroleum fraction having a substantially reduced concentration of the aforesaid substances which tend to precipitate and form deposits on heat transfer surfaces when said fraction is heated to temperatures above 300 F. and fouled treating agent, separating treated petroleum fraction from fouled treating agent, heating said treated petroleum fraction to a temperature in excess of about 300 F., subjecting .said heated treated petroleum fraction to a hydrocarbon conversion, admixing aqueous alkali metal hydroxide solution containing at least 29 weight percent alkali metal hydroxide with the aforesaid separated fouled treating agent to restore the concentration of free alkali metal hydroxide in the aforesaid treating agent and to obtain a liquid heterogeneous mixture, stratify said liquid heterogeneous mixture, to obtain a liquid fouled treating agent layer and an aqueous alkali metal hydroxide solution, separating said fouled treating agent, layer with restored concentration of fre alkali metal hydroxide from said aqueous alkali metal hydroxide solution and contacting further amounts of petroleum fraction boiling above 100 F. and containing substances which tend to precipitate and form deposits on heat transfer surfaces when said fraction is heated to temperatures above 300 F. with the aforesaid separated fouled treating agent having the restored concentration of free alkali metal hydroxide.

2. The method set forth in claim 1 wherein the separated fouled treating agent is regenerated with respect to extracted materials which precipitate and form deposits when a petroleum fraction containing the same is heated to temperatures in excess of about 300 F. prior to restoration of the concentration of free alkali metal hydroxide.

3. In the conversion of a normally liquid petroleum fraction containing substances which tend to precipitate and form deposits on heat transfer surfaces when said fraction is heated to temperatures above 300 F., the improvement which comprises contacting said petroleum fraction with a treating agent comprising an aqueous alkaline solution having as its essential solute an alkali metal salt of at least one organic acid selected from the class consisting of hydroxy aromatic compounds, carboxylic acids, and sulfonic acids which treating agent is substantially mutually immiscible at temperatures below about 200 F., with an aqueous solution containing at least about 29 weight percent of the hydroxide of said alkali metal to obtain treated petroleum fraction and fouled treating agent containing at least a part of said substances, separating said treated petroleum fraction from said fouled treating agent, heating said treated petroleum fraction to a temperature in excess of about 300 F. and subjecting said heated, treated petroleum fraction to a hydrocarbon conversion.

4. The improvement set forth and described in claim 3 wherein the alkali metal salt of an organic acid is an alkali metal salt of alkyl phenols, the separated treated normally liquid hydrocarbon is water-washed and dried and the fouled treating solution is regenerated, and fortified by contact with a substantially immiscible aqueous solution of alkali metal hydroxide.

5. In the hydrocracking of petroleum fractions having an initial boiling point above about 500 F. wherein a petroleum fraction having an initial boiling point above about 500 F. is heated in heat exchangers and furnacesv to a temperature above 300 F., and wherein the heated petroleum fraction is contacted with a hydrocracking catalyst in the presence of hydrogen under hydrocracking conditions of temperature and pressure, the improvement which comprises contacting said petroleum fraction prior to heating above 300 F. with a treating agent comprising an aqueous alkaline solution containing as its essential solute a member from the group consisting of the alkali metal phenolates, alkali metal isobutyrate and mixtures thereof, said treating agent being substantially immiscible at temperatures below about F. with an aqueous solution consisting essentially of at least 29 weight percent alkali metal hydroxide, to obtain treated petroleum fraction and fouled treating agent, separating said treated petroleum fraction from fouled treating agent and water-washing said treated petroleum fraction.

6. In the reforming of a naphtha which contains impurities from the class consisting of compounds of sulfur and nitrogen and which tend to form deposits upon heat transfer surfaces when heated above about 300 F., wherein said naphtha is preheated to temperatures of about 700-800 F., the improvement which comprises contacting said naphtha, prior to said preheating step, with a treating agent comprising an aqueous solution containing potassium hydroxide metal and potassium alkyl phenolates, said treating agent being substantially immiscible with aqueous alkaline solutions containing at least 29 weight percent of alkali metal hydroxide at temperatures below about 200 F. to obtain a treated naphtha and fouled treating agent, and separating said treated naphtha from fouled treating agent.

7. The improvement in the reforming of naphtha as set forth and described in claim 6 wherein the treated naphtha separated from the fouled treating agent is water-washed, dried, heated to reforming temperatures and directly contacted with a nitrogen sensitive reforming catalyst in the presence of hydrogen under reforming conditions of temperature and pressure.

