CS216181B2 - Method of preliminary treating the acidic crude oil distillate - Google Patents

Abstract

For removing acids from liquid hydrocarbons, these are treated with an aqueous base. The mixture of liquid hydrocarbons with the aqueous alkali is introduced into a bed which contains a hydrophilic medium, so that the aqueous phase droplets present in the hydrocarbon phase coalesce to form larger drops and thus settle out of the hydrocarbon phase. The coalescence medium used is preferably activated carbon or anthracite, bituminous coal or lignite. Due to the intimate contact between the aqueous base and the liquid hydrocarbon in the bed of the medium, not only high utilisation of the base is achieved, but a high concentration of salts of the acids removed from the hydrocarbon, for example naphthenic acids, is also obtained in the aqueous phase, so that the acids in question can be recovered as a by-product of the process.

Description

(54) Process for the pre-treatment of acid petroleum distillate

The present invention relates to a process for pretreating an acidic petroleum distillate containing acidic substances which interfere with the subsequent oxidation of the mercaptans contained therein. According to the invention, this treatment is carried out by mixing the distillate with an aqueous base solution, then coalescing the aqueous phase of the resulting mixture and collecting both the aqueous phase and the substantially acid-free petroleum distillate, the aqueous base solution being mixed with the distillate in the base. an amount corresponding to 100 to 200% of the stoichiometric amount of the base required to neutralize acidic substances and the coalescence of the aqueous phase of the resulting mixture is conducted by passing the mixture through a fixed bed of carbonaceous particles not attacked by alkali having hydrophilic properties and having a particle size distribution of 0 , 1-6 mm, liquid hourly space velocity of 0.5 to 20 phases Ir ^first

Many hydrocarbons contain sulfur in the form of mercaptans (thiol). Mercaptans are almost always present in liquefied fuel gas, cracked gasoline, straight-run gasoline distillates, natural gasolines and heavier hydrocarbon distillates such as kerosene or fuel oils.

Mercaptans are a problem in these substances mainly because they have a strong odor, but in some cases also because they react undesirably with other hydrocarbons or fuel constituents.

Many attempts have been made to remove mercaptans or convert them to other substances. According to the oldest processes, it has been proposed to treat the hydrocarbon fraction with alkali metal hydroxides, clay and hydrogenation. A significant improvement in hydrocarbon fraction processing was represented by VOP's Merox process published in · 1959. · A description and discussion of the Merox process and other processes known at the time are given in the Oil and Gas Journal of October 26, 1959.

This process used a catalyst that is soluble in alkali metal hydroxide or supported. Using this catalyst, mercaptans were oxidized to disulfides in the presence of oxygen and hydroxide.

U.S. Pat. No. 3,108,081 discloses a mercaptan oxidation catalyst comprising an adsorption carrier and a phthalocyanine catalyst. The preferred phthalocyanine of this patent is a sulfonated derivative, especially a monosulfonate.

In industrial operation, the hydrocarbon feedstock for the mercaptan removal or conversion unit contains a large number of catalytic poisons or other harmful components. Often these substances are trace amounts of acidic components such as naphthenic acids and hydrogen sulfide.

Hydrogen sulfide is often of natural origin, but it is also a by-product of earlier processing stages in which sulfur compounds decompose to form hydrogen sulfide in the presence of hydrogen and at high temperature. When the hydrocarbon feed being treated is heavy gasoline or kerosene, most of the hydrogen sulfide is removed by distillation; however, such removal is not always complete and the hydrocarbon stream needs to be further processed.

Crude oil often contains naphthenic acids and other carboxylic acids. During the distillation, the naphthenic acids are co-distilled with hydrocarbons of similar boiling range and concentrated in various fractions of the distillate.

Naphthenic acids have properties that allow them to dissolve in both hydrocarbon and aqueous environments and are often considered to be surfactants because they are active at the phase boundary, such as liquid hydrocarbon and water. After neutralization with alkali salts, the naphthenic acids form alkali naphthenates, which are chemically similar to soaps. As such, they tend to emulsify the hydrocarbon and aqueous phases and make it difficult to effectively separate the oil phase from the aqueous phase. Because of these properties, they need to be removed from the resulting products when emulsions are to be avoided or if they are an undesirable component that could interfere with further efficient chemical processing of the products.

