JPS6086002A - Preparation of hydrogen from methanol - Google Patents

Abstract

PURPOSE:To prepare hydrogen easily at low cost, by using methanol and steam in a specific ratio, preparing hydrogen by a contact reaction. CONSTITUTION:In preparing hydrogen by a contact reaction between methanol and steam, a mixture of equimolar ratio of methanol and steam is used as raw materials, and they are reacted in the presence of a proper catalyst at about 250-300 deg.C to give hydrogen. Consequently, unreacted methanol has a ratio of water to methanol of 1 independently of a reaction ratio in preparation process of hydrogen, and since the composition of feed raw materials is not changed even if unreacted methanol is circulated through the raw material, control of variation in production is carried out easily and latent heat of steam of water can be economized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrogen from methanol, and particularly to a method useful when methanol is used as a hydrogen source for industrial use and fuel cell power generation.

If a suitable catalyst exists for the reaction of methanol and steam,
It has been known for a long time that the reaction of the following formula occurs at 250 to 300°C.

CH30H+ H20= COz + 3Hz...
...(1) However, formula (1) is used for industrial hydrogen production.
This reaction has rarely been utilized, and hydrogen production is usually done by catalytic steam reforming of light petroleum hydrocarbons (LPG or naphtha) or natural gas and adding carbon monoxide to the reformed gas. It is carried out by a shift reaction, and the reaction when methane is used is expressed by the following formula.

CH4+ Ha O= Co + 3H2...
・・・(2) CO+HJO=CO2+Hx ・・・・・・
...(3) Therefore, the reaction of formula (2) is operated at 800-850°C over a nickel-based catalyst using at least 2 moles of water vapor per mole of methane, and the reformed gas is heated to about 450 °C. After cooling to ℃, it passes through an iron oxide-based carbon monoxide shift catalyst to proceed with the reaction of formula (3). % or less. In order to separate hydrogen from this reaction gas, it used to be necessary to cool it, wash it with a renewable alkaline aqueous solution such as monoethanolamine to remove carbon dioxide, and then remove the remaining carbon dioxide with an ammoniacal cuprous salt solution. Previously, methods such as absorbing and removing carbon oxide or detoxifying carbon monoxide by hydrogenating it to methane over a nickel-based catalyst have been adopted, but in recent years, adsorption and desorption methods using adsorbents and pressure differences have been adopted. (hereinafter referred to as the PSA method), a method for removing all impurities other than hydrogen has become widespread, and the production of hydrogen has become greatly streamlined.

On the other hand, although the price of oil has fallen somewhat in recent years, it is still quite expensive, and the cost of not only fuel but also light hydrocarbons, which are the raw materials for hydrogen, is no exception, making the cost of hydrogen high. In contrast, importing methanol synthesized on a large scale from natural gas or coal-producing raw materials and using it as fuel would make the price per calorific value equivalent to that of petroleum products. There is a movement to do so. The design of a methanol-only vehicle has already been completed, and the efficiency of using methanol as fuel for boilers and gas turbines has been measured and air pollutants in combustion exhaust gas analyzed. It is technically and economically possible.

The present invention was made for the purpose of providing a method for producing hydrogen, which is a hydrogen source for industrial use and fuel cell power generation, using methanol. A method for producing hydrogen gas characterized by using an equimolar mixture of methanol and steam as a raw material.

The reaction of the above formula (1) can be performed at 250' if an appropriate catalyst is selected.
In contrast, the reaction in equation (2) requires a temperature of 800 to 850°C, and the difference lies in the amount of heating fuel required for both, the construction cost of the reaction equipment, and the cost of waste heat recovery equipment. This causes a large difference in economic efficiency.

The reaction of formula (1) is considered to be the result of the reactions of formulas (4) and (5) below occurring simultaneously.

CHa OH= CO+ 2tlz・・・・・・・・・
...(4) CO + H low 0 = CO gas + H2 ...
(5) It is desirable that the catalyst used in the method of the present invention has activity in both of these reactions. Thus, the equilibrium of the reaction of formula (4) favors the right side at high temperatures, but conversely, the equilibrium of the reaction of formula (5) favors the right side at low temperatures.

However, the reaction of formula (4) and the reaction of formula (5) are combined,
In order to complete the reaction of formula (1), conditions must be selected to complete the reaction of formula (5), ignoring the equilibrium and rate of the reaction of formula (4). This requires the reaction rate to be as low as the activity of the catalyst allows.

