US3882636A - Two-stage steam reforming process of hydrocarbons - Google Patents

Abstract

A process of producing a gas rich in methane by subjecting hydrocarbons having at least two carbon atoms per molecule to steam reforming in two stages. Particularly it relates to a twostage steam reforming process of said hydrocarbons which is characterized by the steps: supplying a mixture consisting of said feed hydrocarbon and steam as pre-heated at a temperature in the range of from 350* to 550*C to the first reaction zone charged with nickel catalyst to thereby effect a reforming reaction adiabatically to the extent of leaving some hydrocarbon substantially unreacted; introducing the mixture gas flowing out of the first reaction zone, that is, the mixture gas substantially comprising the reaction product gas arising from the first-stage reforming reaction, the unreacted hydrocarbon and the unreacted steam, and falling short of the state of so-called equilibrium, into a heater to thereby heat said mixture gas; and supplying the thus heated mixture gas to the second reaction zone charged with nickel catalyst to thereby effect a reforming reaction adiabatically again; through which said feed hydrocarbon is completely converted into a methane-rich gas in the state of so-called equilibrium.

Description

United States Patent [1 1 Horie et al.

[4 1 May 13, 1975 1 TWO-STAGE STEAM REFORMING PROCESS OF HYDROCARBONS [73] Assignee: Japan Gasoline Co., Ltd., Tokyo,

Japan 22 Filed: Oct. 5, 1972 21 Appl.No.: 295,120

[30] Foreign Application Priority Data Oct. 7, 1971 Japan 46-78348 [52] US. Cl. 48/214; 48/197 R [51] Int. Cl C01b 2/14 [58] Field of Search 48/75, 62, 84, 102, 105, 48/89, 211, 214,197 R [56] References Cited UNITED STATES PATENTS 2,513,022 6/1950 l-lelmers et al 196/52 3,395,004 7/1968 Taylor et al. 48/214 3,429,680 2/1969 Watanabe et a1... 48/214 3,433,609 4/1969 Perciual et al 48/214 3,441,395 4/1969 Dent 48/214 3,449,099 6/1969 Taylor et al. ,1 48/214 3,450,514 6/1969 Sinfelt et al 48/214 3,467,506 9/1969 Roche 48/214 3,744,981 7/1973 Ward 48/214 FOREIGN PATENTS OR APPLICATIONS 820,257 9/1959 United Kingdom 48/214 l/l970 Germany 48/214 1/1970 Germany 48/214 Primary ExaminerS. Leon Bashore Assistant Examiner -Peter F. Kratz Attorney, Agent, or FirmWoodhams, Blanchard and Flynn [57] ABSTRACT A process of producing a gas rich in methane by subjecting hydrocarbons having at least two carbon atoms per molecule to steam reforming in two stages. Particularly it relates to a two-stage steam reforming process of said hydrocarbons which is characterized by the steps: supplying a mixture consisting of said feed hydrocarbon and steam as pre-heated at a temperature in the range of from 350 to 550C to the first reaction zone charged with nickel catalyst to thereby effect a reforming reaction adiabatically to the extent of leaving some hydrocarbon substantially unreacted; introducing the mixture gas flowing out of the first reaction zone, that is, the mixture gas substantially comprising the reaction product gas arising from the first-stage reforming reaction, the unreacted hydrocarbon and the unreacted steam, and falling short of the state of so-called equilibrium, into a heater to thereby heat said mixture gas; and supplying the thus heated mixture gas to the second reaction zone charged with nickel catalyst to thereby effect a reforming reaction adiabatically again; through which said feed hydrocarbon is completely converted into a methane-rich gas in the state of so-called equilibrium.

8 Claims, 4 Drawing Figures TEMPERATURE TEMPERATURE FIG. 2b

LENGTH OF THE CATALYST LAYER FIG. 3

TWO-STAGE STEAM REFORMING PROCESS OF HYDROCARBONS BACKGROUND OF THE INVENTION a. Field of the Invention The present invention relates to a process of producing a gas rich in methane by effecting the steam reforming reaction of hydrocarbons in two stages.

b. Description of the Prior Art A process of producing a methane-rich gas by subjecting mainly paraffin hydrocarbons such as butane, light naphtha, etc. or mixtures thereof to steam reforming in the presence of nickel catalyst at the reaction temperature in the range of from 400 to 550C has already been disclosed in British Pat. No. 820,257. However, when this steam reforming reaction is effected adiabatically, the activity of the catalyst used for said steam reforming reaction gradually deteriorates, rendering it difficult to continue a smooth operation of the apparatus for a long period of time. As to the cause of said deterioration of the activity of the catalyst, a view attributing it to a very thin coating layer of polymer which might be formed on the surface of the catalyst by the product arising from decomposition of the feed hydrocarbon has been expressed in Japanese Patent Publication No. 817/1971, (U.S. Pat. No. 3,459,520) etc. Based on this view, said Japanese Patent Publication No. 817/1971 has proposed a process for preventing the above mentioned deterioration of the catalyst by circulating a part of the hot reacted gas flowing out of the catalyst bed, as it is, so as to mix with the mixture of the vapor of feed hydrocarbon and steam before it passes through the nickel catalyst bed.

