GB2110681A - Process for treating spent sulfuric acid streams from the olefin hydration reaction - Google Patents

Abstract

A spent sulfuric acid stream formed in the catalytic hydration of an olefin to prepare an alcohol, and containing organo-sulfonic acid impurities, is contacted with an oxidizing agent selected from ozone, hydrogen peroxide, sources of chlorate and peroxydisulfate, and mixtures thereof, the oxidizing agent being employed in an amount of less than one complete oxidation stoichiometric equivalent of oxidizing agent for each equivalent of the sulfonic acid impurities, to form partially oxidized organic compounds therefrom and thereby provide a sulfuric acid stream of increased thermal stability. The process permits continuous operation at levels of total organic carbon in the treated acid which would otherwise be unacceptable and minimizes the substantial operating problems associated with formation of heavy carbon deposits in the process equipment.

Description

SPECIFICATION Process for treating sulfuric acid streams to provide improved thermal stability Field of the invention This invention relates generally to the purification of spent sulfuric acid streams formed in the manufacture of alcohols via the catalytic hydration of olefins.

Description of the prior art Large volumes of alcohols are produced annually by the catalytic hydration of olefins, in which the selected olefin feed is absorbed in a concentrated sulfuric acid stream to form the corresponding alkyl ester of the sulfuric acid. Thereafter, water is admixed with the ester-containing liquid to hydrolyze the ester and to form the desired alcohol which is then recovered, generally by stripping with steam or other heating fluid. There is thereby produced a diluted sulfuric acid stream which must, for economic reasons, be treated to concentrate it with respect to its sulfuric acid content after which it is recycled to the absorption step.

Organic impurities in these various sulfuric acid streams accumulate due to this continuous acid recycle, and this accumulation results in the deposit of carbonaceous materials on the inner surfaces of process equipment. These carbonaceous deposits, which result from the thermal degradation ("coking") of the organic impurities, can foul equipment, and severely reduce the flow rate of liquids therethrough. Removal of these deposits is, therefore, periodically necessary and requires shutting down of the facilities and physicai removal of these deposits, as by manually scraping the fouled surfaces. This involves considerable expense in manpower and plant downtime, and results in a significant loss of overall annual plant capacity.In addition, the carbonaceous deposits which are thus removed are waste materials which create still further expense, and attendant environmental problems, in the need to safely dispose of these materials.

A variety of methods have been developed to purify various spent sulfuric acid streams.

A process for regenerating certain spent sulfuric acids by the air oxidation of organic impurities is disclosed in U.S. Patent 2,01 5,254.

In US Patent 3,145,080, a process is provided for removing metaliic impurities from dilute sulfuric acid by reaction with excess hydrogen sulfide in the presence of activated carbon, foliowed by destruction of the excess hydrogen sulfide with hydrogen peroxide, also in the presence of activated carbon.

Alkylation refinery sludge, containing unwanted organic matter produced during petroleum refining, is purified according to the method of U.S. Patent 3,477,814, in which the alkylation sludge is first heated to effect dehydration and desulfation of the sludge, followed by a complex series of steps to produce and recover concentrated, pure sulfuric acid.

Spent sulfuric acid streams produced in the nitration of aromatic hydrocarbons, such as toluene are treated in accordance with U.S. Patent 3,856,673 to completely oxidize the nitrated organic compound impurities, such as nitrocresols and other nitriphenolic compounds. Such an oxidation is necessary to avoid the formation of tri-nitro substituted aromatic compounds, which are highly unstable and can explode violently.

U.S. Patent 4,085,016 is directed to electrolytic treatment of sulfuric acid streams formed from sulfur dioxide obtained by the roasting of sulfide ores, and discloses that hydrogen peroxide and peroxy-compounds of sulfuric acid can be used to completely oxidize the organic impurities into CO2 gas and water.

U.S. Patent 4,157,381, relates to a process for purifying sulfuric acid streams, containing organic impurities, by use of superheated steam atomization and a plurality of vapor handling stages. Oxidants such as nitric acid, hydrogen peroxide, and Caro's acid are added at any of several stages in the process.

Spent sulfuric acid streams produced in different processes differ widely in their impurity-content and in their critical process characteristics. Thus, the above methods are not readily adaptable for use in treating spent acid streams formed in dissimilar processes, such as in the hydration of olefins to prepare alcohols.