A number of ways have been developed to overcome these difficulties. One method consists in passing the hydrocarbon stream through a large vessel, the so-called prewash vessel, partially filled with dilute aqueous lye, wherein the hydrocarbon stream containing trace amounts of acidic components is dispersed in the caustic and removed through the top of the vessel. Typically, the hydrocarbon stream enters the vessel for prewashing a series of nozzles to ensure a close contact of the hydrocarbon with the diluted liquor. Sometimes this contact is achieved by means of a circulating lye pump contained in the vessel, in which case the lye is mixed with the incoming hydrocarbon in the line. The concentration and amount of caustic solu- tion used is usually adjusted so that very little acid mercaptans from the feed are absorbed into the caustic soda. Only the more acidic naphthenic acids, hydrogen sulfide and other trace acid compounds are removed by the caustic pretreatment. When a product with a very low acid content is to be obtained, a coalescing sand filter can be placed downstream of the prewashing vessel to remove entrained drops of aqueous salt from the hydrocarbon stream being treated. However, the sand filter requires frequent attention to maintain its coalescing efficiency and the sand itself is attacked by aqueous alkali solutions.

Unfortunately, this process does not always successfully remove acids. The use of large prewash containers increases the investment cost of the production unit and often fails to effectively use the caustic solution. In the case of the removal of naphthenic acids, very dilute caustic must be used for maximum efficiency. The use of a discontinuous pre-wash system also results in the removal efficiency of the naphthenic acids being cyclic. The efficiency is highest when the lye is fresh and the lowest just before liquidation of the weak lye. Due to the discontinuous nature of the process and the fact that naphthene soaps have the character of surfactants, a certain amount of unneutralized caustic is always disposed of along with the lye used.

Although conventional coalescing devices, such as sand filters or sieve coalescing devices, are placed downstream of the prewashing vessel, the entrainment of acid salts is sometimes too great. This is because the efficiency of coalescing devices depends on many factors. Acceptable efficiency can only be achieved within a narrow range of flow rates, and deterioration of the performance and hence efficiency of the device is influenced by the elimination of particulate matter, sand abrasion, channel formation and other factors. The inability of conventional coalescing devices to maintain high efficiency without frequent maintenance has led to the use of electrical coalescing devices. These devices are similar to the well known desalination plants used in crude oil and remove entrained water containing dissolved salts. For. the use of electrical coalescing equipment can be removed from the prewashed hydrocarbon stream by entrained caustic containing naphthenic acid salts to an extent sufficient for the requirements of other processing units, such as the removal of water from jet fuel fuels. Unfortunately, electrical coalescing devices are very expensive and greatly increase the cost of pretreatment equipment. They also require great attention, which increases operating and operating costs.

Another problem encountered in prior art prewashes is the use of large amounts of spent reagent. As already mentioned, efficient operation of the discontinuous prewash container avoids complete depletion of the alkaline solution. In a relatively large amount of alkaline solution, considerable amounts of neutralized caustic remain in the prewash container. Thus, when the acid removal efficiency of the alkaline solution is no longer satisfactory, the disposal of large amounts of unneutralized caustic should not be avoided. This is a problem not only because reagents are inefficiently used, but also because free alkali is a problem in terms of getting rid of it.

Another disadvantage of discontinuous pre-washing is that the naphthenic acids present in the clarified lye are difficult to regenerate. When attempting to regenerate these acids, it is first of all necessary to acidify the spent liquor and then separate the acids from the admixed oil. Since dilute streams are used in the prewash in the sequence of technological operations prior to the mercapan conversion, the naphthenic acid regeneration is not normally considered. as convenient. This loses the source of potentially valuable raw material. Naphthenic acids may be used as a desiccant for paints, wood preservatives and to some extent as lubricants for extremely high pressures. Naphthenic acids have also been used as solvents for vulcanized rubber, various synthetic and natural resins, aniline dyes, as brighteners for mineral oils, as insecticides, and as additives for wood oil to allow it to dry without cracking.

In view of the above, efforts have continued to find an economical and efficient method of acid removal that would allow the use of an alkaline solution approaching stoichiometric utilization. There is also a need for a continuous process in which the frequent discharge and handling of large quantities of alkaline solution can be avoided.

