US3126331A - Purifying hydrocarbons - Google Patents

Description

March 24, 1964 P. s. LANDls ETAL PURIFYING HYDROCARBONS Filed Oct. 5, 1961 United States Patent Ontice 3,126,331 Patented Mar. 24, 1964 The present invention relates to the removal of deleterious substances from hydrocarbons or the conversion of these substances to relatively innocuous products. It is specifically directed .to rendering innocuous certain unsaturated organic cyclic compounds, especially oxygen-l ated and sulfonated aromatic compounds and nitrogencontaining heterocyclic compounds (e.g. pyrroles, phenols, thiophenols, naphthols, indoles, disuliides) any one of which may be present as an impurity in hydrocarbons, such as gasoline, kerosine and fuel oil. It is well known that many of these compounds when present as impurities increase the formation of sludge, color bodies, and of odoriferous compounds during storage of the desired hydrocarbon product. Additional problems arise because of their corrosive action against metal walled containers and pipes, and also because of their lead depreciating properties when present in gasoline; this is especially true for thiophenols.

These compounds are presently being removed by methods which are costly and sometimes relatively ineffectively. Quite often these processes result in products which are almost as deleterious as the original impurities and which are difficult to remove from the desired hydrocarbons. In addition, the treating agent itself may be harmful if left in the hydrocarbon, and there may be diiiiculties is removing it.

As an example, cracked gasoline contains phenols and mercaptans, such as thiophenols, in comparatively high concentrations. These are now being removed by reacting the gasoline with caustic solution, caustic and solutizer solutions, or caustic solution with lead suliide. These processes add further quantities of undesirable water to the gasoline, which must later be removed, as well as caustic and/ or metal mer-captides which are also deleterious to the finished product. The mercaptans are converted to `the disuliides by the lead sulde treatment, commonly known as the Bender Process; the disulfides are only slightly less detrimental as regards octane number depreciation, to lthe final gasoline product, than are the thiophenols.

A method has been sought which does not involve the necessity of adding to the hydrocarbons new, pernicious impurities, but which does effect the removal of the original impurities. This method should result in a product containing the desired hydrocarbons, Without any impurities, or with impurities that are, at worst, inert but which in some cases may even complement the properties of the hydrocarbon.

The present novel process is designed to remove or to rende-r harmless certain harmful impurities which may be present in hydrocarbons. This process accomplishes this aim without incurring the risk of adding to the hydrocarbon new impurities which are equally undesirable in the final product. It is especially directed against those impurities which cause product degradation in storage. The process is also efiective against some of the agents which cause lead depreciation in gasolines.

It has been found that by reacting these impure hydrocarbon which contain low, but still harmful, concentrations of the above-described impurities, with an excess of a lower parafnic alcohol (C1-C4) at about 500 F. to about 1100 F. in the presence of alumina or other solid acid-type catalyst, the above-described deleterious impurities may be converted and removed or converted to relatively harmless materials which may remain in the final product.

To take the example of impure cracked gasoline containing phenols, mercaptans (especially thiophenols) and disuliides, the lower paraiinic alcohol, which is added as a reagent in this process, is not itself deleterious to the `final gasoline product, and need not be removed if it is not convenient to do so. Thi-ophenols as well as the aliphatic mercaptans in cracked gasoline are converted to the thioether, for example, phenylthiomethane (1C6H5-S-CH3), rather than to the disulfide as in commercial practice. Any disuldes already present are also converted to the sullide form. The sulfide is more stable than the disuliide and does not have the tendency `to dissociate back to thiophenol. Fur-ther, and even more important, as shown by Table I the sullide does not have as great a lead depreciating effect as either the mercaptan or disulde forms.

1 Kalichevsky and Stagner, "Chemical Rclning of Petroleum, 2d edition, Reinhold Publishing Gorp., 1942.

.The phenolimpurities in a hydrocarbon stream are converted to a heavy high boiling point poly-alkylated phenol compound which may be easily separated out by distillation.

