JPH05322B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in the production process of ammonia synthesis gas. The most common method for producing ammonia consists of the following steps. 1 Primary steam reforming reaction process CH ₄ +H ₂ O→CO+ _3H 2 2 Secondary steam reforming reaction process CH ₄ +H ₂ O→CO+3H ₂ CH ₄ +O→CO+2H ₂ 3 Carbon monoxide conversion reaction process CO+H ₂ O →CO ₂ +H ₂ 4 Carbon dioxide removal process 5 Carbon monoxide removal process 6 Ammonia synthesis reaction process N ₂ +3H ₂ →2NH ₃ Reaction 1 is based on the water vapor/carbon ratio, temperature, and pressure.
It progresses incompletely under economical conditions;
The small amount of unreacted methane is mostly converted in reaction 2. That is, reaction 2 introduces air into the hot gas from reaction step 1 to obtain a higher temperature by combusting some of the gas and unreacted methane is reduced to a low level over the catalyst. The gas produced in the steam reforming step then converts most of the carbon monoxide into hydrogen in a carbon monoxide conversion reaction step 3. The gas then passes through a carbon dioxide removal step 4, then a carbon monoxide removal step 5, and then enters an ammonia synthesis reaction step 6, where ammonia is synthesized. The conditions for reaction 2 are usually such that the amount of air required to provide oxygen in reaction 2 introduces the amount of nitrogen required in reaction 6. That is, the amount of air introduced in reaction 2 is restricted from this point. Reactions 1 and 2 are both reactions for converting methane into carbon monoxide and hydrogen (finally hydrogen), and if it is possible to introduce a large amount of air in reaction 2, then More reactions are carried out and the load on reaction 1 is greatly reduced. The reformer in which reaction 1 is carried out is usually an external heating type, and its tube is exposed to high temperature and pressure.
The material is under extremely harsh conditions. Reducing the load on reaction 1 under such conditions frees the reformer tube material from this severe condition, and conversely, allows for a higher pressure reforming reaction. If this happens, the compression power in ammonia synthesis will be significantly reduced. Further, the secondary reformer is an internal heating type and has extremely high thermal efficiency, whereas the primary reformer is an external heating type and has a considerably low thermal efficiency, so by doing so, the overall thermal efficiency is increased. That is, this method is extremely attractive. However, for this purpose, the excess nitrogen introduced must be removed somewhere. As a method for this purpose, ammonia synthesis reaction 6
Before this, a method is known that utilizes cryogenic separation. In this method, synthesis gas is adiabatically expanded using an expander to obtain a low temperature, nitrogen is liquefied and separated to some extent, and the ratio of hydrogen and nitrogen is adjusted to an appropriate ratio for the ammonia synthesis reaction. At the same time, methane is almost completely removed, and carbon monoxide and argon are also removed to some extent. A method has also been proposed in which the gas is treated by cryogenic separation in the ammonia synthesis loop.
(Japanese Patent Application Laid-Open No. 54-60298) The former method is an excellent method, but because the separation of carbon monoxide is not sufficient, the synthesis gas must undergo a methanation reaction step and a water removal step using an adsorbent before this separation. installed in the device. Therefore, the process and costs have not been streamlined that much. The latter performs similar treatment in the ammonia synthesis loop, but in order to perform cryogenic separation, ammonia must first be completely removed, and the concentration of nitrogen to be treated is higher than in the former. This is disadvantageous from a nitrogen treatment standpoint. Therefore, if these factors are taken into consideration, it cannot necessarily be said that it is an economical method. In the method provided by the present invention, after ammonia has been synthesized and separated, a portion of the unreacted ammonia synthesis gas is extracted from the synthesis loop and treated with an adsorption separation device. When ammonia and ), nitrogen and non-reactive gases (i.e. methane, argon) are almost completely separated and the gas is made into a hydrogen-based gas and reused as a raw material for ammonia synthesis, the amount extracted from this synthesis loop is , hydrogen in synthesis gas by controlling the throughput,
