US2973395A - Process of producing c3h4 aliphatic hydrocarbons and ethylene from propylene - Google Patents

Description

PROCESS OF PRODUCING C l-I ALIPHATIC HYDROCARBONS AND ETHYLENE FROM PROPYLENE Willis C. Keith, Lansing, Robert H. Elkins, Flossmoor, and Robert R. Chambers, Park Forest, llll., assignors to Sinclair Refining Company, New York, N.Y., a corporation of Maine Filed June 21, 1954, Ser. No. 438,300

9 Claims. (Cl. 260-678) No Drawing.

. version of propylene.

Although the production of acetylene has been established on a commercial basis for many years, there has not to our knowledge been proposed any low cost method for producing C H aliphatic hydrocarbons in good yields at commercially acceptable conversion levels. The C H aliphatic hydrocarbons include methyl acetylene, the first homolog of the acetylene, and allene, the isomer of methyl acetylene. Either of these hydrocarbons is readily converted to the equilibrium mixture which heavily favors methyl acetylene at ordinary temperatures. High temperature methods of preparation lead to mixtures of these hydrocarbons; however, this result is not a serious drawback since both compounds will give the same chemical derivatives in many reactions and if necessary they can be separated by either physical or chemical means. The C H hydrocarbons are useful in preparing many chemical compounds. For instance, the addition of alcohols to methyl acetylene or allene takes place in the presence of bases to form isopropenyl ethers which polymerize readily in the presence of acidic catalysts. Among the other materials which may be added the products from the cracking of low molecular weight hydrocarbons, they have until recently been unsuccessful.

Szwarc in J. Chem. Phys., 17, p. 284 (1949) pyrolyzed 5 propylene at a reduced pressure and a temperature of to the C H hydrocarbons are carboxylic acid, hydrochloric acid, chlorine, mercaptans, and hydrocyanic acid. There have been a number of methods proposed for manufacturing methyl acetylene. Among these are included the dehydrohalogenation of propylene dibromide, the reaction of sodium acetylide with methyl iodie in liquid ammonia, the pyrolysis of quaternary ammonium salts, the electrolysis of sodium crotonate and the pyrolysis of diketene. These methods are more or less representative of laboratory scale preparations. One process which has been considered from a commercial standpoint includes the production of methyl acetylene by hydrolysis of Mg C During World War II the Germans made a considerable study of this method and issuance of US. Patent 2,510,550 may indicate recent interest in this process in this country. However, to our knowledge this latter method is not in commercial practice.

We believe the most promising commercial method of producing C H aliphatic hydrocarbons is through the utilization of a vapor phase cracking or dehydrogenation process. Apparently the occurrence of methyl acetylene in cracked products is not uncommon although it is usually found only in very small percentages. This product was isolated commercially as a by-product in the electric arc process for making acetylene from methane, and .there are also several patents directed to the removal of methyl acetylene formed in making butadiene. Of course the process of most potential interest is one in which methyl acetylene is obtained in good yields by converting an inexpensive raw material. Although workers have for some time searched for methyl acetylene in about 680 to 870 C. His experiments were run at very low conversions (0.01 to 2 weight percent of the feed).

Rice in U.S. Patent 2,429,566, has indicated that most earlier workers had obtained tars and liquid products when they cracked isobutylene under conditions which he felt should give methyl acetylene. The patentee pyrolyzed isobutylene in a quartz tube and indicated that reaction conditions might include temperatures of 700 to 900 C. and pressures of about to A atmospheres while employing about 0.5 to 5.0 seconds contact time. Rice regulated these conditions so that be operated just short of the point at which tar and liquid products formed and be indicated that propylene could be employed as the starting olefin although he apparently did not effect this reaction.

In the present invention we have devised a process for manufacturing C H aliphatic hydrocarbons and ethylene at commercially feasible yield levels. The value and uses of ethylene are well-known and do not need elaboration. In our process we subject propylene to a temperature ranging from about 1300 F. to the decomposition temperature of the C H hydrocarbon product under the reaction conditions and the olefin partial pressure is not greater than about one atmosphere. Further our reaction is conducted in the presence of at least an equal molar quantity (based on the propylene) of a gas inert and not deleterious to the desired reaction. In this process to produce more advantageous yields of the desired products, the conversion of the propylene should not be greater than about 80 weight percent of that charged to the reaction zone.