Summary of the invention According to the present invention, spent sulfuric acid streams formed in the hydration of olefins to prepare alcohols and containing organo-sulfonic acid impurities, are treated to remove deleterious organic impurities therefrom by a process which comprises contacting said spent acid stream with an oxidizing agent selected from the group consisting of ozone, hydrogen peroxide, chlorates, peroxydisulfates, and mixtures thereof, said oxidizing agent being employed in an amount of less than one stoichiometric equivalent of oxidizing agent for each equivalent of the sulfonic acid impurities, to form partially oxidized organic compounds therefrom and thereby produce a treated sulfuric acid stream of increased thermal stability, i.e., carbonaceous solids are formed, if at all, at a rate which is less than are formed in the untreated spent acid stream at a given temperature.

It has been surprisingly found that the fouling problems associated with the formation of carbonaceous deposits in processes for the sulfuric acid catalyzed hydration of olefins to produce alcohols are due to the presence in the spent sulfuric acid streams of chemically-reactive organosulfonic acid impurities which are formed as by-products in the hydration process and which are readily degraded to coke and tars at elevated temperatures, and that these fouling problems can be avoided or greatly minimized by the process of this invention wherein the organo-sulfonic acid impurities are partially oxidized.It has been unexpectedly found that the process of this invention provides a treated sulfuric acid stream having a greatly improved thermal stability and permits recycle of the treated acid stream after concentration, to the olefin hydration process while greatly decreasing the amount of carbonaceous deposits formed by the thermal decomposition of organic impurities in the acid.

Description of the accompanying drawings Figure 1 is a diagrammatic illustration of one embodiment of the process of this invention.

Figure 2 is a diagrammatic illustration of a further embodiment of the process of this invention.

Detailed description of the invention According to the process of this invention, spent sulfuric acid streams obtained in the hydration of olefins are treated to avoid or substantially minimize equipment fouling problems associated with the deposition of carbonaceous impurities on internal process equipment.

The process of this invention can be illustrated by reference to the accompanying drawings wherein like numerals refer to the same or similar elements. Referring to Figure 1, an olefin, for example an aliphatic olefin having from 2 to 8, and preferably from 2 to 4, carbon atoms per molecule, (e.g., ethylene, propylene, butene, pentene, and octene) is fed via line 2 to an absorber 10 wherein it is contacted with and absorbed (at least in part) by a concentrated sulfuric acid stream introduced via line 6, to form the corresponding alkyl ester of the sulfuric acid.

The olefins to be sulfated can be obtained from any available source, such as the destructive distillation of carbonaceous materials, but particularly from the cracking of petroleum hydrocarbons such as is practiced in the petroleum refining of mineral oils. The olefin employed in this invention can also be conventionally obtained by careful fractionation of cracked petroleum gases and is preferably substantially free of higher unsaturates, particularly diolefins such as butadiene, etc. Illustrative of olefins which can be employed are lower branched and straight-chained alkenes (i.e., alkenes of 2 to 6 carbon atoms), such as ethylene, propylene, the butenes and the like.

The sulfuric acid stream 6 which is used to sulfate the selected olefin feed is a concentrated acid stream whose precise acid concentration will vary depending on the olefin which is employed, the temperatures of reaction and other conditions. Generally, however, the sulfuric acid stream 6 will contain from about 45 to 99 wt.%, and preferably from about 65 to 95wt%, sulfuric acid for sulfation of ethylene or propylene and from about 55 to 85 wt. %, and preferably from about 65 to 80 wt. %, sulfuric acid for reaction with butene or higher olefin feeds.

The temperature and pressure employed in absorber 10 will also vary depending on the olefin, the acid concentration and other factors, Generally, a temperature of from about 20 to 1 200C will be used, and the pressure will be sufficient to maintain the desired liquid phase in the absorption.

Typically, for example, propylene is absorbed at a temperature of from about 90 to 110 C, and at a pressure of from about 100-400 psig.

As illustrated, the olefin and sulfuric acid streams are contacted in a counter-current fashion with the sulfuric acid stream being introduced into the upper portion of the absorber 1 0. Unabsorbed gases are withdrawn from the upper portion of absorber 10 via conduit 7 and can be recycled, if desired, to conduit 2 or can be subjected to conventional treatment, as with caustic solutions. A product stream, commonly termed the "extract", is withdrawn via line 4 from the lower portion of absorber 10 and contains the alkyl ester, e.g., di-ethyl sulfate in the instance in which ethylene is the olefin, and di(isopropyl) sulfate in the case of propylene sulfation. The concentration of the alkyl ester in extract stream 4 is not critical and can vary widely.Thus, the extract generally contains 1 5 to 30 wt. % of the total alkyl ester (mono- and di-alkyl ester) in the case of lower alkenes (e.g., propylene and butylene) absorption.

