US2376078A - Treatment of light hydrocarbons - Google Patents

Description

`G. G. OBERFELL ET AL Filed Oct. 5, 1942 f May 15, 1945.

TREATMENT OF LIGHT HYDROCARBONS molecular weight and 4of knock and volatility characteristics, suitable for Patented May 15, 1945 UNiTEo sTATEs PATENT oFFicE v,2,376,073 TREATMENT F LIGHT HYDRooARBoNs George G. Oberfell and Jean PiJones, Bartlesville, Okla., assignors to Phillips Petroleum f Company, a corporation of Delaware Application October 5, 1942, Serial No. 460,796

2 Claims.

This invention pertains to the treatment of hydrocarbons to produce hydrocarbons of higher greatly improved antiuse as motor and aviation' fuels, and as blending 5 components in such fuels. It relates more particularly to the molecular rearrangement and molecular @combination of hydrocarbons of low molecular Weight having three to seven carbon atoms or more per molecule, through two or more of a series of reactions known as isomerization, dehydrogenation, polymerization, alkylation and hydrogenation, to produce higher molecular weight hydrocarbons of more complex structure possessing higher anti-knock properties and volatilities within the motor and aviation fuel range.

This application is a continuation-impart of our application Serial No. 383,430, filed March 14. 1941.

In the production and refining of crude petroleum and natural gas large amounts of both saturated and unsaturated low-boiling hydrocarbons of molecular weights up to seven or eight carbon atoms and higher are produced. The lighter of these hydrocarbons, those containing three and four carbon atoms, are relatively high in antiknock rating but their volatilities are too high for inclusion in motor or aviation fuels used by present-day internal combustion engines. The heavier hydrocarbons mentioned are generally of the simpler, straight-chain structure, low in antiknock properties. Those possessing branchedchain structure are of the simpler type, and those of six or more carbon atoms per molecule are generally also of low anti-knock properties. a general rule the more complex a hydrocarbon molecule which boils in the motor fuel range the higher its anti-knock rating and the more valuable it is for such fuel. Therefore a process which offers a cheap, economical and efficient means for converting hydrocarbons of low molecular weight and anti-knock properties into those having the desired volatility and anti-knock characteristics. is of great commercial importance to the industry. Such an economical, efficient process is the basis of this invention.

As to reactivity the straight-chain paraffin hydrocarbons show the least tendency to enter into reaction with other hydrocarbons or into any sort of reaction with any other chemical. In order to increase the reactivity of these straight-chain hydrocarbons it is necessary to change them into isoparaiinic structure, or to dehydrogenate them to oleflnic structure having fewer hydrogen atoms per molecule than has the paraiiin of the same number of carbon atoms. Both the isoparains and the oleiinsnshow greatly increased reactivity isomeric paraiins,

these changes in fected. Y

Furthermore, in production of these light hydrocrabons in the modern refinery or natural gasoline plant, the proportions of normal and isomeric parailins and of olens may vary widely. In the alkylation process to be described later, wherein isoparaflns are reacted, it is necessary that one molecule of an olen be present to combine with each molecular of isoparaiiin reacted. Therefore, unless the proportions of isoparafn to olen in the light products from a renery are in the desired ratio it is necessary to provide additional material of the molecular structure required to supply the deciency of one or the other. This deficiency may be made up from an outside source if such is available, otherwise it is necessary to change the molecular structure or configuration of some of the material which is available in excess or that excess of material cannot be utilized.

Also, as stated before, the normal parans enter very reluctantly into reaction unless their molecular structure is changed by suitable methods. these light hydrocarbons is often vpractically unutilizable unless treated to change it to a more reactive form. This is accomplished either by dehydrogenation or by isomerization, or both. In the simple dehydrogenation of paraiins to olens a molecule of hydrogen is released for each olefin molecule produced. To exercise the greatest economy and conservation of resources it Vis desirable to bring' this hydrogen again into combination with the hydrocarbons produced by polymerization of the olens insofar as is possible, a step which is accomplished by hydrogenation, preferably with the aid of ecient catalysts. A One main object of this invention therefore is to provide a process of utmost flexibility to convert to more useful hydrocarbons suitable for premium aviation and motor fuels light hydrocarbons of two to seven carbon atoms per molecule, or more, which may contain normal and and/or olefins in any proportions and to so process these hydrocarbons that the entire available production may be utilized to the greatest advantage.

