JP2008290927A - Method and apparatus for refining hydrogen by using organic hydride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for removing a gas from hydrogenation products and performing a dehydrogenation reaction effectively when only hydrogen in a gaseous mixture is added selectively to a hydrogen-unsaturated aromatic compound in a hydrogenation catalyst reactor, high-purity hydrogen is separated from the produced hydrogen-saturated aromatic compound in a dehydrogenation catalyst reactor and the hydrogen-unsaturated aromatic compound produced simultaneously is circulated in the hydrogenation catalyst reactor to alternately perform hydrogenation and dehydrogenation reactions. <P>SOLUTION: The method and the apparatus for refining hydrogen from the gaseous mixture are characterized in that hydrogen is added beforehand to the aromatic compound to decrease the boiling point of the aromatic compound so that the dehydrogenation reaction is performed in a gas phase under conditions of high temperature and high pressure and the gas is removed effectively in a gas removal column. As a result, high-purity hydrogen having ≥99% purity can be obtained from a wide range of hydrogen-mixed gasses from biotechnology, COG, etc. at almost 100% recovery rate without performing special pretreatment to remove impurities. The pressure of a product can economically be made higher than that of a raw material without compressing the gas. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method and a processing apparatus for efficiently producing and purifying hydrogen with high purity in biomass, petroleum-related industries, and steel-related industries.

Conventionally, hydrogen gas has been mainly used in the chemical industry mainly as an ammonia raw material, but recently, the demand for clean energy such as fuel cells is increasing. An issue that is currently being questioned by society is how cheaply this hydrogen can be produced, purified or recovered with high purity quality and stably supplied.

Industrially, as a hydrogen production method and usage destination, most of the hydrogen gas obtained from gasoline catalytic cracking equipment at oil refineries and coke gas at steelworks is consumed in-house. Hydrogen gas from a steam reformer using naphtha or natural gas as a raw material is used in factories and petrochemical plants.

The gas is a mixture of CH ₄ , CO _2, etc., and conventional techniques for separating and purifying hydrogen therefrom include cryogenic separation, membrane separation, and PSA (pressure swing adsorption). In any method, it is indispensable to perform preliminary purification in which easily polymerizable components such as sulfides, oxides and BTX in the gas are removed. Cryogenic separation is a method that removes other impurities that liquefy, focusing on the fact that hydrogen is difficult to condense and liquefy in a refrigerated state, but the problem is that both equipment costs and operating costs for chilling are expensive. There was a point. Membrane separation is a separation method using various membranes and utilizing the difference in gas permeation rate with respect to the membrane, but has a problem of large pressure consumption. Currently, PSA is the mainstream, but since a desorption purge operation using product hydrogen is required, there is a problem that the recovery rate of product hydrogen falls to about 80%. In addition, when the raw material gas is low pressure, unless the raw material gas is pre-pressurized with a compressor or the like, not only high-pressure product hydrogen can be obtained, but also product purity and recovery rate cannot be secured.

Other than the above, an operation of adding hydrogen to a hydrogen unsaturated aromatic compound as an application of organic hydride (hydrogen unsaturated aromatic compound) known as an automobile mobile fuel, and a reaction composition produced in the reaction tower There has been proposed a method for recovering hydrogen with high purity from a mixed gas containing hydrogen using a “reactor filled with a catalyst” that alternately performs an operation for dehydrogenating hydrogen. (Unexamined-Japanese-Patent No. 2005-200253, Unexamined-Japanese-Patent No. 2005-200254). However, these are characterized in that the liquid phase is maintained on the premise of the liquid phase in the dehydrogenation reactor.

The present invention is still industrially applicable to recover high-pressure hydrogen with high purity and almost 100% from a mixed gas containing hydrogen in a wide range of concentrations without any impurity pretreatment, based on the above-mentioned conventional technology. Provided a dehydrogenation reactor principle, structure and hydrogenation device that has not been realized, and a treatment device that removes gas from hydrogenated aromatic compounds, and reduces external heat and compression power by combining with a hydrogen production device For the purpose.