SUMMARY OF THE INVENTION The present invention provides a process for pretreating an acidic petroleum distillate containing acidic substances that interfere with the following oxidation of the mercaptans contained therein, wherein the pretreatment is carried out by mixing said distillate with an aqueous base solution, coalescing the aqueous phase of the resulting mixture. and the aqueous phase and the substantially acid-free petroleum distillate are recovered. The process according to the invention is characterized in that the aqueous base solution is mixed with the distillate in an amount corresponding to 100 to 200% of the stoichiometric amount of base required to neutralize acidic substances and the coalescence of the aqueous phase of the resulting mixture is carried out by passing the mixture through a fixed bed of carbonaceous particles. which are not attacked by alkali having hydrophilic properties and having a particle size distribution of 0.1 to 6 mm, an hourly liquid phase space velocity of 0.5 to 20 h -1.

The process according to the invention is excellent for the treatment of kerosene. The product obtained is kerosene containing not more than 10% of the original naphthenic acid content.

Naphthenic acids are a by-product of the process of the invention. They can be isolated from the coalescing bed where they are trapped in the process of the invention by interrupting the contact of the bed with the petroleum distillate stream and the aqueous stream - and treating the bed with high temperature steam (200-400 ° C) to salt naphthenic acids leaked. According to an alternative method, upon interruption of the contact of the petroleum distillate and the aqueous stream with the bed, the bed is treated with an acidic medium, acidifying the naphthenic acids and then displacing it from the bed with a desorbent.

According to the invention, all hydrocarbon feedstocks containing trace amounts of acids can be processed as acid petroleum distillates. For example, naphthenic acids are typically present in ASTM D 86 end-boiling streams above 150 ° C. Hydrogen sulfide occurs in most of the intermediate streams during refining - oil. Carboxylic acids are often present in catalytically cracked products. The process according to the invention can be applied with great success to all these products.

Many kerosene feedstocks that must be processed by the conversion of mercaptans often contain - a large amount of naphthenic acids. The naphthenic acid content is typically characterized by an acid number, expressed in mg of potassium hydroxide required to neutralize 1 g of the sample. According to the standard, most jet fuels must have a maximum acid value of 0.010 mg KOH / g. However, currently available raw materials often have an acid number above 0.100 mg KOH / g. However, existing discontinuous prewash units with a coalescing device cannot effectively remove naphthenic acids if the acid value of the starting product is greater than about 0.025 mg KOH / g. The presence of such large amounts of naphthenic acids in the feed for the mercaptan conversion unit would result in operating difficulties in the product processing unit and losses if the naphthenic acids were not removed. The acid value of kerosene or other hydrocarbons can be determined by any of the various test methods, such as those described in ASTM · D-3242, A3TM-D-3339, ASTM-D-974,

ASTM-D-664 etc.

As the aqueous base, any inorganic base soluble in an aqueous (or alcoholic) solvent may be used, both sodium hydroxide and potassium hydroxide being suitable, and sodium hydroxide is preferred due to its availability and low cost. The solubility of alkali naphthenates in the aqueous phase decreases with increasing concentration of alkali in the aqueous phase The solubility of other acid salts also limits the concentration of the base which can be practically used at normal temperatures.

Regardless of the type and concentration of the base used, the process of the invention allows operation with only a slight excess of base to compensate for fluctuations in acid concentration in the feedstock.

The feed stream and the aqueous alkaline phase are contacted prior to being introduced into the coalescing bed in a simple mixer.

As the coalescing bed composition, substances selected from the group consisting of substrates which are not attacked by alkali, such as various types of activated carbon, coal, lignite, slag, slag, calcined coke, etc., preferably having hydrophilic properties, are used. Examples of suitable activated carbon include activated carbon obtained from ground wood pulp, lignite, anthracite, lignite, peat, kerosene, and the like. Crushed and graded anthracite is preferred.

The contact of the hydrocarbon with the injected alkali solution and the contact with the coalescing bed may be arranged in any suitable manner. The coalescing agent may be maintained in the form of both fixed and movable beds. It can also be carried out batchwise. The stream may advance through the coalescing means in a bottom-up, top-down or radial direction.

The amount of coalescing agent must be adapted to the characteristics of the batch and the desired properties of the product. It may also be desirable to have a parallel coalescing bed available so that one bed can be put into operation while the other bed is regenerated. Several series-connected beds can be used to achieve maximum acid removal, and in this case, one parallel series of beds may also be available.

