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10 20 30 40 50 60 70 80 90 100 ETHYLENE SPACE VELOCITY.STD. Cc/hr./cc CATALYST
INVENTOR. JOSEPH. K McMAHON
United States Patent Office ^JffiS
This application is a continuation-in-part of my prior and copending application Ser. No. 11,952, filed Mar. 1, 1960, now abandoned. This application is also a division of application Ser. No. 86,045, filed Jan. 31, 1961, which in turn is a continuation-in-part of application Ser. No. 11,952, filed Mar. 1, 1960, said application Ser. No. 86,045 now being U.S. Patent No. 3,119,667.
This invention relates to an improved contact material and process for the conversion of a hydrocarbon to a hydrogen-rich gas. In one aspect this invention relates to an improved process for converting hydrocarbons to hydogen-rich gas in the presence of steam. In a more particular aspect it relates to an improved catalyst and process for the steam reforming of hydrocarbons by 25 which the amount of steam required to achieve carbonfree reforming is substantially lower than the amount required using conventional catalysts.
Hydrogen-rich gases including those containing carbon monoxide produced by steam reforming of hydrocarbons 30 may be used in the Fischer-Tropsch process for the synthesis of hydrocarbons boiling in the gasoline range or oxygenated organic compounds such as alcohols and ketones. These gases may also be used in hydrogenation processes, in ammonia, methanol, or isobutanol synthesis, as well as for the reduction of metallic oxides and as fuel for domestic and industrial uses.
In recent years, the chemical industry has begun to show interest in refinery gases, coke oven gases and low molecular weight normally liquid hydrocarbons as potential catalytic steam reforming feedstocks. Unfortunately, however, the conditions used in the successful catalytic steam reforming of a feedstock containing methane as its predominant hydrocarbon constituent, such as natural gas, are wholly unsuitable to successful reforming of feed- 45 stocks containing significant amounts of hydrocarbons heavier than methane and olefins, such as the feedstocks discussed above. When conditions suitable to natural gas reforming are used with heavier or olefinic feedstocks, carbon is produced. The formation of carbon leads to 50 coking of the catalyst, a severe reduction of catalyst activity and utility, and plugging of the catalyst bed and equipment. Such catalyst deactivation and plugging necessitates frequent interruption of the process in order to clean and recondition, making the process commercially 55 unattractive.
In the manufacture of hydrogen by the reaction of hydrocarbons such as methane with steam at elevated tem
peratures, it is generally the practice to use catalytic masses containing nicket diluted wtih a refractory material such as alumina in various proportions. The higher the molecular weight of the hydrocarbon to be gasified, the greater is the degree of cracking of the hydrocarbon charge to carbon. One method for reducing carbon deposition and coking is to employ high steam to hydrocarbon ratios, which expedient is essential when normally liquid hydrocarbons are employed as the feedstock. However, as the steam requirements become more severe, the commercial feasibility of the process is lessened because of -the cost of steam and considerations of operability. In addition to the drawback of high steam requirements, the prior art steam reforming catalysts generally are operable only with feedstocks which are substantially non-olefinic and sulfur-free.
It is, therefore, an object of this invention to provide a new and improved catalyst for the conversion of a hydrocarbon to hydrogen-rich gas.
Another object is to provide a new and improved catalyst for the conversion of a hydrocarbon to a hydrogen-rich gas in the presence of steam, the use of which permits a decrease in the minimum operable molar ratios of steam to hydrocarbon.
Another object of this invention is to provide an improved catalyst for the conversion of a normally liquid hydrocarbon including saturated and olefinic hydrocarbons and sulfur-containing feedstocks to a hydrogen-rich gas, which catalyst minimizes carbon formation. : Another object of this invention is to provide an improved catalyst for the carbon-free steam reforming of hydrocarbons above methane at steam requirements which are significantly lower than those required when standard catalysts are used.
A further object is to provide a process for the production of a hydrogen-rich gas by steam reforming of hydrocarbons in the presence of a particular catalyst, whereby carbon formation is substantially avoided and steam requirements are drastically reduced.
A further object is to provide a process for the steam reforming of normally liquid hydrocarbons including gas oil and naphtha boiling range hydrocarbons, which process is operable at relatively low steam to hydrocarbon ratios.
A still further object is to provide a method for the production of a catalyst having the above characteristics and advantages in steam reforming of hydrocarbons to hydrogen-rich gas.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.
