DK159020B - PROCEDURE FOR PRE-TREATING A MERCAPTANEOUS ACID SOIL OIL CONDITION FOR THE SEPARATION OF ACID MATERIALS - Google Patents

Description

DK 159020 B

Many hydrocarbons contain sulfur in the form of mer-captans (thiols). Mercaptans are almost constantly present in bottled gas, cracked gasoline, straight run gasoline, natural gasoline and in heavier hydrocarbon distillates, including e.g. petroleum and fuel oil.

These mercaptan components are primarily harmful because of their strong odor, but also in some cases because of their adverse chemical reaction with other hydrocarbons or fuel system components.

Many attempts have been made to provide methods capable of removing or converting mercaptans. Some of the earliest methods included treating the hydrocarbon fraction with caustic, clays and hydro treatment. There was a significant improvement in the treatment of hydrocarbon fractions when the UOP Merox process was announced to the industry in 1959. The Oil and Gas Journal, in its October 26, 1959 edition, discusses the Merox process and also some known methods .

This process used a catalyst soluble in caustic or alternatively supported on a carrier to oxidize mercaptans to disulfides in the presence of oxygen and caustic.

U.S. Patent No. 3,108,081 discloses a catalyst comprising an adsorptive charcoal support and a phthalocyanine catalyst for the oxidation of mercaptans. It is disclosed therein that a particularly preferred phthalocyanine was the sulfonated derivative, with the monosulfonate being particularly preferred. In contrast, the charcoal does not take an active part in the process, but acts solely as a catalyst support.

In commercial operation, a variety of catalyst poisons or other harmful materials are present in the hydrocarbon feedstock of the processing units provided for mercaptan removal or conversion. Trace amounts of acidic components such as naphthenic acids and H2S are frequently encountered.

H2S is often naturally occurring, but also present as a by-product of some earlier stages of treatment, where

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2 sulfur compounds in the presence of hydrogen and at high temperature decompose to form H2S. When the hydrocarbon feed stream being treated is either a naphtha or a petroleum, most H2S is removed by distillation. However, such removal is not always complete and further treatment of the hydrocarbon stream is required.

Naphthenic acids and other carboxylic acids are generally present in crude oil. During the distillation, naphthenic acids are distilled simultaneously with the hydrocarbons having similar boiling ranges which accumulate in the various distillate streams. Naphthenic acids have characteristics that enable solubility in both hydrocarbon and aqueous medium, and they are often referred to as surfactants because of their activity at surfaces, such as the interface between a liquid hydrocarbon and water. When neutralized by alkaline salts, naphthenic acids form alkaline naphthenates that are chemically similar to soaps. As such, they tend to emulsify hydrocarbon and aqueous phases, interfering with efficient separation of oil and water phases. Because of these properties, they must be removed from finished products where aqueous emulsions are unacceptable, or from the feedstock to chemical treatment processes where they interfere with effective processing.

Accordingly, the treatment technique has developed a number of ways to treat these problems. One way is to simply provide a large container, termed a prewashing member partially filled with dilute aqueous caustic, disperse the hydrocarbon containing traces of acidic components in the aqueous caustic and direct the hydrocarbon stream up through the container. The entering hydrocarbon stream typically enters the pre-wash tank through a series of nozzles to ensure that there is intimate contact between the hydrocarbon and dilute caustic. Sometimes the contact is achieved by circulating the caustic volume with a pump for mixing the caustic plug with incoming hydrocarbon in the pipe network. The strength and amount of the caustic solution used is generally adjusted so that very little of the weakly acidic mercaptans in the feed are absorbed by the caustic. Only the more acidic naphthenic acids, H2S and other acidic trace- 3

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adhesives are removed by caustic pretreatment. When very low acidity is required in the product, the prewash vessel may be followed by a sand filter coalescing means which removes entrapped droplets of aqueous salts from the hydrocarbon stream being treated. However, a sand filter requires frequent attention to maintain its coalescing efficiency, and sand is susceptible to attack by aqueous, basic solutions.

