US3216796A - Caustic regeneration - Google Patents

Description

1965 w. K. ROBBINS ETAL 3,216,796

GAUSTIC REGENERATION Filed July 28, 1961 ACID-FREE CATALYTIC HEATING OIL FIG.

MERGAPTANS AND WATER ORGANIC ACID EM P E III 8 L 0 C 4 TEMP. CONTROL I20 i E EvAPoRAToR STEAM GONDENSATE NAOH BLEED CATALYTIC HEATING OIL MAKE-UP NAOH FIG. 3.

FIG. 2.

INVENTORS. WILLIAM K. ROBBINS JAMES o. SCOTT,

BY 2% My ATTORNEY.

United States Patent Ofi .ice

3,215,796 Patented Nov. 9, 1965 3,216,796 CAUSTIC REGENERATION William K. Robbins and James 0. Scott, Baytown, Tex.,

assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Filed July 28, 1961, er. No. 127,527 1 Claim. (Cl. 23-184) The present invention relates to the reconcentration and regeneration of solutions of alkali metal hydroxides which have been used to remove organic acids and mercaptans from flowing hydrocarbon streams. More particularly, the present invention relates to a method and means for concurrently concentrating the caustic solution while utilizing the steam evolved during concentration to strip mercaptans from the solution. In its more specific aspect, the present invention relates to a means and method of regenerating a sodium hydroxide solution which contains dissolved organic acids by concentrating and removing mercaptans from said solution in a first stage and recovering organic acids from said solution in a second stage.

Hydrocarbon streams boiling between about 100 F. and about 800 F. and containing mercaptans and organic acids (including phenols and carboxylic acids) are unsuitable for commercial use because of the corrosivity of the dissolved contaminants. As a consequence of this corrosivity, the product streams must be treated either to remove or to neutralize the effect of these contaminants. One method of removing the contaminants is by contacting the hydrocarbon stream with a concentrated solution of the hydroxide of an alkali metal hydroxide such as sodium, potassium or lithium. The use of these hydroxides is effective in removing the mercaptans, phenols, carboxylic acids and other acidic contaminants from the flowing stream, but are expensive both in the cost of the treating solution as well as in the costs of disposing of the waste liquid after the caustic solution has become spent. By the practice of the present invention, the etfective life of such a caustic solution may be extended to a period of several times that experienced in the manner hitherto utilized. Further, by the practice of the present invention, it has been found that although the caustic solutions which are used in the practice of the present invention are highly viscous, concentrations of the caustic to the desired gravity may be accomplished at atmospheric pressure. Hitherto it has been considered necessary in reconstituting these highly viscous solutions to use a vacuum evaporation system in order to minimize effects of slugging and bubbling within the evaporator. It has further been found by the practice of the present invention, that the steam evolved during the reconcentration or evaporation step may be utilized to strip mercaptans from the solution, thereby obviating the preliminary removal of mercaptans before reconstitution.

During the contacting of the flowing hydrocarbon stream with the caustic solution, the water which normally occurs in the flowing hydrocarbon stream is also removed along with the contaminants sought to be absorbed by the caustic scrubbing solution. The natural result of the absorbing of this moisture is a constant dilution of the scrubbing caustic. If the caustic solution is maintained at a gravity above 42 Baum, the organic acids extracted from the hydrocarbon stream may be separated into a supernatant layer by cooling the caustic to a temperature of about 100 F. to 150 F., but when the caustic strength falls below 42 Baum, particularly where the caustic strength is below 40 Baum, the organic acids are completely soluble in the caustic and will not form the separate layer. Therefore, they cannot be decanted from the caustic tank and an organic acid buildup occurs which causes the caustic to become unusable and spent in a relatively short time. The caustic strength is therefore preferably maintained within a range of about 42 to 50 Baum.

The present invention prevents the buildup of organic acids by reconstituting the caustic solution to the desired gravity. Moreover, the practice of the present invention prevents a buildup of mercaptans within the caustic solution which also would result in an untimely deactivation of the caustic solution.

The practice of the present invention may be more particularly understood by a reference to the appended drawings wherein:

FIG. 1 is a general schematic diagram of the scrubbing system;

FIG. 2 is a representation of a particular feed nozzle into the evaporator;

FIG. 3 is a plan view of the nozzle taken on lines 33 of FIG. 2; and

FIG. 4 is a sectional elevation of the nozzle taken on line 4-4 of FIG. 3.

