US1507634A - Process of making gasoline - Google Patents

Description

Sept. `9 1924.' 1,507,634

Ha E. .THoMPsoN PROCESS OF vMAKING' GASOLINE originen Filed Aug. 29. 1921 Patented Sept. 9, 1924.

HAROLD ,n THOMPSON,

OF CLENDENIN, WESTYVIRGINIA, ASSIGNOR T0 CARBIDE &

CARBON CHEMICALS CTORATION, A. CORPORATION O'F NEW YORK.

i l vraocnss or MAKING GAsoLl-NE.

Original application led August 29, 1921, Serial No. 496,321. Divided and this application iiledll September 8,1922.

To all whom t may concern.'

Be it known that I, HAROLD E. THOMP- soN, a citizen of the United States, residing at Clendenin, in the county of Kanawha and State of West Virginia, have invented` certain new and useful Improvements in Processes of Making Gasoline, of which the following is a specification.

This` invention relates to the manufacture, from natural gas, of liquid mixtures of hydrocarbons adapted for use as `motor fuel and for other urposes. An example is the liquid common y known as natural gas gasoline, natural gasoline casing-head gasoline, etc. The object of the'invention is to improve the processes for making such liquids and to improve the products obtained.

This application is a division of my copending application, Serial No. 496,321, led August 29, 1921, which matured into Patent No. 1,429,175, dated Sept. 12, 1922.

Natural gases are essentially mixtures of parain hydrocarbons. Only the lower members of? the paraiin series are present, and the percentages of `the Individual hydrocarbons present usually bear an inverse relation to their molecular weights. Methane always predominates, and in some gases the content of other members of the series is negligible. Those natural gases which are adapted for the production of gasoline, however, contain considerable quantities of ethane', propane, butane. and the heavier hydrocarbons, and it is with such naturally occurring mixtures that the invention is concerned.

In the natural gas or casing-head gasoline industry, the desideratum is to produce a liquid which can be transported and stored at ordinary temperatures and at or near barometric pressure, in receptacles similar to those used for straight-run gasoline, without undue {ire risk or loss by evaporation. In other words, the problem is to keep down the volatility of the prod'- uct, as evidenced 'by the vapor pressure of the liquid at certain temperatures. A 'high yield is of course desirable.

Serial No. 586,811.

Partially because of lack of knowledge of thecompositions of the natural gas used as raw material and of the products and' by-products obtained, the process as now carried out is largely empirical. As the process is practised, a preliminary product is obtained which is so volatile, or wild, that it cannot be safely stored or shipped. The volatility of this liquid is ordinarilyT reduced by the wasteful process known as weathering, which consists in storing the liquid in open tank-s or tanks maintained at a low pressure and permitting ,spontaneous evaporation to go stable residue remains. Thispresults in the loss in the .aggregate of enormous quantities p f hydrocarbon material suitable for gasolne.

By the application of improved methods of analysis, I have found that the excessive volatility or wildness of freshly made casing-head gasoline is due to the presence of ethane and ropane. Even methane Inay be present 1n traces at times.- Butane, which in pure form has a muclrgreater volatility than is permissible' in merchantable gasoline, can be present in casinghead gosoline in large proportions, the entire butane content of the gas treated,

without excessive wildness of the product` because of the solvent effect of the heavierv hydrocarbons present upon it. I have found that inthe natural weathering process a large proportion of the butane passes off before the residue is suiliciently stable. When this condition is reached, propane and even ethane are still present in the residue, while the butane may have been evaporated and lost infamount in large proportion as compared lwith the residual liquid.