Unfortunately, such an operation does not always provide a satisfactory solution to the problem of acid removal. The use of a large pre-wash container increases the capital costs of the plant and may not provide an efficient utilization of the caustic solution. For naphthenic acid removal, highly diluted caustic must be used to achieve the most effective acid removal. Using a chargeable prewash system also means that the efficiency of the naphthenic acid removal is cyclic. The efficiency is greatest when the caustic is fresh, and the lowest immediately before the weak caustic is discarded. Due to the chargeable nature of the process and due to the surfactant nature of naphthenate soaps, a certain amount of neutralized caustic is always discarded with the spent caustic.

Even using a conventional coalescing means after the pre-wash container, e.g. a sand filter or mesh carpet coalescing means, the entrainment of acidic salts is still sometimes too great. This is because the efficiency of the coalescer is dependent on many factors. Reasonable efficiency can only be achieved within a relatively narrow speed range, and a deterioration in efficiency during use is common since particulate accumulation, sand wear, channel formation and other factors cause performance degradation. The inability of conventional coalescing means to maintain high efficiencies without frequent maintenance has led to the use of electric coalescing means. These devices are similar to the well-known desalination means used in crude soil oil to remove entrained water containing dissolved salts. Using an electric coalescing means, it is possible to sufficiently remove the entrained caustic containing naphtha.

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4 the thenoic acid salts from a pre-washed hydrocarbon to meet the requirements of co-stream processing units and, where applicable, such specifications as e.g. water separation from jet fuel. Unfortunately, the electric coalescing bodies are branded and they greatly increase the cost of the pretreatment apparatus. They also require careful attention, which increases usage costs and operator costs.

Another problem encountered by the known prewashing processes is the disposal of large quantities of consumed reagent. As mentioned earlier, the efficient operation of a prewash container of the batch type precludes a total use of the alkali solution.

There is always a considerable amount of neutralized caustic left in the relatively large liquid reservoir of alkali solution in the prewash vessel. Thus, when the efficiency of acid removal by the alkaline solution is no longer satisfactory, a large percentage of neutralized alkali is discarded. This is a problem not only because of the inefficient use of reagents, but because the free alkali is a disposal problem.

Another disadvantage of a prewash pre-wash is that the naphthenic acids present in the spent caustic phase are difficult to extract. If an attempt is made to extract these acids, it is necessary first to re-acidify the spent caustic and then to separate the acids from the mixed oil. Due to the diluted nature of the streams used in a prewash immediately prior to a mercaptan conversion process, the extraction of naphthenic acids is generally not considered worthwhile. Thus, a source of a potentially valuable raw material is lost. Naphthenic acids can be used as paint desiccants, wood preservatives and to some extent in lubricants under extreme pressure. The naphthenic acids have also been used as solvents for vulcanized rubber, various resins and gums, for aniline dyes, as mineral oil clarifiers, as insecticides and as tree oil additives to enable drying without cracking.

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Accordingly, refinery engineers continue to search for a method that could provide effective acid removal, be economical to operate and provide almost stoichiometric application of the alkali solution. There is also a need for a method that could be continuous to avoid the need for frequent drainage and handling of large volumes of alkali solution.

Accordingly, the present invention provides a process for pre-treating a mercaptan-containing, acidic petroleum distillate for separation of acidic materials, the process of which is (a) mixing the distillate with an aqueous solution of a base containing from ca. 100% to approx. (B) passing the mixture through a fixed mass of charcoal particles having a liquid space velocity of from about 20% of the base stoichiometricly needed to neutralize the acid concentration in the distillate. 0.5 to approx. 20 volumes of mixture per volume of mass per and coalescing the aqueous phase of the mixture therein, the fixed mass having a particle size of from ca. 0.1 to approx. (C) recover the initially mercaptan-containing acidic petroleum distillate from a lower part of the charcoal mass, now practically free of acidic materials, (d) withdraw the coalesced aqueous phase from the bottom of the charcoal mass, and (e) if desired, from the mass of charcoal particles. extracting naphthenic acids.

