DE2453089A1 - REACTION BED FOR A CATALYTIC CRACKING SYSTEM - Google Patents

Description

Lawyer file: U 223

United Aircraft Corporation, East Hartford, Conn. O6108, V. St. A.

Reaction bed for a catalytic cracking plant

The invention relates to the production of hydrogen from hydrocarbon fuels used in conjunction with
Fuel cells can be used, and in particular on the katatytis before cracking of gaseous hydrocarbons fuel fuel fen
and hydrocarbon fuel distillates.

The production of hydrogen from hydrocarbon fuels mostly excludes the use of .dampf in the known Steam reforming reaction. When using con-

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Hydrogen fuels to power a fuel cell with hydrogen, the presence of any water in the fuel cell feed may be inadmissible due to the environment (freezing temperatures) or due to a non-existent feed water supply. That's why it's after others Methods for generating hydrogen have been sought. Most of these processes use hydrogen-containing gases, which are not hydrocarbons are used and these methods are therefore limited to applications in which the source of such a gas is readily available. That of course prevents the widespread use of fuel cells whenever the Fuel cells not using conventionally available fuels, such as motor fuels, natural gas and the like. Can be 'operated'.

Attempts have already been made in the past to use the metals Group VIII, especially nickel, for hydrocarbon cracking fuels to be used. It. however, it is believed that such processes are limited to the cracking of gaseous hydrocarbon fuels such as natural gas, propane and the like have been. In addition, it has been shown that with such Method results in an unacceptably long cleaning cycle following the burn-off cycle, because of the excessive Oxidation of the catalysts during the burn-off cycle (which is inserted between alternate cracking cycles), especially when a high nickel catalyst is used. On the other hand, the use of catalysts with a lower nickel content has led to ineffective processes with a lower yield of hydrogen.

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To overcome these problems, an attempt has been made to use a catalyst at the inlet of the reactor bed low nickel content and to use a high nickel content catalyst at the outlet of the reactor bed. Such Reactors, however, have proven impractical because of the crumbling of the pellets, unreduced oxidation the catalytic converter and other problems.

The invention aims to provide an improved system for catalytic Cracking hydrocarbon fuels for the formation of hydrogen can be created.

According to the invention, a catalytic cracking bed is a Catalyst is used which comprises nickel supported on porous ceramic substrate pellets. In a further development of the invention the catalyst comprises a ring catalyst in which a porous ceramic support subs tr at to a depth in the order of magnitude from 25.5 µm - 2550 µm is impregnated with catalytic material. In a further embodiment of the invention are in a

porous

Cracking bed through / ceramic backed catalysts with graded Nicke oil content used.

The invention enables the use of catalytic beds, which range from a low catalyst level at the inlet to a higher catalyst level at the outlet Have gradation range. The invention also avoids that Build-up of unoxidized carbon after successive burn-off and cracking cycles ("blow-and-run" cycles), the crumbling and the unreduced oxidation of the catalyst. The invention ensures that not only gaseous hydrocarbon fuels but also hydrocarbon fuel distillates.

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can be cracked casually and continuously to hydrogen, and while in a process which is suitable for use in a variety of general and special applications particularly suitable for fuel cells. The invention provides a reliable source of hydrogen from hydrocarbon fuels, without the need for a water source.

Further features and advantages of the invention emerge from the following description of preferred exemplary embodiments of the invention with reference to the accompanying drawing.

The only figure in the drawing contains a schematic diagram a two-chamber system according to the invention for the catalytic cracking of Kohlenwas water fuel with cyclical burning and cracking processes works.

As shown in the figure, two identical reaction vessels 3, 4 are connected to one another in such a way that they are operated in push-pull with one vessel performing a cracking cycle while the other vessel is performing a burn or regeneration cycle, after which roles are reversed. The vessel 3 includes an outer wall 6, a first inner baffle 7 and a second inner baffle 8 such that a reaction chamber 1O, an evaporator chamber 12 and an oxidation center inlet chamber 14 are formed. A bed of uncatalyzed pellets is arranged within the evaporation chamber 16, which are preferably non-porous ceramic particles or the like. Which on a grid or sieve being held. This bed has the simple purpose of absorbing heat in a manner described in more detail below,

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so that liquid hydrocarbon fuel added to the bed is supplied from a fuel inlet pipe 18, is vaporized on contact with the hot pellets, with a slight Amount of steam in the oxidant inlet chamber 14, but essentially all of the steam through a space formed below a grille or screen 22 upwards flows through the reaction chamber IO and through a space 28 to an outlet pipe 3O. The said grid or Sieve 22 is used to trap the catalyst pellets 24, 26 within the reaction chamber lO used.

