NL7811278A - METHOD FOR PROCESSING NITROGEN CONTAINING NATURAL GAS. - Google Patents

Description

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Inventors: John W. GEUS in Bilthoven

Leo .A'.M. HERMANS in Haarsteeg (N.B.) 1 3037

METHOD FOR PROCESSING NITROGEN CONTAINING NATURAL GAS

The invention relates to a method for decomposing methane in carbon and hydrogen using a nickel catalyst at elevated temperature and the use of this method for processing so-called arraer natural gas mixtures into industrially applicable gas mixtures.

It is known that nitrogen is the main constituent of some natural gas deposits in addition to methane. Although the energy content of these sources is considerable, the applications of this gas are limited with the current state of the art. One of those 10 options is to dilute high-calorific gas into a 'Slochteren-quality' gas.

In addition, it has been proposed to physically separate the inert component of such a gas mixture using cold technology. However, this method requires high investments and moreover requires a lot of energy. Due to the high nitrogen content, this gas mixture is virtually unsuitable as a raw material for the chemical industry. The usual chemical conversion of the methane by reaction at elevated temperature (700-1200 ° C) with steam to CO and H0, or

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not in the presence of a catalyst, is unattractive because of the high nitrogen content. Nor is further conversion with air to a mixture of Hg and Ng as ammonia synthesis gas interesting because the mixture will contain too much Ng. For the same reason, the mixture is hardly suitable as fuel gas.

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Methane is known to decompose at a temperature above 500 ° C at a technically useful rate across nickel catalysts into carbon and hydrogen. Starting from the above-mentioned gas, large amounts of nitrogen should be brought to the relatively high reaction temperature of 500 ° C or higher, with said energetic disadvantage.

The object of the invention is to provide a method in which methane can be decomposed at a relatively low temperature using a nickel catalyst.

According to the invention this is achieved when the methane is passed at a temperature between 80 ° C and 500 ° C over a nickel catalyst with at least 10% by weight of nickel on a support, the nickel being present on the support as particles smaller than 10 nm and periodically regenerating the carbon-loaded catalyst in known manner.

Preferably, the largest dimensions of the nickel particles measured are generally between 3 and 6 nm (hereinafter referred to as "size" and "radius"). The temperature at which the methane is passed over the catalyst is preferably 100 ° C to 300 ° C, more particularly 120 ° C to 180 ° C.

The process is usually carried out with a catalyst with a nickel content of more than 30% by weight, preferably even up to a weight ratio of nickel to support material of 95: 5, which allows relatively large amounts of gas per unit volume of a reactor.

The method according to the invention is mainly intended to mix mixtures of methane and nitrogen, more in particular the so-called.

treat 'lean' natural gas mixtures and convert them into industrially applicable gas mixtures.

The process according to the invention achieves that a mixture of and Ng leaves the catalyst bed. By contacting this mixture with a suitable adsorbent or adsorbent for E ^, a separation between and N ^ is made in a simple manner. Such an absorbent may be a catalyst mass as referred to above or, for example, a Habsorbing 7311278 <3 * metal, such as LaNig. Desorption of Hg can easily take place by increasing the temperature of the loaded absorbent.

The catalyst used in the reactor remains in a carbon-charged state. Regeneration of this catalyst 5 for reuse is necessary. Several avenues are open to this.

First, the initially-absorbed hydrogen can be used to convert the carbon on the catalyst to methane at a temperature between 200 and 400 ° C. In this way, it is achieved that by the order of a catalytic reaction and absorption followed by desorption and a second catalytic reaction, methane and nitrogen are separated.

Another possibility is to react the carbon deposited on the catalyst with steam to CO and H 2. This possibility will be preferred when the production of ammonia, methanol or hydrocarbons is envisaged, because in this way more hydrogen is made available. After all the carbon deposited on the catalyst has reacted, reduction of the catalyst must take place to remove the oxygen absorbed by the reaction with steam. This can be done with part of the H2, possibly in the presence of CH. to happen. This H0 may again be the desorbed Hg.

In this way, a separate mixture of CO and Hg is obtained in addition to Ng. This gas mixture can be converted into COg and Hg with HgQ and the H_ separated therefrom. By correct dosing of the 2 previously separated nitrogen it is possible, for example, to compose an ammonia synthesis gas mixture in the correct stoichiometric ratio.

By composing the feed methane-nitrogen mixture by mixing natural gases of different composition, it is even possible to obtain a synthesis gas mixture without hydrogen and nitrogen losses. The feed gas then need not contain more than 60% by volume CH 2.