Another object is to provide methods by' which the molecular structure of available hydrocarbons may be changed and altered so as to produce the desired proportions of the different types of hydrocarbons to meet the requirements of the products and to provide the widest flexibility in operation regardless of the composition of the original materials available.

A further object of our invention is to produce a normally liquid hydrocarbon mixture having characteristics of vapor pressure, volatility, boiling range, octane number, sulfur contenti etc., to

molecular structure may be ef- A Therefore the normal paran content of suit it for use as an automobile or aviation fuel.

Other objects and advantages will become apparent to one skilled in the art from the accompanying disclosure and discussion.

As one modification of our process alkylation and polymerization reactions are carried out in the same reaction vessel, simultaneously. Using trated hydrouoric acid may also be used, al- A though a proper correlation of other reaction conditions to produce both alkylation of isoparaffins and an appreciable amount of polymerization, so that the product contains an appreciable amount of olefinic polymers, is often somewhat difficult to maintain.

Heretofore, in the |preparation of premium motor fuels, it has been considered desirable to have essentially parafiinic products, or at least products essentially free of unsaturates such as olefins, cycloolens, and the like. However', it has more recently been found that when using liquidcooled engines, especially in service requiring frequent and sometimes sustained acceleration, the presence of such unsaturates is not only permissible but often even desirable. In such an instance advantage may be taken of this modification of our invention to produce, in a single operation, aliphatic hydrocarbon material containing substantial and controllable amounts of isoparafiins and isoolens, both of high octane number. At the same time alkylation equipment designed to produce a given amount of a completely paraffinic product can produce greater amounts per unit time of such a mixed product by reason of the greater throughput permitted by a shorter reaction time. When a more highly paramnic product is desired than that resulting from such an operation, the product, or fractions thereof, may beA subjected to non-destructive hydrogenation. Such an operation is simple and can be carried out in simple equipment with hydrogen produced in a previous dehydrogenation step in the process, so that often the net result is an increased yield of a parainic product from existing equipment at less expense of money and time than would result from a similar increase in capacity by installation of additional alkylation equipment.

Such an alkylation-polymerization operation, or polyalkylation, is carried out under conditions such that the concentration of unreacted olefins in the reaction zone is higher than is permitted in usual paraffin alkylation operations, and at somewhat higher temperatures. Generally a greater ow rate, or lower reaction time, is also used. Preferably the concentration of unreacted olefin is maintained above ten per cent by weight. although it should not be above about 40 or 45 per cent by weight. The reaction time, temperature and pressure will be dependent, in each case, upon the catalyst used, its activity, and the reactants, and can be readily determined and established for any particular instance by one skilled in the art. These conditions are best corfill related to sive a normally liquid product containing l0 to 60 'per cent by weight of olenic products of the reaction. Under suitable conditions the initial step of isomerization of norma] parafns present in a mixture of hydrocarbons also may becarried out along with the other steps mentioned above, preferably catalytically in the first section of the combined reaction zone. Such a method permits the utilization of a mixture of normal and isomeric parafiins and oleiins with a minimum of equipment in a simple manner and with the fewest steps. The olelnic polymer formed during the combined reaction may be retained in the mixture of products and used as such. or may be partially or completely hydrogenated catalytically with hydrogen from any source to yield a saturated product of greatly enhanced anti-knock properties.

Another methodof handling a mixture of normal and isomeric parain hydrocarbons is to iractionate the mixture to separate the straightchain or normal paraffin from the isoparafiin. After separation of the normal paraiiln -this stream may be split, part of it being dehydrof genated with a suitable catalyst to supply additional olen charge for the alkylation reaction with the isoparains recovered, while the other part of the vnormal hydrocarbon stream is isomerized catalytically and added to the original isomer stream for use'in the alkylation step. Withany charge stock of light hydrocarbons of any given composition the operator skilled in thc art can easily calculate the proportion of the normal paraffin stream to be isomerized and that to be dehydrogenated. The entire straight-chain fraction may be dehydrogenated and included with the isomer fraction which will combine with the theoretical 'portion of the olen in the alkylation reaction, the remainder of the oleiin present being polymerized in the same or a different step. and hydrogenated in another step if desired, with the hydrogen freed during the dehydrogenation step. The proportion of olen may be any percentage, preferably above ten per cent, in the alkylation-polymerization step.

