WO2005063615A1

WO2005063615A1 - Process for continuous production of carbon monoxide-free hydrogen from methane-rich hydrocarbons

Info

Publication number: WO2005063615A1
Application number: PCT/IN2003/000405
Authority: WO
Inventors: Vasant Ramchandra Choudhary; Amarjeet Munshiram Rajput
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2003-12-29
Filing date: 2003-12-29
Publication date: 2005-07-14
Also published as: AU2003290405A1

Abstract

The present invention relates to a catalytic process for the continuous production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons using a solid catalyst comprising group VIII metal(s) in two parallel catalytic reactors.

Description

IN/PA-506

PROCESS FOR CONTINUOUS PRODUCTION OF CARBON MONOXEDE-FREE HYDROGEN FROM METHANE-RICH HYDROCARBONS

FIELD OF THE PRESENT INVENTION

This invention relates to a process for the continuous production of carbon monoxide-free hydrogen from methane or methanerrich hydrocarbons using group VIII metal(s) containing solid catalyst in two parallel reactors. This invention particularly relates to a process for the continuous production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons using group VIII metal(s) containing solid catalyst in two parallel reactors operated in a cyclic manner for two different reactions, one the decomposition of methane or methane-rich hydrocarbons to hydrogen and carbon, which is deposited on the catalyst, and second the gasification of the carbon deposited on the catalyst by steam in the presence or absence of oxygen, carried out simultaneously in the two reactors, and collecting the product stream of each of the two reactions separately. The process of this invention could be used in the petroleum refining and chemical industries for the production of carbon monoxide-free hydrogen required for proton exchange membrane fuel cells and also for the various hydro-treating processes in the petroleum refining and hydrogenation processes in chemical industries. BACKGROUND OF THE PRESENT INVENTION The demand for hydrogen has been increasing day-by-day for the hydro treating processes in petroleum industries and also for hydrogen fuel cells, both stationery and non- stationery, fuel cells. Since hydrogen is a non-polluting fuel, its use as a fuel, particularly for fuel cells has been increasing very fast. However, the well-established proton exchanged membrane fuel cells require carbon monoxide-free hydrogen as a fuel to avoid deactivation of the noble metal catalyst in the fuel cells. The main natural sources of hydrogen are hydrocarbons and water. Among the hydrocarbons methane has the highest hydrogen to carbon ratio and hence it is the most preferred choice among the hydrocarbons for hydrogen production. The conventional processes for the production of hydrogen are based on steam reforming of hydrocarbons, such as naphtha and methane or natural gas and auto thermal reforming of hydrocarbons, particularly heavier hydrocarbons. The hydrogen production processes have been recently reviewed by Fierro and coworkers [reference : IN/PA-506

Pena, M. A., Gomez, J. P. and Fierro, J. L. G.J Applied Catalysis A- General; volume 144, page 7-57, year 1996].

Both the hydrocarbon steam reforming and auto thermal reforming processes are operated at high temperatures, above about 900"C and the product stream of these processes contains appreciable amounts of carbon monoxide along with hydrogen. The removal of carbon monoxide at low concentrations from hydrogen is very costly. Hence, the hydrocarbon steam reforming and auto thermal reforming processes are not economical for the production of carbon monoxide-free hydrogen. Hence, there is a practical need to develop a process for the production of hydrogen form methane as it has highest hydrogen to carbon ratio among the hydrocarbons, at a temperatures lower than that ' used in the conventional hydrocarbon steam reforming and auto thermal reforming processes. A few processes are known also for the production of carbon monoxide-free hydrogen from methane. Recently, Kikuchi [reference: Kikuchi, E., Hydro gen-permselective membrane reactors, CATTECH, March 1997, page 67-74, Baltzer Science Publishers] has described a process based on steam reforming of methane in membrane reactor to produce hydrogen free of carbon monoxide. By applying Pd/ceramic composite membrane to steam reforming of methane over a commercial supported nickel catalyst, methane conversion upto 100% can be accomplished in Pd-membrane reactor at temperatures as low as 500"C to produce carbon monoxide-free hydrogen. In this process, the hydrogen produced in the steam reforming of methane is continuously removed from the reaction system by the selective permeation of hydrogen through the Pd-membrane. However this process has not yet been commercialized and it has following drawbacks/limitations : l) Because of the use of a number of Pd- membrane tubes, the capital cost of this process is very high. 2) There is a possibility that the Pd-membrane becomes deactivated by deposition of carbonaceous matter. 3) There is also a problem of membrane stability and/or a possibility of membrane failure due to formation of pinholes in the membrane. ^•A Japanese patent [Jpn. Kokai Tokkyo Koho JP 09234372 A2, September 09, 1997] disclosed a process for the manufacture of hydrogen by thermal decomposition of hydrocarbons at 200°C-1000°C using a catalyst containing nickel, alkali or alkaline earth compounds. A Russian patent [Russ. RU 2071932 CI January 20, 1997] disclosed the production of hydrogen and carbon by thermal'decomposition of methane on nickel catalyst. IN/PA-506