As a means for solving the above-mentioned problems, the method according to the present invention comprises, as described in claim 2, when hydrogen is passed through an eductor or a hydrogen pressurizing device when performing a dehydrogenation reaction at a high temperature. In addition to the hydrogen-saturated aromatic compound before entering, the boiling point is lowered by about 50 ° C. to ensure the gas phase reaction in the dehydrogenation reactor. The amount of hydrogen to be added is within 5% by weight of the hydrogen saturated aromatic compound.

Further, as described in claim 3, the dehydrogenation reactor is a heat-insulated fixed bed composed of an upper part and a lower part. It has a structure to advance. The endothermic component is supplied by a high-temperature gas such as a combustion gas from the outside of the reaction tube.

Further, as described in claim 4, a distillation column is installed for heating the hydrogen saturated aromatic compound and removing a mixed gas other than hydrogen.

Further, as described in claim 5 and claim 6, methanol capable of low-temperature reaction is used as a raw material for the steam reforming method for hydrogen production, or 1 MPa using naphtha which has been conventionally used. By carrying out at a low pressure of the order, external heat and power reduction can be expected, and as a result, hydrogen production with a low basic unit becomes possible. This problem has been solved by the means described above. Further, in the method for recovering hydrogen from the mixed gas according to the present invention, the hydrogen unsaturated aromatic compound is naphthalene and the hydrogen saturated aromatic compound produced by the reaction is tetralin as described in claim 7. It is characterized by.

This method recovers high-purity hydrogen from a hydrogen-containing mixed gas by hydrogenating naphthalene into mainly tetralin, then refining and recovering this tetralin into naphthalene and hydrogen, and then separating the hydrogen with high purity. The equilibrium relation of naphthalene-tetralin-hydrogen system over a typical operating range is introduced in Reference ¹ ).
1) Journal of Physical Chemistry Sept. Vol. 62 1059-1061 Pages, 1958, Thomas P. Wilson et al. “THE NAPHTHALEN-TETRALIN = HYDROGEN EQUILIBRIUM AT ELEVATED TEMPERATURE AND PRESSURE”
In the aforementioned Wilson et al. Paper, the basic reaction is shown as: C ₁₀ H ₈ + 2H ₂ = C ₁₀ H ₁₂ and it is assumed that this reaction occurs mainly in the gas phase. On the other hand, as shown below, the critical temperature (Tc) and critical pressure (Pc) of naphthalene and tetralin are very close, and the boiling point is about 430 ° C. at a pressure of 3 MPa, which is slightly higher than the assumed tetralin dehydrogenation reaction temperature. .

反応器入口ではＫｅｑはＫｐより小さいが、触媒に気相が触れることにより反応が進行し熱化学的に安定な反応器出口温度での反応平衡常数Ｋｐ＝０．２＝Ｋｅｑとなり安定し気液平衡も安定なＶ／Ｆ＝０．４３へと変化する。反応器出口温度では入口に比べナフタリンは減少しテトラリンが増加するがＨ_２が大幅に減少するためＶ／Ｆは入口状態よりも小さい値となっている。In the experiment of Wilson et al., The following equation is derived.
_{C 10 H 8 + 2H 2 =} C 10 H 12 -28.8 ± 1.2 (kcal / mol)
LnKp = 161118 / T-30.233
Kp: reaction equilibrium constant (atm) T: reaction temperature (K)
_{Keq = (C 10 H 12 /} (C 10 H 8 * H 2 * H 2)) / (P * P) Keq: Reaction equilibrium number _{C 10 H 12, C 10 H} 8, H 2: in the gas phase The molar fraction P of each component is the pressure during the reaction (atm)
The hydrogen-containing gas from the hydrogen source generator contains about 70 mol% of hydrogen, 24 mol% of CO ₂ , other CO, CH ₄ , H ₂ O and the like. Reaction formula: C ₁₀ H ₈ + 2H ₂ = C ₁₀ H _{12 is used} to hydrogenate naphthalene, and naphthalene is changed to tetralin. Therefore, theoretically, 0.5 mol of naphthalene is sufficient for 1 mol of hydrogen, but the reaction is reversible. Therefore, the transition state of the reaction indicated by the reaction equilibrium number Keq does not shift beyond the chemical thermal equilibrium state represented by the reaction equilibrium constant Kp (a function of the reaction temperature T) at a specific reaction temperature. When C ₁₀ H ₈ / H _{2 is} about 0.6 and the reaction temperature is 290 ° C., the reaction equilibrium constant Kp is about 0.2, and almost 90% of H _{2 in} the raw material gas reacts with naphthalene and changes tetralin. This reaction is an exothermic reaction, and if the reaction proceeds adiabatically, the temperature at the reactor inlet is estimated to be approximately 275 ° C.