On the other hand, U.S. Pat. No. 3,441,395 has proposed a process of producing combustible gases having a relatively low calorific value, which comprises the steps: supplying a mixture of the feed hydrocarbon and steam to the first gasification stage charged with nickel catalyst; adiabatically effecting the reforming reaction at a temperature below 600C so as to convert said feed hydrocarbon completely; introducing the product gas arising from the foregoing reforming reaction into a fired preheater to subject it to heating therein; and supplying the thus preheated gas to the second reforming stage charged with the reforming catalyst to thereby effect the reforming reaction for decomposing methane produced in the first gasification stage by applying a temperature in the range of from 620 to 800C.

SUMMARY OF THE INVENTION The present invention has been achieved as a result of investigation of the steam reforming reaction of hydrocarbons from the viewpoint of chemical equilibrium and is intended to provide a two-stage steam reforming process which renders it possible to continue a smooth operation of the apparatus extending over a long period of time.

To be precise, the present invention relates to a process of producing a methane-rich gas by effecting steam reforming of hydrocarbons having two or more carbon atoms per molecule in two stages, which is characterized by the steps: supplying a mixture consisting of feed hydrocarbon as set forth above and steam preheated at a temperature in the range of from 350 to 550C to the first reaction zone charged with nickel catalyst so as to make the weight ratio (W /F) of the charged catalyst to the feed hydrocarbon per hour be 0.04a to 1104, preferably 0.04a to 0.1404 wherein a= 0.5 0.5 X 10 X [Mean Av. B.P. of Feed IIC (C) 1 to thereby effect reforming reaction adiabatically to the extent of leaving some hydrocarbon substantially unreacted; introducing the mixture gas flowing out of the first reaction zone, that is, the mixture gas substantially comprising the reaction product gas arising from the first-stage reforming reaction, the unreacted hydrocarbon and the unreacted steam and falling short of the state of so-called equilibrium, into a heater to thereby apply heat of 10 to 72 Kcal per Kg of said mixture gas; and supplying the thus heated mixture gas flowing out of the heater to the second reaction zone charged with nickel catalyst so as to make the weight ratio (W /F) of the charged catalyst to the feed hydrocarbon per hour be 1 to 20 times preferably 10 to 20 times as much as W /F, to thereby effect reforming reaction adiabatically again to attain the temperature of said mixture gas in the range of from 350 to 550C at the outlet of the second reaction zone through which steps said feed hydrocarbon is completely converted into a methane-rich gas in the state of so-called equilibrium.

BRIEF DESCRIPTION OF THE DRAWING In the appended drawings,

FIG. 1 is a graph illustrative of relation between the length of the catalyst bed (layer) employed for the conventional single-stage steam reforming process and the distribution of temperature as observed with the passage of time.

FIG. 2 shows graphs illustrative of the relation between the length of the catalyst bed employed for the two-stage steam reforming process in Example 1 embodying the present invention and the distribution of temperature as observed with the passage of time, wherein (a) shows one mode of said distribution in the first reaction zone and (b) shows one mode of said distribution in the second reaction zone.

FIG. 3 is a flow scheme diagrammatically representing one embodiment of the process according to the present invention, wherein the numeral reference 1 denotes a feed inlet, 2 denotes the first reaction zone, 2 denotes the first reaction zone for switchover, 3 denotes a heater, 4 denotes the second reaction zone, 5 denotes an outlet for the product gas, and V,, V V and V respectively denote valves.