The amount of coalescing agent required may be expressed as a function of the liquid phase flow rate. In general, a sufficient amount of coalescing agent should be available so that the hourly space velocity of the liquid phase is in the range of 0.5 to 20 h ^-1 . Similarly, the geometry of the preferred fixed bed of the coalescing agent is such that the surface velocity of the liquid phase in the bed contributes to the highest efficiency and lowest cost.

For best results, the particles of the composition should be between 0.1 mm and 6.0 mm in size, with excellent results with particles of 0.6 to 2.0 mm.

The temperature and pressure conditions under which the aqueous base is contacted with the feed and under which the mixture is contacted with the coalescing environment are not critical. In general, ambient temperatures higher than the freezing point of the aqueous or oil phase can be employed. The typical temperature at which various hydrocarbon streams are obtained during refining is in the range of 10 to 60 ^° C and the process of the invention can be carried out well in this temperature range. The lower temperature limit is usually given by the temperature at which the viscosity of the liquid is so high that good contact of the aqueous phase with the fresh feedstock and subsequent separation of the aqueous phase from the organic phase cannot be achieved. The upper temperature limit is usually determined by the degree of dehydration that can be tolerated in the system and the permissible water content of the treated hydrocarbon stream. Many batches achieve good results at a temperature of from 25 to 60 ° C. Conventional substances are very fluid at these temperatures, which facilitates contact and separation of the aqueous and hydrocarbon phases. It can be operated at temperatures much higher and may be useful in the treatment of very heavy or viscous oils. Higher temperatures improve both phase contact and reaction rate, but good acid removal can usually be achieved without heating the process stream to a high temperature, which increases costs. The acid removal pressure of the process of the invention should be sufficient to maintain the organic and aqueous phases both in contact and in the separation completely in the liquid phase. Pressure is not a significant process variable. As a result, it is usually operated at the minimum overpressure required to pass the liquids through the processing unit.

The caustic solution has a dual function in the process. The caustic not only neutralizes the acid in the feed, but also wets the surface of the co2-coalescing agent. The process according to the invention is effective, since the acids react with the lye not only in a mixing device placed against the coalescing bed. in the upstream direction, but also in the coalescing bed. The efficiency of the process according to the invention is therefore so high that it achieves such good contact of the caustic with the acid.

After the acid-base reaction has ended, the hydrocarbon stream still contains the dispersed aqueous phase, which must be removed. This is another role of the coalescing bed. Under the action of the bed, a gradual flowing of the dispersed aqueous phase into larger droplets and eventually large droplets separates and decreases due to gravity to the bottom of the coalescing vessel from which the aqueous phase can be discharged. Coalescenční. the vessel is preferably provided with a level regulator which automatically discharges the water phase therefrom as it accumulates. The advantage of the automatic level controller is that it allows truly continuous operation with little or no operation at all. operator's attention.

The activated carbon bed is preferably. supported by a flat screen that supports it. coal, but allows the aqueous phase to pass through it. Especially preferred. well known Johnson sieves. This one. sieves. they consist of welded wedge bars. 'to the prop. These sieves are very strong,. usually do not clog and have a large free. cross section for liquid flow. Hydrocarbon stream. can be introduced and removed from the coal bed through circular sieves of the same type of construction.

The drawing shows a simplified schematic diagram. production process according to one embodiment. of the invention, wherein the dilute alkali solution is continuously injected into the acid-containing feed and the mixture is fed into a coalescing bed.

In the first step of the procedure. According to the invention, the feed stream containing the acid in. the conduit 10 contacts the dilute aqueous base advancing. from the storage tank (not plotted) by piping - 21. The water base is specific. pump 1. extruded into the conduit 22 and proceeds to the mixing. 2. Mixture of the batch and base then. it passes through a duct 11 into the coalescing vessel 3. The coalescing vessel 3 consists of a coalescing bed 4, an inlet distributor device. 8, collector pipe 5 and drain screen 6,

The treated acid-free hydrocarbon is discharged from the coal bed through the collector line 5 and further through line 12 for further processing or to a storage tank (not shown).

The droplets of the aqueous phase in the bed sink through the coalescing bed and pass through the discharge screen 6 'to the discharge vessel 7. The discharge vessel 7 comprises a sight glass and a level regulator (not shown) which ensures continuous discharge of the spent water phase through line 23.