In the second step of the hydration process, water is added via line 1 2 to the extract in stream 4 for hydrolysis of the alkyl ester and to liberate the corresponding alcohol, e.g., isopropanol from di(isopropyl) sulfate. The manner in which the water and extract are contacted is not critical, and the art employs a variety of such methods, including (1) in-line addition of water to the extract (as illustrated), with a provision for a suitable length of conduit to provide adequate mixing and reaction time, and (2) contacting of the extract and water in a separate reaction vessel with agitation (not shown).

The amount of water which is added to the extract is also not critical and can vary widely.

Generally, from about 0.3 to 1.0 parts by weight of water is added to the extract per part by weight of alkyl ester in the extract. It is important not to add excessive water, since this only results in increased dilution of the extract and the excess water must subsequently be removed in the concentration step, to be discussed in more detail below.

The diluted extract thus formed generally contains from about 30 to 60 wt.% sulfuric acid, and more preferably from about 40 to 50 wt. % sulfuric acid, and is then passed via line 4 to distillation column 20, herein termed the "alcohol generator", wherein crude alcohol is recovered as an overhead product via line 1 8. The overhead alcohol product can then be passed to further conventional processing to produce alcohol of the required purity.

A bottoms product is withdrawn from alcohol generator 20 via line 24 and comprises a sulfuric acid stream which generally contains from about 40 to 55 wt.%, and preferably from about 45 to 50 wt.%, sulfuric acid.

In conventional processes, the alcohol generator bottoms are passed directly to another distillation column, hereinafter termed the "acid concentrator", wherein this acid stream is distilled for removal of water as overhead and to form a second bottoms product comprising a concentrated acid stream. These concentrated bottoms are generally cooled and passed to storage for ultimate recycle to the absorption step.

According to the embodiment of this invention illustrated in Figure 1, the alcohol generator bottoms, comprising an aqueous liquid containing from about 40 to 55 wt. % H2SO4, and containing organo-sulfonic acid impurities is passed via line 24 to reaction zone 60 wherein the contaminated sulfuric acid stream is contacted with controlled amounts of an oxidizing agent introduced thereto via line 62. The organo-sulfonic acid impurities are generally present in the alcohol generator bottoms 24 in an amount of at least about 500 ppm, usually at least about 700 ppm, more typically from about 9,000 to 30,000 ppm, and most typically from about 12,000 to 20,000 ppm, by weight. These alcohol generator bottoms to be treated by the process of this invention can contain up to 65,000 ppm or more of the organo-sulfonic acid impurities.

The organo-sulfonic acid impurities generally contain from 2 to 16, more typically from 2 to 8, carbon atoms per molecule in the organic moiety and at least one, more typically 1 to 2, sulfonic acid moiety (-S03H) per molecule. When the organo-sulfonic acid impurity is represented by the formula RSO3H, "R" can comprise members selected from the group consisting of alkyl, aryl, alkenyl, alkynyl, alkaryl, aralkyl, cycloalkyl, polynuclear aryl, heterocyclic and derivatives thereof in which one or more carbon is substituted by hydroxy, keto, carboxyl, sulfate, mercapto, or sulfono group.

When "R" is alkyl, the alkyl group can be branched or straight-chained and generally contains from 1 to 12 carbon atoms, and more usually contains from 1 to 6 carbon atoms. Examples of such alkyl groups are methyl, ethyl, isopropyl, pentyl, octyl and dodecyl. When "R" is cycloalkyl, the cycloalkyl group generally contains from 3 to 12 carbon atoms, and more usually contains from 4 to 8 carbon atoms. Examples of such groups are cyclopropyl, cyclobutyl, cyclohexyl, cyclooctyl and cyclododecyl. Illustrative "R" aryl groups are phenyl. When "R" is polynuclear aryl, the "R" group generally contains from 2 to 4 aromatic rings. Examples of such polynuclear aryl groups are naphthenyl, anthracenyl, and phenanthrenyl. When "R" is alkenyl, the alkenyl group generally contains from 2 to 12 carbon atoms, and more usually from 2 to 6 carbon atoms.Exemplary of such alkenyl groups are ethenyl, butenyl, hexenyl and decenyl. When "R" is alkynyl, the alkynyl group will generally contain from 2 to 12 carbon atoms, and more usually from 2 to 6 carbon atoms. Exemplary of such alkynyl groups are ethynyl, butynyl and propynyl. When "R" is alkaryl, the aryl component generally consists of phenyl or tolyl and the alkyl component generally has from 1 to 12 carbon atoms, and more usually from 1 to 6 carbon atoms. Examples of such alkaryl groups are tolyl, m-ethylphenyl, o-ethyltolyl and m-hexyltolyl. When "R" is aralkyl, the aralkyl group generally consists of phenyl or alkyl-substituted phenyl as the aryl component and an alkyl component having from 1 to 12 carbon atoms and more usually from 1 to 6 carbon atoms. Examples of such aralkyl groups are benzyl, o-ethylbenzyl and 4isobutyl benzyl.When "R" is heterocyclic, the heterocyclic group generally consists of a compound having at least one ring of 6 to 1 2 members in which one or more ring carbon atoms is replaced by oxygen or nitrogen. Examples of such heterocyclic groups are furyl, pyranyi, pyridyl, piperidyl, dioxanyl, tetrahydrofuryl, pyrazinyl and 1,4-oxazinyl.

