US2298702A - Hydrocarbon conversion - Google Patents

Description

Oct. 13, 1942.

P. c. KEITH, JR

HYDROCARBON CONVERSION Filed July s, 1938 IN V EN TOR.

l HHHH m\ Il ATTORNEY HHHHM kmvi Patented Oct. 13, 1942 HYDROCARBON CONVERSION Percival C. Keith, Jr., Peapack, N. J., assigner to The Polymerization Process Corporation, Jersey City, N. J., a corporation of Delaware Application July 8, 1938, Serial No. 218,185

5 Claims.

This invention relates to the conversion of normally gaseous hydrocarbons, for example, by polymerization, to normally liquid products including gasoline constituents. More particularly the invention relates to the conversion of normally gaseous hydrocarbons to normally liquid products by the application of heat thereto, under superatmospheric pressure.

In the conversion of normally gaseous hydrocarbons such as gaseous mixtures comprising Ca and C4 p-araflinic and olenic hydrocarbons by the application of heat thereto under pressures in excess of `2'00 pounds per square inch,v and particularly under pressures in excess of 500 pounds per square inch, the liquid product obtained comprises a gasoline fraction which has a relatively high A. P. I. gravity and predominates in relatively low boiling aliphatic hydrocarbons. For example, in the conversion of such gaseous mixtures by thermal means under relatively high pressures the gasoline fraction of the polymer product may be 50% distilled overhead at temperatures below the boiling point of benzene. This tendency is noticeable when operating at pressures in excess of 200 pounds per square inch, is marked at pressures above 500 pounds per square inch, and, at the elevated pressures which are otherwise desirable for this operation, for example at 1000 to 2000 pounds per square inch, the product displays a characteristic gravity and distillation analysis as described above.

It is Ian object of the invention to provide a modification of the thermal conversion method wherein normally gaseous hydrocarbons are subjected to temperatures in the neighborhood of 1000" to 1200" F. under pressures substantially above atmospheric whereby the gasoline product of this method is substantially modied in character in that it is more aromatic, has a substantially lower A. P. I. gravity, and displays a proportion of low boiling aliphatic hydrocarbons more nearly approaching that desirable in a balanced gasoline motor fuel.

The invention contemplates a method of effecting thermal conversion of normally gaseous hydrocarbons, particularly mixtures of olenic and p-araflinic C3 and C4 hydrocarbons, under pressures in excess of 200 pounds per square inch, and particularly in excess of 5 00 pounds per square inch, wherein the normally gaseous hydrocarbons undergoing conversion treatment have adrnixed therewith a small proportion of normally liquid aliphatic hydrocarbons having not more than 6 carbon atoms per molecule, by recycling to the thermal conversion treatment a lll portion of the normally liquid aliphatic C5` and/or C6 hydrocarbon constituents of the reaction product. The Weight per cent of normally liquid hydrocarbons thus introduced will depend upon the nature of the gases undergoing con version treatment, the recycle ratio, the conversion rate per pass, and the temperature and pressure conditions employed. For example, under a given pressure condition the optimum amount of normally liquid hydrocarbons to be recycled to the reaction mixture ordinarily will vary within limits inversely as the temperature. Under any given set of conditions, furthermore, the amount will be limited to a maximum beyond which any further addition will cause excessive formation of coke. However, it may be stated as a general rule that in operations above 500 pounds per square inch and at temperatures in the order of 100,.'0o to 1100 F. to effect the conversion of a gaseous mixture comprising hydrocarbons having at least three carbon atoms per molecule the optimum weight per cent of normally liquid aliphatic hydrocarbons added will be not more than 10, if the reaction time 'is suilicient for a substantial conversion rate per pass.

As stated above the invention may be carried out by recycling to the conversion Zone a portion of the normally liquid Aaliphatic C5 and/or Ce hydrocarbons contained in the reaction product. This portion may be obtained with the C3 and C4 hydrocarbons desired for recycling by suitable control of the fractionation of the reaction products.

The C5 hydrocarbons recycled may be returned f to the entrance of the heating and conversion zone or may be introduced at an intermediate point thereof, either separately or in conjunction with C3 and C4 hydrocarbons recycled to the conversion treatment.