The fuel is fed to the inlet pipe 18 through a shut-off device 32, which is shown and in the open position is in turn connected to a fuel pipe 34 that is connected to a hydrocarbon fuel source 36. The hydrocarbon fuel can include any desired fuel such as heating oils, jet fuel, motor gasoline, Natural gas, or the like. The hydrocarbon fuel source emits substantially continuously as described below Fuel to one or the other vessel and can therefore in the form of a continuously operating bypass pump be designed in which the bypass serves to absorb interruptions in the flow when the shut-off devices be operated.

While the fuel flows through the reaction chamber IO from the source, a shut-off element 39 is in the position shown in the figure and causes the reaction product, which is predominantly hydrogen, to flow into a hydrogen outlet pipe 40. '· ■

5 0 9 8 2 6/0 86 8

When the hydrocarbon fuel is at a suitable temperature Flows over the catalyst pellets 24, 26, the hydrocarbon is fuel plus heat in a gaseous product converted, which mainly contains hydrogen along with small amounts of carbon monoxide and water (as well as Traces of other by-products, depending on the particular hydrocarbon fuel used). At this In the reaction, carbon is deposited in place on the catalyst pellets.

It is known that in order for a cracking cycle to work properly it is necessary to have a nickel catalyst bed at one temperature within the range of 815 C to 1095 C. This is achieved during start-up by an igniter 38, the hydrocarbon fuel ignites for a short period of time until it reaches operating temperature. After that, following each Cracking cycle (just described) the valve 32 closed and a valve 41 (shown in the closed position) opened so that an oxidizing agent such as Air, from a source 42 through a tube 44 and an oxidizer Inlet inlet tube 46 flows into oxidant inlet chamber 14. Most of the oxidant flows between the baffles 7, 8, through the Raem 2O, up through the reaction chamber IO and into the outlet pipe 3O. At this point will the outlet valve 39 rotated by 90 clockwise from the position shown in the figure, so that it. afterward diverts the flow to an outlet pipe 46. The adjustment of the shut-off devices takes place in any known manner, preferably using solenoid shut-off devices which respond to known clock control devices 48.

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When the oxidant over the pellets. 24 and 26 flows, which are still at a relatively high temperature (of the order of 815 C), the carbon burns (oxidizes) and forms gaseous CO which flows through the exhaust pipe 3O, and a large amount of heat is generated, so that the bed is back to a temperature of the order of magnitude

ο -

of 1095 C. Thus removes the burn cycle the carbon deposits from the catalyst 'and reheat the catalyst to a temperature greater than that temperature required for operation. On the other hand, consumed the cracking cycle heats up the catalyst and produces hydrogen, but at the same time also contaminates the catalyst Carbon deposits. Consequently, the nested cracking and regeneration cycles must be repeated at time intervals, which are related to the contamination of the catalyst and the consumption of heat in the catalyst.

While it hasn't been described, it is. however, it is clear that the reaction vessel 4 is provided with the same inlets and outlets is connected to the fuel source by similar shut-off devices 36, the oxidant source 42 and the hydrogen - And outlet pipes 4O, 46 are connected. Whenever the vessel 3 performs a cracking cycle, vessel 4 performs a regeneration cycle, and vice versa, so that the hydrogen flow is essentially continuous.

In an entire process cycle, i. H. from the beginning of a Cracking cycle in the vessel 3 to the beginning of a subsequent cracking cycle in the vessel 3, the time can be of the order of magnitude vary from 4 minutes to 10 minutes. Distributed this time

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essentially evenly affects the cracking and regeneration sub-cycles. Because of the oxidation of nickel catalysts near the end of the regeneration cycle, which leads to the formation of water and carbon oxides at the beginning of the cracking cycle, the regeneration sub-cycle holds a cleaning part in which hydrocarbon fuel is supplied, the outlet valve 39, however, is still rotated in such a way that the outlet pipe 30 is connected to the outlet pipe 46. This is supposed to prevent be that such by-products are fed to the hydrogen stream.

