JPH0751441B2 - 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) In the production of hydrogen by steam reforming of methanol, a mixed solution of water / methanol is evaporated and overheated, and in the presence of a catalyst, 5-40 Kg / c
Steam reforming reaction is carried out at m ² G, 250-300 ℃ to produce hydrogen, carbon dioxide and crude hydrogen gas containing a trace amount of carbon monoxide,
After separating excess water and unreacted methanol as a condensate by heat exchange with the raw material liquid and cooling, carbon dioxide gas, carbon monoxide, entrained water, etc. are adsorbed and removed by an adsorption separation device to obtain 99.999% or more. High purity hydrogen is generally used.

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. This methanol content is PSA
Although it is adsorbed and removed in the equipment, a trace amount of methanol may remain in the purified hydrogen. By absorbing and cleaning this crude hydrogen gas with process makeup water, this methanol content is absorbed by makeup water and the PSA device design becomes easy. However, in this process, a trace amount of oxygen is contained in the crude hydrogen gas at the PSA equipment inlet. Although it is easy to remove nitrogen by PSA equipment, it is difficult to completely remove oxygen with an adsorbent for hydrogen purification, and several PPM of oxygen remains in the hydrogen obtained as a product. In order to remove this trace amount of oxygen, a deoxygenation device that uses precious metals such as palladium is necessary, and the auxiliary equipment such as a preheater, cooler, and dryer is also a drawback of this process.

(Means for Solving Problems) The present inventor has found that the mixing of a trace amount of oxygen in the above-described process is due to the dissolved oxygen in the makeup water released in the methanol absorption / washing step, and the degassing in which the dissolved oxygen is removed in advance. We have found that if water is used for this cleaning process, the amount of oxygen in the crude hydrogen gas entering the PSA device can be significantly reduced effectively and easily, and high-purity hydrogen can be produced.

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 gas, the method for producing high-purity hydrogen characterized in that degassed water from which dissolved oxygen has been removed in advance is used as the washing water. is there.

As deaeration water used in this cleaning process, deaerated pure water such as boiler feed water or steam condensate can be used. In particular, degassing is performed by countercurrent contact between scavenging gas from the PSA device and makeup water. The care method is preferred. This deaerator does not correspond to high-pressure gas in the high-pressure gas control method, and the auxiliary equipment of the desorption tower is only one pump for sending deaerated water to the washing process, which is an expensive catalyst and heat exchanger. Therefore, deoxidation can be performed at a significantly lower cost than conventional deoxygenation equipment.

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 4400 ° 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 50
Pass at 000 1 / H. By this reforming reaction, hydrogen,
In addition to carbon dioxide, a small amount of carbon monoxide, methane, etc. are produced and become 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 the residual gas, use packing materials such as Raschig rings and pole rings.
By countercurrent contact with the degassed water, methanol content of 100PPM
Below.

The PSA device uses a mixture of molecular sieves, zeolite, activated carbon, etc. as an adsorbent, and at the same pressure as the reforming pressure, at a temperature of 50 ° C or less, carbon dioxide, trace carbon monoxide, methane, methanol, nitrogen, etc. Adsorb. The gas scavenged during regeneration of this adsorbent has a pressure of 0.1 to 1.0 Kg / cm ² G, contains 30 to 50 vol% of hydrogen used for scavenging, and produces 50 to 80% of the high-purity hydrogen. Become.

Degassing of 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.

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

FIG. 1 shows a flow when degassed water according to the present invention is used. The raw material methanol is supplied by the methanol supply line 11, merges with the raw material water (condensate + degassed water) supplied by the condensate extraction line 14, and passes through the raw material preheater 6 and the evaporative superheater 5 and the reforming reactor 1 to go into. Methanol undergoes steam reforming at 150 to 400 ° C 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 6 and the cooler 7, and excess water and unreacted methanol are condensed. The cooling gas enters the absorption tower 2 through the crude hydrogen gas line 16, and the degassed water supplied through the makeup water supply line 12 absorbs and cleans the methanol vapor corresponding to the methanol vapor pressure in the condensate. The condensate is mixed with degassed water used for absorption / washing, supplied from the condensate extraction line 14 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, and as a high purity hydrogen gas of 99.999% or more from the high purity hydrogen gas line 18. Taken out. On the other hand, impurities such as carbon dioxide are taken out as PSA scavenging gas by depressurization.
The scavenging gas line 19 is used as fuel in the reforming process.

Figure 2 shows the flow of the equipment for obtaining degassed water using PSA scavenging gas. Make-up water (non-degassed water) is the make-up water supply line
12 makes countercurrent contact with the makeup water inside the stripping tower 4 to diffuse the dissolved oxygen in the makeup water. The makeup water from which the dissolved oxygen has been diffused is stored at the bottom of the diffusion tower 4, is boosted in pressure by the degassed water supply pump 10, and is supplied as degassed water to the absorption / cleaning process in the required amount by the degassed water supply line 13.

(Example) According to the present invention, deaerated water (steam condensate) is used as make-up water, and non-deaerated water is used when the non-deaerated water is diffused by countercurrent contact with the scavenging gas of the PSA device. Table 1 compares the oxygen concentration of crude hydrogen gas at the outlet of the absorption tower and the oxygen concentration of high-purity hydrogen from the PSA unit when using as-is without treatment. 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, mixed steam SV1200 1 / H was used for steam reforming, the resulting crude hydrogen gas 33.7Nm 3 / H was washed with make-up water 6.6Kg / H, and PSA equipment of adsorbent consisting of molecular sieve and activated carbon The high-purity hydrogen of 99.999% or more 20Nm / 3H was obtained. Deaerated water (steam condensate) was used as makeup water.

Example 2 Scavenging gas from the PSA device in the flow of FIG. 2 13.7 Nm3
The high-purity hydrogen device was operated under the same conditions as in Example 1 using / H as the makeup water, which was water that had undegassed water diffused by countercurrent contact.

Comparative Example 1 A non-degassed water was used as make-up water, and the high-purity hydrogen device was operated under the same conditions as in Example 1.

(Effects) According to the present invention as shown in the examples, when the crude hydrogen gas supplied to the PSA device is washed with degassed water, highly pure hydrogen can be efficiently produced from the crude hydrogen gas, and expensive deoxidation is performed. No equipment required.

Moreover, the scavenging gas of the PSA device can be used to effectively degas the makeup water.

[Brief description of drawings]

FIG. 1 shows the flow of the high-purity hydrogen device in the present invention, and FIG. 2 shows the flow of the device of the present invention in which PSA scavenging gas and make-up water are brought into countercurrent contact to diffuse dissolved oxygen.

Claims (2)

[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 gas such as carbon dioxide gas after adsorbing and washing methanol with water to remove methanol vapor, degassed water obtained by previously removing dissolved oxygen as the washing water is used. Method for producing high-purity hydrogen characterized by using 2. The method for producing high-purity hydrogen according to claim 1, wherein degassed water obtained by countercurrently contacting scavenging gas from an adsorption separation device with makeup water is used as cleaning water.