The figure illustrates diagrammatically an example of a process which incorporates the new invention. Conduit 2 leads into :fractionator 3 which has a conduit 4 for taking off a bottoms cut, a middle oli-pipe 5, and an overhead conduit 6. Conduit 6 passes to a mixing valve 3, which may be replaced by a mixing tank or equivalent blending device. Conduit 7 similarly leads to mixing valve S. Conduit 9 continues from the mixing valve 3 through the heater lll. Conduit 1-1 leads from heater 1d to the catalytic reactor 12. Reactor `12 is packed with a solid acidic catalyst such as silica-Zirconia, silica-magnesia, silica-boria, silica-titania, alumina-boria, alumina, boria, silica-alumina, silica and so forth. Reactor unit 12 may be a single reactor vessel or several units in tandem or parallel combination. Conduit 13 connects fractionator ylili with the catalytic reactor 12. Fractionator 14 has an overhead pipe 15 which leads to condenser 16 to which is attached overhead gas vent '19, conduit 17 and recycle conduit 18 which leads back to fractionator 14. Conduit 2li leads from fractionator 14 to storage pot Z2 and recycle conduit 21, which returns to 1fractionator 14. Bottoms pipe 2.3 leads from fractionator y14.

The above-described apparatus may be used for the treatment of almost any hydrocarbon, however, it is especially useful and best adapted for the treatment of complex mixtures of hydrocarbons such as petroleum fractions. An excellent example is the treatment of the eilluent from a catalytic cracking unit.

The total effluent may be treated or, as in the figure, it may be fractionated, and only the light fraction, boiling below about 650 F., may be treated. A middle cut, boiling between 650 F. and 800 F., may be recycled to the catalytic cracking unit. The light fraction of the cracked eluent contains, as impurities, phenols, thiophenols, pyrroles and other compounds which, on standing, tend to form sludge and to discolor the hydrocarbon. An excess of methanol is added through line 7 from a storage tank not shown, in amounts preferably about 100 to 500 percent in excess of that required to completely react with the impurities, and mixed with the hydrocarbon in mixing valve 8. If necessary, the mixture may be heated to the required temperature, in the range of 00u F. to about 1l00 F., preferably about 700 F. to about 1000 F., in heater 10. The reaction mixture is passed through the catalytic reactor which is kept at the proper temperature by heating or cooling means not shown.

The reaction product is then fractionated into an overhead gasoline stream from which the non-condensables are vented in the condenser, a middle heavy naphtha cut, and a bottoms cut containing some naphtha, or light fuel oil, and the heavier reaction products.

The following examples will further illustrate specific embodiments of the process without serving to limit the invention to any specic embodiment described.

EXAMPLE 1 Raw, dehexanized, cracked gasoline prepared by conventional catalytic cracking methods is mixed with 2% by volume methanol and passed over F-lO alumina, a granulated commercial alumina (specific area of 100 m.2/ gm., 99% alumina with small amountsl of other oxides and 0.58 percent of chlorine), at 720 F. to 760 F. at a liquid hourly space velocity of two. The phenol content was reduced from an initial concentration of 2010 parts per million (ppm.) to a final concentration of 71 p.p.m. This is considered a low nal concentration when using conventional treating. In the halogen-containing F-lO alumina, the halogen is thought to be present as an impurity in View of its minor concentration of less than 1% by Weight.

EXMIPLE 2 Untreated number two fuel oil, as dened in ASTM specification D396-60T, is blended with 1.25 percent by volume of methanol and passed over F-lO alumina at 710 F. to 790 F., at a space velocity of 1.8. The phenols content was reduced from 1300 p.p.m. to 90 p.p.m.

Table 1I, below, tabulates the results of the above examples:

TABLE II Cracked Gasoline #2 Fuel Oil Initial Final Initial Final Ihenols, p.p.m 2,010 71 1,300 90 Percent N 0.022 0. 014 0.018 0. 012 Percent S 0. 27 0. 25 0. 37 0. 30 Bromine N o 58 57 3.0 3.2

EXAMPLE 3 A high pyrrole content fuel oil fraction from a catalytic cracking unit Was blended with two percent by volume of methanol and passed over F- alumina (space velocity=3) at 895 F.-925 F. The stability test (48 hours at 205 F.) sediment values were reduced from 107 nig/l. to 31 mg./l.

4i EXAMPLE 4 Pure hydrocarbons containing small amounts of phenol as an impurity were treated with methanol over F-lO alumina at 752 F., at a liquid space velocity of 2. Table I shows the results:

TABLE III Percent Concen- Percent Concentration of Components tration in Product 1n Feed Hydrocarbon Hexamethyl and Pentamethyl Benzene eovery,

Phenol Methanol Hydrocarbon Phenol Percent 94.5-toluene Btl-toluene 79-toluene, heptane, oetenc-l.

nil nil nil say-sv SSE EXAMPLE 5 Pure hydrocarbons, including toluene and heptane, containing small amounts of thiophenol were treated with methanol over F10 alumina at 707 F. The mercaptan sulfur was drastically reduced as indicated in the accompanying Table IV.