My invention comprises a rationaltreatment of material containing the less volatile portions of natural gas, whereby the-material is separated into fractions which do not have more than one common ingredient in substantial quantity. As mentioned above, .the natural weathering process produces a vapor containing ethane,'propane,

on until a sufficiently.

large amounts of butane, and even heavier hydrocarbons, while the residual liquid contains substantial quantities of all these compounds. By my process, I am able to expel substantially all the ethane and propane as vapor while volatilizing only a small quantity of lontane, thus producing a gasoline of as good or-better grade than can be made by natural weathering and at the same time very largely increasing the yield. In man cases I prefer to evaporate a portion o' the but-ane and thus produce a higher-grade or less volatile gasoline, but in such cases butane will be the only hydrocarbon present in substantial quant-ity as a common ingredient in both the expelled vapor and the liquid residue. Even when a portion of the butane is expelled, the product is readily distinguishable from all petroleum distillates employed in the gasoline industry, as these latter contain a much smaller proportion of butane. All the butane might be vaporized, or a portion of the propane might be retained in the residue if desired. Depending on the identity of the hydrocarbon which is thel highest of those in the vaporized portion and the proportion of that hydrocarbon which is evaporated, the vapor pressure of the liquid residue may be adjusted to any desired' value.

Certain procedure in the process now to be described is referred to in the specification and claims as rectili-cation. The term rectification is used herein to describe a process wherein a liquid is boiled, the vapor produced is caused to Contact with a second body of liquid of different composition in. such manner that a second portion of vapor is evolved from the second body of liquid, the second portion of vapor contacts with a third body of liquid which likewise evolves vapor, and so on through a sufficient number of vapor and liquid contacts. Liquid iows from one body to the next in a direction counter to that of the vapor Y flow., and the continuity of the processie maintained by adding liquid to the body from which the final portion of vapor is evolved, the liquid so added being formed, for example, by partial condensation of 'the final vapor. The uncondensed portion of the final vapor, and a continuously-withdrawn portion of the boiling liquid rst referred to, are ordinarily the products sought. It is only with such systematic processes involving repeated liquid and vapor contacts in a series of distinct phases, that the present invention isconcerned.

A complete separation of certain constituents of gas mixtures has sometimes been attempted by a fractional condensation. I have found that complete separation cannot 'be accomplished in this way. In any fractional liqueact-ion process the initial condensation brings down some of the more volatile constituents which' in my process I then remove by boiling and rectification.

For a better understanding of the invention, reference will be made to the accom- 1,70

panying drawing, comprising a diagrammatic illustration of one method of applying my invention.

A typical natural gas gasolineprocess will now be described in connection with the drawing, and the manner in which the roc- 7, where it is brought into contact with an oil of the kind commonly employed for this purpose. The undissolved gas is passed from the absorber to the main 8 while the oil with its dissolved hydrocarbons liows to vent-tank 9 where the pressure on the oil is released by a suitable regulator 9a.

In tank 9, a` pressure of about 60 lbs. per square inch is maintained and as the oil under high pressure iiows into it, a large volume of gas comprising the lighter dissolved constituents is liberated. Using a natural gas of the following composition:

Per cent.

Methane 78.3 Ethane 13.3 Propane 5.6 Butane and less volatile bodies s 2.8

the composition of the gases so liberated may be, for* example, as follows:

v Per cent. Methane 50.1k Ethane 29.8 Propane 16.7 Butane and less volatile bodies 4.3

This gas mixture will be referred to, for convenience, as high-pressure vent gas.

From tank 9 the oil with the substances dissolved therein passes to vent tank 10, in which 3 to 4 lbs. gage pressure may be maintained. The pressure on the oil is released by a suitable regulator 10a. The reduction in pressure causes an additional. evolution of gases which comprise, in general, hydrocarbons heavier than those which constitute the high-pressure vent gas but of. greater volatility than the constituents which remain dissolved n the oil. The analysis ci in the oil are expelled.

the gas liberated in tank 10 may be, for example:

Percent. Methane 14.6 Ethane 36.0 Propane 36.4 Butane and less volatile bodies 13.0

and this gas will be termed low-pressure vent gas.