This controls the nitrogen ratio. When the generated ammonia is separated from the synthesis gas, the separation may be incomplete or almost complete depending on the separation method used. In conventional ammonia synthesis methods, the former is incomplete in all cases. That is, in this case,
By cooling the reacted synthesis gas, ammonia in the gas is liquefied and separated. Therefore, 1 to several percent, usually about 2 to 3 percent, of ammonia remains in the synthesis gas. When the separation is almost complete, ammonia in the synthesis gas is almost completely separated by an adsorption method or an absorption method, although there seems to be no example of this being practiced industrially yet. For an example of the absorption method using water, see JP-A-54-
60299. An example of a method for separating most of the ammonia from synthesis gas by the adsorption method is described in Japanese Patent Application No. 155548/1982, an invention by the inventor of the present invention. Not limited to that invention, when ammonia is separated by an adsorption method, the concentration of ammonia in the separated synthesis gas becomes extremely low. In contrast, in the case of the absorption method using water, the concentration of ammonia is slightly higher, but at a much lower level than in the case of liquefaction separation. In these two cases, the gases to be adsorbed and separated are a small amount of ammonia and nitrogen, methane, and argon in the case of 1, and nitrogen, methane, and argon in the case of 2, and the treatment methods are different for each. Treatment methods in this case include a method in which ammonia is separated by water absorption and then nitrogen, methane, and argon are separated, and a method in which an adsorption device is used to adsorb and separate these at the same time. The former method has no problem in terms of processing, but it is actually a troublesome method. Since the latter method involves mixing ammonia and other gases at low pressure, it is difficult to separate and recover ammonia from this, both in terms of process and equipment. In this case, that is, when the gases to be separated are only nitrogen, methane, and argon, and the amount of ammonia is extremely small, the pressure fluctuation adsorption separation method can be suitably applied to this separation. Nitrogen, methane, and argon have slightly weaker adsorption powers, but if they are all adsorbed, they can be adsorbed and separated without any problem by the commonly used pressure fluctuation adsorption separation method. Moreover, since the adsorption force is not so strong, desorption is easy. In the case of , if ammonia can be removed by appropriate pretreatment, the pressure fluctuation adsorption separation method can be applied as in the case of . As a method for this pretreatment, a method of selectively adsorbing and separating ammonia using type 3A zeolite is suitable. Type 3A zeolite has a pore diameter of 3 Å (angstroms) and can contain hydrogen,
Molecules other than helium, neon, water, and ammonia cannot enter this pore. Therefore, in this case, ammonia is selectively adsorbed, and other components are not adsorbed. That is, ammonia is selectively adsorbed by an adsorption device using type 3A zeolite. On the other hand, in this case, it is better not to reduce the pressure at all, or even if the pressure is reduced, it should be kept at a pressure that would liquefy ammonia at room temperature, so that it is convenient to obtain the liquid base. (Since a large amount of non-condensable gas enters, it is better to set the liquefaction pressure a little higher.) In this case, a suitable desorption method is to heat the adsorption bed to release ammonia. As the heat source, it is desirable to appropriately utilize waste heat such as outflow gas from the ammonia synthesis apparatus. In this way, the synthesis gas from which ammonia has been separated can be suitably subjected to gas composition adjustment processing by the adsorption separation device, whether the ammonia separation is incomplete or complete. Next, a specific example will be explained in more detail.