Although Keq is smaller than Kp at the reactor inlet, the reaction proceeds when the gas phase contacts the catalyst, and the reaction equilibrium constant Kp = 0.2 = Keq at the thermochemically stable reactor outlet temperature becomes stable. The equilibrium also changes to stable V / F = 0.43. At the reactor outlet temperature, naphthalene decreases and tetralin increases compared to the inlet, but H ₂ decreases significantly, so V / F is smaller than the inlet state.

The product obtained by hydrogenating naphthalene into tetralin in the hydrogenation process contains the produced tetralin, the residual naphthalene, as well as CO ₂ , CO, CH 4, H ₂ O reaction residual H ₂ contained in the raw material hydrogen. . Light components other than naphthalene and tetralin are heated after removal and sent to the process of dehydrogenating tetralin. When the content of naphthalene in the naphthalene / tetralin mixture is plotted on the horizontal axis, the boiling point of the mixture, L / F = 50% point, and the Dew point on the vertical axis, the results are estimated as shown in the graph of FIG. From the values in this graph, if the dehydrogenation reaction of tetralin is a gas phase reaction, the dehydrogenation reaction does not occur at 430 ° C. or lower.

The mixing ratio of naphthalene and tetralin is 10:90 and the horizontal axis is mol% of H _{2 in} the mixture. The boiling point of the mixture, V / F = 1.0% point, V / F = 2.5% point, Dew point Is plotted on the vertical axis, and the result is as shown in the graph of FIG. This tendency is similar even when the mixing ratio of naphthalene and tetralin is changed. From the above, it is possible to start the gas phase reaction even at a temperature of 400 ° C. or lower by adding the high-purity product H ₂ to the mixture of naphthalene and tetralin before the dehydrogenation reaction by several percent. The reason for lowering the reaction temperature to 400 ° C. or lower is to avoid generation of impurities due to thermal decomposition of tetralin.

反応は吸熱反応なので加熱されながら進行する。反応器入り口ではＶ／Ｆは上表のごとく０．０２であり反応平衡状態数Ｋｅｑは２３９、反応平衡常数Ｋｐは０．００３と大きく離れており、触媒に触れた気体はかなりの速い速度で熱化学平衡に移行してゆくだろう事は容易に推測できる。一方、反応後の気液状態を見ると全て気体となるわけでこの反応により液体から全気体への移行が起こる。あたかも「Ｄｒｙ ｕｐ」のような状態を呈することになる。After removing light components other than naphthalene and tetralin, the raw material to which H ₂ has been added is heated to 390 ° C. and sent to a process for dehydrogenating tetralin.

Since the reaction is endothermic, it proceeds while being heated. At the reactor inlet, V / F is 0.02 as shown in the table above, the reaction equilibrium state number Keq is 239, and the reaction equilibrium constant Kp is very far from 0.003. It can be easily guessed that it will shift to thermochemical equilibrium. On the other hand, when the gas-liquid state after the reaction is viewed, all of the gas becomes gas, and this reaction causes a transition from liquid to total gas. It will appear as if “Dry up”.