The above objects are accomplished by contacting a hydrocarbon and steam in the presence of an alkalized catalyst comprising nickel and a refractory material under conditions such that hydrogen-rich gas is produced. Numerous advantages are realized by the use of the catalysts of this invention to effect conversion of hydro3
carbons to hydrogen-rich gas in the presence of steam. One advantage is that steam reforming of hydrocarbons is accomplished at ratios of steam-to-hydrocarbon which are significantly lower than those required when standard steam reforming catalysts are employed. Even at these lower steam requirements, carbon deposition is substantially avoided. These advantages are particularly important when olefin-containing feeds, and normally liquid and heavy hydrocarbon feedstocks are employed, since steam reforming of such feedstocks is thereby rendered a commercially feasible process. Thus by the process of this invention, available and relatively inexpensive feedstocks which heretofore could not be used because of the necessity of using prohibitively high steam requirements are rendered useful for steam reforming. In addition, feedstocks currently employed may now be converted to hydrogen-rich gas at steam requirements which are significantly lower than those now employed, thereby improving the general economics of the process. The reduction of steam requirements is particularly marked and outstanding when the catalyst contains an added alkali metal compound.
The catalysts prepared and employed in accordance with the teachings of this invention contain nickel including elemental nickel or a compound of nickel such as nickel oxide, and mixtures thereof. The nickel content of the catalysts may range between about 4 and about 40 weight percent based on the total weight of the catalyst, the high nickel catalysts usually being preferred, such as, for example, those containing between about 10 and about 30 weight percent. A second ingredient of the catalyst is an added alkaline compound of which alkali metal compounds, including those of sodium, lithium and potassium, are preferred. Typical examples of such compounds are the alkali metal salts of an oxygen-containing acid such as the carbonates, bicarbonates, nitrates, sulfates, silicates, oxalates and acetates of sodium, potassium and lithium; the alkali metal oxides or an alkali metal salt capable of yielding the oxides at elevated temperatures including the aforesaid salts, as well as the alkali metal hydroxides. Particularly efficacious catalysts are those to which an alkali metal carbonate or hydroxide has been added, especially sodium carbonate and sodium hydroxide. The catalysts are prepared as so as to provide a concentration of added alkali of at least 0.5 weight percent calculated as the metal, preferably at least 2.0 weight percent. The concentration of added alkali may be as high as 30 weight percent, and usually an amount below 20 weight percent calculated as the metal, is employed.
FIGURE 1 of the accompanying drawing presents experimental data correlating percent reduction in the minmum steam-carbon ratio required for carbon-free steam reforming, with the concentration of added alkali in the catalysts of this invention.
FIGURE 2 of the accompanying drawing shows experimental data obtained with an ethylene-ethane feed using a standard commercial catalyst as a basis of comparison.
The remainder of the catalyst charge is a porous refractory material capable of maintaining high mechanical strength and possessing steam and high temperature stability. Thus, for example, this component of the catalyst may be various non-reducible or difficulty reducible inorganic oxides such as alumino-silicates; calcium silicates; silica; zirconia; magnesia; alumina such as alpha-alumina or a form which converts to alpha-alumina under the process operating conditions; and various admixtures thereof as well as in combination with other inorganic oxides. Examples of refractory materials of the latter type are porous refractory brick and cements including chrome and hydraulic cements, which usually contain various inorganic oxides such as magnesia, calcium oxide, etc., as binding agents, combined with silica and/or alumina. From the standpoint of catalyst life, it is preferred
to employ a refractory material which is substantially inert to attack by the added alkali upon prolonged use. If the refractory does contain components capable, for example, of neutralizing the added alkali, the added alkali
5 component should be added in an amount sufficient to compensate for any loss due to neutralization and still have the net requisite amount of uncombined alkaline compound to achieve reduction of steam requirements. Thus, if it is not desired to utilize more alkali than is
10 necessary to achieve the desired effects on reduction of of steam requirements, the preferred support, from the standpoint of catalyst life, is one which is not attacked by the added alkaline compound, such as zirconia or cement-type supports which are either neutral or alkaline
15 in the presence of the added alkaline compound.
The catalysts may be prepared by a variety of methods without departing from the scope of this invention. One method comprises depositing nickel oxide on the refractory support or carrier material by soaking the support
20 with a nickel precursor compound such as nickel nitrate, nickel carbonate or nickel sulfate, by forming a slurry of the support and nickel salt and agitating, or by spraying the nickel salt solution on the support. The catalyst may then be dried and/or calcined, followed by addition
25 of the alkaline compound usually in the form of a solution, by an impregnation or soaking technique and then dried and/or calcined. Another method comprises depositing the alkaline compound on the refractory support, followed by addition of the nickel salt to the dried and/or
30 calcined composite. Alternatively, the catalysts may be prepared by simultaneous addition of the nickel and alkaline compound to the support.