A recent Japanese patent [Jpn. Kokai Tokkyo Koho JP 11228102 A2, August 24, 1999] disclosed reactors for thermal decomposition of methane to form carbon and hydrogen. Hydrogen production by catalytic cracking of methane or natural gas and other hydrocarbons, at below 900°C using nickel-based catalyst is disclosed in a few publications [reference: Zhang, T and Amiridis, M. D., Applied Catalysis A: General, volume 167, page 161-172, year 1998; Muradov, N. Z., Energy Fuels, volume 12, page 41-48, year 1998; Kuvshinov, G. G. et. al. Hydrogen Energy Progress XI Proceedings of World Hydrogen Energy Conference, 11^th, Volume 1, page 655-660, Edited by Veziroglu, T., year 1996; Muradov, N. Z., Proceedings of US DOE Hydrogen Program Review, volume 1, page 513-535, year 1996].

In the above prior art processes based on catalytic cracking or thermo-catalytic decomposition of methane or other hydrocarbons, the hydrogen produced is free from carbon monoxide and carbon dioxide but the catalyst deactivation is fast due to the carbon formed on. the catalyst and this is accompanied with a fast increase in the pressure drop across the catalyst bed, making the process unpractical for the hydrogen production. Recently, Choudhary and Goodman reported a process for the production of carbon monoxide-free hydrogen involving stepwise methane steam reforming [reference: Choudhary, T. V. and Goodman, D. W., Catalysis Letter, volume 59, page 93-94, year 1999]. In this process, methane pulse and water pulses are passed over a pre-reduced nickel-based catalyst at 375°C, alternatively. When methane pulse is passed over the catalyst, the methane from the pulse is . decomposed to hydrogen and carbon, leaving the carbon deposited on the catalyst according to the reaction: CH → C + 2H₂ t (1) When the water pulse is passed over the catalyst With the carbon deposited on it, the carbon on the catalyst reacts with steam to form CO2, hydrogen and methane according to the reaction:

In this process although the carbon monoxide-free hydrogen is produced by catalytic cracking of methane and the carbon deposited on the catalyst is removed by the cyclic operation of the methane and water pulses in the same reactor, the process is not operated in the steady state and the hydrogen produced is not continuous one. Hence, it is not practical and also not economical to produce carbon monoxide-free hydrogen on large scale by this transient process involving cyclic operation of methane and water pulses. IN/PA-506 Very recently, Choudhary et al have reported a possibility of the continuous production of hydrogen at 500°C by carryin out the above two reactions, Reactions and 2 simultaneously in two parallel catalytic reactors in cyclic manner by switching a methane containing feed, 18.2 mol% CH* in Na, and a steam containing feed, 20.5% steam in Na, between the two reactors at predecided intervals of time and combining the product streams of the two reactors (reference: V.R. Choudhary, S. Banerjee and A. M .Rajput,

Journal of Catalysis, vol. 198 page 136 and year 2001). However, both the reactions,