DETAILED DESCRIPTION OF THE INVENTION According to studies of the mechanism of the steam reforming reaction of hydrocarbons having two or more carbon atoms per molecule in relation to the distribution of the temperature, there first occurs an endothermic reaction between the feed hydrocarbon and steam to produce hydrogen, carbon monoxide, etc., next there occurs exothermic reaction between the thus produced hydrogen and the hydrocarbon to produce methane, and at the same time, there occur exothermic reactions between the carbon monoxide and the hydrogen together with an exothermic reaction between the carbon monoxide and the steam to produce carbon dioxide, whereupon the reforming reaction is complete. In the present invention, the condition in which the steam reforming reaction of feed hydrocarbons has been completed is meant by the so-called equilibrium state, namely, said reaction resulting in the production of a gaseous mixture consisting of methane, hydrogen and oxides of carbon due to the complete conversion of feed hydrocarbons with steam. On this occasion, the relation between the length of catalyst bed indicated by the abscissa and the temperature indicated by the axis of ordinate can be expressed by the curve 1 in FIG. 1. This curve, however, gradually changes to a curve having a widely depressed portion such as the curve 2 in FIG. 1 with the passage of time of the steam reforming reaction of hydrocarbon, and it becomes a curve having a flatly depressedportion such as the curve 3 in FIG. 1 with the passage. of further prolonged reaction time. Such lowering of the temperature of the catalyst bed as shown by these curves 2 and 3 hampers the action of the desired reforming reaction and entails the deterioration of the activity of catalyst. In case saidreforming reaction is effectedextending over a long period of time, the feed hydrocarbon falling short of the state of equilibrium flows out of the reforming reaction zone, rendering it infeasible to attain a desired conversion rate. Although, it is possible to check the lowering of temperature of said catalyst bed on this occasion by means of application of a higher inlet temperature of the reforming reaction zone, namely, a temperature of more than 550C, this method causes undesirable effects such as the occurrence of thermal cracking of said feed hydrocarbon so that it deviates from the scope of the lowertemperature steam reforming process claimed in the present invention.

As the means to cope with the foregoing troubles and to render it possible to effect said reforming reaction smoothly at a desired conversion rate and extending over a long period of time, the following three processes are conceivable.

i. A process wherein the catalyst for use in the steam reforming reaction of hydrocarbon is employed in a large excess amount.

ii. A process wherein hydrogen is introduced into the steam reforming reaction system with the hydrocarbon and the exothermic reaction between the hydrocarbon and the supplied hydrogen to generate methane is effected simulutaneously with the aforementioned endothermic reaction to generate carbon monoxide, hydrogen, etc., to thereby minimize the lowering of the temperature in the reforming reaction zone.

iii. A process comprising the steps that a fluid whose temperature has been lowered as a result of the endothermic reaction effected in the steam reforming reaction zone is temporarily taken out of the reaction system to elevate its temperature by means of a heater, and subsequently the thus treated fluid is again subjected to reforming reaction in the second reforming reaction zone, whereby the feed hydrocarbon is completely converted.

The present invention relates to the process (iii) in the foregoing.

Typical hydrocarbons having two or more carbon atoms per molecule to be subjected to the process according to the present invention include the exhaust gas arising from petroleum oil refining, LPG, light naphtha, heavy naphtha, kerosene, and the like. And, the steam reforming reaction in the first reaction zone is adiabatically effected in the presence of a nickel catalyst under the reaction conditions of the molar ratio of steam per carbon atom of the feed hydrocarbon being 1.0 to 5.0, the inlet temperature being 350 to 550C and the pressure being to 100 Kglcm This nickel catalyst is selected from among the conventional catalysts used in low-temperature steam reforming reaction. Suitable catalysts include those comprising the metals belonging to Group. VIII, the I I metals belonging to the left column in Group VII, the

metals belonging to the left column in Group VLthe I nickel oxide with magnesium oxide. to the extent' of 5 to 60% of magnesium oxide by weight, based on the weight of nickel oxide, adding the oxide of at least one metal selected from the group conweight, based on the weight of nickel oxide contained therein, carrying the thus obtained catalyst on asupport consisting of diatomaceous earth, and then acti-,-

vating this catalyst by reducing at a temperature in the range of 400 to 500C. This nickel catalyst is also applicable to the reforming reactioncarried out in the second reaction zone. In the embodiments of the present invention shown later on, the catalyst charged in' the first reaction zone and thatin the second reaction zone are identical, but they maybe different from each other.