TABLE IV Reactions of Tlzoplzenol in Hydrocarbons With Methanol Over Alumina Analysis- Mercaptan S (p.p.m.)

Reaction Conditions Reactants Catalyst Tgrlnp., LHSV Before Alter Run l:

Toluene, g Thiophenol, 2 g. Methanol, 5 g un 2:

Heptane, 95 ec. Thiophenol, 1 cc.- Methanol, 5 ce.

The above examples are cited merely to illustrate variousl applications for the invention, and should not in any way be construed as serving to limit the scope of the invention.

It is equally within the scope of the invention to substitute any of the following solid catalysts, or others of similar type, for the halogen-containing alumina used above: silica-zirconia, silica-titania, silica-magnesia, silica-thoria, silica-boria, alumina-boria, silica, silica-alumina.

Similarly the temperatures may be varied within the range 500 F.1100 F. as stated earlier.

This new process offers important advantages over the previous chemical methods of removing these impurities. There is no danger of adding water to the hydrocarbons, which tend to form hard-to-break emulsions. This is especially true when aqueous caustic solutions are used.

The earlier methods for converting the thiophenols usually required the addition of sulfur or sulfdes. This sometimes resulted in an increase in the total sulfur content of the hydrocarbons, if extreme care was not exercised, and also resulted in the formation of the less desirable disulfides.

Treatment with paraffnic alcohols does not cause this trouble. If it is necessary that the alcohol should not remain in the hydrocarbon, it is possible to choose an alcohol whose boiling point is not close to that of the hydrocarbon product; it may then be easily distilled and fractionated. However, in many cases, especially where the hydrocarbons are intended for use as fuel, the methanol may be left in the product to improve its properties. Methanol is often added to gasoline to improve its characteristics, especially to prevent carburetor icing in cold weather. In regard to gasoline, it has further been found that formaldehyde, which is useful as a lead appreciator, is sometimes one of the products from this process.

Other by-products of this purification process are polyalkylated aromatic compounds. These compounds are not only easily separable from lighter hydrocarbons, such as in the gasoline range, but in certain circumstances may remain as part of the final product, such as in fuel oils.

This new process will probably find great use in the petroleum refining field. It may be used for treating both straight-run petroleum fractions and the effluent from the various catalytic or thermal cracking, reforming, alkylating and other processes which are presently being used in reiineries. By-products from coking ovens, such as benzene or toluene streams, which may be contaminated by some of the above impurities, may also be satisfactorily treated by the novel process of this invention. It will of course be practicable to employ this process for use in the purification of many hydrocarbons which contain these undesirable sludge, odor, and color producing compounds.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and Variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

What is claimed is:

l. A process comprising mixing an impure hydrocarbon having at least one impurity which in storage tends to cause a harmful change in the properties of said hydrocarbon, with an amount of a paraflinic alcohol having fewer than five carbon atoms in excess of that required to completely react with all of the above-described irnpurity present in the hydrocarbon, and passing the mixture of alcohol and hydrocarbon over a solid, acid-type catalyst at a temperature of 500 to 1100 F.

2. The process of claim 1, wherein the hydrocarbon contains as an impurity at least one of the unsaturated organic cyclic compounds selected from the group consisting of: hydroxyaromatics, mercaptans and heterocyclic nitrogen compounds.

3. The process of claim 1, wherein the lower parainic alcohol is selected from the group consisting of methanol and ethanol and is added in an amount 100 to 500 percent in excess of that required to completely react with the impurity.

4. The process of claim 1, wherein the solid acid-type catalyst is selected from the group consisting of halogencontaining alumina, alumina, silica, alumina-silica, silicazirconia, silica-thoria, silica-magnesia, silica-boria, silicatitania, alumina-boria, and boria, said halogen-containing alumina having said halogen present as an impurity.

5. A process for treating a petroleum fraction comprising mixing with an impure distillate fraction having sludge, odorand color-producing impurities, an amount of methanol about 100 to 500 percent in excess of that required to completely react with the sludge-, odorand color-producing impurities and passing the mixture of fraction and methanol over a solid halogen-containing alumina catalyst at a temperature in the range of about 700 F. to 1000 F., said halogen-containing alumina having said halogen present as an impurity in a minor concentration of less than 1% by weight.

6. The process of claim 5, wherein the petroleum fraction is the part of the effluent from a catalytic cracking unit boiling below about 650 F.