Referring more particularly to FIG. 1, the practice of the present invention relates to the treatment of catalytic heating oil, for example, which is introduced into a scrubber by way of line 102 and is discharged after contacting with the caustic solution by way of line 104. A scrubbing caustic solution, such as sodium hydroxide, is introduced into the scrubbing tower by way of line 106 and is passed downwardly through the tower in contact with the flowing hydrocarbon stream to be discharged at the bottom of the tower by way of line 108. During the passage through the scrubbing tower, the caustic solution absorbs the mercaptans, phenols, carboxylic acids, other aromatic and paraflinic acids, and water, which are present in the catalytic heating oil feed stock. Therefore, the caustic solution passed by way of line 108 is contaminated with the absorbed acidic and sulfur-containing compounds as well as being diluted to a gravity somewhat below the optimum.

The solution is then charged by Way of line 108 into an evaporator 110 and is passed into the shell 112 of the evaporator in a distributed form by means of a bafile 114 which is arranged above the inlet so that the material charged into the evaporator impinges upon the bafile and is well distributed. It should be apparent from FIG. 1 that the solution is not contacted with air during the heating step within evaporator 110, and is not contacted with air anywhere in the closed circulation system. The evaporator 110 provides a plurality of tubes 116, each of which defines a vertically disposed, elongated heating zone having a cross section which is small relative to the elongation thereof. The distributed caustic feed is then passed through a series of tubes 116 and is discharged by way of line 118. During passage through tubes 116, the caustic is heated to a temperature of 215 F. to 300 F. by means of steam which is introduced by way of line 120 controlled by valve 122 and passes through the steam jacket within the shell 112 to be discharged by way of line 124 as condensate. The caustic soda is maintained within the evaporator at a temperature of about 215 F. to 300 F. for a time period sufiicient to evaporate enough water to concentrate the solution from the operating gravity of about 40 to 43 Baum to a gravity of about 45 Baum or higher, preferably about 44 to 48 Baum. Also, the time period should be suflicient to allow the mercaptans to be stripped from the caustic solution and carried into the vapor phase with the evolved steam.

The total efiiuent, liquid, gas and vapor, from the evaporator 110 is passed by way of line 118 into a first separator 126 wherein the vaporous steam and gaseous mercaptans are allowed to pas overhead by way of line 128 through condenser 130 for disposal. The liquid is passed from the separator by way of standpipe 132 and line 134 into pump 136, and is discharged from pump 136 by way of line 138, valve 140, and cooler 142 into a second separator 144, from whence an organic acid suprenatant layer is withdrawn by way of line 146 and a reconstituted and regenerated caustic soda solution is discharged by way of line 148 for recycle by way of line 150 into line 106 and into the scrubber 100. The caustic may be discharged intermittently or continuously by way of the caustic bleed line 152, while makeup caustic of 45 to 50 Baum or higher is introduced in offsetting amounts through line 154.

Returning now to the evaporator system proper, it is seen that a line 156 interconnect the discharge line 134 from the first separator and the evaporator 110. This line 156 recirculates a portion of the caustic to the evaporator to assure a complete concentration of the caustic and removal of the mercaptan. The evaporator 110 is provided with an inlet 158 for this recycle stream, and the inlet 158 is further provided with an orifice plate or choke plate 160 which provides sufiicient pressure drop to prevent the passage of a portion of the feed which is introduced by way of line 108 into the line 156 to bypass the evaporation system. The orifice should be about 1% to of the area of the return conduit. It should be understood that the recycle stream being recharged into the evaporator 110 may be provided with suitable pumping means if necessary to provide sufficient head for the recirculation rate desired. Preferably, however, the recycle is accomplished by relying on the pressure head differential which may be obtained by mounting the separator 126 at a slightly higher elevation than the evaporator 110, and allowing the evolved steam within the tubes 116 to provide a vapor lift for the solution into the separator 126.

Referring now to FIG. 2, a particular form of injection nozzle is disclosed which obviates the necessity of using a choke plate such as the plate 160 shown in FIG. 1. In the modification of FIG. 2, a feed nozzle 200 is shown within an evaporator 210 which is generally similar to that shown in FIG. 1. The recycle inlet 220 shown in FIG. 2 is free of obstruction, and need not be provided with a choke plate. This is accomplished by mounting the feed nozzle 200 at a position at least as high as the bottom of the recycle inlet pipe, but preferably above this position, and in forming the feed nozzle with a generally hemispherical upper surface with discharge passages extending radially therethrough so that the feed stream will be directed above the inlet 220.