Example 1

A miniature model pilot plant unit was used to test the invention. Like handles. kerosene with. very high acid number 0.084 mg KOH / g. The coalescing bed consisted of 50 ml of activated carbon (Norit Co.). Activated carbon was designated as 10/30 mesh and 90% of its particles had a size of 0.6 to 2.0 mm. The activated carbon was arranged as a fixed bed in a small pressure vessel. The inner diameter of the container was 25. mm. and bed height 100 mm. It was at the bottom. aerated coal supported by a glass wool plug. Dilute was used as the alkali solution to neutralize the naphthenic acids. aqueous sodium hydroxide solution. The lye concentration was 1.5% by weight. The base was added by slow movement of the syringe. It was necessary to use such a method of adding lye because the device was small and according to the invention an efficient use of lye was achieved. Mixing. kerosene s. with sodium hydroxide solution prior to entering the coalescing bed was performed in an ultrasonic manner. mixer.

The acid number of the batch was determined. after passing through the bed. activated carbon was determined. first, the sodium content. and the acid number. At the handle. it was after. mixing with lye, but before coalescence measurements are taken to confirm. calculated addition of sodium hydroxide solution. For ... determination of the alkali content was used as titration. ... by acid and atomic absorption spectroscopy.

Tests were carried out at hourly space. speed. liquid phase 2 to 4 h -1, i. at. feed rate of 100 ml / h and 200 ml / h.

Experiment results. are given in Table 1.

NaOH moles / mol acid titration added

TABLE 1

Clock Hourly liquid phase velocity [h-1]

Product number Na (ppm) of acid in the batch by atomic absorption spectroscopy

0—8 2 0.001 0.25 8—17 2 0.010 17—38 2 0.011 38—73 4 0,029 1.5 73—80 4 0.009 0.34 80—100 4 0.004 0.45 100—124 4 0,023 2.2 124—152 4 0.005 3.6 152—179 4 0.018 8.1 179—197 4 0,036 19 Dec 197—221 4 0.006 3.6 221—248 4 0.004 7.1 248— —273 1/2 4 0.003 6.1

1.11 0.46 1.77 1.29 0.27 1.26 0.60 0.10 1,28 1.29 0.10 1.14 0.60 0.34 1.14 0.58 0.77 1.14 0.40 0.74 1.14 0.48 1.03 1.14 0.34 0.53 - - 0.80 '- - 0.74

Example 2

Another test according to the invention was carried out in an industrial size unit. Kerosene from Louisiana and Illinois were used as raw materials. The existing refining vessel was used as a coalescing bed in the unit. No attempt has been made to design the container prior to the experiment, but rather has been attempted to utilize the plant existing in the plant to test the invention on a larger scale.

There was no device to ensure close contact of the kerosene handle with the alkaline environment. As a replacement, a partially closed choke valve was placed in the line before entering the coalescing device.

The alkaline medium used was a sodium hydroxide solution available in the refinery at a concentration of 4-6 ° B. This concentration was higher than intended, but this was the only concentration available for the experiment. Calculations showed that about 11.4 L / h of sodium hydroxide was needed to neutralize kerosene from Louisiana, and 5.7 L of sodium hydroxide / h was required to neutralize the acids contained in kerosene from Illinois Basin. A Calgon SGL 8 x 30 mesh activated carbon bed was used as a coalescing bed. The injection of caustic into the Louisiana batch was initiated at a rate of 37.8 l / h, i.e. at a rate well above that required by stoichiometry for neutralizing acids, especially naphthenic acids. At this caustic injection rate, the original kerosene acid number dropped from 0.10 mg KOH / g to 0.0096 mg KOH / g. However, spent liquor was only 50% exhausted. The caustic injection was then reduced to about 28.8 l / h, but this resulted in incomplete acid removal. According to the analysis, the kerosene product contained an unacceptably high amount of naphthenic acids corresponding to an acid number of 0.032 mg KOH / 100 ml. This analysis is debatable given the difficulty of obtaining a representative sample. However, 60% of the outbreaks were exhausted. The amount of caustic entrained in the kerosene product ranged from 0.042 to 0.067 ppm NaOH. This lower entrainment of lye was expected because, according to the experience of the inventor, the alkaline lye is easier to separate from hydrocarbons in industrial-size units than in laboratory units.