In a more limited embodiment, the present invention provides a continuous process for removing naphthenic acids from an acidic petroleum distillate, characterized in that the aqueous solution of a base used in step (a) contains 100-120% of the amount of base. preferably a 1-3 wt% aqueous sodium hydroxide solution which is stoichometrically necessary to neutralize the acid concentration, i.e. the naphthenic acids, in the distillate.

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The hydrocarbon streams that can be treated by the process of the present invention are those containing any trace amount of acid. Naphthenic acids are found e.g. usually in streams with ASTM D 86 endpoints above 150 ° C. H2S can be found in most intermediate streams from refineries. Carboxylic acids are often present in catalytically cracked materials. The present process can be used with excellent results on all these materials.

Many petroleum charge materials to be processed for mercaptan conversion have frequently high naphthenic acid contents. The naphthenic acid content is generally indicated by the acid number, with typical units being the number of mg of KOH needed to neutralize 1 g of the sample. The product specification for most jet fuels sets the maximum acid number of 0.010 mg KOH / g.

Charge materials today having acid numbers greater than 0.100 mg KOH / g are encountered. The existing precharge type pre-wash units followed by a coalescant cannot remove naphthenic acids in the range of over approx. 0.025 mg KOH / g effectively. The presence of such large amounts of naphthenic acids in the feed material of a mercaptan conversion unit would, if not removed, result in operating difficulties with the processing unit and loss of product. The acid number of a petroleum or other hydrocarbon can be determined by any of several test methods such as ASTM-D-3242, ASTM-D-3339, ASTM-D-974 and ASTM-D-664.

The aqueous base proposed for use may be any inorganic base soluble in aqueous (or alcoholic) solvent. Both NaOH and KOH are suitable, with NaOH being preferred because of its availability and low cost. A relatively dilute aqueous base is required to effect solubility of the naphthenic acid in the aqueous phase. The solubility of the alkali naphthenates in the aqueous phase decreases as the concentration of alkali in the aqueous phase increases. The solubilities of other acid salts also limit the concentration 7

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solution of base in the solution which can be used in practice at normal temperatures.

Regardless of the type or concentration of the base used, the present invention allows operation with only a slight excess of base to take into account variation in the feed's acid concentration.

The feed stream and the aqueous alkali phase are contacted in a simple mixing means before entering the coalescing mass.

The coalescing mass is selected from the group of substrates not attacked by alkali, such as various activated charcoal, lignite, slate, slag and calcined coke, preferably with hydrophilic properties. Examples of suitable wood species include those derived from ground wood pulp, lignite coal, anthracite coal, bituminous coal, peat, petroleum carbon black and similar wood species. Particularly preferred are ground and sieved anthracite coal.

The contact between hydrocarbon and injected alkali and the coalescing mass can occur in any suitable manner. The coalescing medium can be maintained as a fixed or moving mass. Charge switch can also be used. The current may pass over the coalescing medium in upward, downward or radial flow.

The amount of coalescing medium provided must be adjusted to suit the characteristics of the feed material and the desired properties of the product. It may be desirable to provide parallel coalescing masses so that one mass can be used while regenerating the other. Serial flow can also be used to promote the maximum removal of acids. The use of several different masses in series flow with a parallel run is also possible.

The required amount of coalescing medium can be specified as a function of the fluid flow rate. Generally, sufficient coalescing medium should be provided for the liquid space velocity to be in the range of 0.5 to 20. Similarly, the geometry of the preferred fixed mass of catalyst is such that the velocity of the supernatant liquid through the mass is chosen to

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providing the highest efficiency and the lowest cost.

For best results, the particle size distribution of the medium should be in the range of 0.1 to 6.0 mm, with particle sizes in the range of 0.6 to 2.0 mm exhibiting excellent properties.