With the exception of the fact that two different arrangements of pellets 24, 26 are mentioned above, all are related on the drawing described up to this point known. It is further already known, catalyst pellets 24 with a low Catalyst content (on the order of 5 weight percent or less) at the inlet end of the reactor chamber (below the dash-dotted line 50) and a high catalyst content (over 5 percent by weight "catalysts at the outlet end the reaction chamber IO (above the dash-dotted line 50) to use. As already explained above, such Attempts before the priority date of the present invention are unsuccessful.

In accordance with the invention, it has been found that pure metallic substrates (such as Incolo.y) are likely to melt and otherwise cannot withstand the changes in temperature and the successive oxidations and reductions that occur with burning - and cracking cycles are required.

The catalyst is known to be used during the regeneration

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Cycle oxidized. The metal oxide breaks down to powder'imd becomes · "'" Secreted by the substrate pellet, Bas Metalt remains, if it is reduced in the subsequent cracking cycle »in Palverform« But that is necessary to the surface of a Catalyst material itself increases considerably. enlarge to thereby the number of active regions that can promote the desired response rather than other responses is considerable to enlarge. It turned out, that the powder the Has a tendency to mix with the gaseous stream and / ο the bed at the lower end of the reaction or of an assigned room anztts amine In. Therefore, according to of the invention used extremely porous ceramic sticks since the pores of the substrate and other spaces in it Pick up powder to make it available for reaction. do, while at the same time essentially all of the powder remains in place at the substrate in the desired manner »

In addition, the invention provides for less crumbling or other mechanical crushing of the catalyst pellets, by using only ring-catalyzed material. This is based on the knowledge that crumbling and crushing during Burning off and catalytic cracking as a result of the formation of Carbon deposits within the Safostratsöriiktiir always occur when the substrate tractiair so sufficiently porous is "that the catalyst material, and vaporous hydrocarbon fuel penetrate into internal passages of the Sabstrat can. In the invention ring catalysts are used, in which catalyst material in the interstices of porous substrate material only up to. a depth in of the order of 25.5 µm to 2550 µm is introduced,

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so that the Katalysatormafcerial fiir the hydrocarbon fuel readily available _r ISFC the carbon in-

Follow the process is formed, strives to focus on the

A cz mustard pool instead of getting caught in the pores, and any expansion that involves the formation of carbon results (in the same way as the expansion of ice when water freezes) that the catalytic substrate material is not structural stressed because it affects the surface areas is limited.

A preferred embodiment of a catalyst used in the invention is . Micke l-King catalyst which on a porous substrate of zirconia _r .Aluminiumoxid or a mixture of the two F or even other refractory oxides such as silica and mixtures ,,! is formed by a plasma spray process. In short, this process sprays molten powder onto substrate pellets as they move around a basket "rotated 45" and weighs the product to determine when the desired percentage by weight of Nikkei is added to the pellets Subs tr atpe llets has been applied. Instead, the catalyst pellets useful in the invention may be pellets (although they have not been shown to perform as satisfactorily over a long period of time) formed in a chemical conversion bath process , in which the porous ceramic pellets are immersed in a salt solution such as nickel nitrate, so that the salt solution penetrates the pores of the substrate; then the substrate is dried and then the salt is broken down into nickel oxide and nitrogen dioxide by leaving it in air for about four hours at a temperature in

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ff

of the order of 26O C is fired. Then will the product is placed in a muffle furnace or the like with a hydrogen atmosphere at 54O C for about two hours, with it the oxide dissociates and thus forms nickel and water. The nitrogen dioxide escapes during the reduction process, see above that when the nickel oxide is converted into nickel and water, the pure nickel remains, which is in the pores on the surface of the substrate adheres. One improvement to the immersion process is to use a substrate material which has a non-porous core with a thin porous surface layer, which ensures that the nickel only extends into one penetrates relatively small depth of the surface, so that the advantages of a ring catalyst are achieved.