Reactions 1 and 2 are thermodynamically favored at higher temperatures. The methane decomposition, Reaction , is also favored at lower pressure or lower concentration of methane. Our preliminary studies showed that both the methane conversion in Reaction and degree of carbon gasification in Reaction 2 are decreased sharply with increasing the methane concentration and for decreasing the temperature. Hence, for using undiluted or less diluted methane as a feed so that the very high cost of separation of the diluent can be reduced and also for obtaining high conversion of methane, Reactions 1 and 2 need to be carried out at higher temperature, above about 600°C. However at such a high temperature a significant amount of carbon monoxide is formed in Reaction 2 and therefore, carbon monoxide-free hydrogen cannot be obtained by the above cyclic process Because of the above mentioned drawbacks and limitations of all the prior art processes, there is a great need for developing a process for the continuous production of carbon monoxide-free hydrogen by catalytic decomposition of methane or natural gas at a temperature below about 900°C, while avoiding the carbon build up on the catalyst by its time-to-time removal by some means. OBJECTS OF THE PRESENT INVENTION Accordingly the main object of this invention is to provide a process for the continuous production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons at a temperature above about 600°C but below about 900°C, involving catalytic decomposition of methane to hydrogen and carbon, which is deposited on the catalyst used, and removal of the carbon by its gasification by steam with or without oxygen, while avoiding carbon build up on the catalyst and thereby avoiding the catalyst deactivation and increase in a pressure drop across the catalyst bed during the process, SUMMARY OF THE PRESENT INVENTION Accordingly, the main object of the invention was accpmplished by providing a process for the continuous production of carbon monoxide-free hydrogen by operating the process in two IN/PA-506 parallel reactors, both containing a solid catalyst comprising group VQI metal(s) and having different feeds so that the methane decomposition reaction and the carbon gasification reaction, involving the formation of CO, CC>2 and H2 are carried out simultaneously in cyclic manner in the two parallel reactors by regularly svritehing between them at an interval of time two different feed streams - one comprising methane and second comprising steam with or without oxygen, and thereby a continuous production of carbon monoxide-free hydrogen is effected from the methane decomposition reaction, the products of which are collected using the product stream switching valve, while collecting separately the products of the carbon reforming or gasification reaction and flushing them from the reactor by pure hydrogen or by the products of methane decomposition, before switching simultaneously both the feed and product switching valve, without the catalyst deactivation and development of high pressure drop across the catalyst bed in both the reactors,

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 shows a schematic flow sheet of the process of this invention. The description of labels 1-9 in the drawing are as follows: 1= Reactor A 2 = Reactor B: 3 = catalyst fixed bed or fluid bed; 4 = Feed A (which comprises methane or methane-rich hydrocarbons); 5 = Feed Bl (which comprises steam with or without oxygen gas) or Feed B2 (which is pure H2 or product of Feed A); 6 = Products Gas A (CO-free H2 with unconverted methane, obtained from Feed A); 7 = Products Gas B (CO, CO2, CH* and H2, with or without O2, obtained from Feeds Bl and B2); 8 = Feed stream switch over valve and 9 = product stream switch over valve. The methane decomposition and carbon gasification reactions occur in Reactor A and Reactor B, respectively After switching the two valves simultaneously, the methane decomposition and carbon gasification reactions occur in Reactor B and Reactor A, respectively. The gaseous products of the two reactors are collected separately in the cyclic operation, as shown in Figure 1 DETAILED DESCRIPTION OF THE PRESENT INVENTION Accordingly this invention provides a process for the continuous production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons, using a solid catalyst comprising group VHI metal(s) in two parallel catalytic reactors, said process comprising the steps of i.) packing the solid catalyst in the two different catalytic reactor kept parallel; ii.) pretreating the catalyst of step (0 in kept in both the reactors with a reducing agent, such as pure H2 or H2-N2 mixture containing at least 5 mol % HI at a gas hourly space velocity in the range of about 500 to 20,000 cm³.^'¹^"¹ at a temperature in the range of IN/PA-506 about 600°C to 800°C and at a pressure at least about 1.0 atm for a period of at least 0.5 hour; iii.) contacting the pretreated catalyst of step (ii) with a first gaseous feed comprising methane or natural gas, called Feed A, at a gas hourly space velocity in the range of about 250 cm³.^¹.^¹ to about 50,000 cm³.^¹.^¹ with the solid catalyst of first reactor, called Reactor A, at a temperature in the range of about 600°C to 1000°C and at a pressure of at least one atmosphere, iv.) contacting simultaneously a second gaseous feed comprising steam with or without oxygen, called Feed Bl, at a gas hourly space velocity- in the range of about 250 cm³.g ^h^"1 to 50,000 cmlg'¹.]!"¹ with the solid catalyst in the second reactor, called Reactor B, which is similar to Reactor A, at a temperature in the range of about 600°C to 1000°C, at a pressure of at least one atmosphere, while simultaneously switching over to the two feeds, Feed A and Feed Bl, 1 using a feed stream switch over valve, the two product lines for the gaseous products obtained from Feed A, called Product Gas A, and the gaseous products obtained from the other feed(s), called Product Gas B, using product switch over valve situated between the two parallel reactors, Reactor A and Reactor B, at an interval time in the range of about 0.1 min to about 100 min, such that, before the simultaneous switching of the two switch over valves for the next cyclic operation, Feed Bl is replaced by pure Ha or by the product gases obtained from Feed A, called Feed B2, to flush the reactor through which Feed Bl was passed so that all the products obtained from Feed Bl are removed from the reactor before Feed A enters the reactor, and collecting separately the two different gaseous products one consisting of carbon monoxide-free H2 and unconverted methane, obtained from Feed A, and second consisting of COi, CO2, CH4, and H2, with or without 02, obtained from Feeds Bl and B2 after the removal of water by condensation; and v) separating the carbon monoxide-free hydrogen from Product Gas A and the hydrogen, methane and carbon monoxide from Product Gas B. One of the embodiment of the invention provides a process, wherein the gas hourly space velocity of Feed A used is preferably in the range of about 500 cm³.g^"1.h^"1 to 25,000 cm^ ^"1.^¹ . i nother embodiment, the preferred temperature maintained in the two reactors, Reactor A and Reactor B, is in the range of about 600°C to 800°C. Still another embodiment, the gas hourly space velocity of Feed Bl is in the range of about 500 c s.gⁱ.h^"1 to 25,000 c ⁸.g-ι.h^"1 . IN/PA-506 Still another embodiment, the oxygen to steam ratio in Feed Bl is in the range of from 01 to