Generally, the optimum temperature for the reaction of formula (1) is much lower than the optimum temperature for hydrocarbon steam reforming of formula (2), so the residual amount of carbon monoxide in the reaction gas can be kept sufficiently low.
Although the shift of carbon monoxide in equation (3) is not required, the presence of trace amounts of carbon monoxide is generally disfavored in many applications of hydrogen, so it is necessary to use excess water vapor, and in particular, the shift of carbon monoxide in equation (1) is not required.
) When the appropriate temperature of the reaction catalyst is high, the carbon monoxide in the reaction gas cannot be sufficiently lowered unless excess steam is used.

However, if hydrogen is purified by the psA method as mentioned above, it is relatively easy to remove hydrogen oxide.
There is less need for efforts to make the residual amount of carbon monoxide in the reaction gas particularly low.

From this point of view, the inventor of the present invention determined that the amount of water vapor to be used per 1 mole of methanol was 1.5 moles.

We tried cases where the amount was 1.2 mol and 1.0 mol. The results are shown below.

Reaction temperature 250°C Space velocity of liquid methanol 1.5 Methanol reaction rate Approx. 80% Molar ratio of water to methanol 1.5 1.2 1.0 Composition of reaction gas (volume %) COx 23.22 23.28 23. 57 (01,
071,461,52 1st z75.7175.2674.91 From this result, when the reaction temperature is low enough and the one-pass reaction rate is not very high, the excess amount of water vapor relative to methanol is the carbon monoxide in the reaction gas. It was found that the effect on the concentration of It is natural that if the reaction temperature is low, the concentration of carbon oxide will be low from the reaction equilibrium of equation (5), and also,
This is because if the reaction rate is low, water vapor will be present in excess of the carbon oxide produced by the reaction of formula (4).

One of the benefits of eliminating this excess of water vapor to methanol is the recycling of unreacted methanol and water. Generally, in a catalytic reaction, in order to increase the yield of a target product per unit time (space-time yield) using a fixed amount of catalyst, it is necessary to increase the flow rate (space velocity) of the raw material relative to the fixed amount of catalyst. Therefore, if the one-pass reaction rate is low, it is necessary to separate the target product from the reactor outlet material and circulate the unreacted material to the raw material. However, if raw materials with a molar ratio of water and methanol greater than 1 are used, unreacted water and
The methanol molar ratio is different from that of the raw material, and if it is recycled to the raw material, the water and methanol molar ratio of the entire raw material will change. This fluctuation is due to an increase in water vapor relative to methanol.

Although no problems occur, if the production rate of the device changes or the catalyst deteriorates, the circulation rate changes and the molar ratio of methanol and water supplied changes accordingly.

When supplying hydrogen to a fuel cell, the supply of hydrogen must be varied in response to fluctuations in electricity demand from 100% to 25aIo, but it is difficult to maintain the methanol reaction rate constant against such large fluctuations. Although it is almost impossible to control the simultaneous fluctuations of the carbon monoxide concentration in the reaction gas and the operation of the l'sA method must be changed accordingly, It is difficult.

Now, if we use a raw material with a molar ratio of water to methanol of 1, the unreacted methanol will also have a molar ratio of water to methanol of 1 regardless of the reaction rate, and even if this is recycled to the raw material, the composition of the feedstock will not change. Therefore, in response to fluctuations in production volume, it is not necessary to control the concentration only by controlling the raw material supply amount.

The second advantage of using raw materials with a molar ratio of water and methanol of 1 is that the latent heat of vaporization of water can be saved.

The amount of heat required by the method of the present invention is the sum of the reaction heat and the amount of heat for heating water and methanol to the reaction temperature, M1.
The latent heat of vaporization of water accounts for a considerable portion of this. If excess water is not used as a raw material, the latent heat of vaporization of the excess water can be saved.7 This greatly contributes to reducing the amount of heat required for the process of the present invention. In particular, when the method of the present invention is used to produce hydrogen for fuel cell power generation, the energy conversion efficiency of producing the hydrogen supplied to the battery must also be high in order not to reduce the advantage of the high energy conversion efficiency of the fuel cell. Must be. For this purpose, the method of eliminating excess water vapor in the hydrogen production process of the present invention is extremely effective.

The present invention is as described above, and since an equimolar mixture of methanol and steam is used as a raw material when producing hydrogen gas through a catalytic reaction between methanol and steam, no reaction occurs regardless of the reaction rate during the hydrogen production process. For methanol, the molar ratio of water to methanol is 1, and the composition of the feedstock does not change even if it is circulated through the feedstock, so it is not only easy to control fluctuations in production volume, but also saves the latent heat of vaporization of water. Therefore, the hydrogen production cost can be significantly reduced compared to the conventional method.

Agent Yoshikuni Koizumi

Claims (1)

[Claims] 1. A method for producing hydrogen gas from methanol using a catalytic reaction between methanol and steam, the method comprising using an equimolar mixture of methanol and steam as a raw material.