The structure of the nozzle 200 may better be understood by referring to FIGS. 3 and 4 wherein there is disclosed a plan view and a sectional elevational view of the nozzle. In particular, referring to FIG. 4, the nozzle 200 is seen to communicate with the feed pipe 240 which contains the charge stream. Radial passages 250 are formed in the head of the nozzle for directing the feed stream in a direction above the horizontal plane defined by the lower portion of the nozzle indicated by the numeral 260. Therefore, with the nozzle mounted above the recycle pipe, the vector forces imported to the feed stream will prevent the fresh feed stock from entering the recycle nozzle.

By the practice of the present invention, caustic consumption has been reduced over 50%. In the practice of caustic scrubbing of a catalytic heating oil stream without regeneration, an average life span of a caustic solution charged had been established at about five days. By

utilizing the present invention, the life span of the caustic has been extended to about 21 days. This increase in life of over four times that previously experienced indicates the importance and the effectiveness of the present invention. As a further description of the benefits of the present invention, the following examples are set forth.

Example I Catalytic heating oil (30,000 bbls./day) was passed through a caustic scrubber in contact with a total charge of 1,000,000 lbs. of 50 Baum sodium hydroxide solution (circulated at a rate of 2% to 5% by volume-dilution from water in feed decreasing the Baum gravity). The caustic was recirculated until the specific gravity reached 40 Baum, at which time the caustic was discarded and a new caustic charge of 50 Baum specific gravity was injected into the system. Under these conditions, the caustic consumption of 50 Baum sodium hydroxide was about 2,000 bbls. or 520,000 l bs/month.

Example II Utilizing the evaporator system as described in FIG. 1, the catalytic heating oil (30,000 bbls./day) was passed in contact with a total charge of 1,000,000 lbs. of caustic soda which was circulated at 2% to 5% by volume. The caustic soda solution was reconstituted as set forth in the discussion of the aforesaid figure with mercaptans and organic acids being removed in accordance with the invention.

By utilizing the practice of the present invention, the caustic consumption is about 800 to 900 bbls./month of 50 Baum caustic or slightly less than 235,000 lbs./ month, less than 50% of the caustic consumption heretofore experienced. Also, during the operation of the evaporator system, 95,000 lbs. of marketable organic acids were recovered in a months operation.

As may 'be seen by comparison of Examples I and II above, besides the recovery of marketable by-product organic acids, the caustic consumption has been reduced over 50%. In the practice of the present invention, the steam consumption on a monthly basis is about 7,000 to 12,000 lbs./hr. (estimated average is 8,000 lbs/hr.) of steam, which results in a high, attractive economic advantage based on the saving of caustic solution. An added advantage is the lessening of spent caustic solution which must be disposed of.

The nature and practice of the present invention having been set forth in detail, including a preferred manner and best mode of practicing the invention, what is desired to be protected by Letters Patent should be determined only by the appended claim and should not be limited by the specific examples hereinabove given.

We claim:

A method for regenerating a sodium hydroxide solution having a gravity less than 42 Baum and containing dissolved mercaptans and organic acids which comprises the following steps in sequence:

in the absence of air indirectly heating said solution in at least one vertically disposed, elongated heating zone having a cross section which is small relative to the elongation thereof,

to a temperature of about 215 F. to 300 F.,

for a time sufficient to concentrate said solution to a gravity of at least 42 Baum,

while evolving steam generated solely from the solution and mercaptans in the vapor phase,

the evolved steam being the only source of stripping steam for removing mercaptans from said solution,

separating said evolved steam and mercaptans in the vapor phase from said solution,

cooling said solution to a temperature from F. to

whereby said organic acids form a supernatant layer,

and separating said organic acid from said solution,

whereby said sodium hydroxide solution is rendered ered.

References Cited by the Examiner UNITED STATES PATENTS Smith 23260 Fleming et a1. 23-260 Hewlett 23184 Payne et a1./ 23-1-84 6 Harper et a1 208235 Gleim et a1 2082'35 Hainsworth 23184 Urban 208235 Childs 23184 Thomas 23-184 Shirley et a1. 23-185 MAURICE A. BRINDISI, Primary Examiner.

Pye 23 1, 4 10 ALPHONSO D. SULLIVAN, Examiner.

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