JPH0751442B2 - Method for producing high-purity hydrogen - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-purity hydrogen by steam reforming of methanol, and more specifically, it is inexpensive from crude hydrogen gas obtained by catalytically reacting methanol and water. The present invention relates to a method for efficiently producing high-purity hydrogen.

Hydrogen gas is often used for hydrogenation of various organic compounds, petroleum refining, desulfurization, etc. Further, it is also used in the fields of metallurgical industry, semiconductor industry, etc. The demand for hydrogen gas is increasing year by year and high purity is required.

Compared with conventional steam reforming of natural gas, naphtha, and liquefied petroleum gas, the hydrogen production method by steam reforming of methanol has many advantages such as low reaction temperature and no desulfurization. Recently, it has attracted much attention because it uses inexpensive methanol as a raw material.

(Prior Art) A method of producing hydrogen by steam reforming of methanol involves evaporating and heating a water / methanol mixture, and in the presence of a catalyst, 5 to 40 kg
/ cm ² G, steam reforming reaction at 250-300 ℃ is carried out to obtain crude hydrogen gas containing hydrogen, carbon dioxide and a trace amount of carbon monoxide. After separating reaction methanol as a condensate, carbon dioxide, carbon monoxide, entrained water and the like are adsorbed and removed by an adsorption separation device to obtain high purity hydrogen of 99.999% or more.

This adsorption / separation device is a device that performs gas separation by utilizing the fact that the amount of adsorbed molecules such as molecular sieves and activated carbon differs depending on the substance and pressure, and is generally called the PSA device. The adsorbent that adsorbed carbon dioxide at a pressure equivalent to that of the reforming reaction is desorbed by depressurization, and these desorbed impurities are released to the outside of the system. Perform scavenging of layers.

(Problems to be Solved by the Invention) In this hydrogen production device, in the crude hydrogen gas cooled and separated after the reforming reaction, a methanol content corresponding to the vapor pressure at that temperature remains. By absorbing and cleaning this crude hydrogen gas with process make-up water, this methanol content is absorbed and recovered by the make-up water, and the PSA device design becomes easy. However, in this process, trace amounts of oxygen and nitrogen are contained in the crude hydrogen gas at the PSA equipment inlet. The equilibrium adsorption amount of impurities to the adsorbent of the PSA device is
Carbon dioxide is the largest, followed by carbon monoxide, nitrogen, and oxygen in that order. For this reason, a trace amount of oxygen is likely to remain in the high-purity hydrogen gas taken out from the PSA device, and nitrogen can be adsorbed and removed, but the equilibrium adsorption amount is small, so that high-purity hydrogen gas can be obtained even with slight fluctuations during operation of the PSA device. It was easily mixed in hydrogen gas, and in order to prevent this, it was necessary to reduce the hydrogen recovery rate or increase the adsorbent filling amount, which was a problem of this process.

(Means for Solving Problems) The present inventor has known that the mixing of a trace amount of oxygen and nitrogen in the above process is due to oxygen and nitrogen dissolved in methanol and makeup water, and if these gases are removed in advance. Oxygen and nitrogen are not contained in crude hydrogen gas, and as a result, high-purity hydrogen is stabilized, and dissolved oxygen and nitrogen are removed by previously contacting methanol and make-up water with PSA scavenging gas countercurrently. I found that I can do it.

That is, in the present invention, hydrogen is produced by catalytically reacting methanol and water.
Crude hydrogen gas containing carbon dioxide and a trace amount of carbon monoxide is cooled, the excess water and unreacted methanol are condensed and separated, and the residual gas is washed with water to remove methanol vapor, and then an adsorption separation device In the method for obtaining high-purity hydrogen gas by adsorbing and removing impure gases such as carbon dioxide, high-purity methanol characterized by previously degassing the raw material methanol and make-up water by countercurrent contact with the scavenging gas of the adsorption separator. It is a method of producing hydrogen.