7. A process for treating petroleum fractions comprising mixing a petroleum fraction boiling below about 650 F. containing as an impurity at least one of the organic, unsaturated cyclic compounds selected from the group consisting of: hydroxyaromatic compounds, thiophenols, pyrroles, and aromatic disulfides, with an amount of methanol to 500 percent in excess of that required to completely react with all of the above-described impurity present in the fraction, passing the mixture of alcohol and fraction over a solid, acid-type catalyst at a temperature in the range of about 700 F. to about 1000 F. to form a treated effluent, fractionally distilling said treated ef'liuent into a gasoline fraction, a heavy naphtha fraction and a bottoms fraction containing light fuel oil and the heavier reaction products from the methanol treatment.

8. The process of claim 7, wherein the solid, acid-type catalyst is selected from the group consisting of a halogen-containing alumina catalyst, alumina, silica, aluminasilica, silica-zirconia, silica-thoria, silica-magnesia, silicaboria, silica-titania, alumina-boria, and boria, said halogen-containing alumina having said halogen present as an impurity.

9. A process for treating a petroleum fraction boiling below about 650 F. and containing an impurity deleterious thereto in the form of at least one organic unsaturated cyclic compound selected from the group consisting of hydroxyaromatics, thiophenols, pyrroles, heterocyclic nitrogen compounds, and aromatic disulfides which comprises adding to said fraction a paraflinic alcohol having l to 4 carbon atoms in an amount which is 100 to 500% in excess of that required to react completely with all of said impurities, passing the resulting mixture at a temperature in the range of about 500 to about 1100o F. over a solid acid-type catalyst selected from the group consisting of halogen-containing alumina, alumina, silica, alumina-silica, silica-zirconia, silica-thoria, silica-magnesia, silica-boria, silica-titania, alumina-boria, and boria, thereby to react said impurity with the alcohol and to convert the impurity to a product which is innocuous to said fraction, said halogen-containing alumina having said halogen present in an amount of less than 1% by weight.

10. A process for treating a light fraction from a catalytic cracking unit, said fraction boiling below about 650 F. and containing an impurity deleterious thereto in the form of at least one organic unsaturated cyclic compound selected from the group consisting of hydroxyaromatics, thiophenols, pyrroles, heterocyclic nitrogen compounds, and aromatic disulfides, which comprises adding to said fraction a paraffinic alcohol having 1 to 4 carbon atoms in an amount which is in excess of that required to react completely with all of said impurity, passing the resulting mixture at a temperature in the range of about 700 to about 1000 F. over a solid acid-type catalyst selected from the group consisting of halogen-containing alumina in which said halogen is present in minor concentration, alumina, silica, alumina-silica, silica-zirconia, silica-thoria, silica-magnesia, silica-boria, silica-titania, alumina-boria, and boria, thereby to react said impurity with the alcohol and to convert the impurity to a product which is innocuous to said fraction, distilling tne treated mixture into a gasoline fraction, a heavy naphtha fraction, and a bottoms fraction containing light fuel oil and heavier reaction products from said alcohol reaction.

1l. A process for treating a cracked gasoline containing an impurity deleterious to the gasoline in the form of at least one organic unsaturated cyclic compound selected from the group consisting of hydroxyaromatics, thiophenols, and aromatic disulfides which comprises adding to said gasoline a paraffinic alhohol having 1 to 4 carbon atoms in an amount which is 100 to 500% in excess of that required to react completely with all of said irnpurity, passing the resulting mixture at a temperature in the range of about 700 to about l000 F. over a solid acid-type catalyst selected from the group consisting of halogen-containing alumina, alumina, silica, alumina- References Cited in the ille of this patent UNITED STATES PATENTS Mueller June 23, 1942 Myers May 29, 1956 Junk et al Feb. 5, 1957 Schmidt June 18, 1957

Claims (1)

1. A PROCESS COMPRISING MIXING AN IMPURE HYDROCARBON HAVING AT LEAST ONE IMPURITY WHICH IN STORAGE TENDS TO CAUSE A HARMFUL CHANGE IN THE PROPERTIES OF SAID HYDROCARBON, WITH AN AMOUNT OF A PARAFFINIC ALCOHOL HAVING FEWER THAN FIVE CARBON ATOMS IN EXCESS OF THAT REQUIRED TO COMPLETELY REACT WITH ALL OF THE ABOVE-DESCRIBED IMPURITY PRESENT IN THE HYDROCARBON, AND PASSING THE MIXTURE OF ALCOHOL AND HYDROCARBON OVER A SOLID, ACID-TYPE CATALYST AT A TEMPERATURE OF 500 TO 1100*F.

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