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The invention is illustrated with examples and experimental data on the catalyst. The examples will demonstrate, inter alia, that the interaction of methane with nickel particles depends on the size of these particles. It will also appear that the reactivity of the carbon deposited on the nickel surface with hydrogen is determined by the size of the nickel particles. A number of patents have described how the dimensions of nickel particles applied to thermostable carriers can be varied in a controlled manner. Because of the great importance of this, the preparation and thermal pretreatment of the catalysts will be described by examples. Generally, the preparation of kata. lysators according to British Patents No. 1,220,105 or No. 1,295,440 are suitable, but not limited to.

To illustrate the process according to the invention, three different nickel-on-silicon catalysts were prepared and indicated, denoted respectively. "A *," "B" and * Cr.

Catalyst A mainly contains nickel particles with a diameter below 5 nm, while catalyst B contains a not insignificant fraction of larger particles, with dimensions from 4 to 8 nm.

The catalyst C contains more particles, the dimensions of which lie between those of the catalysts A and B. The catalyst mass was always processed into tablets.

The difference of the catalysts in the reaction with methane is shown in Figure 1. In this figure the reaction temperature in ° C is plotted horizontally, while vertically the decomposed amount of methane is plotted in 0.01 ml (standard temperature v 2 pressure) per m nickel surface.

At a temperature above 280 ° G, the admitted methane appears to react completely to carbon, which is deposited on the catalyst surface, and hydrogen, which desorbs in the gas phase.

At lower temperatures, the interaction of the admitted methane remains limited to the nickel surface, without growth into large carbon particles.

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Fig. 1 shows that a large fraction of the surface of the catalyst C already clearly reacts with methane in a temperature range of 100 ° C to 300 ° C. The other two catalysts. only show a far-reaching reaction of the nickel surface at higher temperatures of 200 to 300 ° C; at lower temperatures the amount of decomposed methane is clearly smaller. It is clear from this figure that there is an optimum in the size of the nickel particles to be used.

It is important for the processing of the deposited carbon into methane that little growth of carbon occurs on the catalyst particles. With the growth of carbon particles, the pores of the porous catalyst tablets can clog, while with the deposition of a large amount of carbon, even the catalyst tablets can break up or clogging can occur, while with the deposition of large amounts of carbon, even the catalyst tablets or with clogging of the catalyst bed for can come.

The reactivity of the carbon deposited on the catalyst with hydrogen to methane also appears to vary for different catalysts. Catalyst C is at a temperature between 150 ° C and 250 ° C, for example at about 200 ° C

more than 90% of the carbon deposited on the catalyst is desorbed by treatment with hydrogen as methane. With catalyst B, up to 95% of the incorporated carbon desorbates as methane when treated with hydrogen. However, this already requires a temperature of 350 ° C. With catalyst A, only about 35% of the amount of carbon absorbed can be desorbed when treated with hydrogen at the temperature of 350 ° C.

These examples demonstrate the great importance of accurately controlling the dimensions of the nickel particles.

The examples of the catalysts will demonstrate that catalysts of the preferred size of the particles can be prepared with a loading degree of more than 30% by weight of nickel, allowing a relatively large amount of gas mixture to be processed per unit volume of a reactor. The invention is not limited to catalysts prepared according to the process of the examples, but also includes catalysts which are optimized in other ways.

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Preparation Catalyst * A '

37.6 kg of ΝΐίΝΟ ^^ ΘΗ ^ Ο was dissolved in 800 l of water, after which 6.8 kg of finely divided silicon dioxide (Aerosil 200V, marketed 2 by Degussa, West Germany, area 200 m / g) in the 5 solutions were suspended. The pH of the suspension was adjusted to 2.5 with nitric acid. 2.31 kg of urea was dissolved in 10 l of water in a separate vessel. After the suspension was brought to a temperature of 90 ° C, the urea solution was added to the suspension with intensive stirring. As a result of the hydrolysis of the urea, the pH value of the suspension rose, whereby the nickel (II) precipitated on the silicon dioxide. After 14 hours, all dissolved nickel (II) had precipitated; the pH of the suspension at that time had risen to 6.3.

The loaded carrier was allowed to settle and the supernatant was siphoned off. Then the loaded carrier material was washed three times with water at 90 ° C. This was done by adding about 700 liters of water, raising the temperature to 90C with stirring, then allowing the carrier to settle and decanting the supernatant liquid. Finally, the loaded carrier was dispersed in about 100 L of water and filtered.

After drying at 120 ° C, the catalyst was tableted into cylindrical tablets with a length of 1 cm and a diameter of 0.5 cm. After calcination at 350 ° C (2 hours), the mechanical strength of the catalyst tablets was excellent.

The catalyst tablets were reduced in a reactor.