In addition to the above methods, the catalysts employed in accordance with the process of this invention
3o may be prepared by impregnation or incorporation of the alkaline salt in the form of a solution, slurry or solid into a mixture comprising nickel compounded with the support. The catalysts also may be prepared by admixing the three principal components in the dry state in the desired
40 proportions without departing from the scope of this invention.
When the precursor of the nickel and/or alkali compounds are added in the form of a solution, intermediate or final drying steps may be employed to remove the
45 solvent such as water and are usually conducted at a temperature between about 200° and about 400° F. for between about 2 and about 30 hours. Those methods which employ a nickel salt include an intermediate or final calcination step to convert the nickel salt to nickel
50 oxide or nickel or mixtures thereof. Calcination may be effected at a temperature between about 800° and about 1700° F., more usually at a temperature below 1200° F., in the presence of air, nitrogen, or reducing gas for between about 2 and about 36 hours. It has been found that
55 heat treatment of the catalyst at temperatures above those ordinarily employed for calcination has a beneficial effect on the catalyst. Thus, instead of (or in addition to) the usual calcination treatment, the catalyst may be heattreated at a temperature between about 1700° F. and
GO about 2000° F. for between about 1 and about 36 hours, the catalysts so treated leading to further reduction of steam requirements.
The catalytic steam reforming process of this invention is applicable to a feedstock containing aliphatic and
C5 aromatic hydrocarbons from methane to higher molecular weight hydrocarbons including acyclic and alicyclic paraffimc and olefinic organic compounds such as those containing up to about 40 carbon atoms per molecule or molecular weights as high as about 560. The feedstock
70 may be a single hydrocarbon such as ethylene, ethane, propane, propylene, hexene, hexane, normal heptane, heptene, etc., and mixtures thereof including various petroleum fractions such as light naphtha (e.g. boiling range of about 100°-250° F.), heavy naphtha (e.g., boiling
75 range of about 200°-400° F.), gas oil (e.g., boiling range
of about 400°-700° F.), as well as mineral oils, crude petroleum including topped and residual oils, and refinery and coke oven gases.
The steam requirement for the steam-hydrocarbon reforming process is defined by the steam/carbon ratio, which is the number of mols of steam charged to the reaction zone per atom of carbon charged. For example, a feed gas composition of 6 mols of steam per mol of propane corresponds to a steam/carbon ratio of 2.0 For any individual hydrocarbon from methane to gasoline boiling range hydrocarbons and higher molecular weight fractions, including olefinic hydrocarbons, there is a minimum steam to carbon ratio required for the carbon-free (operable) catalytic reforming of that individual hydrocarbon. Among olefinic and non-olefinic hydrocarbons as distinct groups, the minimum operable steam to carbon ratios for individual members of the group vary in accordance with molecular weight. That is, as the molecular weight of the hydrocarbon to be gasified increases, the steam requirements also increase. Further, for any mixtures of hydrocarbons, the critical minimum amount of steam which may be used with the mixture for its carbon-free catalytic reforming is also dependent upon molecular weight and increases as the molecular weight of the mixture increases. From the standpoint of operability of any given steam reforming process including the process of this invention, there is no upper limit to the steam to carbon ratios which can be used. However, as stated above, there is a critical minimum steam to carbon ratio which is essential to the successful or carbon-free operation of such a process. As a practical economic matter, it is always preferred to operate with the lowest possible steam to carbon ratio in view of the cost of steam, and from the standpoint of operation of the process and size of equipment. Since it is highly desirable to operate close to the minimum operable amount of steam, and since the catalysts of this invention allow for successful continuous operation of the process at a steam/carbon ratio which is itself below the critical minimum value required for standard and presently employed catalysts, it is readily apparent that the catalyst and process of this invention constitute valuable advancements in the field of steam reforming of hydrocarbons.