The temperature and pressure conditions at which the aqueous base contacts the feedstock and under which the mixture contacts the coalescing agent are not critical. Generally, ambient temperatures above the freezing point of the aqueous phase or the floating point of the oil phase can be used. The typical "sundown" temperatures of hydrocarbon product streams from refineries are 10-60 ° C, and the present invention works excellently within these temperature ranges. The lower temperature limit is usually set by the temperature at which the viscosity of the liquid becomes so high that a good contact between aqueous phase and fresh feed material is excluded, and a subsequent separation of aqueous phase from organic phase is prevented. The upper limit of temperature is usually set by the degree of tolerability of the tolerable dehydration in the system and the permissible water content of the treated hydrocarbon stream. Operation at temperatures of 25-60 ° C gives satisfactory results with many feed streams. The normal materials are very fluid at these temperatures and the contact and separation of aqueous phase and hydrocarbon phase are facilitated. Operation at much higher temperatures is possible and may be desirable in the case of very heavy or viscous oils to be treated. Higher temperatures promote contact and reaction speed, but adequate acid removal can e.g. usually obtained without the expense of heating the high temperature stream. The pressure at which this acid removal process works here should be sufficient to maintain liquid phase operation since both contact and separation of organic and aqueous phase occurs completely in liquid phase. Pressure is not considered to be a significant variable. Accordingly, the pressure is usually the minimum amount of pressure required to get the fluids through the treatment units.

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The function of the caustic injection is twofold. The caustic not only neutralizes the acid in the feed, it also moistens the surface of the coalescing medium. Thus, the process of the present invention works effectively because acids and caustics not only react in the mixing means immediately before the coalescing mass in the flow direction, but also in the coalescing mass. It is because of this extensive and effective contact between caustic and acid that the present invention works so effectively.

There is still an aqueous phase dispersed in the hydrocarbon stream after the acid-alkali reaction has ended. This aqueous phase must be removed. This of another function of the coalescing mass. The dispersed aqueous phase is gradually coalesced into larger droplets of the pulp, eventually forming large droplets that separate and gravitate toward the bottom of the coalescent container for removal. A level control means preferably automatically drains the aqueous phase from the coalescing vessel as it accumulates. The advantage of the automatic level control means is that it makes the process completely continuous, requiring only little or no attention from the operator.

The charcoal pulp is preferably supported by a flat screen which holds the charcoal back but allows the spent aqueous base to pass through to remove the pulp. Particularly preferred are the well-known Johnson sieves negotiated by the Johnson Division of UOP Inc. These sieves consist of wedge-shaped rods welded to a carrier. They are very strong and usually do not clog and provide a relatively large open area for the fluid flow. The hydrocarbon stream can be added to and removed from the charcoal mass via circular screens of the same construction type.

In the drawing, a simplified schematic flow diagram of an embodiment of the present invention is shown, wherein a dilute alkaline solution is continuously injected into an acid-containing feed and the mixture is passed through a coalescing mass.

In the first step of the present process, an acidic feed stream in a conduit 10 is contacted with a dilute aqueous base from (not shown) storage vessels, which base is charged by a measuring pump 1 which sucks in via a conduit 21 and discharges via a line 22. The caustic is charged to 10

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to a mixing means 2. The feed material and base mixture is charged via a conduit 11 to a coalescing container 3. The coalescing container 3 consists of a coalescing mass 4, an access distribution means 8 / collecting tube 5, and a drain screen 6.

Treated hydrocarbons which are practically free of acids are removed from the charcoal mass via the collection tube 5 and a product line 12 and then charged to other processing units (not shown) or storage (not shown).

The aqueous phase coalesced by the charcoal mass seeps down through the coalescing mass as it exits via the drain screen 6 into a drain tank 7. The sight glass and level control means (not shown) provide for the continuous withdrawal of spent aqueous phase via a conduit 23.

Example 1

A miniature experimental system is used to test the present invention. The feed material is a petroleum with an extremely high acid number of 0.084 mg KOH / g. The coalescing mass consists of 3 cm of charcoal made by Norit Co. The charcoal is referred to as 0.59 / 2.00 and 90% of it has a particle diameter of between 0.6 and 2.0 mm. The charcoal is placed as a fixed mass in a small pressure vessel. The inside diameter of the container is 25 mm and the height of the mass is 100 mm. The charcoal is supported at the bottom by a plug of glass wool. The alkali solution added to neutralize the naphthenic acids is a dilute aqueous solution of NaOH. The caustic strength is 1.5% by weight. The base is added by slowly closing a syringe. Such a method of adding caustic is necessary because the plant is small and because the present invention makes very efficient use of caustic. An ultrasonic mixer is used to mix the petroleum with.