To this end, a hydrogen-argon stream (10% hydrogen in argon) was passed through the catalyst bed at a spatial throughput speed 3 (space velocity) of 500 m / (m reactor / hour). During the first 70 hours, the temperature was ramped up from 20 ° C to 475 ° C at regular intervals. The catalyst was kept at 475 ° C for another 50 hours.

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The degree of reduction of the nickel in the catalyst after this treatment was 99%. The nickel content of the reduced catalyst was 40.9% by weight. The accessible nickel surface was determined from the hydrogen adsorption; this was 177 m per g of nickel. The magnetization of the reduced catalyst was measured as a function of the magnetic field strength. Figure 2 shows the particle size distribution calculated from the magnetization curve. Horizontally, the radius of the nickel particles in nm is given in logarithmic units, while vertically the number and volume of the nickel particles are plotted. The dotted line indicates the volume, the solid line the number.

Preparation Catalyst TB *

32.8 kg of ΝΐίΝΟ ^^. ΒΗ ^ Ο were dissolved in 800 l of water, after which 6.8 kg of finely divided silicon dioxide (Aerosil 380V, marketed by Degussa BRD, area 380 m per g) in the solution were suspended. The temperature of the suspension was brought to 90 ° C. Subsequently, 1 N ammonia was injected via four tubes under the liquid surface of the intensively stirred suspension. Compression wind boilers were included in the injection lines, which were pressurized to 1.5 atmospheres with nitrogen; sucking the suspension back into the injection pipe was hereby prevented. The injection rate of the ammonia quench was 0.075 L / min per injection point, so a total of 0.30 L / min. After the injection was continued for 12 hours, all nickel (II) had precipitated on the support material. The loaded carrier material was again processed into tablets of said dimensions in the manner described above.

The catalyst tablets were reduced in a reactor.

To this end, a hydrogen-argon flow (10% hydrogen in argon) was passed through the catalyst bed at a spatial throughput speed of 3 3 30 ("space velocity") of 500 m / (m reactor / hour). During the first 200 hours, the temperature was gradually increased from 20 ° C to 550 ° C.

The catalyst was kept at 550 ° C for another 50 hours.

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The degree of reduction of the nickel in the catalyst after this treatment was 99%. The nickel content of the reduced catalyst was 49.1% by weight. The accessible nickel surface was determined from the hydrogen adsorption; this was 79 m per g of nickel. The particle size distribution was calculated from the magnetization curve. The result is given in Fig. 3. The radius of the nickel particles is given horizontally in logarithmic scale, while vertically the number and volume of the nickel particles are plotted. The dotted line indicates the volume, the solid line the number.

10 Preparation Catalyst 'C'

32.8 1 NiCNOg 4 .0HgO was dissolved in 800 l water, after which 6.8 finely divided silicon dioxide (Aerosil 380V, marketed by Degussa, BRD, area 380 m per g) was grazed in the solution suspended. The temperature of the suspension was brought to 25 ° C, after which a 1 N ammonia solution was injected into the suspension through four injection nozzles emerging under the liquid surface of the suspension. The injection pipes included pressurized wind boilers equipped with. nitrogen were kept at a pressure of 1.5 ato; this will prevent sucking back of the suspension into the injection pipe. The injection rate of the ammonia solution was 0.075 L / min for each injection point, bringing the total injection rate to 0.30 L / min. After the injection was continued for 12 hours, all nickel (II) had precipitated on the support material. The loaded carrier material was again processed in the manner described above into tablets of the above-mentioned dimensions, with the difference that, in order to counteract the reaction of nickel (II) with silicon dioxide as much as possible, the water from the catalyst is kept as low as possible. temperature was removed. To this end, the catalyst was kept in a vacuum dryer at 25 ° C for 24 hours. Then the catalyst was pressed into cylindrical bodies set 1 cm in length and 0.5 cm in diameter. After calcination at 350 ° C, the tablets were placed in a reactor.

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The catalyst tablets were reduced in the reactor.

To this end, a hydrogen-nitrogen stream 9 (6% hydrogen in nitrogen) was passed through the catalyst bed with a spatial velocity (space velocity) of 1500 m / m (m / reactor / hour). The temperature was gradually increased from 20 ° C to 450 ° C for 80 hours. The catalyst was kept at 450 ° C for an additional 100 hours, and finally to be heated at 475 ° C for another 48 hours.

The nickel reduction rate in the catalyst after this treatment was 86%. The fennel content of the reduced catalyst was 42%. The accessible nickel surface was determined from the hydrogen adsorption; this was 81 m per g of nickel. The particle size distribution was calculated from the magnetization curve. The result is given in Fig. 4. The radius of the nickel particles is given horizontally in logarithmic scale, while vertically the number and volume are plotted. The dotted line indicates the voltime, the solid line the number.