The dehydrogenation reaction of an aromatic hydrogen compound is an endothermic reaction, and generally the reaction does not proceed unless the temperature is raised. Conventionally, various methods have been proposed for this dehydrogenation reaction, and typical ones are listed below.
1. The dehydrogenation reaction from tetralin to naphthalene is carried out under conditions of thermodynamically maintaining a liquid phase at a pressure of 2 to 4 Mpa and a temperature of 80 to 160 ° C. There are (Document ^2), etc.) but the conversion rate is low problem.
2) Liquid-Phase Hydrogenation of Naphtalene and Tetralin on Ni / Al 2 O 3: Kinetic Modeling, Petri A. et al, Ind. Eng. , Chem. , Res. , 2002, 41, 5966-5975
2. If the hydrogen produced by the hydrogen reaction is removed from the system through a heat-resistant selective permeable membrane (porous glass, ceramic, etc.), the equilibrium is shifted to the production side and the conversion rate is improved. As an example, in Document ²⁾ , dehydrogenation from cyclohexane to benzene (catalyst Pt—Al203), a conversion rate of 80% was obtained at a reaction temperature of 230 ° C. Since the equilibrium temperature at the same conversion is 230 ° C., the equilibrium is exceeded by 30 ° C. Membrane reactors aiming to lower the reaction temperature by performing hydrogen production reforming reaction and hydrogen separation simultaneously are in the same direction.
3) Osamu Shinji et al., 46th Catalytic Conference (A), 4Q05, Sendai, 1980
3. Although the temperature is higher than the above 1, there is a concept that if the generated hydrogen is released as bubbles in the gas phase on the premise of a liquid phase reaction, a high conversion rate can be expected without being restricted by equilibrium. As a problem at that time, if there is a large amount of hydrogen to be dehydrogenated, the droplets are accompanied by rapid bubble formation, resulting in “Dry Up” in which the liquid phase disappears, so a structure that avoids this is necessary. It is. However, according to the autoclave experiment, the composition exceeding the reaction equilibrium was not obtained even though the hydrogen extraction was free, and the reaction did not proceed when the experiment was started with only naphthalene and tetralin without hydrogen filling. Therefore, this idea does not hold, but rather it is considered that the reaction is carried out between gas phase components evaporated in vapor-liquid equilibrium while contacting the catalyst from the liquid phase portion. It is reasonable to consider this as a reaction mechanism in which the components vaporized due to endotherm react around the catalyst.

The dehydrogenation reaction from tetralin to naphthalene performed at 3 to 4 Mpa and 300 ° C. or higher is a reaction in the vicinity of the critical region. (Critical pressure and critical temperature of tetralin and naphthalene are 3.7 MPa, 447 ° C. and 4.1 MPa, 475 ° C.) At the same pressure and temperature, metastable state (rich in liquid phase), stable state (rich in gas phase) Is present (corresponding to the retrograde phenomenon with a pure component), and between these regions, a slight amount of hydrogen addition or temperature change causes a sudden transition from a metastable state to a stable state, apparently suddenly changing from the liquid phase to the gas phase. This is observed by simulation using commercial software, and it is determined that this corresponds to so-called Dry up (dry up).

  Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

The reactor of FIG. 3 was charged with 260 kg / h of tetralin at 374 ° C. and 4 / h of naphthalene, and finally reacted under the conditions of 390 ° C. and 3 MPa for 30 minutes under a Ni—Mo-based catalyst, 190 kg / h of naphthalene, tetralin 95 kg / h and hydrogen 45 Nm ³ / h were obtained. The generated hydrogen gas contains almost no naphthalene or tetralin vapor.

In the flow shown in FIG. 4, the balance shown in the table below is 99.99 using a mixed gas of hydrogen 73.6 mol%, CO 0.4 mol%, CO ₂ 23.5 mol%, CH ₄ 2 mol%, and moisture 0.5 mol% as a raw material. % Hydrogen was obtained with 99% recovery.