In the further description of the invention the normally liquid aliphatic hydrocarbons recycled to the gas conversion treatment will be referred to as C5 hydrocarbons. It is to be understood, however, that this expression is intended to include not only C5 hydrocarbons but aliphatic Ce hydrocarbons or mixtures thereof.

The accompanying drawing is a diagrammatic view in elevation of apparatus suitable for carrying out the invention. Further description "of the invention will refer to this drawing but it is to be understood that the drawing represents merely an embodiment of the invention, the latter' being capable of other embodiments which may be beyond the physical limitations of the apparatus diagrammatically illustrated.

In the drawing there is indicated a heater I containing a coil 2 for effecting the thermal treatment of the reaction mixture, a separator 3, a gas fractionator 4, a polymer fractionator 5, a gasoline receiver 6, and suitable pipe connections and auxiliary equipment for carrying out the process as described below.

The gas charge, which may consist of normally gaseous hydrocarbons suitable for thermal conversion treatment such as C2, Ca, and C4 parafnic and olefinic hydrocarbons, is introduced into the system through line 1, which contains a pump 8 for forcing the reaction mixture into coil 2 against the pressure maintained therein. In coil 2 the reaction mixture is heated under a pressure in excess of 200 pounds per square inch and preferably in excess of 500 pounds per square inch. The reaction temperature will depend upon the pressure employed, the proportion of C5 hydrocarbons in the reaction mixture, the nature of the gaseous mixture undergoing conversion, and the conversion rate per pass desired. However, in the treatment of a gaseous mixture consisting predominantly of C3 and C4 hydrocarbons and including a substantial proportion of unsaturated constituents, a temperature of 975 to 1075 F. may be employed undera pressure of 1000 to 2000 pounds per square inch, the proportion of C5 hydrocarbons in the reaction mixture being less than 10%.

In the apparatus as illustrated in the drawing there is provided a coil only for carrying out the conversion treatment. It is to be understood, however, that this invention contemplates the optional use of a suitable reaction drum or soaker in conjunction with a heating coil whereby a substantial part of the conversion reaction is eifected in such a drum or soaker. For simplicity of illustration, however, this modification is not included in the drawing.

After the desired conversion treatment the reaction products are withdrawn from coil 2 through line 9 and passed to separator 3. Any desired reduction in pressure may be effected by means of pressure control valve I in line 9. If desired the reaction products may be cooled by suitable heat exchange, or by admixture therewith of suitable cooling fluid, b-y means not shown, prior to their introduction into separator 3.

In separator 3 conditions of temperature and pressure are maintained to effect condensation of liquid constituents including a gasoline fraction and passage overhead of a gaseous fraction which may include a portion of the C hydrocarbons contained in the reaction products. For example, the separator 3 may be operated under a pressure of 300 pounds per square inch with a bottom temperature of 400 to 450 F., maintained by means of suitable heating means such as heating element II and a top temperature of 170 to 180 F., maintained by suitable control of cooling means such as cooling element I2.

The gases and any accompanying vapors uncondensed in separator 3 pass overhead and are withdrawn through line I5 which connects with gas fractionator 4. In fractionator 4 conditions of temperature and pressure are maintained to effect condensation of material therein desired for recycling to the gas conversion treatment. For example, under a pressure of 300 pounds per square inch a top temperature of -30 to 20 F. may be maintained by suitable means such as cooling element I6. Gases uncondensed are withdrawn overhead from fractionator 4 through 75 line II, valve I8 being provided to control the pressure on the system. The gases thus withdrawn, which ordinarily include hydrogen, methane, and any portion of the C2 hydrocarbons undesired for recycling, are withdrawn from the system for further treatment or use, for example, as fuel. The bottom temperature to be maintained in fractionator 4 will depend somewhat on the nature of the material to be recycled. However, as an example a temperature of to 125 F., at 300 pounds pressure, may be mentioned. The temperature required in the bottom of fractionator 4 may be maintained by suitable means such as heating coil I9.

The recycle material collected in the bottom of fractionator 4 is withdrawn therefrom through line 20 provided with valve 2|. Line 20 connects with line 'I whereby the recycle material is introduced into coil 2 through pump 8.

