CS258512B1 - A method for removing carbon oxides from technical hydrogen by methane - Google Patents

Abstract

The solution relates to the purification of technical hydrogen, produced from producer gas by conversion from carbon oxides by methanation on a catalyst containing nickel oxide on a support, in which the purified gas is fed to a catalyst bed, which is filled in the inlet and, optionally, also the outlet part with a catalyst with a NiO content of 30 to 55% by weight in the form of surface-grooved cylindrical extrusions and in the lower part with a catalyst with a NiO content of 15 to 30% in the form of tablets, balls or preferably Raschig rings, with the ratio of the volumes of the catalyst in the inlet to the lower part being 1:4 to 4:1.

Description

The invention relates to the removal of carbon oxides from technical hydrogen, their hydrogenation to methane, so-called methanation, mainly on catalysts containing nickel Ni as oxide in amounts ranging from 15 to 40% by weight, on suitable carriers. However, technical hydrogen also contains trace amounts of various catalytic poisons, such as sulfur compounds S and chlorine Cl, which reduce the activity of all catalysts used so far. Iron carbonyls and, in the case of non-nickel methanation catalysts, nickel carbonyls also act in a similar way. The resistance of Ni catalysts to catalytic poisons increases partly with the Ni content in the catalyst, but at the same time its price also increases. Therefore, catalysts with a Ni content ranging from 15 to 25% by weight are usually used, which also determines the maximum volumetric loading of the catalyst, i.e. the performance of the given reactor. The increased volumetric loading can be used practically only shortly after the catalyst has been run in. At elevated volumetric loadings, the commonly used particle shape, which is usually small pellets or spheres, in axial adiabatic bed or tubular reactors causes a pressure drop that increases sharply with volumetric loading.

It has now been confirmed that to eliminate or reduce the influence of the above-mentioned facts while simultaneously increasing the reactor output, i.e. the volume load, it is advantageous to use a combination of nickel catalysts of different shapes and with different Ni contents suitably axially distributed in the reactor, thereby achieving a higher volume velocity, i.e. a higher load on the reactor charge at the same degree of carbon oxide removal, under otherwise normal operating conditions, which may also eliminate the need to build an additional methanation device in a certain specific case.

The method of removing carbon oxides from technical hydrogen by methanation on catalysts containing nickel oxide on a support as an active component consists, according to the invention, in that the gas containing carbon oxides enters the catalyst bed, in the inlet part of which, optionally also *

outlet part, a nickel catalyst with a NiO content of 30 to 55 wt. % is placed in the form of surface-grooved cylindrical extrusions and in its lower part a catalyst with a NiO content of 15 to 30 % in the form of tablets, balls or preferably Raschig rings, the ratio of the volumes of the catalyst of the inlet to the lower part being 1:4 to 4:1, preferably 1:2 to 1:1. The lower part of the filling can be further divided into 2 parts in the ratio 1:2 to 2:1, which are filled at the top with a catalyst in the form of Raschig rings with a NiO content of 15 to 30 wt. % and at the bottom with a catalyst in the form of surface-grooved cylindrical extrusions with a NiO content of 30 to 55 wt. %. Thus, a nickel catalyst with a content of 25 to 55% NiO is placed in the input layer of the methanation reactor, preferably in the form of cylindrical extrusions with longitudinal surface grooves, which, due to its Ni content and the size of the outer surface, exhibits high effective activity and considerable resistance to trace catalytic poisons. A Ni catalyst of classical shapes is filled into the lower part of the combined charge of the methanation reactor, i.e. tableted or pelletized with a NiO content of 15 to 25% by weight, or a catalyst with a similar NiO content, but preferably in the form of Raschig rings, which again, with its outer surface and shape, brings an increase in the effective activity of the catalyst and a reduction in the pressure drop in the layer. The arrangement of the lower layer charge significantly affects the required reactor load, the required methanation efficiency, i.e. the degree of removal of carbon oxides from technical hydrogen and the optimization of the reactor charge with regard to its price.

Therefore, under particularly demanding methanation conditions at high volumetric loading, in the presence of trace poisons and with increased demands on hydrogen purity after methanation, the lower part of the charge is also divided into two layers consisting of one of the last two types of catalysts mentioned and the catalyst charged to the upper layer of the reactor, which is preferably charged to the lowest part of the combined charge.