From tank 10 the oil passes to heat` exchanger 11 and thence to still 12 where it is blown with live steam, the result being that practically all the substances remaining The mixture of steam and hydrocarbons formed in the still passesto condenser 13 maintained at a temperature somewhat below the boiling point of water. In this condenser most of the aqueous Vapor is condensed and is withdrawn through trap 14, but the hydrocarbons remain in vapor state as does also a considerablelamount of water. The oil from still 12, after being freed from dissolved substances, returns through heat-exchanger .11 to absorber 7 after being cooled by water.

The hydrocarbon vapors pass from condenser 13 to the precooler 15, where they are cooled to substantially atmospheric temperature with the condensation of the heavier hydrocarbons present and most ofthe remaining water. The li uid formed in the precooler is drawn cgi' into storage tank 16, where the Water is separated from it in any suitable way, The liquid in tank 16 will be referred to as the precooler liquid. It may have, for example, the following compositlon:

Per cent by weight.

, Ethane 0.1

Propane 2.0 Butane 9.0 Pentane and less volatile bodies 88.9

Vapors not condensed in the precooler pass to a compressor 17, where their pressure is raised to about 50 lbs., and then to another cooling unit 18, where they are again brought to atmospheric temperature. This cooling" unit is termed the intercooler. The condensed liquid is drawn into the storage tank 19 and is termed the intercooler liquid. It may have, for example, the following composition:

Per cent by weight.

Methane 0.1 Ethane 0.7 Propane` 10.0 Butane 52.3 Pentane and less volatile bodies 36.9

The vapors from the intercooler pass into compressor 20, where the pressure is further increased to, say, 150 lbs. per square inch, and then to a third cooling unit 21 which is Per cent byA weight. Methane f 0.3 Ethane 2.9 Propane 17.4 Butane 71.0 Pentane and le volatile bodies 8.4

A portion of the vapors still remain uncondensed -by the aftercooler and they are herein termed, for convenience, fixed gases. Their composition may be as follows:

Per cent by volume.

Methane 5.2

Ethane 48.2

Propane 41.6

Butane and less volatile bodies 4.6

Absorption natural gas gasoline processes now in Vgeneral use are similar in their general aspect to that outlined above. The low-pressure and high-pressure vent gases and the fixedl gases are ordinarily used only as fuel. The precooler, intercooler, and aftercooler liquids are combined to produce the gasoline, the product be- 'ing highly volatile and requiring a further treatment in order to fit it for use. This is accomplished by the natural weathering process already referred to, wherein the wild product is stored in tanks at low pressure until a portion of it has evaporated. By such procedure there is a total loss of the ethane, propane, but-ane and higher hydrocarbons which evaporate during weathering, while the butane in the highand low-pressure vent gases and the ixed gases is not incorporated into the gasoline produced.

Inaccordaiice with my invention, substantially the entire quantity of butane which dissolves in the oil in the absorber 7 may be worked into gasoline, while the ethane and propane which escape to the air in the natural weathering process may be recovered. The manner in which this may be accomplished is as follows:

The precooler, intercooler and aftercooler liquids, the highand low-pressure vent gases, and the fixed gases, are introduced at appropriate points into the rect-ifying column 23, the most volatile mixtures being introduced nearest the top and those most nearly approaching the volatility desired in the final product being led int-o the column near its base. vided lwith trays 23a which divide it into compartments, means being provided `:for

The column is pro'- the downward How of liquid and the upward passage of vapors, and the column is fitted with devices for drawing ofi water and for testing and regulation which need not be described here.

Connected to the base of column 23 is a vessel 24: adapted to receive the liquid leaving the bottom of the column. The vessel 24 is provided with a heating coil 25, and a vapor pipe 26 is arranged to lead vapors evolved in vessel 24 into the column 23. The liquid from the column passes through trap 27 to the vessel 24.

The various mixtures are introduced into column 23 in the following order, beginning at the top: high-pressure vent gas, lowpressure vent gas', fixed gas, aftercooler liquid, intercooler liquid and precooler liquid. The last-named contains only small amounts of hydrocarbons more volatile than butane, and requires but little rectification; while the high-pressure vent gas, having only 4.3% of butane, and less volatile bodies, requires the most thorough treatment. The highand low-pressure vent gases are compressed and cooled so that they enter the column in liquid phase, as subsequently described. The expansion of the mixtures into the upper part of the column absorbs heat, while the temperature at the foot of the column is kept up by warm vapors entering through pipe 26. The temperature gradient necessary for rectification is thus maintained. The gasoline is Withdrawn from tank 24C at 29, continuously or at intervals.