In addition, scavenging gas for PSA equipment is generally hydrogen, carbon dioxide,
It contains carbon monoxide, nitrogen, etc. and is used as a fuel in the reforming process. However, according to the present invention, the amount of nitrogen is remarkably reduced, so P
By absorbing and removing the carbon dioxide gas in the SA device inlet or the scavenging gas, even if the scavenging gas is returned to the raw material system, it can be circulated without nitrogen accumulation and the hydrogen yield is significantly improved. As a result, the amount of gas released to the outside of the system is reduced, hydrogen is effectively used, and the purity of the high-purity hydrogen gas obtained is extremely high.

That is, in the present invention, in the above-mentioned invention, the raw methanol and the makeup water are previously degassed by countercurrent contact with a part of the scavenging gas of the adsorption / separation device, and the crude hydrogen gas after washing and removing the methanol vapor is converted into carbon dioxide gas. A method for producing high-purity hydrogen, which is characterized in that the carbon dioxide gas is introduced into an absorption device, absorbed and removed, and then introduced into an adsorption separation device, and the remaining scavenging gas of the adsorption separation device is circulated and used as a raw material for the catalytic reaction. After degassing the raw material methanol and make-up water by countercurrent contact with a part of the scavenging gas of the adsorption / separation device, and guiding the rest of the scavenging gas of the adsorption / separation device to the carbon dioxide absorption device to absorb and separate the carbon dioxide gas, A method for producing high-purity hydrogen, which is characterized in that this is recycled as a raw material for a catalytic reaction, is included.

The catalytic reaction between water and methanol in the present invention is
A catalyst containing chromium and aluminum is preferably used, a reaction temperature of 150 to 400 ° C., a pressure of 1 to 50 Kg / cm ² G, and a mixed vapor of 1 to 20 mol of water per 1 mol of methanol SV50 to 5000
Pass by 0 1 / H. By this reforming reaction, in addition to hydrogen and carbon dioxide gas, a trace amount of carbon monoxide and the like is produced, and becomes crude hydrogen gas.

Cooling of the reaction gas is generally performed by preheating the raw material liquid and cooling water or air cooling, and is kept at 50 ° C or lower. For cleaning residual gas, use packing materials such as Raschig rings and ball rings.
By countercurrent contact with the degassed water, methanol content of 100PPM
Below.

The PSA device uses a mixture of molecular sieve, zeolite, activated carbon, etc. as an adsorbent, and adsorbs carbon dioxide, a trace amount of carbon monoxide, methane, methanol, nitrogen, etc. at a pressure equal to the reforming pressure and at a temperature of 50 ° C or less. To do. The gas scavenged during regeneration of this adsorbent had a pressure of 0.1 to 1.0 Kg / cm ² G and contained 30 to 50 vol% of the hydrogen used for scavenging, and the generated amount was 50 to 80% of the high-purity hydrogen amount. Becomes

Degassing of methanol and make-up water is performed by countercurrent contact with this scavenging gas at room temperature and pressure using a packing such as Raschig rings and pole rings. The scavenging gas used after degassing the makeup water is used as fuel in the reforming process.

For removal of carbon dioxide in the crude hydrogen gas or scavenging gas at the PSA inlet, a chemical absorption method using an alkaline solution such as ordinary monoethanolamine or hot potassium carbonate or a physical absorption method using low-temperature methanol (rectisol method) is used. The liquid is regenerated by depressurizing and heating and is recycled.

When carbon dioxide is removed from the crude hydrogen gas at the PSA device inlet,
Due to the small amount of impurities in the crude hydrogen gas, the hydrogen concentration in the PSA scavenging gas is 80-90%. PSA scavenging gas generation rate 0.1
~ 10%, preferably 0.2 ~ 5% of the scavenging gas is used for deaeration of methanol and makeup water, and the remaining gas is circulated in the raw material system after being pressurized to a pressure higher than that of the reforming process by a compressor. .

PSA scavenging gas can be introduced either in series or in parallel with the methanol stripping tower and the makeup water stripping tower. In the case of introducing in series, the methanol that accompanies the outlet gas of the methanol stripping tower is absorbed by the makeup water, which is advantageous because there is no loss of methanol.

Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a flow of degassing methanol and make-up water with a scavenging gas of an adsorption separation device according to the present invention. The raw material methanol is supplied by the methanol supply line 11,
After being guided to the methanol stripping tower 4 and degassed by the scavenging gas 21 of the PSA device, it joins with the raw material water (condensate + degassed water) taken out from the water washing tower 2, and the raw material preheater 8 and the evaporation superheater 7 After entering the reforming reactor 1, it undergoes steam reforming in the presence of a catalyst to become crude hydrogen gas. The crude hydrogen gas from the reforming reactor is cooled by the raw material preheater 8 and the cooler 9, and excess water and unreacted methanol are condensed. The cooling gas enters the water washing tower 2 through the crude hydrogen gas line 16, and the degassed water supplied through the degassed water supply line 14 absorbs and cleans the methanol vapor corresponding to the methanol vapor pressure in the condensate. The condensate is mixed with the degassed water used for absorption / washing, supplied from the condensate extraction line 15 as raw water, and reused.

The crude hydrogen gas exiting the absorption tower 2 is sent to the PSA device 3 by the crude hydrogen gas line 17 to adsorb and remove impurities such as carbon dioxide gas, and as a high purity hydrogen gas of 99.999% or more from the high purity hydrogen gas line 19 Taken out. On the other hand, impurities such as carbon dioxide are taken out as PSA scavenging gas by depressurization.
It is guided to the methanol stripping tower 4 by the scavenging gas line 21, countercurrently contacts with methanol from the methanol supply line 11 to diffuse dissolved oxygen and nitrogen, and then is supplied to the makeup water stripping tower 5 to dissolve dissolved oxygen and nitrogen in the makeup water. It releases nitrogen and is used by the offgas line 23 as fuel in the reforming process. Make-up water from the make-up water supply line 12 is dispersed in the diffusion tower 5 and then enters the washing tower 2 from the degassed water supply line 14. The PSA scavenging gas can also be introduced in parallel to the methanol diffusion tower 4 and the makeup water dispersion tower 5.

FIG. 2 shows a flow when the carbon dioxide gas in the crude hydrogen gas at the inlet of the PSA device is removed and the PSA scavenging gas is circulated and used as a raw material according to the present invention. The crude hydrogen gas taken out from the absorption tower 2 is introduced into a carbon dioxide gas removing device 6 to remove almost all the contained carbon dioxide gas, and then to a PSA device 3 to remove a small amount of remaining impurities, and 99.999% The above high-purity hydrogen is extracted from 19. Part of the scavenging gas from the PSA scavenging line 21 is guided to the methanol stripping tower 4 and the makeup water sprinkling tower 5. Most of the other gases are introduced into the PSA scavenging gas compressor 10, are pressurized to a pressure higher than the pressure of the raw material system, and are combined with the mixed gas leaving the evaporator / superheater 7 for circulation and use.

FIG. 3 shows a flow when carbon dioxide gas in the PSA scavenging gas is removed and is circulated according to the present invention. Part of the scavenging gas from the PSA scavenging line 21 is guided to the methanol stripping tower 4 and the makeup water stripping tower 5. Most other gases are PSA
After being introduced into the scavenging gas compressor 10 and having a pressure higher than the pressure of the raw material system, it is introduced into the carbon dioxide gas removing device 6 where most of the carbon dioxide gas contained therein is removed and merges with the mixed gas leaving the evaporator / superheater 7. Used in circulation.

(Example) According to the present invention, when degassing methanol and make-up water by PSA scavenging gas, when carbon dioxide gas in PSA device inlet gas is removed and circulated, and when degassing of methanol and make-up water is not performed The oxygen and nitrogen concentrations are compared and shown in Table 1. The operating conditions of each example are as follows.

Example 1 In FIG. 1, methanol 12.2 Kg / H, makeup water 6.6 Kg / H reactor inlet water / methanol molar ratio 2.0 and 270 ° C., 15 Kg / cm
² G, subjected to steam reforming at SV1800 1 / H of the vapor mixture, the crude hydrogen gas 33.7 nm ³ / H obtained is washed with makeup water 6.6 kg / H, PSA apparatus of adsorbent comprised of a molecular sieve and activated carbon The high-purity hydrogen of over 99.999% was obtained at 20 Nm ³ / H. For degassing methanol and make-up water, 0.14 Nm ³ / H, which corresponds to 1% of the PSA scavenging gas generation rate of 13.7 Nm ³ / H, was used.