FIG. 1 shows a flow sheet of an adsorption device for adsorbing and separating ammonia from synthesis gas containing a small amount of ammonia. The adsorption beds 1a, b, and c are filled with 3A type zeolite, and heat exchanger tubes for heating and cooling are installed in the beds. The process gas is introduced from 21 into an adsorption bed in an adsorption step, ammonia is adsorbed and separated, and the gas flows out from 22. Once the adsorption bed is saturated, it is switched to desorption, heated to release ammonia, then cooled and recycled back to the adsorption process. The desorbed gas is sent to a liquefier by a purge gas, where it is liquefied and separated. The reaction gas discharged from the ammonia synthesis apparatus is suitable as the heating medium for this desorption. Next, FIG. 2 shows a flow sheet of an example of a pressure fluctuation adsorption separation device for separating nitrogen, methane, and argon from a gas containing almost no ammonia, and FIG. 3 shows its cycle diagram. As an adsorption/separation device for such a gas, a commonly used pressure fluctuation adsorption/separation device can of course be used. However, it should be noted that when incorporated into the process in this way, the recovery rate of hydrogen is particularly important. In this respect, the device shown in this example has a high recovery rate despite its simplicity. The adsorption bed is of three bed type, 1a, b, and c. (The cycle will be mainly described with respect to the adsorption bed 1a.) Processing gas flows into the adsorption bed from 21. The gas leaves 22 with most of the adsorbed components nitrogen, methane and argon adsorbed, ie almost pure hydrogen. When the adsorption bed becomes saturated and the adsorbed components begin to leak, the flow into the adsorption bed 1a is reduced to half of the normal flow rate, and at the same time the flow of process gas into 1b is started at half the normal flow rate. By cutting the flow into the adsorption bed in half in this way, there is less unused adsorption bed at the time of switching to the desorption step. At this time, a small amount of the adsorbed component leaks from 1a, but the concentration of the leaked adsorbed component is half of that of 1a and 1b as a whole, and this does not particularly interfere with ammonia synthesis, so there is no problem. The time during which these two beds are used in parallel can be changed after determining in advance how much leakage of adsorbed components is allowed. Therefore, this process can be completed in a short time, and 1
1b continues the adsorption process at full flow rate. The reduced pressure gas from the adsorption bed 1a is first flowed into the reduced pressure gas tank 2, and when both pressures are approximately equal, it is allowed to flow into the adsorption bed 1c which is in the repressurization process. 1a
When the pressures of 1c and 1c become approximately equal, the reduced pressure gas is then allowed to flow into 1c from tank 2 until the pressures of 1c and 2 become equal. Next, replacement gas is introduced into 1a from the inlet side from the replacement gas tank 4,
Purge gas tank 6 to expel void gas in the floor.
flow into. By this gas replacement, most of the hydrogen in the bed is recovered. The inside of this purge gas tank is filled with a material such as a honeycomb or pipes arranged in the axial direction to prevent radial mixing, so that the composition of the gas that flows in remains unchanged. It is now possible to store it while it is hanging. Therefore, the gas from the entrance to the back of this tank has a high concentration of hydrogen, and the gas toward the entrance has a low concentration of hydrogen. After the gas exchange is complete, the bed is then further depressurized.
The gas that flows out here contains almost no hydrogen, and gases that have weak adsorption power, such as nitrogen and argon, flow out.
Since this effluent gas is suitable as a replacement gas,
The replacement gas is received in the replacement gas receiving tank 3, compressed by the replacement gas compressor 5, stored in the replacement gas tank 4, and used for replacement. The adsorption bed 1a is further reduced in pressure and the desorbed gas flows out through the exhaust gas line 27. When the pressure in the bed approaches the lowest level, the next purge gas tank 6
The gas stored in the bed is introduced into the bed from the purge line 25, and the desorbed gas in the bed is introduced into the exhaust gas line 2.