Separation of Methane from a Nitrogen-Methane Mixture

For the separation of methane from a nitrogen-methane mixture, use was made of a mixture containing 40% methane. This mixture was passed through two reactors connected in series. Both reactors were charged with a bed of catalyst C. The first reactor, which was kept at a temperature of 150 ° C, contained 5 kg of catalyst, the second reactor had a temperature of 25 ° C and contained 2 kg of the same catalyst.

The said gas mixture was passed through the two catalyst beds with a spatial velocity (space velocity1) of 40 m gas / (m reactor / hour). At the exit of the bed held at 25 ° C, the vented gas no longer contained methane. After 15 liters of gas, i.e. containing 6 liters of methane, had been passed through for 10 minutes, the feed was stopped.

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Then the second reactor was brought to 300 C, 3 3 7811278 after which a hydrogen stream with a throughput speed of 30 m / (m reactor / hour) was inverted first through the second and then through the first reactor. A * 1 ° methane-hydrogen mixture was released at the outlet of the first reactor, so that the methane and the nitrogen were completely separated. In total, the 6 liters of methane could be desorbed.

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After the second reactor had cooled to 25 ° C, the nitrogen-methane mixture was again able to pass through the reactors at the temperatures indicated previously. Carbon loading and removal was found to be repeatable many times without noticeable drop in catalyst capacity.

The described separation of methane and nitrogen can also be carried out as a variant in four fluidized beds.

The first two beds are used for binding and desorbing resp. the hydrocarbon and methane, while the hydrogen is adsorbed and desorbed in the second set of fluidized beds.

15 Conversion of Methane from a Nitrogen-Methane Mixture into Synthesis Gas (Carbon Monoxide and Hydrogen)

In this case, the methane-nitrogen mixture was decomposed in the same manner as in the previous example. After loading the catalyst beds with carbon, hydrogen and methane, the second reactor was also brought back to 300 ° C, the adsorbed hydrogen being desorbed in a hydrogen stream.

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The first reactor was now brought to a temperature of 600 ° C, while 50% steam was added to the hydrogen flowing from the second reactor into the first. The carbon deposited on the catalyst reacted to form carbon monoxide and carbon dioxide to form hydrogen. It was found that the reactivity of the carbon in this case did not vary noticeably for the different catalysts. The catalyst in the first reactor can now be loaded more heavily by keeping the reactor temperature at 300 ° C during the decomposition of the methane. However, the loading must not be increased too high, otherwise the pores in the catalyst tablets will clog and the tablets may even disintegrate. In this case too, working with four fluidized beds as a variant can be advantageous.

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If ammonia is to be produced from the methane, use can advantageously be made of the nitrogen from the gas mixture. For this purpose it is possible to add such a stream of the residual separated nitrogen to the gas mixture that the hydrogen / nitrogen ratio required for the ammonia synthesis is obtained.

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Claims (12)

1. Process for the decomposition of methane into carbon and hydrogen using a nickel catalyst at elevated temperature, characterized in that the methane is passed over the nickel catalyst at a temperature of between 80 ° C and 500 ° C with at least 10 ° C. weight percent nickel on a support, the nickel on the support being present as particles smaller than 20 nm and periodically regenerating the carbon-loaded catalyst in known manner. 2. A method according to claim 1, characterized in that the largest dimensions of the nickel particles lie substantially between 3 and 6 nm. Process according to claim 1 or 2, characterized in that the O o methane is passed over the catalyst at a temperature between 100 c and 300 c. 4. Process according to claims 1-3, characterized in that the methane is passed over the catalyst at a temperature between 120 C and 180 C. Process according to claims 1-4, characterized in that the nickel content is at least 30% by weight. 6. Process according to conelusion 1-5, characterized in that the weight ratio of nickel to support material is up to 95: 5. 78 1 1 2 7 8. 13 i, Process according to claims 1-6, characterized in that a mixture of methane and nitrogen is passed over the catalyst and the hydrogen formed is separated from the nitrogen. 8. A method according to claim 7, characterized in that it is separated from the nitrogen by absorption of the hydrogen formed. Process according to claim 8, characterized in that the hydrogen is absorbed by a catalyst as defined in one or more of claims 1, 2, 5 or 6. Process according to claims 1 and 9, wherein the catalyst is regenerated with hydrogen, characterized in that the regeneration takes place at a temperature between 150 ° C and 400 ° C. 11. A method according to claim 9, characterized in that the size of the nickel particles is substantially between 3 and 6 nm and regeneration takes place at a temperature between 150 ° C and 250 ° C. Process according to claim 10 or 11, characterized in that the hydrogen is at least in part the hydrogen desorbed again after absorption. 7811278