Further, the reaction in the firstreaction zone according to the process of the present invention is effected on the premise that it should be stopped while. the steam reforming reaction of the feed hydrocarbon is short of attaining the state of so-called equilibrium,

that is, prior to complete conversion of said hydrocar I bon. On this occasion, however, as the catalyst is pos- I sessed of sufficient activity for a time following the start, of reaction, there is an instance of said reforming reac- 1 tion in the first reaction zone attaining temporary equilibrium. But; this is just a temporary phenomenon sub- 4O sequent to the start of reaction, and does not constitute the present invention, at the time of effecting the steam reforminng reaction of hydrocarbon, the quantity of i catalyst to be charged in thefirst reaction zone should be sufficient for attaining the conversion rate of the feed hydrocarbon to the extent of about 20. to 80% preferably 20 to 35%. On this occasion, the quantity of catalyst necessary for complete conversion of the feed actlon time and, at the same time, varles with the properties of said catalyst and feed hydrocarbon as well as the reaction conditions. And, especially it depends on g the mean average boiling point (C), which willbe hereinafter referred'to as Mean Av; B.P.of Feed H.C.,l

first reaction zone, that is, the quantityof catalyst necessary for converting 20 to 80% of thefeed hydrocar-,

following equation. In this equation, W /FrepreSents the weight (W,) of catalyst to be charged relative to the weight (F) of feed hydrocarbon per hour.

W /F= 0.5 0.5 X 10 X [Mean Av..B.P. of Feed H.C. (OC) (0.04 to 0.22)

On this occasion, when the conversion rate of the,

feed hydrocarbon attains more than 35%, there occurs mainly an exothermic reaction producing methane and, the temperature of catalyst bed rises, so that the merit:

of application of heat half-way between the firstreacsisting of copper, chromium and: manganese to the re- 7 sulting co-precipitate to the extent of 4 to 15% by.

any particular impediment to the purpose of the present invention. Therefore, according to. the process of V hydrocarbon per hour increases with the passage of re,-

When the quantityofcatalyst to be charged inth'e I bon, was estimated in due consideration of said Mean Av. B.P. of Feed II.C. (iCLit can be expressed by the tion zone and the second reaction zone diminishes. Therefore, it is preferable to set the conversion rate of the feed hydrocarbon in the first reaction zone to be in the range of 20 to 35%. When the quantity of catalyst necessary for converting 20 to 35% of the feed hydrocarbon was estimated, it can to be expressed by the following equation, W lF therein being identical with W /F in the previous equation.

W,/F= 0.5 0.5 X X [Mean Av. B.P. of Feed l-I'.C. (C) 1 (0.04 to 0.14)

In case of continuous operation extending over a long period of time, however, it is anticipated that the conversion rate in the first reaction zone may become less than To cope with this as another object, the present invention proposes the provision of a reaction zone for switchover denoted by 2 in FIG. 3 disposed parallel with the first reaction zone denoted by 2 in FIG. 3. A pair of the first reaction zones disposed parallel to each i other as above are alternately employed through operation of the relevant valve. Referring still to FIG. 3, the feed hydrocarbon and steam supplied through the line 1 is introduced into the first reaction zone 2 through the opened valve V and is subjected to adiabatic 'steam reforming to the extent of conversion rate in the jected to steam reforming adiabatically. As a result,

saidfeed hydrocarbon is completely converted and is taken out through the line 5.

In the case of effecting this steam reforming reaction continuously extending over a long period of time, at the point of time where the deterioration of activity of the catalyst charged in the first reaction zone 2 has been observed, that is, at the point where it has become impossible to keep the conversion rate of 20 to 35% any longer, said valve V and valve V are opened, while the valve V and valve V are closed.

In the meantime, the first reaction zone 2 is charged with active catalyst and is employed alternately until the activity of the catalyst charged in the second reaction zone 4 deteriorates. As a result, the feed hydrocarbon supplied through the line 1 is introduced into the first reaction zone 2' and subjected to adiabatic steam reforming at the aforementioned conversion rate again, so that a continuous operation extending over a long in the second reaction zone, it is required to be sufficient for effecting complete conversion of undecomposed feed hydrocarbon extending over a long period of time. According to the process of the present invention, it is desirable to charge the second reaction zone with said catalyst to the extent of 1 to 20 parts by weight per part by weight of the catalyst charged in the first reaction zone, namely, the weight ratio (W jF) of the charged catalyst in the second reaction zone to the feed hydrocarbon per hour being 1 to 20 times as much as that (W /F) of the charged catalyst in the first reaction zone to the feed hydrocarbon per hour.

As discussed in the foregoing, the process of the present invention is intended to produce the methane-rich gas at the desired conversion rate byeffecting a steam reforming reaction of hydrocarbons in two stages, not in a single stage as in'the conventional process, and further minimizing the effect of the lowering of temperature of the catalyst bed within the steam reforming reaction zones for hydrocarbons by virtue of the provision of a heater to heat the reacted gas between the first reaction zone and second reaction zone.