7 to be kicked out. As mentioned above, the purge gas tank is filled with gas with a low concentration of hydrogen gas near the inlet, and with a high concentration of hydrogen gas toward the back. Therefore, the flow into the exhaust gas line is stopped at an appropriate point in this purge step, the gas with high hydrogen concentration is retained in the adsorption bed, and the repressurization step begins. Next, the reduced pressure gas from 1b and then the reduced pressure gas from the reduced pressure gas tank 2 are introduced into the adsorption bed 1a. Thereafter, hydrogen gas, which is a product gas, is introduced into 1a from the hydrogen gas tank 7 through the filling line 24. The hydrogen gas tank 7 is placed as a buffer tank so that the flow rate of the treated gas line 22 does not fluctuate too much. The adsorbents used in this adsorption device include:
Since nitrogen adsorption is the first priority, it is desirable to use a material with a large adsorption capacity for nitrogen, such as zeolite. Depending on the scale of the device, the adsorption device may be of a four-bed type or an adsorption device with more beds based on a cycle based on substantially the same idea. This adsorption device achieves a high hydrogen recovery rate through a relatively simple process, but this is due to the fact that two beds are used in parallel for a short period of time when changing adsorption beds to reduce the number of unused adsorption beds. , performing gas replacement in the middle of reduced pressure to recover hydrogen-containing gas, and using the recovered gas as a purge gas to effectively desorb the adsorption bed. Next, an example in which this invention is combined with the invention related to a method for separating ammonia by adsorption method by the same inventor will be explained. Although the invention includes three inventive methods, only the first inventive method will be described since the synthesis gas from which ammonia has been separated is generally the same in each method. FIG. 4 shows an example in which the first method is combined with the present invention. The high-temperature reaction gas flowing out from the ammonia synthesis device 12 flows into the adsorption beds 14c and 14d in the desorption process of the adsorption separation device 14, where the ammonia adsorbed there is desorbed, and the ammonia concentration increases. It flows into the liquefaction device 16. Here, most of the ammonia is liquefied, and the gas then flows into the adsorption beds 14a and 14b in the adsorption stage of the adsorption separation device 14, where the ammonia is almost completely adsorbed and separated and flows out of the adsorption separation device. The synthesis gas compressor 11 circulates the ammonia synthesizer. In the desorption process, desorption is mainly performed in the first adsorption bed (in the figure) 14c, and in the next adsorption bed 14d, the adsorption bed is preheated with this desorption gas. In addition, in the adsorption process, the first adsorption bed 14a
At the next adsorption bed 14b, the bed heated by desorption is cooled. Once these adsorption beds reach saturation, they are sequentially switched to the next step. A portion 21 of the synthesis gas leaving the adsorption bed 14a
flows into the pressure fluctuation adsorption separation device 17, where most of nitrogen, methane, and argon are adsorbed and separated. The processed gas 22 immediately joins the synthesis feed gas 31 and is sent from 32 to the synthesis gas compressor 1.
1 and fed into the synthesizer. The synthesis feed gas from 31 is in a state of significant nitrogen excess, but by joining the process gas consisting almost only of hydrogen from 22, the hydrogen/nitrogen ratio is corrected to the stoichiometric ratio, and the synthesis gas from 32 sent to Modification of the ratio is easily accomplished by controlling the amount of gas 22 processed. Simultaneously with this ratio correction, methane and argon are also effectively removed, keeping the inert gas concentration in the synthesis loop at a low level. Since the pressure drop in the pressure fluctuation adsorption separation device can be kept small, there are no problems with inserting this adsorption device into this part. Next, according to the present invention shown in Fig. 4, 1000 tons/
Showing the balance of the ammonia plant for the day. Prerequisites Nitrogen excess rate in raw gas 40% Hydrogen recovery rate of pressure fluctuation adsorption separation device 95% Ammonia concentration at inlet of ammonia synthesizer 0% 〃 Outlet 〃 10% Synthesis gas compressor outlet pressure 55Kg/cm ² g 31 etc. The lines in Figure 4 are shown.