The high-pressure vent gas and low-pressure vent gas pass through heat exchanger 31 on their way to the column, and therein are cooled, giving up their heat to the gases from pipe 28 which flow through exchanger 31 in heat-interchanging relation to the vent gases. The high-pressure vent gas may be compressed in compressor 3 2, before it enters the heat exchanger 31, to such a pressure that there will be a .partial or complete liquefaction of this gas as it passes through the expansion valve 34 and enters the column 23. The pressure in column 23 may advantageously be about 9 lbs. gage and may be maintained by the regulator 80. The pressure in vessel 24 is, of course, somewhat higher than at the top of the column because of the head of liquid on the trays 23a. The pressure before expansion may be 800 to 1000 lbs. per square inch, depending on the proportion of liquefaction desired and the eiciency of the heat exchanger 3l..

In a similar manner the low-pressure vent gas is compressed in compressor 33 to a pressure which may be 600 to 800 lbs. per square inch before it enters the heat exchanger and is expanded from this pressure to column pressure through valve 35 wherein a partial or Complete liquefaction may occur,

The fixed gas from the aftercooler may likewise be further compressed before expansion but in general this will bei unnecessary to obtain the desired liquefaction at the expansion valve. The gases escaping at the top of column 23, consisting of constituents eX- cluded from the gasoline, pass through the regulator 30 and may be used as Jfuel or for any other purpose.

The control of the process is very simple. If it is desired to change the quality of the final product, this may conveniently be accomplished by varying the rate at which heat is supplied to vessel 24, the pressure in the system remaining unchanged. More heat supplied will obviously result in the evaporation of more material in unit time, and more vapors are released at 30 to keep down the pressure. Since a larger proportion of material then enters the vapor fraction, the liquid fraction will decrease vin quantity, and since the hydrocarbons escaping at 30 are the most volatile of those entering the column, the volatility of the liquid fraction will be decreased. Furthermore7 the vapor pressure of the liquid product can be accurately predetermined from the conditions under which the column is working, namely, the pressure and the temperature of the vapors passing through line 26. These vapors may be maintained, for example, at a temperature of from 70 to 90o F. In a particular instance when the vapors in pipe 26 had a temperature of 83 F., the material produced had a `vapor pressure of 8 lbs. at 70 F. and a vapor pressure of I4 lbs. at 100 F. By increasing the temperature of the vapor entering the column, the above figures can be considerably reduced, but with a decreased yield of material. The composition of the vapor fraction canot course be regulated as easily as that of the liquid, and by the same means.

While the above description shows` the most complete utilization of all the gasoline constituents removed from the natural gas by the absorbing oil, in many instances other embodiments of my invention will recommend themselves on the grounds of their simplicity. A simplified embodiment of the invention in which only the ,liquid condensates are subjected to rectification and in which exit gases from the rectification column are added to gas passing to the precooler, is described in the parent application referred to above and is claimed in the patent into which said application matured.

Besides the absorption process, there is another principal type of natural gas gasoline process, frequently styled the compression process, which is simpler in its general execution in that it does not involve an absorbing medium. In this process, the condensation 'is eected by Compression and very closely in their composition and further treatment to the condensates obtained in the absorption process described above, although in some cases there is no fraction corresponding to the precooler liquid. In the simplest case in which there is but one stage of compression, the condensate corresponds most closely to the intercooler liquid above. In theexecution ofmy process there is no fundamental diierence betweenI the treatment of the liquid fractions obtained in the absorption process and those obtained in the compression process.