It has been found that, according to the process of the present invention which features the adoption of the steam reforming reaction zone consisting of two stages and the heater disposed between them, the life span of the catalyst applied is about twice as long as that of the catalyst applied to the conventional process employing a single-stage reaction zone when the steam reforming reaction is effected under the same reaction conditions by employing the same catalyst in the same quantity. This is considered attributable to the avoidance of the lowering of temperature of the catalyst bed as shown by the curve 2 and curve 3 in FIG. 1 which is rendered possible by the present process.

I-Iereunder will be given concrete examples illustrative of the present invention. In practicing the process of the present invention, in order to equalize the composition of its product gas and the counterpart in the conventional process, the feed hydrocarbon was preheated by applying heat which value had been reduced by the heat value to be furnished by the heater disposed between the first reaction zone and the second reaction zone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1.

By employing naphtha having six carbon atoms on the average per molecule, IBP of 35C, FBP of C and specific gravity (1,, 4 of 0.67 as the feed hydrocarbon, a steam reforming reaction was effected adiabatically by applying the conventional single-stage process and the two-stage process according to the present invention respectively.

i. Steam reforming reaction according to the conventional single-stage process (Comparative Example 1) The feed hydrocarbon was first mixed with steam at the rate of 1.5 mol of steam per carbon atom of hydrocarbon. Then, this mixture was introduced into an adiabatic reaction zone charged with 0.64 Kg of nickel catalyst prepared by the method disclosed in Japanese Patent Publication No. 7580/1971 (that is, a nickel catalyst obtained by the process: adding diatomaceous earth to an aqueous solution of nickel sulfate and magnesium sulfate, adding a complex salt of ammonia containing Cu, Cr, and Mn at the molar ratio of 111:0.1 to the resulting cake, and filtering the resulting mixture) at the mass velocity of 5,000 Kg/m hr and inlet temperature of 503C, and was maintained at an absolute pressure of 21 atom. As a result, the outlet temperature became 535C as shown in FIG. 1l. The distribution of temperature in the nickel catalyst bed in the adiabatic reaction zone on this occasion was as shown in FIG. l, and, with the lapse of reaction time, the curve i changed to the curve 3 through the curve 2.

This indicates that the activity of nickel catalyst gradually deteriorated and that a lot of catalyst is still necessary before the steam reforming reaction of hydrocarbon attains the state of so-called equilibrium and is completed. In this connection, through measurement of said distribution of temperature at this pointof time, it is possible to calculate the quantity of catalyst still necessary for completion of the reaction. Besides, on the basis of application of a fixed quantity of catalyst, through measurement of the time required for making the gas produced in the steam reforming reaction zone exit in the state of falling short of equilibrium, it is possible to measure the condition of deterioration of the catalyst.

Therefore, by applying the above procedures, the duration of effective operation of the steam reforming reaction and the composition of the product gas corresponding to it were measured. The results were as shown in Table l-a below.

ii. Steam reforming reaction according to the two-stage process of the present invention (Example 1) The feed hydrocarbon was first mixed with steam at the rate of 1.5 mols of steam per 1 carbon atom of said hydrocarbon; Then, this mixture was introduced into the first adiabatic reaction zone charged with 0.004 Kg of the same nickel catalyst as that described in Comparative Example 1 above at the mass velocity of 5,000 Kg/m .hr and inlet temperature of 480C, and was maintained to have the absolute pressure of21 atm. As a result, the outlet temperature became 490C as shown in FIG. 2, curve 1. Thereafter, with the passage of reaction time, the temperature distribution curve l" for the catalyst bed changed to the curve 3 through the curve 2. With this, the outlet temperature also lowered gradually. With said lowering of temperature of catalyst bed, the content of the undecomposed hydrocarbon in the mixture gas flowing out of the first reaction zone showed a tendency toward gradual increase, though in small increments. Next, the mixture gas thus flowing out of the first reaction zone was introduced into a fired heater, whereby heat was supplied to the mixture gas at the rate of 14 Kcal per Kg of said gas. The thus heated mixture gas was then introduced into the second reaction zone charged with 0.60 Kg of the same nickel catalyst as that charged in the first reaction zone and was again subjected to a steam reforming reaction adiabatically under the absolute pressure of 21 atm. The outlet temperature ofthe second reaction zone on this occasion was 535C.

When the duration of the effective operation of steam reforming reaction and the composition of product gas corresponding to it were measured in the same way as in Comparative Example. 1 by applying the above procedure, the results were as shown in Table l-b below.

Table 1 duration of effective operation of steam reforming reaction l890 hrs. 4120 hrs.

corresponding to it were measured in the same way as *The composition of product gas was analyzed by gaschromatography.

EXAMPLE 2.