The polymer condensate in separator 3 is withdrawn therefrom through line 29 provided with valve 30 and introduced into polymer fractionator 5 wherein conditions of temperature and pressure are maintained to effect condensation and withdrawal of high boiling liquids undesirable for inclusion in the gasoline product. These may be withdrawn through line 3| provided with valve 32. For effecting the desired fractionation under the above-mentioned 300 pounds pressure a top temperature of to 200 F. and a bottom temperature of 400 to 450 F. may be maintained in fractionator 5. For this purpose cooling means such as cooling coil 33 and heating means such as heating coil 34 may be provided. Vapors uncondensed in fractionator 5 are withdrawn therefrom through line 35 provided with a condenser 36. By passage of the vapors through condenser 36 condensation of the gasoline is effected. The gasoline condensate is collected in receiver 6 from which it may b-e withdrawn through line 3'! provided with valve 38. Gases uncondensed are withdrawn through line 39 provided with valve 40. These gases may be passed to any suitable further treatment. For example, they may be returned to gas fractionator 4, by means not shown, for recovery therein of constituents suitable for recycling to the gas conversion treatment.

As mentioned above, the amount of C5 hydrocarbons recycled for admixture with the gases undergoing conversion will depend upon a number of factors such as the constitution of the gases undergoing treatment, the temperature employed, the pressure employed, and the reaction time. However, within limits it may be said that the aromatic content of the gasoline product will vary with the amount of C5 hydrocarbons recycled. At the same time the A. P. I. gravity of the liquid product will vary inversely with the amount of C5 hydrocarbons recycled to the reaction. These points are illustrated in In Table I the characterization factor is employed to illustrate the nature of the product obtained. The characterization factor is calculated according to the method. prescribed by Watson and Nelson in vol. 25 of Industriali and Engineering Chemistry at pages 880-886. A characterization factor of 12.5 indicates a stock predominantly parannic in nature. Lower values of the factor indicateY increasing deviation from the parailinic toward the naphthenic and aromatic properties, approaching 10 as a minimum Value. It will be noted from the results set forth in Table I that, in treating reaction mixtures of substantially the same character under substantially the same conditions of temperature and pressure, the characterization factor decreases with increasing amounts of C5 hydrocarbons recycled to the furnace charge, indicating progressive increases in the aromatic content of the liquid product. At the same time the A. P. I. gravity of the liquid product decreases with increasing amounts of C5 hydrocarbons recycled to the furnace charge, indicating successive decreases in the proportion of lower boiling aliphatic hydrocarbons in the liquid product. It will be noted in run D that the reaction time is shorter than in runs A, B and C. ThisA procedure is adapted to compensate for the substantial increase in the proportion of C5 hydrocarbons in the furnace charge. It will be noted that in spite of the decrease in reaction time the increase in amounts of C5 hydrocarbons effected a substantial change in the nature of the liquid product.

The eifect of recycling varying amounts of C5 hydrocarbons to the furnace charge in the treatment of similar gaseous reaction mixtures is illustrated in Table II.

Table II Run E F G H Temperature .F 1,080 1,060 1,060 1,065 Pressure #sq. in.. 1,600 1,600 1,600 1,600 Reaction time ,.sec... 57 57 56 Wt. p. c. O5s in furnace charge 3.7 5.1 5. 3 Gasoline product:

Gravity-A. P. I 65. 6 55. 3 53. 9 47.1 Aniline pt.-F 67 G4 35 Octane No.-C. F. R. M 77.0 78. 5 77. 5 78.5 Octane No.-C. F. R. M. (blending value) 89.0 92. 91.0 92. 0 S T M distillation In the results set forth in Table II it will be noted that, as in Table I, increasing amounts of C hydrocarbons recycled to the furnace charge result in decreases in A. P. I. gravity and in the aniline point. These results are evidence of increases in the aromatic content of the gasoline product. By reference to the A. S. T. M. distillation included in Table II it will be noted that the recycling of C5 hydrocarbons to the furnace charge in successively increasing quantities results in successive changes in the nature of the gasoline product. In run E wherein no appreciable proportion of C5 hydrocarbons was included in the furnace charge the 50% point in the distillation was at a temperature well below the boiling point of benzene. In run F with the recycling of a small amount of C5 hydrocarbons the 50% point was well above the boiling point of benzene while in run H the point was above the boiling point of benzene. This illustrates the effect of recycling C5 hydrocarbons to the furnace charge in causing a drastic change in the nature of the gasoline product, in reducing the relative proportion of the low boiling aliphatic hydrocarbons and increasing the relative proportion of the aromatic constituents thereof. Furthermore, the resultsy shown in Table II illustrate the fact that the change in the character of the polymer product, with its substantial decrease in the proportion of low boiling hydrocarbons, is effected without loss of anti-knock value, the octane number of the gasoline product showing an increase.