Reference will now be made to the drawing which forms a part of the specification and which. illustrates diagrammatically by use of a ow sheet an arrangement of apparatus in which our invention may be practiced together with various modifications thereof. The description of this drawing will serve to exemplify our invention and optimum conditions will be given for operation of various process steps.

Referring now to the drawing, a suitable hydrocarbon mixture such as a raw natural gasoline having a composition as indicated in the following table, is passed through pipe I0 Ato an alkali washer Il.

Mol per cent Ethane 1.2 Propane 46 .9 Isobutane 8.4 N-butane 26.4 Isopentane 5.4 N-pentane 4.9 Isohexane 2.9 N-hexane 1.9 Heptane 2,0

The hydrocarbon material may contain substantial amounts of organic sulfur compounds such as mercaptans which are not indicated in the table just mentioned, but which will be distributed throughout the various fractions shown, particularly those of the C4 and heavier hydrocarbons. In the alkali washer II such a sulfur-containing material is contacted with aqueous solution of a suitable alkali such as sodium hydroxide or sodium carbonate which will remove any residual hydrogen sulfide andl also any lower boiling mercaptans, particularly methyl mercaptan. From alkali washer II the hydrocarbon material may be passed through copper sweetening unit I2 wherein mercaptans are converted to disuliides. This operation may be a so-called solid copper sweetening unit in which the liquid -hydrocarbon material is contacted with an absorbent such as fullers earth on which is an aqueous' solution containing copper and chloride ions, such as is found in a solution of copper sulfate and sodium chloride.

Other sweetening treatments known to the art may be used instead, however we have found the one just described to be most eilicient.

From copper sweetening unit I2 the hydrocarbon material is passed to suitable separating means represented by fractlonator I3. By means of such a fractionator, which in reality includes a series of fractionating columns together with normally occurring auxiliary apparatus, the hydrocarbon material is separated into various fractions as will be discussed. Low boiling hydrocarbons such as ethane and perhaps a portion of the propane can be discharged from the system through valved pipe I4. A propane fraction is pipe I5 controlled by valve I6 to a dehydrogenation step, which is preferably catalytic, carried out in dehydrogenator I l. A suitable catalyst may .comprise chromium oxide, preferably a black unglowed chromium oxide, which may be associated with other constituents such as alumina or zirconia or the like and which is preferably on a supporting material such as pumice, dehydrated bauxite, etc. Dehydrogenation can be carried out at a temperature within the range of about 900 to 1100 F, with a contact time such as to produce from to 40% of olens in the eiiiuent material. From dehydrogenator I1 the eilluent is passed through pipe I8 to separating means 20. In separating means hydrogen is separated from hydrocarbon constituremoved through ents and may be discharged through valved pipe 2I. In some instances it may be found desirable to include also apparatus for separating paralns from olefins as by selective solvent extraction, as is known to the art. A propylene-containinig,r material is passed from separating means 20 through valve 2I to conduit 22 for reacting in the polyalkylation step to be described.

An isobutane fraction is removed from fractionator I 3 through pipe 23 and valve 24 to a suitable alkylation unit or polyalkylation unit 25. A normal butane fraction is removed from fractionator I3 through pipe 26 and is passed at least in part through valve 21 to dehydrogenator28 wherein dehydrogenation cipally butenes. ably catalytic and may be carriedtout in the presence of a catalyst such as has been discussed in connection with the operation of dehydrogenator Il and under similar conditions. ture range'within which the dehydrogenation is carried out may be somewhat lower, such as within the range of about 800 to 1050 F. with a similar extent of conversion. From dehydrogenator 28 eluents are passed through pipe 30 to is eiected to form prin- This dehydrogenation is prefer.-v