By combining the hydrogenation reactor and the dehydrogenation reactor as described above and circulating the tetralin and naphthalene solution, the crude hydrogen mixed gas can be purified to j-purity hydrogen. As a result, almost 100% of high-purity high-pressure hydrogen can be recovered from a gas containing a wide range of hydrogen without a special pretreatment for removing impurities such as NH3, SO2, and BTX. Moreover, if the hydrogen concentration in the crude hydrogen is high, hydrogen purification is possible even at a low pressure. Further, the product pressure can be increased to a high pressure up to 5 MPa without using a gas compressor that requires power.

It is the figure which showed the boiling point of naphthalene and tetralin. FIG. 4 is a diagram showing how the boiling point / dew point temperature of a naphthalene-tetralin mixture varies depending on the presence of hydrogen. It is the schematic which showed the dehydration reactor of Example 1 of this invention. A dotted arrow on the outside of the body side indicates the flow of the heating side hot gas. It is the figure which showed an example of the schematic process drawing using this invention.

Explanation of symbols

1 ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. Flow 5 …………… Off-gas flow 6 …………… Raw material flow 7 to the dehydrogenation reactor …………… Product hydrogen flow

Claims (7)

Hydrogen in the mixed gas is selectively added to the hydrogen unsaturated aromatic compound by a catalyst in a hydrogenation reaction tower. Then, the hydrogenation and dehydrogenation reaction operations in which hydrogen is separated with high purity from the produced reaction composition in a dehydrogenation reactor packed with a catalyst, and simultaneously the produced hydrogen unsaturated aromatic compound is circulated to the hydrogenation reaction tower. In the case where the dehydrogenation reaction is carried out alternately, when the dehydrogenation reaction is carried out at high pressure and high temperature, the boiling point is lowered by adding hydrogen to the aromatic compound in advance so that the reaction is carried out in the gas phase. Processing equipment for carrying out hydrogen purification from gas In the above dehydrogenation reactor, an eductor is installed upstream thereof, and hydrogen is sucked by liquid pressure to add hydrogen into the raw material liquid or to mix the pressurized hydrogen into the raw material liquid. How to add hydrogen In the above-mentioned dehydrogenation reactor, two stages of catalysts such as Ni-MO, CO-MO, Pt, etc. inside a large number of tubes inside the tower are installed, and a hydrogenated aromatic compound containing hydrogen is sent between them. The structure of the dehydrogenation reactor, where evaporation and dehydrogenation reactions are performed in the lower stage, gas phase reactions are further advanced in the upper stage, and the amount of heat required for the endothermic reaction is given from high-temperature gas such as combustion gas outside the tube In the hydrogenated aromatic compound circulation system of the hydrogenation reactor and dehydrogenation reactor, a distillation column made from the hydrogenated aromatic compound from the hydrogenation reactor is installed, and heat is supplied from the reboiler at the bottom of the column. In addition, the mixed gas from the hydrogenation reactor is removed from the top of the column, and the raw material for the dehydrogenation reactor heated from the bottom is produced. In the upstream of the hydrogenation reactor and dehydrogenation reactor, a steam reforming reactor for producing hydrogen at about 200 ° C. to 250 ° C. using hydrocarbons having OH groups such as methanol and steam as raw materials is installed, A method of effectively utilizing the heat generated at 300 ° C. generated from the hydrogenation reactor as a heat source of the reformer A steam reforming reactor that efficiently produces hydrogen at a low pressure of about 1 Mpa using hydrocarbons and steam as raw materials is installed upstream of the hydrogenation reactor and dehydrogenation reactor. A method that achieves power reduction by eliminating the need for a gas compressor by performing hydrogen purification without a gas. The method for recovering hydrogen from a mixed gas, wherein the hydrogen unsaturated aromatic compound is naphthalene and the reaction composition is tetralin

Images