The product of my invention may, in some cases, difl'erfrom natural gas gasoline, prepared by prior process, in havin high gravity on the Baume sca e, varying from 87 to 92 B., and at the same time having a vapor pressure of from 10 to 12 lbs. at 100 F., which pressure is characteristic of ordinary natural gas gasoline of gravity from 72 to 84 B.

It will be noted that the execution of my process requires the use of only moderate pressures in the rectifying column, the pressures specifically mentioned herein being less than one atmosphere gage. Pressures of this order, viz not substantially in excess of one atmosphere, are suilicient to permit the upper portion of the rectifying column to be relatively furnishedA with the necessary liquid material without special difficulty, for example by the expansion thereinto of hydrocarbon material which has been compressed and cooled, and the use of such low pressures simplifies the design of the column and cheapens its construction.

While I have described my invention in connection .with certain particular Ways of producing a series ofmixtures containing the heavier hydrocarbons of natural gas, and in connection with certain series of mixtures of particular composition, this is done merely to illustrate the invention. My invention is equally applicable Where a greater or less number of fractional mixtures are produced, and where the relative volatility of the various fractional mixtures is entirely different from what has been instanced. Furthermore, I am not limited to the treatment of Anot go to the rectifying process. My invention is limited only by the appended claims.

lI claim:

l. Process of making gasoline which comprises producing from natural gas a con'- centrate of its heavier hydrocarbons, separating from said concentrate a more volatile fraction and a less volatile fraction, rectifying said less volatile fraction in a rectifying co umn to produce a liquid and a vapor, compressing said more volatile fraction, cooling it by heat-interchange With the vapor from the less volatile fraction, and expandi ing the material so cooled into the rectifying column at a point above the place of introduction of said less volatile fraction.

2. Process of making gasoline which com'- prises producing from natural gas a con-A centrate of'its heavier hydrocarbons, separating from said concentrate a more volatile fraction and a less volatile fraction, rectifying said less volatile fraction in a rectfying column at a pressure not substantially in excess of one atmosphere to produce a liquid and a vapor, compressing said more volatile fraction, cooling it by heat-interchange lwith the vapor from the less volatile fraction, and expanding the material so cooled into the rectifyng column at a point above thev place of introduction of said less volatile fraction.

3. Process of decreasing the volatility of Wild natural gasoline which comprises rectifying the wild material in a rectifying column at a pressure not substantially in excess of one atmosphere to produce a liquid .upper part of the rectifying column by expanding into it the hydrocarbons so cooled.

4. Process of making gasoline which comprises producing from natural gas by absorption a concentrate of its heavier hydrocarbons, separat/ing from said concentrate a more volatile fraction and a less volatile fraction, rectifying said less volatile fraction in a rectifying column to produce a liquid and a vapor, compressing said more volatile fraction, cooling `it by heat-interchange with the vapor from the less volatile fractlon, and expanding the material so cooled into the rectifying column at a point above the place of introduction of said less volatile fraction. i

5. Process of making gasoline which comprises producing from natural gas by absorption a concentrate of its heavier hydrocarbons, separating from said concentrate a more volatile fraction and a less volatile fraction, rectifying said less volatile fraction in a rectifying column at a pressure not substantially in excess of one atmosphere to produce a liquid and a Vapor, compressing said more volatile fraction7 cooling it by heat-interchange with the vapor from the less Volatile fraction, and expanding the material so cooled into the rectifying column at a Ipoint above the place of introduction of said less Volatile fraction.

6. Process of making gasoline Which comprises treating natural gas under pressure with an absorbent, separatin the hydrocarbons taken up by the absor ent into more und less volatile fractions, producing .from a less volatile fraction a liquid having a,

Leonesa higher volatility than that desired in the gasoline, rectifying said liquid'at a pressure not substantially in excess of one atmosphere in a rectifying column to produce a still less Volatile liquid and avapor, and cooling the upper part of the column by compressing a more volatile one of said fractions cooling the compressed material by heat-interchange with said vapor, and expanding it into the column.

ln testimony whereof, I alx my signature.

HAROLD E. THOMPSON.

Images