0.51.0

Yet another embodiment, the interval times for the feed stream and product stream switch over ranges preferably from about one minute to 30 min

Yet another embodiment, the concentration of methane used in Feed A is at least 80%.

In yet another embodiment, .the concentration of steam used in Feed Bl is in the range of about 50mole% to 100mole%.

In yet another embodiment, the concentration oxygen in the Feed Bl ranges from about zero mole

% to 50mole%.

In yet another embodiment, the two parallel reactors used are either fixed-bed reactors or packed bed reactors.

In yet another embodiment, the solid catalyst used in step (i), is a group VIII meta s) selected from Fe, Co, Ni, Ru, Rh, Pd, Pt, Ir, Os or mixtures thereof.

In yet another embodiment, the group VIII metal(s) in the solid catalyst is preferably selected from nickel, cobalt or mixtures thereof. In yet another embodiment, the concentration of steam in the Feed Bi ranges from about 50mol% to 500mol%. In yet another embodiment, the preferred concentration of steam in the feed Bi ranges from about 50mole% to 100mole%. . . ^• The process of this invention will be more fully understood by reference to the attached drawing to which reference is made in the examples. In the process of this invention, the two parallel reactors may be two parallel fluid bed reactors or _* two parallel fixed-bed reactors,^* the preferred two parallel reactors are fixed bed reactors. The two different feed streams, Feed A and Feed Bl and also the two different product streams, Product Gas A (products of Feed A) and Product Gas B (products of Feeds Bl and B2), can be switched between the two reactors simultaneously using the two feed and product switch over valves operated manually or automatically, as shown in Figure 1. The group VIII metals are Fe, Co, Ni, Ru, Rh, Pd, Pt, Ir and Os. The main product of the process of this invention is carbon monoxide-free hydrogen, which is formed in the methane decomposition reaction. The side products are a mixture carbon dioxide, carbon monoxide and hydrogen, which are formed in the reforming or gasification by steam and/or oxygen of the carbon deposited on the catalyst. At a particular time, the main reactions occurring in the two parallel reactors are as follows: In the ReactorA through which the feed IN/PA-506 comprising methane (Feed A) is passed, the catalytic decomposition of methane occurs producing two moles of hydrogen and one mole of carbon, which is deposited on the catalyst, per mole of methane reacted. At the same time, in the second reactor through which the feed comprising steam with or without oxygen, Feed Bl, is passed, the steam and/or oxygen react with the carbon deposited on the catalyst to produce carbon monoxide, carbon dioxide and hydrogen. These two different reactions occur in a cyclic manner when the two feeds and two product lines are simultaneously switched between the two reactors at an interval of time and the gaseous products of the two reactions are collected separately.