By employing the same feedhydrocarbon and nickel catalyst as in Example 1 above, a steam reforming reaction was effected adiabaticallyfunder the following action conditions.

i. Steam reforming reaction according tothe, conventional single-stage process (Comparative Example 2) t The feed hydrocarbonwas first mixed with steam at" the rate of 4.0 mols of steam per carbon atom of hydrocarbon. Then, this mixture was introduced intofadiabatic reaction zone charged with 0.31 Kg of nickel cat- I alyst at the inlet temperature of 535C. Theapplied pressure and mass velocity were. equal to those in Com-" 1' parative Example 1. As a result, the outlet temperature I was 500C. When the duration .of effective operation of steam reforming reaction and the composition of product gas corresponding to it were measured inthe same" way as in Example 1, the results were as shown in Table 2-a below.

ii. Steam reforming reaction according to the two stage process of the present invention (Example '2) The feed hydrocarbon was mixed with steam at the rate of 4.0 mols of steam per carbon atom of hydrocarj bon. Then, this mixture wasintrjoduced into the first re-.

action zone charged with 0.08 Kg ofnickel catalyst at I the inlet temperature of 495C. The applied pressure and mass velocity on this occasion were equal to those in Example 1 above. Next, the mixture gas flowing out of the first reaction zone was introduced into a fired heater, whereby heat was supplied to the. mixture gas at the rate of 22 Kcal per Kg of said gas. The thus heated gas mixture was then introduced into theseco'nd reaction zone charged with 0.23 Kg of nickel catalyst and was again subjected to a steam reformingreaction adiabatically so as to attain 500C.

When the duration of effective operation of steam i i reforming reaction and the composition of product gas in Example 1, the results. were as shown in Table 2 -h below.

Table 2 the outlet temperature of duration of effective operation of steam reforming reaction 753 hrs. 1533 hrs.

Table 2-Continued Table 3 a b a b 5 duration of effectquantity of catalyst 0.31 Kg 0.31 Kg ive operation of 536 hrs. 1045 hrs.

(first stage 0.08 Kg steam reforming second stage 023 Kg) reaction composition of mol% mol% quantity of Catalyst Kg t t 80 08 K d t 2 HS s age g pm He gas 10 second stage 0.23 Kg) (Dry Base) *CHJ 44-6 44.6 COUAPOSIUOIl of mol% mol% pro uct gas. 2 32.5 32.3 (Dry BaSe) CO 0.7 0.8 C 4 49.7 49.6 CO 22.2 22.3 l-l 28.4 28.4 CO 1.5 1.5 The composition of product gas was analyzed by gas-chromatography. CO2 204 Example 3.

By employing heavy naphtha having seven carbon atoms on the average per molecule, IBP of 40C, FBP of 180C and specific gravity d 15 of 0.69 as the feed hydrocarbon and the same nickel catalyst as described in Example 1, a steam reforming reaction was effected adiabatically.

i. Steam reforming reaction according to the conventional single-stage process (Comparative Example 3) The feed hydrocarbon was first mixed with steam at the rate of 2.0 mols of steam per carbon atom of hydrocarbon. Then, this mixture was introduced into an adiabatic reaction zone charged with 0.31 Kg of nickel catalyst at the inlet temperature of 530C. The applied pressure and mass velocity on this occasion were equal to those in Comparative Example 1. As a result, the outlet temperature became 500C.

When the duration of effective operation of steam reforming reaction and the composition of product gas corresponding to it were measured in the same way as in Example 1, the result were as shown in Table 3-a below.

ii. Steam reforming reaction according to the two-stage process of the present invention.

The feed hydrocarbon was first mixed with steam at the rate of 4.0 mols of steam per carbon atom of hydrocarbon. Then, this mixture was introduced into the first reaction zone charged with 0.008 Kg of nickel at the inlet temperature of 510C. The applied pressure and mass velocity on this occasion were equal to those in Example 1 above. Next, the gas mixture flowing out of the first reaction zone was introduced into a fired heater, whereby heat was supplied to the mixture gas at the rate of 12 Kcal per Kg of said gas. The thus heated gas mixture was then introduced into the second reaction zone charged with 0.23 Kg of nickel catalyst and was again subjected to a steam reforming reaction adiabatically so as to attain the outlet temperature of 500C.

When the duration of effective operation of steam reforming reaction and the composition of product gas corresponding to it were measured in the same way as in Example 1, the results were as shown in Table 3- below.

*The composition of product gas was analyzed by gas-chromatography.