The tempera- CII the simplest and separating means 3l, the operation of which will be similar to Athat just discussed for separating means 20. Hydrogen is discharged through valved pipe 32. A butene-containing material is passed through valved pipe 33 to unit 2li. The operation in unit may be entirely one of alkylationto produce as highly a parainic product as possible under alkylation conditions, preferably in the presence of a catalyst such as will be readily ascertained by one skilled in the art. However, we prefer to operate unit 25 as a polyalkylation unit under conditions such as have been discussed hereinbefore to produce a product which contains both normally liquid paramn hydrocarbons resulting from alkylation and nor- Thus, we may maintain a relatively high olen concentration such as one substantially above 10% by weight and react the material charged in the presence of a catalyst comprising sodium chloroalurninate at a ternperature between about 300 and 450 F. Eluents of the polyalkylation step pass through pipe tl and are preferably passed through valve 35 to separating means such as fractionator 36. From fractionator it? propane may be removed through valved pipe 3l' and returned to pipe i5 and de- 'hydrogenator il'. for dehydrogenation. An isoa temperature of about 200 to 450 butane fraction may be removed through valved pipe 38 and returned to pipe 23 and unit 25. A normal butane fraction valved pipe l0 to pipe 2t and dehydrogenator 2t. Undesirable low boiling material may be discharged through valved pipe el, and undesired high boiling material may be discharged through valved pipe d2. One or more normally liquid hydrocarbon fractions boiling in the motor fuel range may be removed through suitable pipes represented by pipe i3 and may be passed directly through valve lill for inclusion in a nal motor fuel product. When unit 25 is operating as a pipe it through valve t5 to hydrogenator t6. In hydrogenator llt a hydrocarbon material is reacted With free hydrogen, which may be introduced with valved pipe lll, in the presence of a The reaction may be satisfactorily carried out at F. Hydrogen introduced through pipe il is preferably secured from one of the previous dehydrogenation steps and discharged through pipes 2l and/or 32. The hydrogenated material is passed from hydrogenator It@ through pipe fit and may be passed through valve t9 to pipe d3 for inclusion in motor fuel products.' If it is desired to fractionate this material, it may be sent to suitable yfractionating equipment such as by being passed from pipe 48 through valve 5@ back to separating means 36.

In some instances it may be found expedient tosubject the hydrocarbon effluent of unit Z to pipe Sil through pipe 5I and valve 52 directly to hydrogenator tt, in which case separating means 36 may have as the charge only material which is eil'luent from hydrogenator llt.

An isopentane fraction is removed from fractionator it through pipe 53 and may be passed pipe 1I and valve 12 ,can be operated under conditions similar to those through valve 54 to pipe 43 for direct inclusion in the final motor fuel produced. If desired, a portion of this material may be passed from pipe 53 through valved pipe 55 to pipe 23 and unit 25 for alkylation.

When a sulfur-containing natural gasoline or l straight-run gasoline is charged through pipe IU and is given the preliminary treatment indicated for units Il and l2, the amount of sulfur compounds which will be present in the fractions just discussed will generally be negligible and all of the sulfur will be concentrated in the heavier fractions. Some of this sulfur may or may not in particular cases be in the lower boiling portions of these fractions. When sulfur compounds are present in the lower boiling fractions a normalpentane-and-heavier fraction is removed through pipe 55 from fractionator I3 and may be passed through pipe 51 and valve 5B to desulfurizer 60. In desulfurizer 60 sulfur is removed by many suitable means, preferably by passing the stock in the vapor phase into contact with a catalytic material such as bauxite, brucite, etc. at a temperature between about 500 and r150" F. for a time such as to effect a substantially complete decomposition of sulfur compounds, primarily into hydrogen sulfide and olens with at most only a slight decomposition of hydrocarbon constituents. Hydrogen sulfide may be separated from the effluents by suitable means, such vas distillation or alkali wash, and removed through valved pipe 6I, and the desulfurized hydrocarbon material may be passed through pipe 62 and valve 63 to fractionator 64. If the low boiling fractions do not contain sufficient sulfur compounds to warrant desulfurization at this point, the fraction of normal-pentane-and-heavier may be passed directly through valve to fractionator 64 with desulfurizer omitted. From fractionator 54 a normal pentane fraction is removed through valved pipe 56 and may be passed directly to isomerizer 8D. An isohexane fraction may be removed from fractionator 64 and passed through valved pipe 61 to pipe 43`for inclusion in the final motor fuel product. A normal hexane fraction may be removed through valved pipe 68 and passed to pipe 66 and isomerizer- 80. A heptaneand-heavier fraction is removed through pipe 10. If further desulfurization is desired at this point, or desulfurizer 6D has been by-passed, this heptane-and-heavier fraction may be passed through to a desulfurizer 13 which described for desulfurizer 60. Hydrogen sulfide may be removed through valve pipe 14 and a desulfurized material is passed through pipe 15 and valve 1B to fractionator 11. When desulfurizer 60 has been previously used and has effected a satisfactory extent of desulfurization, desulfurizer 13 may be omitted andthe heptane-andheavier fraction passed through valve 18 directly to fractionator 11. An iso-heptane fraction is removed from fractionator 11 through valved pipe 19, and is passed to pipe 43 for inclusion in the motor fuel product. A normal-heptane-andheavier fraction is removed through valved pipe 8| and is passed to pipe 66 and isomerizer 8U. In some instances it may be desirable to remove from the material passed through valved pipe 8|, an