NaOH immediately before the coalescing mass in the flow direction.

The feed material is tested for acid numbers. After passing through the mass of activated charcoal, the hydrocarbon product is analyzed for both sodium content and acid numbers. After mixing with the caustic plug, but prior to coalescing, the feedstock is measured to confirm the calculated addition of NaOH. Both acid titration and atomic absorption spectroscopy analyzes of the mixture are used to determine the alkali content.

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Experiments are performed at a liquid space velocity (VRH) 3 of 2.0 and 4.0, i.e. a charge rate of 100 cm / hr 3 and 200 cm / hr respectively.

The test results are given in Table I below.

Table I

Product: Mole NaOH / mole acid in the feed

Hours VRH Acid Number Na (ppm) added_titration_AAS

0-8 2 0.001 0.25 8-17 2 0.010 1.11 0.46 17-38 2 0.011 38-73 4 0.029 1.5 1.77 1.29 0.27 73-80 4 0.009 0.34 1 , 26 0.60 0.10 80-100 4 0.004 0.45 1.28 1.29 0.10. 100-124 4 0.023 2.2 1.14 0.60 0.34 124-152 4 0.005 3.6 1.14 0.58 0.77 152-179 4 0.018 8.1 1.14 0.40 0, 74 179-197 4 0.036 19 1.14 0.48 1.03 197-221 4 0.006 3.6 1.14 0.34 0.53 221-248 4 0.004 7.1 - 0.80 248-273 1 / 2 4 0.003 6.1 - - 0.74

Example 2

Another experiment according to the present invention is carried out in a commercial sized unit. The charge materials used are petroleum species originating from Louisiana and from Illinois. The unit uses an existing refinery container as a coalescing mass. No attempt is made to pre-design the container, rather attempts are made to use the apparatus present in the plant to test the present invention on a slightly larger scale.

No mixing device is readily available to allow for intimate contact between the petroleum feedstock and the alkaline medium. As a substitute, a valve is partially squeezed together immediately prior to the coalescer in the flow direction.

The alkaline medium used is a caustic available in the refinery which has a concentration of 4-6 ° Baume. This concentration is higher than desired, but it is the only strength available for the experiment. Calculations indicate, 12

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that approx. 11.4 liters / hour caustic injection to neutralize the petroleum derived from Louisiana crude, while requiring 5.7 liters / hour caustic to neutralize acids contained in the petroleum originating from the Illinois base material . The coalescing medium used is "Calgon SGL" charcoal, 0.59 x 2.38 mm. Using the Louisiana crude oil, the caustic injection is started at a rate of 37.8 liters per liter. hourly or significantly above what is required by stoichiometry to neutralize acids, primarily naphthenic acids. This caustic injection rate reduces the initial acid number of the petroleum from 0.10 mg KOH / g to 0.0096 mg KOH / g. The resulting drained caustic is only approx. 50% consumed. The caustic injection is further reduced to approx. 28.8 liters per but this results in insufficient acid removal. By analysis, the petroleum product has an unacceptably high naphthenic acid content, 0.032 mg KOH / 100 ml. This analysis can be called into question because of the difficulty of obtaining a representative sample. However, the drained caustic is 60% consumed. The amount of caustic remaining in the product petroleum ranges from 0.042 to 0.067 ppm NaOH. This lower caustic entrapment is expected because it is experience-wise easier to separate caustic from hydrocarbons in a commercial size unit than in an experimental plant.