Illustrative of typical such impurities are alkenylsulfonic acids of 2 to 4 carbon atoms and hydroxy-substituted alkyl sulfonic acids of 2 to 4 carbon atoms and the like, and mixtures thereof.

Exemplary of the hydroxyalkyl sulfonic acids are CH3CH(OH)CH(CH3)S03H, HOCH2CH2SO3H, CH3CH(OH)SO3H

and the like. Illustrative of alkenyl sulfonic acids are CH3CH=CHCH2S03H, CH2=CHSO3H, CH3CH=CHSO3H and the like. The most typical organo moieties are alkenyl and hydroxyalkyl wherein the number of carbon atoms in each moiety correspond to the number of carbon atoms in the olefin feed introduced via conduit 2 to absorber 10.

The oxidizing agents comprise at least one member selected from the group consisting of ozone, hydrogen peroxide, chlorates and peroxydisulfates. The chlorates and peroxydisulfates can be added as salts which are soluble in the spent sulfuric acid stream which is treated. Exemplary of such salts are NH4+, alkali metal, alkaline earth metal chlorate and peroxydisulfate compounds. Illustrative oxidizing agents, therefore are 03, H2O2, Na, K and Mg chlorate, persulfuric acid (H2S2Os), ammonium peroxydisulfate, and the like.

The selected oxidizing agent is employed in an amount of less than one, preferably less than 80% of one, more preferably less than 50% of one, and most preferably less than 10% of one, completeoxidation stoichiometric equivalent of oxidizing agent per equivalent of sulfonic acid impurity. By the term "complete-oxidation stoichiometric equivalent" herein is meant the equivalents of the selected oxidizing agent required to completely oxidize the organo-sulfonic acids in the treated acid to form carbon dioxide gas (CO2) and water.

Since the stoichiometric equivalents required for complete oxidation of the organo-sulfonic acid impurities will vary depending on the oxidant selected, the precise sulfonic acids present and other factors, the amount of oxidizing agent introduced to reaction zone 60 according to this invention will also vary.The complete oxidation of a typical alkenyl-sulfonic acid to carbon dioxide and water with a variety of oxidants can be illustrated by the following equations (I-V): CH3CH=CHCH2SO3H + 1 2H202e4CO2+ 1 5H2O+H2SO4 (I) CH3CH=CHCH2SO3H + 1 1203e4C02+3 H2O f H2SO4+ 1202 (11) CH3CH=CHCH2SO3H+12H2S208+9H2044CO2+25H2SO4 (111) CH3CH=CHCH2SO3H + 12 K2S208+9 H2O~4CO2+25K2SO4 (lav) CH3CH=CHCH2SO3H + 1 2KCIQ4CO2+3H2O+ 1 2KClO2+H2SO4 (V) The oxidizing agent and the spent sulfuric acid stream can be contacted in zone 60 in a batchwise, continuous or semi-continuous manner. The manner of contacting is not critical. Thus, for example, the selected oxidizing agent can be added to a conduit containing the spent sulfuric acid stream.In this case, zone 60 can be viewed as a tubular reactor. Alternatively, zone 60 can comprise a reaction vessel to which the oxidizing agent and spent acid are introduced. Preferably, the oxidizing agent is continuously introduced into the spent acid stream so as to continuously partially oxidize the organic impurities therein and, therefore, to substantially avoid the fouling problem associated with carbonaceous deposits on process equipment.

The conditions of temperature and pressure necessary for reaction of the oxidizing agent and the non-volatile organic impurities can vary widely, but generally a temperature of from about 70 to 1900 C, more preferably from about 100 to 1 500 C, and most preferably from about 110 to 1300 C, is employed. Temperatures outside of these ranges can also be used. Any pressure sufficient to maintain the treated sulfuric acid in the liquid state can be employed, and thus atmospheric, subatmospheric, and superatmospheric pressures are suitable. A pressure of from about -15 to 30 psig is entirely suitable for propene or butene absorption.The residence time of the spent sulfuric acid in zone 60 is not critical and will generally range from about 2 seconds to 2 hours, or more preferably from about 10 seconds to one hour, for most efficient utilization of the added oxidizing agent.