What is claimed is:

l. A process for producing a methane-rich gas by the steam reforming of feed hydrocarbons having two or more carbon atoms per molecule and capable of being steam reformed, comprising:

A. supplying a preheated gaseous mixture consisting of said feed hydrocarbon and steam, at a temperature in the range of 350 to 550C, to a first reforming reaction zone charged with a nickel reforming catalyst, the hourly rate of supplying such mixture being such that the following equation is satisfied:

W /F= 0.0401 to 022a wherein W, weight of charged catalyst F weight of supplied hydrocarbon per hour M mean average boiling point of feed hydrocarbons in C,

to effect an incomplete adiabatic reforming reaction in said first reaction zone to react from 20 to of said feed hydrocarbon and with the remainder of said feed hydrocarbon being unreacted, thereby to produce a first gaseous reaction product containing unreacted feed hydrocarbon and unreacted steam,

B. withdrawing said first reaction product from said first reforming reaction zone and introducing it directly into a heating zone and heating it in said heating zone sufficiently to add to said first reaction product from 10 to 72 Kcal per Kg of said first reaction product to produce a heated reaction mixture, and

C. introducing said heated reaction mixture into a second reforming reaction zone charged with a nickel reforming catalyst at the rate such that W /F= l to 20 times W /F wherein W weight of charged catalyst in the second reforming reaction zone, and

W and F are as defined above, to effect a second adiabatic reforming reaction of said heated reaction mixture to complete reaction of said feed hydrocarbon, thereby to produce a final gaseous product in which the carbon compounds present therein connsist essentially of CH.,, CO and CO said final gaseous product at the exit end of the second reforming reaction zone having a temperature in the range of 350 to 550C, and withdrawing said final gaseous product from said second reforming reaction zone.

2. A process according to claim 1, wherein the weight ratio W /F of the catalyst charged in the first reaction zone to the feed hydrocarbon per hour is in the rannge of 0.040: to 0.1401.

3. A process according to claim 1, wherein the weight ratio W /F) of the catalyst charged in the second reaction zone to the feed hydrocarbon per hour is in the range of 10 to 20 times the weight ratio W /F of the catalyst charged in the first reaction zone to the feed by drocarbon per hour.

4. A process according to claim 1, wherein the reforming reaction in said first reaction zone is effected at a ratio of steam to carbon atom of the feed hydrocarbon in the range of 1.0 to 5.0 mols, and the pressure is in the range of to 100 Kg/cm G.

5. A process according to claim 1, wherein said hydrocarbons having two or more carbon atoms per molecule are selected from the group consisting of the off gas arising from a petroleum oil refinery, LPG, light naphtha, heavy naphtha and kerosene.

6. A process according to claim 1, in which said first reaction zone consists of at least two reaction chambers j connected in parallel and in which said preheated gaseous mixture is supplied to one of said chambers until i the reaction of said feed hydrocarbon therein becomes less than 20%, then terminatingsupply of said preheated gaseous mixture to said one chamber and supplying it to another reaction chamber.

7. A process according to claim 1, wherein said the group consisting of copper, chromium and manga-,

nese; said catalyst being supported on a carrierof" idatomaceous earth.

8. A process according to claim 1, in which from 20% to a maximum of of said feed hydrocarbon is re acted in said first reforming reaction zone.

UNITED STATES PATENT OFFICE QER'HHCATE 0F QURRECTWN 9 Patent No. 3 882 636 Dated May 13, 1975 Inventor(s) Akira Horie, Seiichi Matsuoka and Kenzo Yamamoto It is certified that error appears in the above-identified patent Q and that said Letters Patent are hereby corrected as shown below:

Col. 11, line 3; change "rannge" to range-.

Col. 11, line 6; change "W /F) to -W /F-.

Q Col. 12, line 7; after "chamber" and before the period insert of said first reaction zone.

Col. 12, line 17; change "idatomaceous" to -diatomaceous fia'gmd and eae this twenty-sixth Day 0f August 1975 [SEAL] Arrest:

RUTH- C. M A SON C. MARSHALL DANN Arresting Officer Commissioner uj'Patents and Trademarks

Claims (8)