Example 3

Further experiments are carried out in the experimental facility described in Example 1. These tests are conducted with charcoal obtained from the Darco Company having a nominal size of 0.59-2.00 mm (90% of the particles have a diameter of between 0.6 and 2.0 mm). The charge material used is identical to that used in Example 1. In Example 3, the target amount of injected caustic is 1.2 times that theoretically needed to neutralize naphthenic acids. The caustic material used is slightly more concentrated than that used in the first experiment, namely 5 ° Baume NaOH (equivalent to 3.2% by weight NaOH). The reactor temperature is 25.6 ° C and the reactor pressure is 5.6 kg / cm 2 overpressure.

The test results are given in Table II.

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Table II

Product: Added ppm NaOHx

Hours VRH Acid Number Na '(ppm). titration addition 0-12 4 0.005 73 18 12-23 4 0.017 73 16 23-37 4 0.010 1.2 73 22 37-45 4 0.007 1.4 (Temporary ambiguity of the product) 45-53 4 0.005 73 32 53-64 4 0.016 (Gélé occurs in the separator) 64-73 4 0.009 75 20 73-80 4 0.006 75 19 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 15 137-150 4 0.010 2.8 73 13 150-159 4 0.007 73 19 159-166 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 x 62 ppm NaOH required by stoichiometry.

A gel-like substance appears in the separator after 64 hours of operation and continues to be produced during the remainder of the experiment. A temporary plug is developed 99 hours into the experiment. From time to time there is some temporary fuzziness in the product, but this usually disappears after several hours. However, the unclear product at the end of the experiment requires a delay period of up to 7 days to become clear. It is believed that the higher concentration of NaOH causes the production of the gel-like substance, indicating a need for careful adjustment of the caustic concentration.

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Example 4

The same test apparatus and batch material is used as in Examples 1 and 3. In this example, the coalescing material used is ground anthracite coal. The nominal particle size of the coal is 0.84 to 2.0 mm, ie. it is termed 0.84 x 2.00.

A slightly more dilute caustic is used in this experiment, namely 3 ° Baume NaOH (equivalent to 1.8% by weight NaOH). The test is carried out at a liquid space rate of 4.0 and is continued until the supplies of feedstock are depleted. The test results are given in Table III.

Table III

Product: ppm NaOH

Hours VRH Acid Na (ppm) addition titration 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 is generally more favorable in lowering the naphthenic acid content of the product as evidenced by its acid number. This experiment is also very satisfactory because the sodium content of the product is considerably lower than the content given in previous examples, although the sodium content of the product of Examples 1 and 3 is satisfactory.

Most of the improvement in Example 4 is due to the lowered NaOH concentrations, but there is perhaps a synergistic effect due to the use of anthracite as a coalescing medium.

When the present coalescing mass is used to remove naphthenic acids, it may eventually become saturated with naphthenic acid salts. To enable reactivation of the pulp and also to allow recovery of the naphthenic acid salts for use

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As a valuable by-product, a variety of regeneration methods can be used.

It is believed that a reasonable regeneration can be accomplished by simply removing the pulp from the process stream and passing hot water vapor over the pulp. In order to provide a more complete regeneration of the pulp and to enable recovery of the naphthenic acid salts in the form of the acid rather than the salt, it is also possible to re-acidify the salts in situ. It can be accomplished by isolating the coalescing mass from the hydrocarbon stream and the aqueous stream, circulating an aqueous acidic solution over the pulp and desorbing the naphthenic acids from the charcoal. If a sufficient amount of acidic water is used, much of the naphthenic acids are displaced at the acidification step. The desorption of naphthenic acids can be promoted by the transfer of hot water vapor over the reactor. The naphthenic acids are volatile with water vapor, and this process should provide almost complete regeneration of the coalescing mass. If the charcoal mass cannot be readily regenerated with this gentle technique, it may be necessary to proceed to a treatment with higher temperature steam or a treatment with various well known hydrocarbon solvents such as benzene, acetone and methanol mixtures to assist in removal. of naphthenic acids and acid salts from the coalescing mass.