By the above means, it has been surprisingly found that the organo-sulfonic acid impurities are converted to oxidation products which are significantly more thermally stable than the organic sulfonic acid impurities themselves. Thus, the treated spent sulfuric acid stream containing these oxidation products exhibits markedly reduced tendencies to form carbonaceous deposits in process equipment associated with the production and recovery of the alcohol product and the concentration and recycle of the sulfuric acid.

The precise oxidation products formed will, of course, vary depending on the type of organo sulfonic acid impurity, the amount of oxidant and other factors. Generally, however, these oxidation products comprise a mixture of lower aliphatic carboxylic acids (e.g., acetic acid, propionic acid), sulfuric acid, carbon monoxide and carbon dioxide, in addition to unknown organic oxidation products formed by carbon-carbon scissions in the molecules of the organo-sulfonic acid impurities.

At least a portion of these oxidation products are substantially more volatile than the organo sulfonic acid impurities themselves. Thus, the treated spent sulfuric acid stream containing the oxidation products can be further treated to remove at least a portion of (and preferably at least a majority of) these more volatile oxidation products, as by distillation or by fiashing at reduced pressure.

It has been surprisingly found that it is not necessary to remove the oxidation products which are less volatile than the organo-sulfonic acid impurities in order to achieve a more thermally stable sulfuric acid.

In the embodiment of Figure 1, the treated alcohol generator bottoms are withdrawn via line 64 from reaction zone 60 and passed to concentrator 30 wherein the treated spent acid is contacted with a heating fluid, such as steam introduced via line 34, to remove water as an overhead product via line 32 and to form a concentrated sulfuric acid stream which can be withdrawn via line 38. The conditions of temperature and pressure within concentrator 30 are not critical and will vary widely, depending on the alcohol stream treated. Thus, a temperature of from about 80 to 1800 C, preferably from about 80 to 1 300C, and a pressure of from about -1 5 to 100 psig, will generally be employed in the hydration of butenes or propene.

The aqueous overhead vapors withdrawn via line 32 will also contain at least a portion of the oxidation products which are fed to concentrator 30 and which vaporize under the temperature and pressure conditions employed in concentrator 30.

The concentrated sulfuric acid stream withdrawn via line 38 can be recycled, after cooling in heat exchanger 40 if desired, to vessel 50 for intermediate storage of the concentrated acid intended for ultimate recycle to absorber 10 via line 6, with the addition of make-up sulfuric acid via line 5, as required.

If desired, a portion or all of the effluent from reaction zone 60 can be passed via conduit 39 to a separate distillation zone 40 wherein volatile organic impurities, formed by the partial oxidation in zone 60 and having boiling points lower than water, are removed as overhead via conduit 42. The resulting liquids, now depleted of organic impurities more volatile than water, are then passed to conduit 64 for introduction into concentrator 30. In this embodiment, the aqueous overhead 32 from concentrator 30 contains decreased amounts of organic impurities.

It will be understood that, if desired, a portion of the bottoms product recovered from the alcoholic generator 28 via conduit 24 can be passed directly as feed to concentrator 30 via conduit 28.

In this embodiment, therefore, the stream passed as feed to contacting zone 60 can comprise a slipstream or sidestream of the alcohol bottoms otherwise recycled as feed directly to concentrator 30.

The portion of the alcohol bottoms treated in zone 60 will, of course, depend on the amount of impurities in the alcohol bottoms, the desired purification level in the treated stream to be achieved, and other factors, and can be controlled by means of valve 21. Generally, however, at least about 1 0% by volume, and preferably from about 50 to 100% by volume, of the alcohol bottoms will be treated in zone 60 according to the process of this invention for partial oxidation of the organo-sulfonic acid impurities therein.

Referring now to Figure 2, an embodiment of this invention is illustrated wherein the bottoms product from concentrator 30, comprising concentrated sulfuric acid, e.g., 50 to 99 wt. % H2SO4, and containing at least about 1 500 ppm, usually from about 8,000 to 30,000 ppm or more, and more typically from about 10,000 to 20,000 ppm, of the organo-sulfonic acid impurities, is withdrawn via conduit 38 and at least a portion thereof is passed to contacting zone 70 wherein such portion is contacted with the selected oxidizing agent, introduced thereto via conduit 72, as described above. A liquid effluent is withdrawn from zone 70 via conduit 74.The oxidation zone effluent is then passed to a separate distillation zone 40 wherein the volatile organic impurities are removed as overhead via conduit 42, as described above. The resulting liquids, depleted of organic impurities more volatile than water, are then passed to conduit 39 and can next be recycled, after cooling in heat exchanger 40 if desired, to vessel 50 as described above.