【table】

【table】

【table】

[Table] As can be seen from the above balance, even though the methane concentration in the raw material gas is as high as 2.4%, the inert gas concentration at the inlet of the synthesizer remains at a few percent.
That is, by using the method of this invention, on the one hand, by reducing the load on the reformer,
By increasing the pressure, on the other hand, it becomes possible to synthesize ammonia at low pressure. The advantages of this treatment method are as follows. 1. The amount of nitrogen removed in this treatment step must be the same as the excess nitrogen in the feed gas. Therefore, the amount of gas treated in this treatment step varies depending on the excess ratio of nitrogen in the raw material gas, but is approximately 50% or less of the amount of raw material gas. (As shown in the example above, when the nitrogen excess rate is 40%, the amount of processed gas is 41% of the amount of raw material gas.) When processing before synthesis by cryogenic separation, naturally the entire amount of raw material gas is must be processed.
Even when processing in a synthesis loop, nitrogen cannot be removed to such a large extent due to the cooling temperature. (If you increase the pressure drop in the expander,
(This results in lower temperatures and more nitrogen removal, but requires more power to restore pressure.) That is, in this case as well, there is no big difference from the case where the treatment is performed before synthesis, and therefore, the amount of gas to be treated in the present method using the adsorption separation method is significantly smaller than that in cryogenic separation. Since the amount of gas to be processed is small, the cost of the apparatus is advantageously reduced, but at the same time, the loss of hydrogen, which occurs approximately in proportion to the amount of gas, is also reduced. 2 Generally, the pressure drop within an adsorption separation device is smaller than that in cryogenic separation. In particular, as mentioned above, since the amount of gas is small, it is possible to design the pressure drop to be small. It is therefore easy to combine the treated gas with the feed gas at the inlet of the synthesis gas compressor, so that the increase in power for gas treatment is small. 3 In this adsorption, not only nitrogen but also methane,
Argon is also almost completely adsorbed and separated, resulting in low methane and argon concentrations in the synthesis loop. Therefore, a high concentration of methane in the raw material gas can be tolerated, and a high leakage of methane at the outlet of the secondary reformer can be tolerated. This has the effect of increasing the amount of air fed into the secondary reformer, with very favorable results such as increased operating pressure in the reformer, lower operating temperature, lower steam/carbon ratio, etc. It can be realized in a practical manner. 4 The treated gas is mixed with the raw material gas which is in a state of excess nitrogen, and the excess is corrected before being sent to the ammonia synthesis equipment, so there is no negative effect from excess nitrogen and it is easy to control the hydrogen/nitrogen ratio. be. 5. When the treated gas contains ammonia, its separation can be achieved by a combination of an adsorption device and a cooling liquefaction device, eliminating the need for absorption with water and simplifying the process.

[Brief explanation of the drawing]

Figure 1 Flow sheet for adsorption separation equipment that pre-processes synthesis gas containing a small amount of ammonia, Figure 2
Flow sheet for a pressure fluctuation adsorption separation device that processes synthesis gas containing almost no ammonia, Figure 3. Cycle diagram, Figure 4. Same as above. Cycle diagram, Figure 4. A pressure fluctuation adsorption separation device is combined with a synthesis equipment that separates ammonia by adsorption method. Example flowsheet. 1a, b, c...Adsorption bed, 2...Reduced pressure gas tank, 3...Replacement gas receiving tank, 4...Replacement gas tank, 5...Replacement gas compressor, 6...Purge gas tank, 7...Hydrogen gas tank, 11...Synthesis gas compressor, 12...Ammonia synthesis device, 14
a, b, c, d...Adsorption bed, 16...Ammonia liquefaction device, 17...Pressure fluctuation adsorption separation device, 21
...Processed gas inlet, 22...Processed gas outlet, 2
3...Decompression gas line, 24...Repressurized filling gas line, 25...Purge gas line, 26...Replacement gas line, 27...Exhaust gas line, 31...
Raw material gas inlet, 32... Synthesis gas compressor inlet, 3
3... Circulating gas inlet, 34... Synthesis gas compressor outlet, 35... Ammonia synthesis equipment inlet, 36...
Ammonia synthesizer outlet.

[Claims]

1. In a method for producing tin hydride from stannic chloride and lithium aluminum hydride, the general formula CmH ₂ m+ ₁ OCnH ₂ n+ ₁ (where m and n are
1≦m≦3, an integer of 1≦n≦3), methyl tertiary-butyl ether, and tetrahydrofuran.
A method for producing tin hydride, comprising preparing a mixture of a seed ether and the stannic chloride, and then reacting the mixture with the lithium aluminum hydride at -60°C to -40°C.

Claims (1)

A method for producing ammonia characterized by controlling the ratio of hydrogen and nitrogen in ammonia synthesis to their stoichiometric ratio. 2 If the ammonia separation in step (e) is incomplete, first use the adsorption separation device in step (f).
Using an adsorption separation device using type 3A zeolite as an adsorbent, ammonia is mainly separated, and then
Claim 1, which uses a pressure fluctuation adsorption separation device using an adsorbent other than type 3A zeolite.
The method for producing ammonia as described in Section. 3. The method for producing ammonia according to claim 1, wherein when the separation of ammonia in step (e) is almost complete, a pressure fluctuation adsorption separation device is used as the adsorption separation device in step (f).