One of the interesting features of the present invention is that while doing an excellent job of removing acids in the petroleum product or feed material into a mercaptan conversion unit, it also produces as much as a 1000-fold increase in the concentration of naphthenic acids. , allowing the possible extraction of naphthenic acids when they are a desired by-product, and simplifying the disposal of these compounds when there is no market for them. Most of the naphthenic acids are recovered in the aqueous phase once an equilibrium amount of coalescing mass has accumulated.

The present invention can also be used to remove H 2 S from hydrocarbon streams. A hydrocarbon stream which e.g. contains 0.01% by weight of I ^ S, can be contacted with an aqueous 6% by weight NaOH stream and conducted downstream in co-flow through a coalescing mass. The coalescing mass is preferably a charcoal having a nominal granulation range of 0.6 to 2.0 mm, which is available under the trade name "Calgon". When using 30% excess base, the hydrocarbon product from

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the scissors contain less than 0.0005% by weight t ^ S.

The efficiency of the removal of certain acids is limited by equilibrium considerations under the desired operating conditions. Partial removal of very weak acids, e.g. mercaptans and phenols, are also possible while observing equilibrium considerations and adjusting the base concentration as well as depending on the specific acidic component being removed.

It is preferred to use more concentrated base for the removal of H2S than for the removal of naphthenic acids. This is because salts of I ^ S are more soluble than salts of naphthenic acids. NaOH concentrations of from 2 to 10% by weight give good results.

When used for the removal of naphthenic acids, the data obtained indicate that the process of the present invention is very effective in reducing the acid number of a petroleum heavily contaminated with naphthenic acid. The naphthenic acid content can generally be reduced to acceptable levels for further treatment or sale.

It can be seen that the present process provides an almost stoichiometric utilization of the caustic plug. There is also more effective acid neutralization due to the larger, effective surface area of the basic medium, not only in the mixing means and the pipe network, but also in the coalescing mass. Greater flexibility and efficiency are available, enabling operation with hydrocarbon flow rates much lower than normal.

There is an insignificant entrapment of aqueous solution with the hydrocarbon due to the ability of the coalescing mass to coalesce aqueous droplets into a separate phase which, due to gravity, separates from the hydrocarbon. A reduction in the cost of pre-treatment facilities is also provided.

Claims (8)

A process for pre-treating a mercaptan-containing acidic petroleum distillate to separate acidic materials, characterized in that (a) it is mixed with an aqueous solution of a base containing from ca. 100% to approx. (B) passing the mixture through a fixed mass of charcoal particles with a liquid space velocity of from about 20% of the base stoichiometricly needed to neutralize the acid concentration in the distillate. 0.5 to approx. 20 volumes of mixture per volume of mass per and coalescing the aqueous phase of the mixture therein, the fixed mass having a particle size of from ca. 0.1 to approx. (C) recover the initially mercaptan-containing acidic petroleum distillate from a lower part of the charcoal mass, now practically free of acidic materials, (d) withdraw the coalesced aqueous phase from the bottom of the charcoal mass, and (e) if desired, from the mass of charcoal particles. extracting naphthenic acids. Process according to Claim 1, characterized in that the aqueous solution of a base used in step (a) contains from ca. 100% to approx. 120% of the amount of stoichiometric base needed to neutralize the acid concentration in the distillate. Process according to claim 1 or 2, characterized in that the mass of charcoal particles is derived from ground wood pulp, lignite coal, anthracite coal, bituminous coal, peat and petroleum carbon black. Method according to any one of claims 1-3, characterized in that the particle size is from 0.6 to 2.0 mm. Process according to any one of claims 1-4, characterized in that the aqueous base contains from 0.01 to 50% by weight of alkali. Process according to any one of claims 1-5, characterized in that the acidic material comprises naphthenic acid and that the aqueous base is NaOH in a concentration of 1-3% by weight. Process according to any one of claims 1-6, characterized in that naphthenic acid salts absorbed on the charcoal mass are recovered by removing the pulp from contact with the flowing distillate and the aqueous streams and treating the pulp with an acid medium for acidification. of the naphthenic acids which are then displaced from the mass by a desorbent. Process according to claim 7, characterized in that the desorbent is water vapor with a temperature of 200-400 ° C.