8. The improvement set forth and described in claim 3 wherein the separated treated normally liquid hydrocarbon fraction is water-washed and dried and the fouled treating solution is regenerated and the regenerated treating solution is admixed with an aqueous alkali metal hydroxide solution containing more than 29 weight percent alkali metal hydroxide to res-tore the alkali metal hydroxide content of said treating solution for reuse.

References Cited in the file of this patent UNITED STATES PATENTS 1,859,015 Albright May 17, 1932 2,478,916 Haensel et a1. Aug. 16, 1949 2,552,399 Browder May 8, 1951 2,585,284 Tom et al. Feb. 12, 1952 2,771,404 Jezl et a1. Nov. 20, 1956 2,772,220 Bushnell et al Nov. 27, 1956

Claims (1)

1. IN THE CONVERSION OF A PETROLEUM FRACTION BOILING ABOVE 100*F. AND CONTAINING SUBSTANCES WHICH TEND TO PRECIPITATE AND FORM DEPOSITS ON HEAT TRANSFER SURFACES WHEN SAID FRACTION IS HEATED TO TEMPERATURES ABOVE 300* F., THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID PETROLEUM FRACTION WITH A TREATING AGENT, SAID TREATING AGENT CONSISTING OF AN AQUEOUS ALKALINE SOLUTION OF AT LEAST ONE SALT OF AN ORGANIC ACID AS HEREINAFTER DEFINED WHICH AQUEOUS ALKALINE SOLUTION IS SUBSTANTIALLY IMMISCIBLE WITH AN AQUEOUS SOLUTION OF ALKALI METAL HYDROXIDE CONTAINING AT LEAST 29 WEIGHT PERCENT ALKALI METAL HYDROXIDE AT TEMPERATURES OF ABOUT 60*F., SAID ORGANIC ACID BEING AN ORGANIC COMPOUND HAVING A HYDROGEN ATOM ATTACHED TO AN ATOM SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND SULFUR WHICH HYDROGEN ATOM IS REPLACED BY AN ALKALI METAL ATOM SUPPLIED BY AN ALKALI METAL HYDROXIDE AT AMBIENT TEMPERATURES IN AQUEOUS SOLUTION, TO OBTAIN A TREATED PETROLEUM FRACTION HAVING A SUBSTANTIALLY REDUCED CONCENTRATION OF THE AFORESAID SUBSTANCES WHICH TEND TO PRECIPITATE AND FORM DEPOSITS ON HEAT TRANSFER SURFACES WHEN SAID FRACTION IS HEATED TO TEMPERATURES ABOVE 300*F. AND FOULED TREATING AGENT, SEPARATING TREATED PETROLEUM FRACTION FROM FOULDED TREATING AGENT, HEATING SAID TREATED PETROLEUM FRACTION TO A TEMPERATURE IN EXCESS OF ABOUT 300*F., SUBJECTING SAID HEATED TREATED PETROLEUM FRACTION TO A HYDROCARBON CONVERSION, ADMIXING AQUEOUS ALKALI METAL HYDROXIDE SOLUTION CONTAINING AT LEAST 29 WEIGHT PERCENT ALKALI METAL HYDROXIDE IN THE AFORESAID SEPARATED FOULDED TREATING AGENT TO RESTORE THE CONCENTRATION OF FREE ALKALI METAL HYDROXIDE IN THE AFORESAID TREATING AGENT AND TO OBTAIN A LIQUID HETEROGENEOUS MIXTURE, STRATIFY SAID LIQUID HETEROGENEOUS MIXTURE, TO OBTAIN A LIQUID FOULED TREATING AGENT LAYER AND AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION, SEPARATING SAID FOULED TREATING AGENT LAYER WITH RESTORED CONCENTRATION OF FREE ALKALI METAL HYDROXIDE FROM SAID AQUEOUS ALKALI METAL HYDROXIDE SOLUTION AND CONTACTING FURTHER AMOUNTS OF PETROLEUM FRACTION BOILING ABOVE 100*F. AND CONTAINING SUBSTANCES WHICH TEND TO PRECIPITATE AND FORM DEPOSITS ON HEAT TRANSFER SURFACES WHEN SAID FRACTION IS HEATED TO TEMPERATURES ABOVE 300*F. WITH THE AFORESAID SEPARATED FOULED TREATING AGENT HAVING THE RESTORED CONCENTRATION OF THE FREE ALKALI METAL HYDROXIDE.