Another method of making ring catalysts useful in the invention is the ^{method known as "Mulling 11} ", in which nickel powder and pellets of porous ceramic substrate are circulated together so that a substantial amount of the metal adheres to the substrate. Subsequently, after heat treatment in the burn-off and cracking process or following sintering of the product, an acceptable catalyst is formed.

As mentioned above, it has been shown that a preferred Embodiment of a catalyst bed ε for the hydrocarbon cracking process results when at the inlet end of the bed a low concentration of catalyst and at the outlet of the A high concentration of catalyst is used. It is believed that this is mainly because a high one Catalyst content leads to the production of considerable carbon oxides and water during the cracking cycle, namely

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gen undesirable side reactions with the nickel catalysts. Furthermore, the nickel oxide that is formed during the burn-off or regeneration cycle is reduced and leads to the formation of water and carbon oxides. This is undesirable, since hydrogen is wasted in the formation of water and since the carbon oxides contaminate the hydrogen stream (this is the same reaction that was explained on the cycle's clean flow). This undesirable effect is greatly enhanced or promoted when a high nickel content is used. On the other hand, although the use of a low nickel catalyst bed reduces the formation of water and carbon oxides, it tends to produce methane because the catalyst does not adequately promote the preferred reaction. All these effects are more pronounced, when hydrocarbon fuel distillates instead of gaseous hydrocarbon fuels used, these effects are however mitigated by the low catalyst content is used at the inlet ₀ where the reaction rate is high, and the high catalyst content in the vicinity of the off passage used where the reaction rate is slower. However, it is not necessary that a rigid separation be observed. Indeed, catalysts with several different contents can be placed between the inlet and outlet of the chamber. It is also possible to provide a central area in which a low catalyst content is mixed with a high catalyst content, so that a more uniform gradation is created if necessary. It has been found, however, that the use of two concentrations gives fairly satisfactory results even with a substantially abrupt separation.

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The importance of the invention is that it provides an improved, Cracking process that works without water creates. However, it can also be used in a method in which low Amounts of water added to the hydrocarbon fuel feed will. This results in a higher yield of hydrogen, but at the same time small amounts of carbon oxides in the H stream.

It can be assumed that other metals besides nickel are also present of Group VIII give suitable catalysts useful in the invention, although these metals have not been tested have been. Implementation examples of several different Combinations of ring catalysts which can be used according to the invention are in the following table aagegebea.

TABEL

Ge w ο ■ = »% Ni => Filling likes

filled with low catalyst content

■ § ■)

Immersion bath

O, 56

1.5

Zirconia alumina

Flame spraying MuLLing "

Zirconia zirconia

Immersion bath Flasxi ice spraying Flame spraying immersion bath

75

• 5-S All® Substrates are balls with a diameter of 1.25 cm

Within the scope of the invention, the person skilled in the art is offered a Numerous possibilities for simplification and improvement with regard to the form and details of the invention.

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Claims (5)

Godfather tans prii ehe; - '' "-. ·, <· .- ... - [l) Catalyst reaction bed for a regeneration and cracking plant for the production of hydrogen from hydrocarbon fuel gases and distillates, characterized by supported metal ring catalyst pellets with nickel deposited to a depth between 1270 µm and 5080 µm from the surface of porous ceramic substrates, the largest of which Dimension is between 6.35 mm and 19.0 mm. 2. Catalyst reaction bed according to claim 1, characterized in that that the substrate material comprises ceramic selected from the group consisting of zirconia, alumina and mixtures of zirconia and alumina. 3. Catalyst reaction bed according to claim 1, characterized in that that the substrate mainly comprises spheres which have a diameter between 6.35 mm and 15.85 mm. 4. catalyst reaction bed according to one of claims 1 to 3, characterized in that the catalyst pellets are different Have catalyst concentrations. 5. Catalyst reaction bed according to claim 4, characterized in that that the catalyst pellets between 0.5 weight percent and 5 weight percent nickel at the inlet end of the catalyst reaction bed and that the catalyst pellets have between 15 weight percent and 50 weight percent nickel at the outlet end of the catalyst reaction bed. 509826/0668