In step-ii of the process of this invention, the preferred gas hourly space velocity of Feed A ranges from about 500 cm³, g^"1. h^"1 to about 25,000 cm³, g"¹. h'¹, the preferred temperature in each of the two reactors, Reactor A and Reactor B, ranges from about 600°C to about 800°C, the preferred gas hourly space velocity of Feed Bl ranges from about 500 cm³, g^"1. h^'1 to about 25,000 cm³, g^'1. h^"1, the preferred oxygen to steam ratio in Feed Bl ranges from zero to about 1.0, the preferred interval of time of the feed stream and product stream switch over ranges from one minute to about 30 minute, the preferred concentration of methane in the Feed A is above 80 mol%, the preferred concentration of steam in the Feed B2 ranges from about 50 mole% to about 100 mole%, the preferred concentration of oxygen in the Feed Bl ranges from zero mole% to about 50 mol % and the preferred group VIII metaKs) in the solid catalyst is nickel, cobalt or a mixture thereof. In the process of this invention, the two parallel reactors, Reactor A and Reactor B, are preferably fixed-bed reactors. The preferred solid catalyst used in the process of this invention may be selected from nickel, with or without cobalt, deposited on various micro or meso porous metal oxides, such as alumina, silica-alumina, silica, zerconia, yettria, ceria, magnesia and the like or zeolites or zeolite-like materials, such as HY, Ce-Na-Y, HM, Hβ , H-ZSM-5, MCM-41 and the like. The nickel and/or cobalt present in the catalyst are in their reduced form or in their zero oxidation state The solid catalyst comprising group VIII metaKs) used in the process of this invention can be prepared by the coprecipitation or impregnation catalyst preparation techniques known in the prior art. The role of step-i of the process of this invention is to reduce the transition metal oxide present at least on the surface of the catalyst, for example nickel oxide, cobalt oxide, iron oxide, etc., present in the catalyst are reduced to the corresponding metal. This step is important one! the reduction of group VIII metal oxide present on the catalyst surface to its metallic form is essential for the catalytic activity of the in the process of this invention. IN/PA-506

In step-ii of the process of this invention, the methane or methane-rich hydrocarbons, and steam with or without and oxygen are reactants, which are converted at least partly in the process. The role of steam is to react with the carbon, which is formed in the decomposition of methane on the reduced catalyst, producing carbon monoxide, carbon dioxide and hydrogen and thereby removing the carbon deposited on the catalyst. The role of the oxygen is to activate the carbon, which is otherwise difficult to gasify by steam alone. The oxygen is consumed at least partly by its reaction with the carbon to form CO and CO2. Role of the solid catalyst is to catalyse the methane decomposition reaction and the carbon gasification by steam and/or oxygen.

In the process of this invention, two different products obtained from the two different feeds, Feed A and Feed Bl are collected separately. The product stream obtained from Feed A contains only hydrogen and unconverted methane; it is free from carbon monoxide. The unconverted methane is separated from hydrogen by the pressure swing adsorption-separation processes known in the prior art, and thereby, carbon monoxide-free hydrogen is produced by the process of this invention. The product stream obtained from Feed Bl contains the carbon gasification products CO, CO2, H2, methane and unconverted steam and/or oxygen, which may be separated by processes known in - the prior art. In the process of this invention, the flushing of Feed Bl and the products of its reaction from the reactor by pure H2 or by the products of Feed A, before switching simultaneously the two switch over valves, "as shown in Figure 1, is essential to avoid contamination of the products of Feed A by the product of Feed B 1 in the next cycle. The present invention is described with respect to the following examples illustrating the process' of this invention for the production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons and steam, with or without oxygen, over different solid catalysts comprising nickel, with or without cobalt, at different process conditions, These examples are provided for illustrative purposes only and are not to be construed as limitations on the process of this invention

EXAMPLES

DEFINITIONS OF THE TERMS USED IN THE EXAMPLES GHSV = Gas hourly space velocity, defined as the volume of a gaseous feed, measured at 0°c and 1.0 atmospheric pressure, passed over unit mass of catalyst per unit time. IN/PA-506

Percent methane conversion is defined as the mole% of methane present in the feed converted into products other than methane. It is estimated as follows.