The feed to our process is propylene; however, it can be a mixture of propane and propylene containing up to about by volume of propane. When using mixtures of propane and propylene we prefer that they not con tain more than about 10% by volume of propane in order to produce more advantageous yields of the C H hydrocarbons. In operation of our process the feed can be converted either on a once-through or a recycle basis.

The temperature of our reaction can vary from about 1300 F. to the decomposition temperature of the 0 H, hydrocarbon product under the reaction conditions. However, we prefer reaction temperatures of about 1400 to 1800 F. These temperatures can be produced by passing the propylene-inert gas mixture through an externally heated reaction tube to raise them simultaneously to reaction temperature. However, we particularly prefer that the inert gas be preheated to a temperature sufliciently above the reaction temperature to heat the feed to reaction temperature. Propylene feed is supplied to the reaction zone as a vapor at a temperature sulficiently below reaction temperature that the feed is substantially unreacted until mixing with the inert gas, and accordingly the exact temperature of the preheated inert gas will depend upon the temperature of the incoming feed, the ratio of the propylene to the inert gas, as well as the desired reaction temperature to be maintained while taking into account the heat supplied to the reaction zone .by indirect heat exchange. As an example, the temperature of the inert gas may be in the range of about 1500 to 2000 F.; however, a temperature should not be used which is high enough to destroy its inert state. The present process is most advantageously conducted at at mospheric pressure although elevated pressures such as 2 or 3 atmospheres or subatmospheric pressures may be employed. However, the partial pressure of the propylene feed should not exceed about one atmosphere.

Among the non-reacting gases which can be employed as the inert gas in our process is steam which is preferred; however, other inert gases or their mixtures can be utilized such as nitrogen, carbon dioxide and methane. As previously noted, the amount of inert gas passed to the reaction zone is at least 1 mole per mole of propylene feed. Although there is no theoretical upper limit on the amount of inert gas which can be employed, it would hardly be economically feasible to use more than about 40 moles of inert gas per mole of propylene. A preferred ratio of inert gas to propylene feed is about to 40 moles per mole. Increasing the amount of inert gas results generally in increased yields of QR; hydrocarbons. The increase of the inert gas also results in decreased coke formation; however, from the commercial point of view the exact inert gas ratio employed will be determinedby compromise between the beneficial results obtained and the heating costs incurred.

We have found that the yields of C l-I hydrocarbons and ethylene in our process are essentially functions only of the percent of the feed converted. Therefore, temperature and contact time are equivalent variables for controlling the degree of conversion at a given propylene partial pressure and inert gas to propylene ratio. At very low conversions the yield of C H hydrocarbons approaches about 35 weight percent of the propylene converted, and as the conversion increases say to 100% the C l-L; yield apparently decreases to the neighborhood of about weight percent of the propylene converted. Ethylene yield at very low conversions is just above weight percent of the propylene converted. Ethylene yield is at a maximum of about 40 weight percent between about to 55 weight percent conversion of the propylene, and the yield then apparently decreases to just below 25 at 100% conversion. Acetylene and C production varies from 15 to 5 weight percent over the conversion range. Thus to obtain more desirable yields of the C H hydrocarbon and ethylene, we have found that the reaction conditions including temperature, contact time, and ratio of inert gas to propylene should be limited in severity so that not more than about 80% by weight, based on the propylene charged to the reaction zone of the feed is converted. The yield can be as low as desired and still produce a substantial amount of the C H hydrocarbon and ethylene. However, we prefer to maintain the conversion of the propylene from about 20 to 80 weight percent based upon the propylene charged to the reaction zone. Our work has indicated that allene may be the principal immediate C H product of our reaction and that methyl acetylene may be formed by isomerization.