Optionally, a portion (or all) of the liquid effluent in conduit 74 can be recycled via conduit 73 to concentrator 30 wherein the more volatile partial oxidation products, which were formed in zone 70, are vaporized and withdrawn with the overheads via conduit 32. To the extent that such a recycle via conduit 73 is employed, the need for a separate distillation zone 40 is minimized or even eliminated.

If desired, a portion of the concentrated sulfuric acid in conduit 38 can be passed directly to conduit 39 via conduit 38a for recycle to the process. In this event, the acid stream treated in zone 70 can be viewed as a slipstream of the concentrated acid bottoms withdrawn from concentrator 30.

The relative flows of liquids to zone 40 and through conduits 73 and 38a can be controlled by means of valves 75, 77, and 35, respectively.

The process of this invention can be further illustrated by reference to the following examples, wherein parts are by weight unless otherwise indicated.

In the examples, total soluble organic carbon (TSOC) measurements are made by employing a Beckman Total Organic Carbon Analyzer (Model 21 5B), using liquid samples which are first filtered by means of vacuum fiitration through a funnel equipped with glass fiber filter discs (Reeve Angel 934 AH, Whatman Co.) mounted on a glass vacuum flask to remove carbonaceous solids particles having a size greater than about 1.5 microns.

Distillations of samples are accomplished in the examples by charging each sample to a 500 ml, 2-neck round bottom flask equipped with a thermometer and a 9-inch long glass cooling water condenser. The liquid is stirred by means of a magnetic stirrer and heated by means of an electric heating mantle. Distillations are effected at atmospheric pressure and at a rate such that about 0.5 ml of water is recovered as condensate per minute. The distillation is terminated when the pot temperature achieves a temperature of 1 780 C, which corresponds to the atmospheric boiling point of 72 wt.% sulfuric acid. After cooling to room temperature, both the condensate and the liquid remaining in the flask are analyzed for TSOC. In addition, the condensate is analyzed by gas chromatography.

The heat soaking treatments in the examples are performed by charging each sample so treated to a 250 ml 2-neck round bottom glass flask equipped with a thermometer, 9-inch long glass cooling water condenser and magnetic stirring bar. The flask is heated by means of an electric heating mantle.

The liquid is then distilled with stirring and with complete liquid reflux for the selected period of time, after which the liquid is analyzed for TSOC.

Example 1 In runs 1-2, 220 gram samples of a spent sulfuric acid (72 wt. % H2SO4), withdrawn from a process for the hydration of n-butene to form the corresponding alcohols, and containing the indicated concentrations of organo-sulfonic acid impurities and TSOC, is charged to separate 500 ml 3-neck round bottom flasks, each equipped with a thermometer, a water-cooled condenser open to the atmosphere, a magnetic stirring bar and a pressure-equalized dropping funnel which is charged with 40.7 mls of 30% hydrogen peroxide. In Run 1, the acid is diluted with water to a strength of 60 wt. % H2SO4.The liquid in each flask is heated to a temperature of 1 250C by means of an electric heating mantle, and the hydrogen peroxide is added to the sulfuric acid dropwise in order to control the resulting exothermic reaction and to maintain the liquid temperature at 1 25+30C. Addition of the peroxide is completed in about 1 5 minutes, and the resulting reaction mixture is then cooled to room temperature and weighed. A sample of the acid before and after addition of the peroxide is taken and analyzed forTSOC and organosulfonic acid impurities.

Thereafter, the liquid in Run 1 is distilled using the above-described procedure to concentrate the acid to 72 wt. % H2SO4. The reconcentrated acid is then withdrawn from the reaction flask and passed to a separate flask wherein it is subjected to the above-described heat soaking treatment at a temperature of 1 780C for a period of 4 hours to determine the degree of "coking", i.e., the amount of carbonaceous solids formed by thermal degradation of the TSOC in the heat-arranged sulfuric acid.

The liquid in Run 2, after the H202 addition, is diluted with sufficient water to bring the acid concentration down to 60 wt. % H2SO4, and the diluted sample is then distilled, using the abovedescribed procedure, to reconcentrate the acid to 72 wt. % H2SO4 and thereby provide a thermal history comparable to the acid sample in Run 1. Thereafter, the reconcentrated acid is subjected to the same heat soaking treatment as described for Run 1.

In order to illustrate the improvement achieved by the process of this invention in lowering the amounts of carbonaceous solids formed in such impure acids, a separate series of runs is performed in which the impure concentrated sulfuric acids (72 wt. % H2SO4), containing the indicated concentrations of total soluble organic carbon and organo-sulfonic acids, and which have not been treated in accordance with the process of this invention, are first diluted with water to a 60 wt. % H2SO4 and then distilled and thereby reconcentrated to 72 wt. % to provide a comparable thermal history to Runs 1-2. The reconcentrated samples are then subjected to the above-described heat soaking treatment, again at 1 780C for 4 hours.