Methane conversion (%) = [(moles of methane in feed - moles of methane in products) ÷ (moles of methane in feed)] x 100

Hydrogen productivity in the process is expressed as the amount of hydrogen in mmol produced per hour per gram of the catalyst used in the process.

EXAMPLES 1 -8

These examples illustrate the process of this invention for the continuous production of carbon monoxide-free hydrogen from methane, using Ni-Zrθ2 (Ni/Zr mole ratio = 1.0) catalyst at different process condition.

The Ni/Zr0₂ catalyst was obtained by reducing NiO/Zr0₂ by hydrogen at 600°C for 6h. The NiO- Zrθ2 catalyst was prepared by coprecipitating mixed hydroxides of nickel and zirconium from a 650 cm³ aqueous solution containing 58.78g Ni(N0₃)2.6H2θ and 46.76g ZrO(Nθ3 xH2θ using an aqueous solution of NaOH at a pH of 9.0 at room temperature, filtering and thoroughly washing the precipitate with deionized water, drying the washed precipitate at 105°C for 18 h, pressing and crushing to particles of 0.3O.4 mm size and calcining in air at 600°C for 2h. The surface area of the NiO/Zr02 catalyst was 63 m^-¹. The process of this invention using the Ni/ZrO₂ catalyst was carried out in two parallel stainless steel fixed bed reactors as shown schematically in Figure 1 Each reactor was packed with 0.4 g catalyst particles of size 0.3-0.6 mm and was kept in a tubular furnace. The two parallel reactors had two different feeds connected through a four way flow switch valve and also had two different product lines connected through a four way flow switch valve, as shown in Figure 1. Both the flow switch valves were operated simultaneously at an interval of time. The temperature in both the reactors was measured by a Chromel- Alumel thermocouple located at the center of the catalyst bed in both the reactors. Before carrying out the catalytic reaction, the catalyst in both the reactors was reduced by pretreating it with a H2-N2 mixture at the conditions given in Table- 1. After the reduction of catalyst in both the reactors, Feed A comprising methane was passed over the reduced catalyst in Reactor A and simultaneously Feed B2 containing steam with or without oxygen was passed over the reduced catalyst in Reactor B, and before switching the two valves for the next cyclic operation, the Feed Bl was replaced by pure H2 and the reactor and feed and product lines are flushed by the H2 of volume at least one IN/PA-506 time the volume of the reactor and feed and product lines between the two switch valves.

The cyclic process operation was accomplished by switching Feed A and Feed Bl between the two reactor regularly at an interval of time and replacing Feed Bl by pure H2 as described above before switching simultaneously the two switch valves, at the process conditions given in Table- 1

The gaseous products obtained from the two different feeds were collected separately in two gas collectors after condensing and removing the water from them by condensation. The collected two different gaseous products were analyzed by gas chromatograph using a spherocarb column and thermal conductivity detector. For the gas chromatographic analysis of hydrogen in the products, high purity nitrogen was used as a carrier gas. Whereas, for the gas chromatographic analysis of the methane, carbon dioxide and carbon monoxide present in the products, helium was used as a carrier gas. The results obtained at the different process conditions are presented in Table-1. The results in Example 7 clearly show that when the cyclic process is operated at lower temperature, 501°C, than that, >600°C, used in the process of this invention, the conversion of methane and the productivity of CO-free H2 are very poor.