isooctane fraction, in which case additidnal fracy tionating equipment, not shownfcan be included for use in the process. However, in many instances further fractionation cannot be economically justified and the operation indicated will be found most satisfactory.

In lsomerizer the various hydrocarbon materials charged through pipe 63 are subjected to the action of an isomerization catalyst and converted primarily into parain hydrocarbons having` more highly branched molecular structure. Such isomerization may be carried out in the presence of a catalyst such as aluminum chloride, aluminum bromide, ferrie chloride and the like known to the art, preferably in the presence of small amounts of the corresponding hydrogen halide. Concentrated hydrouoric acid is also an effective and efficient catalyst for this operation. The reaction temperature will generally be in the range of about 200 to 350 F. and the pressure may be such as to maintain a liquid phase or a gas phase as may be found most suitable in any particular instance.. The reaction should be conducted with a reaction time such that about 30 to 50% of the parafns charged undergo reaction. The resulting isoparainic fraction may be removed from isomerizer-80 through valve 82 and passed to pipe 43 for inclusion in the final motor fuel products. Undesired heavy material maybe discharged through valved pipe 83. Low boiling isoparafiins primarily isobutane, may be passed through valved pipe 84 to pipes 38 and 23 and unit 25. Such isbutane may result from decomposition reacton of higher boiling hydrocarbons in isomerizer 8U. In some instances it may be desirable to charge normal butane to isomerizer 80 by removing a portion of the stream passing through pipe 26 through pipe 85 and valve 86, and passing it through valve 81 to pipe 66 and isomerizer 80. In such a case at least a considerable portion of the isobutane which is passed through pipe 84 will be a product of the isomerization of normal butane. of normal butane may be recovered as an independent product of the process. through valve 8H. If desired some normal butane so removed may be included in the nal motor fuel product to produce a desired vapor pressure. l

It will be appreciated that the various separating and Yfractionating units I3, 36, 64 and 11 will be operated so as to effect a production of the fractions having substantially the composition of the hydrocarbons used to identify them, particularly for the lower-boiling fractions. Each such fraction may be associated with small amounts of hydrocarbons in adjacent boiling ranges but such other hydrocarbons should not be present in quantities so large that the fraction cannot be satisfactorily identified as indicated. In some instances the individual fraction may comprise the indicated hydrocarbon ina purity of about ormore. It has also been found that some of the fractions of some natural gasolines and also some straight-run gasolines will include cycloparafns and this is particularly true in connection with some of the higher boiling isoparalnic fractions. Such cycloparafns often contribute to the desired characteristics of the nal motor fuel product. In some types of motor fuels aromatic hydrocarbons are desirable, particularly alkyl benzenes in aviation gasolines. One or more of the dehydrogenation steps may be directed to the production of such aromatics. The various normal parafn fractions have been shown as being isomerized in a single operation4 but it will be understood that one or more fractions may be treated individually in this manner. As a variant, one or more of such fractions, particularly the normal heptane or the normal octane fraction, may be subjected to aromatiza- If desired a substantial amount tion to form alkyl benzenes for inclusion in the l iinal product.