The data thereby obtained are set forth in Table I below.

Table I H2O2 treatment (30%H2O2) Heat soak treatment initial: 30% H2O2: Post-treatment Initial: Post-treatment: Run TSOC RSO3H(1) Gms. Complete-Oxid, TSOC RSO3H TSOC RSO3H TSOC RSO3H % Rate of No. (ppm) (ppm) added equivalent (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) Coking(2) coking(3) A B C D E F G H I J K L 1 7143 22930 4.0 4.1 3187 10230 2537 8140 2250 7220 11 0.07 2 7629 24490 4.0 4.3 2352 7550 2321 7450 2069 6640 11 0.06 3 - - - - - - 7680 24650 1828 5870 76 1.46 4 - - - - - - 4447 14270 1698 5450 62 0.69 5 - - - - - - 3500 11230 1446 4640 59 0.51 6 - - - - - - 2250 7220 682 2190 70 0.39 7 - - - - - - 900 2890 350 980 61 0.14 8 - - - - - - 484 1550 221 710 54 0.07 "TOSC"=total soluble organic carbon; ppm by weight (1) ROS3H=organo-sulfonic acid;R=hydroxybutyl; ppm by weight (2) % coking, K=[(G-1)#G]x100 (3) rate of coking, L [(gms/hr)/1000 gms of solution]=(G-1)#4000 As can be seen from the data reported in Table I, the hydrogen peroxide partial oxidation treatments of Runs 1 and 2 produces sulfuric acids of greatly enhanced thermal stability. Only 11 wt. % of the TSOC in the sulfuric acid subjected to H202 treatment in Runs 1 and 2 is thermally degraded to non-soiuble carbonaceous solids in the subsequent heat soak treatment. By contrast, from about 54 to 76 wt. % of the TSOC present in the spent sulfuric acid streams of Runs 3 to 8, which are not treated in accordance with this invention, is thermally degraded into non-soluble carbonaceous solids in the heat soaking treatment.In addition, the rate of coking (i.e., the grams of carbonaceous solids formed in the heat soaking test per hour in 1 ,000 gms of solution) in Run 1 and 2 is also far less than the rate of coking for the heat soaked sulfuric acid streams in control Runs 3-5 which contained even greater initial TSOC levels and is still far less than the rate of coking for the heat-treated acids of Runs 6 and 7 containing lower initial TSOC levels.

Therefore, at equivalent TSOC levels, the process of this invention, which can be used in a batchwise, semi-continuous or continuous manner, allows one to operate an olefin hydration process with less attendant coking, and hence less carbonaceous depositions to foul process equipment, than could be tolerated in the absence of acids having such improved thermal stabilities. As a consequence, the process ot this invention allows operation of the olefin hydration process with "dirty acid", e.g., acids having up to about 2Q,000 ppm, preferably from about 500 to 1 5,000 ppm, more preferably from about 1,000 to 10,000 ppm of total organic carbon (calculated as elemental carbon) in the effluent from the reaction zone without significant carbonaceous fouling problems.Thus, the invention removes the need to treat spent sulfuric acid to remove all soluble organic carbon to produce "white acid" in order to avoid the fouling problem as has been thought essential by the prior art.

Preferably, the acid streams treated by the process of this invention form carbonaceous solids, when exposed to elevated temperatures (e.g., 1 50 to 1 800 C), at a rate which is at least about 50%, and more preferably at least about 90%, less than the rate in which such solids would be formed under such conditions in the untreated acid stream.

It will be obvious that various changes and modifications may be made without departing from the invention and it is intended, therefore, that all matter contained in the foregoing description shall be interpreted as illustrative only and not limitative of the invention. For example, as an alternative embodiment to that illustrated in Figure 2, and a preferred embodiment of this invention, a sidestream acid containing at least about 500 ppm organosulfonic acid impurities can be withdrawn from concentrator 30 above or below the acid feed conduit 24 and passed to contacting zone 70 for treatment with the selected oxidizing agent according to the process of this invention, as described above, to form partially oxidized organic compounds from the organo-sulfonic acid impurities. The thus-treated acid stream can then be returned from zone 70 to concentrator 30 via conduit 73, as described above.

In yet a further, most preferred embodiment of this invention, the selected oxidizing agent can be added directly to one or more points of the acid concentrator, e.g., concentrator 30 in the embodiment of Figures 1 or 2, in which case the desired partial oxidation of the organo-sulfonic acid impurities occurs in situ in the acid concentrator and the more volatile oxidation by-products are then removed as overhead from the acid concentrator and a concentrated sulfuric acid is formed, and is withdrawn as a bottoms product.