EXAMPLES 9-11

These examples also illustrate the process of this invention for the production of carbon monoxide-free hydrogen from methane and steam with or without O2, using following solid catalysts: Ni/Si-MCM-41, Ni/Ce-NaY and Co-Ni/MgO/SA5205. The Ni/Si-MCM-41. (12 wt% Ni) was prepared by impregnating 5.0g particles (0.3-0.4 mm of size) of high silica MCM-41 [prepared by the procedure given in the reference: Choudhary, V. R. and Sansare, S. D., Proc. Indian Acad. Sci. (Chem. Sci.}, volume 109, number 4, page 229-233, August 1997] with 3.4g Ni(NO₈)2.6H2θ from its aqueous solution by the incipient wetness technique, followed by drying at 501°C for 12h and calcining at 500°C for 2h and by reducing the catalyst by hydrogen at 500°C for 4h. The NiO/Ce-NaY (10 wt% Ni, 72% Ce-exchanged NaY) was prepared by impregnating 5.0 g particles (0.3-0.4 mm of size) 72% Ce-exchanged NaY (prepared by the procedure given in the reference'- Choudhary, V. R., Srinivasan, K. R. and Akolekar, D. B., Zeolites, volume 9, page 115-119, year 1989) with 2.75g Ni(NO3)2.6H2O from its aqueous solution by the incipient wetness technique, followed by drying at 105°C for 12h and calcining at 500°C for 2h and then reducing the catalyst by H2 at 600°C for 12h.. IN/PA-506

The NiO-CoO/MgO/SA5205 with Co/Ni mole ratio of 0.2 and NiO-CoO and MgO loadings on

SA 5205 support, which is macroporous low surface area sintered silica-alumina catalyst carrier obtained from Norton Company (USA), of 14.5 wt.% and 7.2 wt.%, respectively was prepared by the procedure described by Choudhary et al (Ref. V.R. Choudhary et al AIChEJ

Journal vol. 47 page 1632 year 2001). The catalyst was reduced by 20 % H2 in N2 at 800°C for4h.

The process of this invention over each of the above catalysts was carried out in the two parallel reactors and following the procedure same as that described in (he earlier examples (Examples 1^*10), at the catalyst pretreatment and catalytic process conditions given in Table-2. The results, the methane conversion and the CO-free hydrogen produced in the process of this invention over the above mentioned catalysts are included in Table-2..

Table l: CO-free hydrogen production from the process of this invention using the Ni/Zrθ2 catalyst at different process condition Catalyst Pretreatment Conditions Employed in Step-I

IN/PA-506

IN/PA-506

Table 2: CO-free hydrogen production by the process of this invention using different catalysts comprising nickel and/or cobalt

Natural gas containing 94.7 mol % methane, 2.5 mol % ethane, 1.0 mol % C₃-C₄ hydrocarbon, 0.2 mol % CO₂ and balance nitrogen Novel Features and Advantages of the Process of this Invention over the Prior Art Processes for the Production of Hydrogen

1. Unlike the prior art steam reforming and auto thermal reforming processes, carbon monoxide-free hydrogen can be directly produced by the process of this invention.

2. Unlike the prior art steam reforming and autothermal reforming processes, the conversion of methane and steam take place separately in two different reactors, two parallel reactors, each having a different feed, and the two different feeds: one comprising methane and second comprising steam with or without oxygen, are switched regularly between the two reactors at an interval of time so that when methane decomposition reaction occurs in one reactor producing hydrogen and carbon deposited on the catalyst, at the same time the gasification of the carbon by its reaction with steam and/or oxygen, producing carbon monoxide, carbon dioxide and hydrogen, takes place in the second reactor, and these two reactions in two separate reactors occur place in cyclic manner and the products of these two reactions are collected separately, so that there is no build up of carbon on the catalyst in both the parallel reactors and CO-free H₂ is produced from the hydrocarbon decomposition reaction. 3. Unlike the prior art processes based on low temperature methane decomposition, the production of carbon monoxide-free hydrogen in the process of this invention is continuous without build up of carbon on the catalyst and consequently without the build up of a large pressure drop across the catalyst bed and also without the catalyst deactivation by carbon deposition or coking. 4. Since in the process of this invention, the hydrocarbon decomposition and carbon gasification reactions are carried out at higher temperature than that employed in the prior art processes based on the methane decomposition, the thermodynamic barrier on both the reactions in the present case is much lower and also the conversions of methane are much higher.