Although our reaction may be conducted with simultaneous heating of the steam and propylene vapors to reaction temperature, we particularly prefer to employ the method in which the inert gas is preheated to 'a temperature above the reaction temperature to raise the propylene to the temperature of reaction through mixing in a reaction zone with the feed. Thus the temperature of the propylene feed should be below that which a reaction would be effected before being mixed with the preheated inert gas to bring the propylene to reaction temperature. The simultaneous heating of the inert gas and propylene leads to excessive reactor wall temperatures which give rise to considerable coking. Further difficulty is experienced in the latter reaction in achieving constant temperature distribution in the reactor.

Our most successful reactor comprised an upper furnace section about 3 feet long surrounding a mm. quartz reactor tube which extended downwardly through a second furnacesection about 1 foot long. The two furnace sections were separated by glass wool insulation. A water inlet was provided in the quartz tube at its upper end just above the first furnace section. Extending downwardly through the first furnace section and into the second furnace section was a platinum/platinum-rhodium thermocouple for indicating the temperature of the reaction. Between the two furnace sections and at the glass wool insulation was provided a propylene inlet tube leading into the quartz reactor. The lower end of the reactor tube opened into a coil condenser which was cooled by water and provided recovery of gases and condensed liquids. The section of the quartz tube surrounded by the first furnace section preheated the inert gas to a temperature above the reaction temperature. The inert gas then flowed downwardly into the reactor section of the quartz tube packed with ceramic beads and surrounded by the second furnace section, and the gas was mixed with the propylene feed as it passed the hydrocarbon inlet. The furnace surrounding the reactor section of the tube was maintained at the reaction temperature to prevent heat loss. The results obtained with the use of this reactor system were considerably better than those produced in reactors providing for heating the inert gas and propylene feed to reaction temperature after their mixture by passage through a hot reaction tube.

It has been found desirable to conduct our reaction in a quartz reactor. For instance, the yields of C H hydrocarbons in a stainless steel reactor are considerably lower than those obtained in a quartz reactor. There is an indication that although the primary reactions follow the same course in both of these reactors, the stainless steel catalyzes the conversion of the C H hydrocarbons to carbon monoxide, carbon dioxide and hydrogen in the presence of steam.

The separation of the C H aliphatic hydrocarbons andethylene from our reaction mixtures can be effected either by chemical or physical means but the latter method is more desirable. For instance, an ethylene-containing fraction and the C H aliphatic hydrocarbons can be separated from their reaction mixture by fractionation. Ethylene can be separated from its fraction by conventional procedures.

In order to illustrate our invention in more detail we include the following specific examples which are not to be considered limiting. The reaction of each of the examples was conducted in the reactor described above in detail.

EXAMPLE I Water was pumped to the top section of the reactor by a proportioning pump and passed downwardly through the quartz reactor opposite the top furnace section maintained at a temperature sufiicient to vaporize and preheat the resulting steam to 1800 F. by the time it reached the propylene feed inlet tube. Propylene (5% propane) was vaporized and passed through the feed inlet tube and mixed with the preheated steam. The mole ratio of steam to propylene feed in the mixture was 40 to l. The flow rates of the feed and inert gas were regulated so that their contact time at reaction temperature was 0.080 second. The reaction temperature maintained was a mean 1570 F. The bottom furnace section was employed to control the temperature in the reaction zone and prevent heat losses. The reactor section was brought to reaction temperature by passage of steam and control of the furnace temperatures before propylene was admitted to the reactor. The reaction products were passed to a water coil condenser and the steam and condensable gases were collectedin traps cooled by Dry Ice and acetone. The non-condensable gas was measuredby a wet test meter and a composite .gas sample was taken for mass spectrometer analysis. The materials condensed were submitted for low temperature distillation andthe C C and 0 fractions were analyzed on amass spectrometer. The amount of coke formed was determined from analysis of the non-condensable gas (CO and CO inert gas were calculated from the free space of the reactor and the volume of gases at reaction temperature.

The run just described was No. 540-63 and the total conversion was 22.5 weight percent based on the propylene feed charged to the reactor. The product analysis based upon the weight percent of the feed charged is expressed in Table I which also shows the results obtained in several other runs in Examples II toIV made with the same propylene feed under conditions essentially as described in run No. 544-63 but with the changes noted in the table. Similar conditions were observed in Examples V and VI but the feed was 99% pure propylene in Example V and 50% propylene-50% propane in Example VI.