Example 3

Further tests were carried out in a model pilot plant described in the example

1. The experiments were carried out using activated carbon obtained from the Darco Company with a nominal grain size of 10 to 30 mesh (90% of the particles with a diameter of 0.6 to 2.0 mm). The raw material used was the same as in Example 1. In this example, an attempt was made to adjust the injection amount of caustic to 1.2 times the theoretical amount required to neutralize naphthenic acids. A slightly more concentrated caustic was used than in the first experiment (5 ° Baume, corresponding to 3.2% NaOH). The reactor temperature was

25.6 ° C and the reactor overpressure was 550 kPa.

The results of the experiment are shown in Table 2.

Amount of NaOH added *) Titration added

TABLE 2

Clock

Hourly space velocity of liquid phase [h-1]

Product number Sodium acidity content (ppm)

0—12 4 0.005 - 73 18 12—23 4 0.017 73 16 23—37 4 0.010 1,2 73 22nd 37—45 4 0.007 1.4 (temporary turbidity of the product) 45—53 4 0.005 73 32 53—64 4 0.016 (appeared in the separator) gel-like substance) 64—73 4 0.009 75 20 May 73—80 4 0.006 *. „X .. 75 19 Dec 80—89 4 0.005 - - 89—99 4 0.005 75 45 99—108 4 0.003 75 64 108—118 4 0.005 75 11 118—126 4 0.008 - - 126—137 4 0,023 73 15 Dec 137—150 4 0.010 Z, 8 73 13 150—159 4 0.007 73 19 Dec 159—166 4 0.005 71 68 166—189 4 0.006 71 11 189—196 10 0.012 2.5 69 78 196—204 10 0.011 12.9 68 39 ) Note: stoichiometric NaOH consumption 62 ppm.

After 64 hours of operation, a gel-like substance appeared in the separator and was still formed in the course of the experiment. After 99 hours of operation, the device temporarily clogged. From time to time a temporary cloudy product was formed. The formation of a cloudy product always took several hours. However, at the end of the experiment, the cloudy product had to stand for up to 7 days to clear. It is believed that a higher concentration of NaOH. caused gel formation. substances. This shows the importance of adjusting the lye concentration correctly.

Example 4

Was used . the same equipment and the same raw materials as in. Examples 1 and 3. As a coalescing material it was in this. ground anthracite was used. The nominal particle size of the coal was 0.84 to 2.0 mm (parallel designation. 10 x 20 mesh).

A more dilute caustic, i.e. caustic, was used in this experiment. with a concentration of 3 ° Baume (corresponding to a concentration of 1.8% by weight of NaOH). . The experiment was carried out at hourly space velocity liquid. phase 4 h ¹ and continued to 'do'. ' stock depletion . raw materials. The external results are shown in Table 3,

TABLE 3

Clock

Hourly space velocity of liquid phase [h-i]

Product number Sodium acidity content (PPm)

Titration added amount of NaOH added

0-11 4 0,046 - 68 - 11—23 4 0.014 3.9 68 12 23—35 4 0.008 - - 8 35—48 4 0.007 1.9 67 31 48—70 4 0.005 0.63 67 60 70—89 4 0.006 0.50 67 23 89—97 4 0.005 - 67 28 97—120 4 0.004 0.92 67 31 120—144 4 0.006 0.66 67 40 144-168 4 0.006 1.05 67 36 168—175 4 0.006. - 67 35

This experiment was generally more successful in reducing the naphthenic acid content as evidenced by its acid number. The experiment was also very successful in that the sodium content of the product was substantially lower than in the previous examples, although the sodium content of Examples 1 and 3 was satisfactory.

Most of the improvements in Example 4 can be explained by decreasing the sodium hydroxide concentration, but perhaps the synergistic effect resulting from the use of anthracite as a coagulating agent has also been exerted.

When the coalescing bed of the invention is used to remove naphthenic acids, it may eventually become saturated with naphthenic acid salts. A number of regeneration processes can be used to reactivate the bed and to obtain naphthenic acid salts as a valuable by-product.