Under otherwise similar conditions of operation the optimum proportion of C5 hydrocarbons to be recycled to the furnace charge may be changed or may be controlled by minor changes in other operating conditions. This point is illustrated in Table III which sets forth the results obtained in the treatment of similar gaseous mixtures while recycling varying amount of C5 hydrocarbons.

Table III Run .T K L M N Temperature ..F.. l, 045 1,045 1, 045 1, 035 1,055 Pressure ..#sq. in... 1,600 1,600 1,600 1, 600 1,600 Reaction time sec.. 58. 8 58. 5 59. 2 60. 0 56. 5 Wt. p.c. C5s in furnace charge. 1.2 2. 3 9. 0 4.2 Gasoline product:

GraVity- A. P. 1..... 62.4 58. 4 58.8 50. 3 49. 4 Aniline pt.-F.... 89.5 73 72 46 35 Octane N0.C.F.R.M.. 78.8 79. 0 78. 3 80. 4 80. 0 Octane No.-C.F.R.M.

(blending value) 93. 4 98. 4 98.1 100. 8 96. 4 A. S. T. M. distillation:

Initial B. P.-F. 94 101 104 102 108 l0 125 129 129 149 158 146 157 159 194 197 172 187 190 230 229 212 231 236 275 272 314 328 332 362 349 404 405 398 414 404 In Table III runs J, K and L were made under identical conditions with runs M and N varying only as to reaction temperature. It will be noted that by a reduction in the temperature in run M from that employed in runs J, K and L a substantial proportion of C5 hydrocarbons could be recycled to the reaction mixture with resulting drastic change in the nature of the product. By reference to run N it will be noted that at a higher temperature than in runs J, K and L the optimum proportion of C5 hydrocarbons in the furnace charge was lower than in run M. It will be noted, however, that the products obtained in runs M and N are similar except as to aniline point and octane number, the high anti-knock Value of the product of run M indicating a larger proportion of the octane isomers having a high anti-knock value in the gasoline product of run M. In Table III there will be noted also the beneficial results of the recycling of C5 hydrocarbons to the reaction mixture as to the distillation of the gasoline product, the gravity, and octane number.

The invention thus provides a method for the thermal conversion of normally gaseous mixtures containing substantial proportions of paramnic constituents under relatively high pressure to produce a gasoline motor fuel which is highly aromatic in character and has a proportion of low boiling aliphatic hydrocarbons not in excess of that desired in a balanced motor fuel. The invention provides for accomplishing these results a method which involves only a slight, but significant, change in the operating conditions for carrying out a thermal conversion process of that nature, whereby the invention may be adapted to existing apparatus without the need for drastic changes in structure or operation.

The invention has been described with reference to specific examples thereof. It must be understood, however, that the invention is not intended to be limited by reference to these specific examples r embodiments but is capable of other embodiments within its scope.

I claim:

1. The method of converting normally gaseous hydrocarbons to normally liquid products which comprises heating normally gaseous hydrocarbons having at least two carbon atoms per molecule and normally liquid aliphatic C hydrocarbons from a source described below to a temperature of 10001200 F. under superatmospheric pressure to effect non-catalytic thermal conversion thereof to normally liquid hydrocarbons including a gasoline fraction containing an excessive proportion of low-boiling normally liquid constituents, recovering from the products of conversion as recycle material normally gaseous hydrocarbons having at least two carbon atoms per molecule and a portion of the normally liquid aliphatic C5 hydrocarbon constituents of said conversion products, separating from the remaining portion of the products of conversion a gasoline motor fuel product and a fixed gas fraction including the constituents of said reaction product undesired in the feed to said conversion treatment, withdrawing from the process said gasoline product and said xed gas fraction, admixing said recovered recycle material with normally gaseous hydrocarbons having at least two carbon atoms per molecule, and subjecting the resulting mixture to said thermal non-catalytic conversion treatment to effect conversion thereof to gasoline motor fuel of high anti-knock value, the quantity 0f normally liquid hydrocarbon constituents of the conversion products thus recovered and returned tothe thermal conversion zone being regulated whereby the recycled normally liquid hydrocarbons constitute 1 to 10 weight per cent of the total hydrocarbons charged to the reaction Zone.