Table 1 1321.1 EX.II Ex.III Ex.IV Ex.V Ex.VI

Run Run Run Run Run Run 540-63 540-72 540-64 540-67 540-81 540-69 Reaction Temp,

F. (mean) 1,570 1,520 1,675 1,670 1,575 1,480 Contact time,

seconds 0.080 0.065 0.0765 0.146 0.129 0.068 Steam/propylene,

mole ratio 40 40 40 40 40 40 Total conversion,

Wt. percent 22.5 5.7 45.2 62.1 21.1 10.4 Products, Wt. percent of propylene feed:

a 9. 4 1. 6 16. 3 22. 2 7. 9 3. 3 01H; 5.2 1.7 8.1 8.8 4.8 1.2 Ultimate yield, Wt.

percentz' 1 Based on propane decomposed. 9 Based on 100% material balance.

We claim:

1. The method of producing C H aliphatic hydrocarbons and ethylene which comprises subjecting propylene to a temperature from about 1300 F. to the decomposition temperature of the C H product under the reaction conditions, at a partial pressure of propylene not greater than about one atmosphere in the pressure of at least an equal molar quantity of an inert gas and recovering C l-I aliphatic hydrocarbons and ethylene from the reaction products.

2. The, method of claim 1 in which the inert gas is steam.

3. The method of claim 1 inwhich the reaction is carried out in a quartz reaction zone.

4. The method of claim 1 in which the conversion of the propylene is not more than about weight percent.

5. The method of producing (1 H, aliphatic hydrocarbons and ethylene which comprises subjecting in a quartz reaction zone propylene to a temperature from about 1300 F. to the decomposition temperature of the 0 1-1 product under the reaction conditions at a partial pressure of propylene not greater than about one atmosphere in the presence of at least an equal molar quantity of steam which is preheated above the reaction temperature and then mixed with the propylene to bring it to reaction temperature while limiting the conversion of the propylene to not more than about 80 weight percent and recovering C H aliphatic hydrocarbons and ethylene from the reaction products.

6. The method of claim 5 in which the conversion of the propylene is limited to about 20 to 80 weight percent.

7. The method of claim 6 in which the steam is present in the ratio of about 5 to 40 moles per mole of the propylene.

8. The method of producing C H aliphatic hydrocarbons and ethylene which comprises subjecting propylene to a temperature from about 1300 F. to the decomposition temperature of the QR; product under the reaction conditions at a partial pressure of propylene not greater than about one atmosphere in the presence of at least an equal molar quantity of an inert gas which was preheated above the reaction temperature and then mixed with the propylene to bring it to reaction temperature and recovering C H aliphatic hydrocarbons and ethylene from the reaction products.

9. The method of claim 8 in which the inert gas is steam.

References Cited in the file of this patent UNITED STATES PATENTS 1,986,876 Baxter et al. Jan. 8, 1935 2,429,566 Rice Oct. 21, 1947 2,649,485 Taylor et a1 Aug. 18, 1953 2,719,872 Happel et al. Oct. 4, 1955 2,752,405 Happel et al. June 26, 1956

Claims (1)

1. THE METHOD OF PRODUCING C3H4 ALIPHATIC HYDROCARBONS AND ETHYLENE WHICH COMPRISES SUBJECTING PROPYLENE TO A TEMPERATURE FROM ABOUT 1300*F. TO THE DECOMPOSITION TEMPERATURE OF THE C3H4 PRODUCT UNDER THE REACTION CONDITIONS, AT A PARTIAL PRESSURE OF PROPYLENE NOT GREATER THAN ABOUT ONE ATMOSPHERE IN THE PRESSURE OF AT LEAST AN EQUAL MOLAR QUANTITY OF AN INERT GAS AND RECOVERING C3H4 ALIPHATIC HYDROCARBONS AND ETHYLENE FROM THE REACTION PRODUCTS.