Decent regeneration can already be achieved by putting the bed out of operation and conducting hot steam. In order to more fully regenerate the bed and to obtain naphthenic acids in free form and not in the form of salts, the salts may also be acidified in situ. This can be done by decommissioning the coalescing bed, i.e., disconnecting the hydrocarbon and aqueous stream, circulating an aqueous acidic solution through the bed, and desorphizing the naphthenic acids from the coal. When sufficient acidic water is used, most of the naphthenic acids displace from their salts during this operation. The desorption of naphthenic acids can be carried out by providing hot steam through the reactor. Naphthenic acids are volatile with water vapor and this procedure should achieve almost complete regeneration of the coalescing bed. If the activated carbon bed is not readily regenerable by this steep process, higher temperature vapors or various well-known hydrocarbon solvents such as benzene, other acetone / methanol and the like are needed to remove the naphthenic acids and their salts from the bed.

One of the interesting features of the invention is that the method of the invention both removes acids well from the kerosene product or mercaptan conversion unit feed and at the same time increases the naphthenic acid concentration by 100-fold so that naphthenic acids can be isolated when they represent the desired by-product or easier to dispose of if there is no commercial use for them. Most of the naphthenic acids are obtained in the aqueous phase after the accumulation of an equilibrium amount of acids in the coalescing bed.

The present invention can also be used to remove hydrogen sulfide from hydrocarbon streams. A hydrocarbon stream containing, for example, 0.01% by weight of hydrogen sulfide can be contacted with an aqueous stream of sodium hydroxide at a concentration of 6% by weight and conducted upstream downstream of the coalescing bed. The coalescing bed preferably comprises activated carbon with a nominal granulation of 0.6-2.0 mm, available under the trade name Calgon. When a 30% excess of base is used, the hydrocarbon product leaving the coalescing bed contains less than 0.0005% by weight of hydrogen sulfide.

The removal efficiency of certain acids is limited by chemical equilibrium under the desired operating conditions. Partial removal of very weak acids, such as mercaptan and phenols, may also occur depending on equilibrium conditions, base concentration adjustment and the nature of the specific acid component being removed.

Preferably, more concentrated bases are used for hydrogen sulfide removal than for the removal of naphthenic acids. This is because the hydrogen sulfide salts are more soluble than the naphthenic acid salts. Good results are obtained with 2-10% by weight sodium hydroxide.

With regard to the removal of naphthenic acids, the data obtained show that the process of the invention is very effective in reducing the acid number of kerosene heavily contaminated with naphthenic acids. Typically, the naphthenic acid content may be reduced to a value acceptable for further processing or sale.

The process according to the invention allows an almost stoichiometric utilization of alkaline lye. More efficient acid neutralization occurs due to the increase in the effective surface area of the alkaline composition, not only in the mixer and piping, but also in the coalescing bed. The process of the invention achieves greater flexibility and efficiency using much lower hydrocarbon flow rates than conventional speeds. There is a negligible entrainment of the aqueous solution into the hydrocarbon phase due to the ability of the coalescing bed to cast the water droplets into a separate phase which separates from the hydrocarbon by gravity. The cost of the pretreatment equipment is also reduced.

Claims (6)

OBJECT OF THE INVENTION A process for pretreating an acidic petroleum distillate containing acidic substances which interfere with the subsequent oxidation of the mercaptans contained therein, said pretreatment being carried out by said distillate. mixed with an aqueous base solution, the aqueous phase of the resulting mixture is coalesced and the aqueous phase and the substantially acid-free petroleum distillate are isolated, characterized in that the aqueous base solution is mixed with the distillate in an amount corresponding to 100 to 200% stoichiometric amount The alkali required to neutralize acidic substances and the coalescence of the aqueous phase of the resulting mixture is carried out by passing the mixture through a fixed bed of carbon particles which are not attacked by alkalis having hydrophilic properties and having a particle size distribution of 0.1 to 6 mm at a liquid phase rate of 0.5 to 20 h ^-1 . 2. The process of claim 1 wherein the aqueous base solution comprises from about 100 to about 100%. 120 ° / o of the stoichiometric amount of base needed to neutralize the acidic substances contained in the distillate. 3. The process according to claim 1, wherein the carbonaceous particles are activated carbon obtained from ground wood pulp, lignite, anthracite, lignite, peat and kerosene. 4. The method of claim 1 wherein the carbonaceous particles are of medium size. from. 0.6 to 2 mm. 5. The process of claim 1, wherein the aqueous base solution used is an aqueous alkali metal hydroxide solution at a concentration of 0.01 to 50% by weight. 6. The process of claim 1, wherein the aqueous base solution is an aqueous sodium hydroxide solution having a concentration of 1 to 3% by weight.