Example 2 In the flow of FIG. 2, 1% of the amount of scavenging gas generated from the PSA device was used for degassing methanol and makeup water, and the remaining gas was pressurized to 16 kg / cm ² G and circulated to the reforming reactor. used.
The operating conditions of the reforming process and the cleaning process were the same as in Example 1, and the high-purity hydrogen generation rate was 25.5 Nm ³ / H, and the PSA scavenging gas circulation rate was
13.56 Nm ³ / H, P used in the diffusion tower of methanol and makeup water
The amount of SA scavenging gas was 0.14 Nm ³ / H.

Comparative Example 1 A high-purity hydrogen device was operated under the same conditions as in Example 1 without degassing methanol and makeup water.

(Effect) As shown in the examples, according to the present invention, the oxygen and nitrogen concentrations in the crude hydrogen gas at the PSA device inlet are remarkably lowered and the high concentration is eliminated by removing the dissolved oxygen and nitrogen in the methanol and the makeup water in advance by the PSA scavenging gas. Purity The purity of hydrogen is improved.

This also stabilizes the operation of the PSA unit, improves the hydrogen recovery rate, or reduces the amount of adsorbent in the PSA unit, which can reduce the cost of high-purity hydrogen.

Further, by removing carbon dioxide gas in the crude hydrogen gas or scavenging gas supplied to the PSA apparatus according to the present invention, nitrogen does not accumulate even when the scavenging gas is returned to the raw material system, and the scavenging gas can be circulated and used, and hydrogen can be collected. The rate can be significantly improved. As a result, the amount of gas released to the outside of the system is reduced, hydrogen is effectively used, and the purity of the high-purity hydrogen gas obtained is extremely high.

[Brief description of drawings]

FIG. 1 is a flow chart of degassing methanol and make-up water in the present invention with a scavenging gas of a PSA apparatus, and FIG. Flow for cyclic use, PSA in Fig. 3
The flow when carbon dioxide gas in the scavenging gas is removed and it is reused is shown.

Claims (3)

[Claims] 1. A crude hydrogen gas containing hydrogen, carbon dioxide gas and a trace amount of carbon monoxide by catalytically reacting methanol and water, cooled to condense and separate excess water and unreacted methanol to obtain a residual gas. In order to obtain high-purity hydrogen gas by adsorbing and removing impure gases such as carbon dioxide gas after adsorbing and washing methanol with water to remove methanol vapor, the raw material methanol and make-up water are used as scavenging gas for the adsorption and separation device in advance. Of high-purity hydrogen, characterized by degassing by countercurrent contact of hydrogen 2. A crude hydrogen gas containing hydrogen, carbon dioxide gas and a trace amount of carbon monoxide by catalytically reacting methanol and water, and cooling this to condense and separate excess water and unreacted methanol to obtain a residual gas. In order to obtain high-purity hydrogen gas by adsorbing and removing impure gases such as carbon dioxide gas after adsorbing and removing methanol vapor by washing the methanol with water, the raw material methanol and make-up water are preliminarily added to the scavenging gas of the adsorption separator. While degassing by countercurrent contact with a part, washing and removing methanol vapor, the crude hydrogen gas is led to the carbon dioxide absorption device,
A method for producing high-purity hydrogen, characterized in that after absorbing and removing carbon dioxide gas, it is led to an adsorption separation device, and the remaining scavenging gas of the adsorption separation device is circulated and used as a raw material for the catalytic reaction 3. A crude hydrogen gas containing hydrogen, carbon dioxide gas and a trace amount of carbon monoxide by catalytically reacting methanol and water, cooled to condense and separate excess water and unreacted methanol to obtain a residual gas. In order to obtain high-purity hydrogen gas by adsorbing and removing impure gases such as carbon dioxide gas after adsorbing and removing methanol vapor by washing the methanol with water, the raw material methanol and make-up water are preliminarily added to the scavenging gas of the adsorption separator. It is characterized by degassing by countercurrent contact with a part and guiding the rest of the scavenging gas of the adsorption separation device to a carbon dioxide gas absorption device to absorb and separate the carbon dioxide gas, and then recycle this as a raw material for the catalytic reaction. High-purity hydrogen production method