Claims (9)

Claims

1. A process for improving the thermal stability of spent sulfuric acid streams formed in the catalytic hydration of olefins to prepare alcohols and containing organo-sulfonic acid impurities which comprises contacting the spent sulfuric acid stream with an oxidizing agent selected from the group consisting of ozone, hydrogen peroxide, sources of chlorate, peroxydisulfate, and mixtures thereof, said oxidizing agent being employed in an amount of less than one compiete-oxidation stoichiometric equivalent for each equivalent of the sulfonic acid impurity in said spent acid stream, to form partially oxidized organic compunds therefrom and thereby provide a treated sulfuric acid stream of increased thermal stability.

2. The improved process of Claim 1 wherein the organo-sulfonic acid impurities are present in the spent sulfuric acid stream in an amount of at least about 500 ppm by weight.

3. The improved process of Claim 1 wherein the treated spent sulfuric acid stream containing said partially oxidized organic compounds is treated at elevated temperature to volatilize and remove at least a portion of said partially oxidized organic compounds.

4. The improved process of Claim 1 wherein the spent sulfuric acid stream comprises from about 45 to 99 weight percent H2SO4.

5. An improved process for preparing alcohols which comprises: (a) absorbing an olefin in an absorbing zone with an aqueous concentrated sulfuric acid solution to form an alkyl ester of the sulfuric acid corresponding to said olefin; (b) recovering a liquid stream from said absorbing zone containing said sulfuric acid alkyl ester and contacting said recovered liquid with water for liberation of the corresponding alcohol; (c) passing the resulting diluted liquid to an alcohol generation zone for recovery of said alcohol as a vaporous product, thereby forming a spent sulfuric acid stream containing from about 40 to 55 wt. % sulfuric acid and at least about 500 ppm by weight of organo-sulfonic acid impurities; characterized by: (d) contacting at least a portion of said spent acid in a contacting zone with an oxidizing agent as set forth in claim 1; and (e) recovering an acid stream containing said partially oxidized organic compound from said contacting zone and passing said recovered stream, in combination with the remaining portion of the spent sulfuric acid stream not treated in said contacting zone, to an acid concentrator wherein aqueous vapors are removed to form a concentrated sulfuric acid solution of enhanced thermal stability suitable for recycle to the absorbing zone.

6. An improved process for preparing alcohols which comprises: (a) absorbing an olefin in an absorbing zone with an aqueous concentrated sulfuric acid solution to form an alkyl ester of the sulfuric acid corresponding to said olefin; (b) recovering a liquid stream from said absorbing zone containing said sulfuric acid alkyl ester and contacting said recovered liquid with water for liberation of the corresponding alcohol; (c) passing the resulting diluted liquid to an alcohol generation zone for recovery of said alcohol as a vaporous product, thereby forming a spent sulfuric acid stream; (d) passing said spent acid stream to an acid concentrator wherein the spent acid is distilled for removal of aqueous vapors to form a concentrated spent acid containing from about 45 to 99 wt. % sulfuric acid;; characterized in that after said steps a, b, c, and d, one of the following e, f, or g is carried out: (e) withdrawing an acid sidestream from said acid concentrator containing at least about 500 ppm by weight of organo-sulfonic acid impurities, contacting said acid sidestream in a contacting zone with an oxidizing agent as set forth in claim 1; and recycling at least a portion of the thus-treated sulfuric acid sidestream to said acid concentrator; or (f) introducing into said acid concentrator, which receives from the alcohol generation zone a spent sulfuric acid stream containing at least about 500 ppm by weight of organo-sulfonic acid impurities, an oxidizing agent as set forth in claim 1; or (g) passing at least a portion of concentrated spent acid containing at least about 1 500 ppm by weight of organo-sulfonic acid impurities to a contacting zone and contacting said acid stream therein with an oxidizing agent as set forth in claim 1; and subjecting at least a portion of the thus-treated sulfuric acid stream to conditions of temperature and pressure such as to volatilize and remove at least a portion of said partially oxidized organic compounds which have a higher volatility than water or which co-distill therewith; thereby forming a sulfuric acid stream of increased thermal stability suitable for recycle to said absorbing zone.

7. The process according to claims 1,5 or 6 wherein a temperature of from about 70 to 1 900C is employed in the contacting with the oxidizing agent.

8. The improved process of claims 1-7 wherein the organo-sulfonic acid impurities comprise hydroxy-alkyl-sulfonic acid, alkenyl-sulfonic acid or mixtures thereof.

9. The improved process of claims 1-8 wherein the number of carbon atoms in the organo- moiety of the organo-sulfonic acid impurities corresponds to the number of carbon atoms in the olefin.