In the inlet part of the charge, due to the high effective activity of the loaded catalyst placed in the first layer, the methanation reaction starts up quickly and thus, due to the released reaction heat, the temperature in the bed increases rapidly, which is advantageous for increasing the effective activity of the catalyst in the second or lower layer of the charge with a catalyst with a lower NiO content. The first layer with a high NiO content is at the same time, with its high capacity for poisons, a protective layer for the lower charges and then allows for long-term use of their optimal activity. Reactor charges of the above-mentioned type can be used at practically any working pressure, determined essentially only by the pressure and ^temperature resistance of the reactor jacket. The working temperatures of the reactor charge are determined by the temperature stability of the catalysts used, but in order to achieve maximum performance of the reactor charge, catalysts active in the temperature range of 200 to 400 °C, preferably 260 to 350 °C, are used. At pressures around 3 MPa, the volume velocity has so far been 3 to 5,500, while with a combined charge, depending on the type of catalyst, a two-layer or, more preferably, a three-layer charge, a volume load of 6 to 10,000 h ^-1 is achieved, while the carbon oxide content remains below the required limit of 10 ppmv. and the pressure loss of the reactor practically does not change from the original values or remains within the limits permitted by the design of the reactor grates. At the same time, optimization of operating costs is achieved also in terms of the price of the catalyst charge. Such charges can be advantageously used even in situations of reduced gas consumption for methanol synthesis and, conversely, increased hydrogen requirements for ammonia production in cases where both productions are operated in parallel. This also applies to any other possible consumption of pure hydrogen.

Example 1

Parallel operation of two methanation reactors with a total volume of 9 m ³ with a conventional charge and with a combined charge according to the invention.

Inlet gas composition (mol.%):

_CO2 0.15

CO 0.40 inerts 2.45

With 20 ppbv

H, 97

Catalyst fillings:

classic combined ball catalyst ball diameter 4 to 7 mm NiO content 25% by weight

input layer: 3 m of cylindrical longitudinally grooved catalyst with a content of 40 wt. % NiO bottom layer: classic

Exploitation conditions: 55,000 3 gas input (m/h) 60,000 6,100 volume velocity (h ^χ ). 6,700 300 gas temperature (°C) 300 338 outlet temperature (°C). 339 8 pressure loss (kPa) 9 3 lifespan (years) 3 residual content in (ppmv) 4 what ₂ 2 6 WHAT 1

Example one confirms not only the higher productivity of the combined filling, but also its higher activity.

Example 2

Two-layer combined methane reactor filling of total volume

Bottom layer: 4 m ³ of catalyst with 25% NiO content, shape: Raschig rings with a diameter of 5 mm

Top layer: 5 m ³ of catalyst with 40% NiO, shape: longitudinally grooved cylinders

Input gas composition as in example 1.

Reactor capacity: m gas/h inlet 72,000.0 vol. speed (h ^-1 ) 8,000 temperature (<°C) inlet 300 outlet 340 pressure drop (kPa) 10 in gas: ppmv CO ₂ 4

CO 2 cartridge life (estimated ¹ year) 3

Example 3 about

Three-layer combined filling of a methane reactor with a total volume of 9 m.

Top layer: as in example 2, catalyst volume 3 m ^{2 3} o

Middle layer: as bottom layer in example 2, volume 3 m

Lower layer: same as upper layer, volume 3 m

Inlet gas composition: as in example 1.

Reactor capacity: m gas/h inlet 72,000.0 vol. speed (h ³ ) 8,000 temperature (°C) inlet 300 outlet 340 pressure drop (kPa) 11 in gas: ppmv CO ₂ 2

CO 1

The results given in examples 2 and 3 show that the reactor fillings mentioned will allow for a higher volumetric loading in the future, if an increase in the carbon oxide content in total up to 10 ppmv is allowed. Also, the expected service life will be at least 3 years, depending on the loading.

Claims (2)

SUBJECT OF THE INVENTION Method for removing carbon oxides from technical hydrogen by methanation on catalysts containing as an active ingredient nickel oxide on a support, characterized in that the carbon-containing gas enters the catalyst bed, in which the nickel catalyst containing NiO 30 to 55 wt. in the form of surface grooved cylindrical extrusions and at the bottom thereof a catalyst with a NiO content of 15 to 30% in the form of tablets, spheres or preferably rashig rings, the ratio of catalyst to inlet to bottom volumes being 1: 4 to 4: 1, preferably 1: 2 to 1: 1. 2. A process according to claim 1, wherein the lower part of the catalyst packing is divided into 2 parts in a ratio of 1: 2 to 2: 1, which are filled at the top with a catalyst in the form of a peat ring with a NiO content of 15 to 30 wt. and a surface-grooved cylindrical catalyst with a NiO content of 30 to 55 wt.