2. In the process for converting normally gaseous hydrocarbons to normally liquid hydrocarbons wherein normally gaseous hydrocarbons having at least two carbon atoms per molecule are passed through a thermal reaction zone under superatmospheric pressure at reaction temperatures of 1000 to 1200D F. whereby said normally gaseous hydrocarbons are converted to normally liquid hydrocarbons including a gasoline fraction containing an excessive proportion of low boiling normally liquid constituents, the products of conversion are treated to separate normally liquid products and normally gaseous hydrocarbons having at least two carbon atoms per molecule, and normally gaseous hydrocarbons thus recovered are recycled to the said thermal conversion zone, the steps comprising recovering from the conversion products a portion of the normally liquid aliphatic C5 hydrocarbon constituents thereof, and introducing said recovered normally liquid hydrocarbons into said thermal conversion zone to effect conversion thereof in admixture with normally gaseous hydrocarbons to gasoline motor fuel of high antiknock value, the quantity of normally liquid hydrocarbons thus returned to the termal conversion zone being regulated whereby the recycled normally liquid hydrocarbons constitute 1 to 10 weight per cent of the total hydrocarbons charged to the reaction zone.

3. The process in accordance with claim 2 wherein the products of conversion are fractionated to separate a recycle fraction consisting of normally gaseous hydrocarbons and a portion of the normally liquid aliphatic C5 hydrocarbon constituents of the reaction products, a gasoline motor fuel product and a fixed gas fraction :fncluding reaction products unsuitable as feed to the conversion treatment, and said recycle fraction is introduced into said thermal conversion zone to effect conversion thereof to gasoline motor fuel of high anti-knock value.

4. In the process for converting normally gaseous hydrocarbons to normally liquid hydrocarbons wherein a fresh feed essentially consisting of normally gaseous hydrocarbons having at least two carbon atoms per molecule is passed through a thermal reaction zone to under superatmospheric pressure at reaction temperatures of 1000D to 1200 F. whereby said fresh feed is converted to normally liquid hydrocarbons including a gasoline fraction containing an excessive proportion of low-boiling normally liquid constituents, the products of conversion are treated to separate normally liquid products and normally gaseous hydrocarbons having at least two carbon atoms per molecule, and normally gaseous hydrocarbons thus recovered are recycled to the said thermal conversion zone, the steps comprising recovering from the conversion products a portion of the normally liquid aliphatic C5 hydrocarbon constituents thereof, and introducing said recovered normally liquid hydro-carbons into said thermal conversion Zone to effect conversion thereof in admixture with normally gaseous hydrocarbons to gasoline motor fuel of high anti-knock value, the quantity of normally liquid hydrocarbons thus returned to the thermal conversion zone being regulated whereby the recycled normally liquid hydrocarbons constitute 1 to 10 weight per cent of the total hydrocarbons charged to the reaction zone.

5. The method of converting normally gaseous hydrocarbons to normally liquid products which comprises heating normally gaseous hydrocarbons having at least two carbon atoms per molecule and normally liquid C5 hydrocarbons from a source described below to a temperature of about 1000 F. under superatmospheric pressure to effect thermal conversion thereof to normally liquid hydrocarbons, separating from the products of conversion and withdrawing from the system a light gaseous fraction having less than two carbon atoms per molecule and a liquid product boiling in the gasoline range, also recovering from the products of conversion as recycle material an intermediate fraction containing normally gaseous hydrocarbons having at least two carbon atoms per molecule and a portion of the normally liquid C5 hydrocarbon constituents of said conversion products, admixing said intermediate fraction with fresh normally gaseous hydrocarbons having at least two carbon atoms per molecule, the quantity of normally liquid hydrocarbon constituents returned to the conversion zone constituting about 2 to 6 per cent by weight of the total hydrocarbons charged to the conversion zone, and subjecting the mixture to said thermal conversion treatment.

PERCIVAL C. KEITH, JR.

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