Many other modifications and variations of this invention may obviously be used and can be adapted by one skilled in the art Without departing from the spirit of the disclosure. ,It will be understood that the flow diagram is schematic, that only essential pieces of equipment and conditions have been described, and the reactions and modications are discussed in suiiicient detail to serve as eiiicient guides.

We claim:

1. A process for converting a natural, sulfurbearing saturated hydrocarbon mixture containingl propane and heavier hydrocarbons including normally liquid hydrocarbons Ainto a substantially sulfur-free normally'liquid motor fuel product, which comprises washing said mixture with an alkali to remove low-boiling mercaptans, subjecting the Washed mixture to a sweetening treatment to convert remaining mercaptans to higher boiling disuldes which are higher-boiling than hexanes, subjecting the sweetened mixture to fractional distillation and removing therefrom a propane fraction, an isobutane fraction, a normal butane fraction, an isopentane fraction, a normal pentane fraction, an isohexane fraction, a normal hexane fraction, and a heptanes-andheavier fraction, subjecting said heptanes-andheavier fraction to a catalytic desulfurization at an elevated temperature to convert organic sulfur compounds into hydrogen sulfide and removing same from the process, subjecting the desulfurized material to fractional distillation and removing therefrom an isoheptane fraction, a normal heptane fraction, an isooctane fraction, and a normal octane fraction, each of which is substantially sulfur-free, subjecting said propane fraction to dehydrogenation to form propylene, subjecting at least a portion of said normal butane fraction to dehydrogenation to form butylenes, reacting said propylene and said butylene with said isobutane fraction in a catalytic alkylation step to form normally liquid hydrocarbons boiling in the motor fuel range, subjecting said normal pentane, normal hexane, normal heptane and normal octane fractions to isomerization in the presence of an isomerization catalyst to form more highly branched normally liquid parain hydrocarbons, and blending Iproducts of said alkylation, products of said isomerization, said isopentane fraction, said isohexane fraction, said isoheptane fraction and said isooctane fraction to form a normally liquid hydrocarbon mixture having motor fuel characteristics of vapor pressure, volatility, and boiling range, and having high antiknock characteristicsand a low sulfur content.

2. A process for converting a natural, sulfurbearing saturated hydrocarbon mixture containing propane and heavier hydrocarbons including normally liquid hydrocarbons into a substantially sulfur-free normally liquid motor fuel product, which comprises washing said mixture with an alkali to remove low-boiling mercaptans, subjecting the washed mixture to a sweetening treatment to convert remaining mercaptans to higher boiling disuldes which are higher-boiling than hexanes, subjecting the sweetened mixture to fractional distillation `and removing therefrom a propane fraction, an isobutane fraction, a normal butane fraction, an isopentane fraction, a normal pentane fraction, an isohexane fraction, a normal hexane fraction, and a heptanes-and-heavier fraction, subjecting said heptanes-and-heavier fraction to a catalytic desulfurization at an elevated temperature to convert organic sulfur compounds into hydrogen sulfide and removing same from the process, subjecting the desulfurized material to fractional distillation and removing therefrom an isoheptane fraction and a heavier motor-fuel-range fraction, each of which is substantially sulfur-free, dehydrogenating said propane fraction to form propylene, dehydrogenating at least a portion of said normal butane fraction to form butylenes, reacting said propylene and said butylenes with said isobutane fraction in a catalytic alkylation step to form normally liquid hydrocarbons boiling in the motor fuel range, subjecting said normal pentane, normal hexane, and heavier motor-fuel-range fractions to isomerization to form more highly branched normally liquid paramn hydrocarbons, and blending products of said alkylation, products of said isomerization and said isopentane, isohexane and isoheptane fractions to form a normally liquid hydrocarbon mixture having motor fuel characteristics of vapor pressure, volatility, and boiling range, and having high antiknock characteristics and a low sulfur content.

GEORGE G. OBERFELL. JEAN P. JONES.

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