1. A PROCESS FOR PRODUCING A METHANE-RICH GAS BY THE STEAM REFORMING OF FEED HYDROCARBONS HAVING TWO OR MORE CARBON ATOMS PER MOLECULE AND CAPABLE OF BEING STEAM REFORMED, COMPRISING: A. SUPPLYING A PREHEATED GASEOUS MIXTURE CONSISTING OF SAID FEED HYDROCARBON AND STEAM, AT A TEMPERATURE IN THE RANGE OF 350* TO 550*C, TO A FIRST REFORMING REACTION ZONE CHARGED WITH A NICKEL REFORMING CATALYST, THE HOURLY RATE OF SUPPLYING SUCH MIXTURE BEING SUCH THAT THE FOLLOWING EQUATION IS SATISFIED: W1/F =0.04A TO 0.22A WHEREIN W1 = WEIGHT OF CHARGED CATALYST F = WEIGHT OF SUPPLIED HYDROCARBON PER HOUR A = 0.5+0.5$10*5$M2.77 M = MEAN AVERAGE BOILING POINT OF FEED HYDROCARBONS IN *C, TO EFFECT AN INCOMPLETE ADIABATIC REFORMING REACTION IN SAID FIRST REACTION ZONE TO REACT FROM 20 TO 80% OF SAID FEED HYDROCARBON AND WITH THE REMAINDER OF SAID FEED HYDROCARBON BEING UNREACTED, THEREBY TO PRODUCE A FIRST GASEOUS REACTION PRODUCT CONTAINING UNREACTED FEED HYDROCARBON AND UNREACTED STEAM, B. WITHDRAWING SAID FIRST REACTION PRODUCT FROM SAID FIRST REFORMING REACTION ZONE AND INTRODUCING IT DIRECTLY INTO A HEATING ZONE AND HEATING IT IN SAID HEATING ZONE SUFFICIENTLY TO ADD TO SAID FIRST REACTION PRODUCT FROM 10 TO 72 KCAL PER KG OF SAID FIRST REACTION PRODUCT TO PRODUCE A HEATED REACTION MIXTURE, AND C. INTRODUCING SAID HEATED REACTION MIXTURE INTO A SECOND REFORMING REACTION ZONE CHARGED WITH A NICKEL REFORMING CATALYST AT THE RATE SUCH THAT W2/F = 1 TO 20 TIMES W1/F WHEREIN W2 = WEIGHT OF CHARGED CATALYST IN THE SECOND REFORMING REACTION ZONE, AND W1 AND F ARE AS DEFINED ABOVE, TO EFFECT A SECOND ADIABATIC REFORMING REACTION OF SAID HEATED REACTION MIXTURE TO COMPLETE REACTION OF SAID FEED HYDROCARBON, THEREBY TO PRODUCE A FINAL GASEOUS PRODUCT IN WHICH THE CARBON COMPOUNDS PRESENT THEREIN CONNSIST ESSENTIALLY OF CH4, CO AND CO2, SAID FINAL GASEOUS PRODUCT AT THE EXIT END OF THE SECOND REFORMING REACTION ZONE HAVING A TEMPERATURE IN THE RANGE OF 350* TO 550*C, AND WITHDRAWING SAID FINAL GASEOUS PRODUCT FROM SAID SECOND REFORMING REACTION ZONE.

2. A process according to claim 1, wherein the weight ratio W1/F of the catalyst charged in the first reaction zone to the feed hydrocarbon per hour is in the rannge of 0.04 Alpha to 0.14 Alpha .

3. A process according to claim 1, wHerein the weight ratio W2/F) of the catalyst charged in the second reaction zone to the feed hydrocarbon per hour is in the range of 10 to 20 times the weight ratio W1/F of the catalyst charged in the first reaction zone to the feed hydrocarbon per hour.

4. A process according to claim 1, wherein the reforming reaction in said first reaction zone is effected at a ratio of steam to carbon atom of the feed hydrocarbon in the range of 1.0 to 5.0 mols, and the pressure is in the range of 0 to 100 Kg/cm2G.

5. A process according to claim 1, wherein said hydrocarbons having two or more carbon atoms per molecule are selected from the group consisting of the off gas arising from a petroleum oil refinery, LPG, light naphtha, heavy naphtha and kerosene.

6. A process according to claim 1, in which said first reaction zone consists of at least two reaction chambers connected in parallel and in which said preheated gaseous mixture is supplied to one of said chambers until the reaction of said feed hydrocarbon therein becomes less than 20%, then terminating supply of said preheated gaseous mixture to said one chamber and supplying it to another reaction chamber.

7. A process according to claim 1, wherein said nickel reforming catalyst consists of a coprecipitate of nickel oxide with magnesium oxide containing 5 to 60% of magnesium oxide by weight, based on the weight of nickel oxide, said coprecipitate having mixed therein from 4 to 15%, based on the weight of nickel oxide, of an oxide of at least one metal selected from the group consisting of copper, chromium and manganese; said catalyst being supported on a carrier of idatomaceous earth.

8. A process according to claim 1, in which from 20% to a maximum of 35% of said feed hydrocarbon is reacted in said first reforming reaction zone.

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