It has been found that when conventional high nickel compounded steam reforming catalysts are employed to convert methane to hydrogen-rich gas, the molar ratio of steam to hydrocarbon is close to the theoretical value of 1.0 and is about 1.1. In addition, steam reforming of methane presents relatively no problem from the standpoint of carbon deposition, and can be converted with conventional catalysts at close to theoretical steam values with substantially no carbon deposition, although standard catalysts generally require the use of a relatively high excess of steam as a safety factor. As the molecular weight increases above that of methane, the steam requirements become progressively more severe. For example, when using a standard nickel steam reforming catalyst, the minimum critical steam/carbon ratio for the conversion of hydrocarbons having a molecular weight from 16 (methane) to about 110 (e.g., naphtha) or higher, increases from 1.1 to about 4, the heavier hydrocarbons requiring still higher amounts of steam. For the conversion of propane (molecular weight=44) and of heptane (molecular weight=100), for example, to hydrogen-rich gas with conventional high nickel steam reforming catalysts, the minimum steam to carbon ratios are 1.5 and 3.0, respectively.
When using the catalysts of this invention, particularly for the gasification of hydrocarbons having a molecular weight above methane, the minimum operable molar ratio of steam to organic carbon, that is, the molar ratio required for the conversion of the particular feedstock to hydrogen-rich gas with substantially no carbon formation, is significantly and markedly less than the minimum 75
operable molar ratio required for the conversion of the same feedstock in the presence of a conventional high nickel steam reforming catalyst to which no alkali metal compound has been incorporated or added. Thus, for example, when a high nickel reforming catalyst is employed to effect conversion of normal heptane to hydrogen-rich gas, the minimum operable steam/carbon ratio is about 3, whereas substantially the same conversion is continuously effected in the presence of the catalysts of this invention at significantly lower steam requirements. The same marked decrease in steam requirements is also realized when lower and higher molecular weight hydrocarbons or mixtures thereof are employed.
When saturated hydrocarbons or fractions thereof having a molecular weight from 16 (methane) to 110 (e.g., naphtha), for example, are steam reformed in the presence of the catalysts of this invention, they may be converted to admixtures of hydrogen and oxides of carbon or hydrogen-rich gas at minimum steam/carbon ratios of from 1 to about 2.0, the lower steam ratios within this range applying to the lower molecular weight hydrocarbons or mixtures thereof, the higher steam ratios applying to the higher molecular weight hydrocarbone or mixtures thereof.
When olefinic hydrocarbons or feedstocks containing olefins are steam reformed with conventional catalysts, the steam requirements are even more severe than those required for paraffinic and other saturated feedstocks of about the same molecular weight, since such feedstocks tend to deposit carbon rapidly, resulting not only in loss of carbon values but also making continuous operation impossible. On the other hand, the catalysts of this invention allow continuous steam reforming of such feedstocks at steam/carbon ratios which again are significantly lower than those required when using standard catalysts. To reduce the required steam/carbon ratio for a highly olefinic feedstock, such feedstock can be partially or wholly hydrogenated, if desired, prior to treatment by the process of this invention, such treatment being largely dependent upon economic considerations. However, due to the fact that the present catalysts permit the use of feedstocks relatively high in olefins, hydrogenation is not a necessity.
Similarly, when sulfur-containing feeds are employed, steam requirements are more severe than when sulfurfree feedstocks are utilized, sulfur tending to cause a rapid decline in the selectivity of standard catalysts and promote carbon lay down on the catalyst. Thus, presently employed high nickel steam reforming catalysts are necessarily used to effect conversions of hydrocarbon feedstocks which have been desulfurized to very low sulfur contents such as below 5 or 2 parts per million (p.p.m.). It has been found quite unexpectedly that the contact materials of this invention possess improved resistance to the usual adverse effects of sulfur-containing feeds, and may be used for the steam reforming of hydrocarbon feeds containing sulfur contents up to about 2000 p.p.m. Thus, for example, the process of the present invention may be used to reform naphtha fractions containing from about 50 to about 500 p.p.m. sulfur. The addition of hydrogen will usually be found beneficial where the feed contains sulfur compounds.
The process of the present invention may be effected over a relatively wide range of operating conditions including temperatures between about 600 and about 1800° F. When high B.t.u. hydrogen-containing gas is desired, the lower temperatures within this range are employed, such as between about 600° F. and about 1000° F. Usually the feed is preheated before introduction to the catalyst bed. Thus, for example, suitable operating conditions also include initial hydrocarbon feedstock temperatures or pre-heat temperatures of about 600° F. to about 1200° F. atmospheric or superatmospheric reforming pressures, space velocities in the reforming zone of about 50 to about 1000 volumes of hydrocarbons, ex