Claims

IN/PA-506 17Claims'

1. A process for the continuous production of carbon monoxide-free hydrogen from methane or methane-rich hydrocarbons, using a solid catalyst comprising group VHI metaKs) in two parallel catalytic reactors, said process comprising the steps of i) packing the solid catalyst in the two different catalytic reactor kept parallel; ii) pretreating the catalyst of step 0) in kept in both the reactors with a reducing agent, such as pure H2 or H2 "N₂ mixture containing at least 5 mol % H2 at a gas hourly space velocity in the range of about 500 to 20,000 cm³. g^" . h^'1 at a temperature in the range of about 600°C to 800°C and at a pressure at least about 1.0 atm for a period of at least 0.5 hour ; iii) contacting the pretreated catalyst of step (ii) with a first gaseous feed comprising methane or natural gas, called Feed A, at a gas hourly space velocity in the range of about 250 cm³.g"ⁱ. h'ⁱ to about 50,000 cm³, gⁱ. h'ⁱ with the solid catalyst of first reactor, called Reactor A, at a temperature in the range of about 600°C to 1000°C and at a pressure of at least one atmosphere; iv) contacting simultaneously a second gaseous feed comprising steam with or without oxygen, called Feed Bl, at a gas hourly space velocity in the range of about 250 cm³. g^"i. h^'i to 50,000 cm³, g"¹. h^'i with the solid catalyst in the second reactor, called Reactor B, which is similar to Reactor A, at a temperature in the range of about 600°C to 1000°C, at a pressure of at least one atmosphere, while simultaneously switching over to the two feeds, Feed A and Feed Bl using a feed stream switch over valve, the two product lines for the gaseous products obtained from Feed A, called Product Gas A, and the gaseous products obtained from the other feed(s), called Product Gas B, using product switch over valve situated between the two parallel reactors, Reactor A and Reactor B, at an interval time in the range of about 0.1 min to about 100 min, such that, before the simultaneous switching of the two switch over valves for the next cyclic operation, Feed Bl is replaced by pure H2 or by the product gases obtained from Feed A, called Feed B2, to flush the reactor through which Feed Bl was passed so that all the products obtained from Feed Bl are removed from the reactor before Feed A enters the reactor, and collecting IN/PA-506 separately the two different gaseous products, one consisting of carbon monoxide-free H^Λ and unconverted methane, obtained from Feed A, and second consisting of CO, CO2 CH4 and H₂, with or without O2 , obtained from Feeds Bl and B2 after the removal of water by condensation; and v) separating the carbon monoxide-free hydrogen from Product Gas A and the hydrogen, methane and carbon monoxide from Product Gas B.

2. A process as claimed in claim 1, wherein in step-iii the gas hourly space velocity of Feed A used is preferably in the range of about 500 cm³, g'.ⁱ. h^"1 to 25,000 cm³. g^"i. h^'i.

3. A process as claimed in claim 1, wherein the preferred temperature maintained in the two reactors, Reactor A and Reactor B, is in the range of about 600°C to 800°C.

4. A process as claimed in claim 1, wherein in step-iv the gas hourly space velocity of Feed Bl is in the range of about 500 cm³. g^"i. h^"1 to 25,000 cm³, gⁱ. h'ⁱ .

5. A process as claimed in claim 1, wherein in step-iv the oxygen to steam ratio in Feed Bl is in the range of from 0:1 to 0.5:1.0 6. A process as claimed in claim 1, wherein in step-iv the interval time for the feed stream and product stream switch over ranges preferably from about one minute to 30 mm. 7. A process as claimed in claim 1, wherein i step-iϋ the concentration of methane used in Feed A is at least 80%. 8. Process as claimed in claim 1, wherein in step-iv the concentration of steam used in Feed Bl is in the range of about 50 mole% to 100 mole%. 9. A process as claimed in claim 1, wherein in step-iv the concentration oxygen in the Feed Bl ranges from about zero mole % to 50 mole%. .10. A process as claimed in claim 1, wherein the two parallel reactors used are fixed-bed reactors or packed bed reactors. 11. A process as claimed in claim 1, wherein the solid catalyst used in step (0, is a group Vm metaKs) selected frτ>m Fe, Co, Ni, Ru, Rh, Pd, Pt, Ir, Os or mixtures thereof. 12. A process as claimed in claim 1, wherein the group VDI metaKs) in the solid catalyst is preferably selected from nickel, cobalt or mixtures thereof. 13. A process as claimed in claim 1, wherein in step Gv), the concentration of steam in the Feed Bi ranges from about 50 mol% to 500 mol%. 14. A process as claimed in claim 1, wherein the preferred concentration of steam in the feed Bi ranges from about 50 mole% to 100 mole%.