TWI391321B - Process for producing hydrogen from ethanol under low temperature - Google Patents

Description

Low Temperature Catalytic Hydrogen Production of Ethanol

The present invention relates to a process for producing hydrogen from ethanol, and more particularly to a hydrogen production process for low temperature catalyzed ethanol oxidation steam reforming.

The fuel cell is a technology developed by NASA to provide a lightweight, high-efficiency power source for space missions. After nearly half a century of development, fuel cell technology has entered the mainstream of technology. Today, with the gradual exhaustion of fossil fuels, clean and pollution-free fuel cells are an important direction for people to find new energy sources. Fuel cell conversion efficiency is 40-50%, which is better than the average internal combustion engine conversion efficiency of 18%, and the system output range can range from several watts to millions of watts, which also makes this technology have many applications.

Fuel cells are classified according to the type of electrolyte, from the early alkaline fuel cell (AEC) to the most widely used proton exchange membrane fuel cell (PEMFC). The advantage of proton exchange membrane fuel cells (PEMFC) is that the operating temperature is low, and the disadvantage is that the storage and transportation technology of the raw material hydrogen needs to be broken. This shortcoming can now be overcome by using hydrocarbons as the primary primary fuel for PEMFCs, converting them to on-site hydrogen rich gas (HRG). The hydrogen-rich gas is a mixed gas with a high hydrogen content and is one of the fuels suitable for use in a fuel cell.

In the study of hydrocarbon conversion to PEMFC hydrogen-rich gas fuels, the provision of hydrogen-rich gas by chemical reaction of methanol has been extensively studied. At present, portable fuel cells are also dominated by direct methanol batteries (DMFC). This is because methanol has the advantages of high chemical activity, high yield and low price. However, the disadvantage of using methanol as fuel is that methanol is highly toxic and users are poisoned. risks of. Therefore, the use of abundant sources, low toxicity, and renewable fuel ethanol as a source of hydrogen-rich gas is an emerging research direction.

The source of ethanol is mainly derived from the fermentation of cereals or sugar crops. In addition, the current technology has been studied to use enzymes to decompose plant fibers, such as crop roots, tree debris, weeds and fast-growing tree species, and release the sugar as a refinement. For ethanol.

At present, there are four main ways to produce hydrogen via ethanol:

I. Direct decomposition (Ethanol Decomposition; ED) reaction formula: C ₂ H ₅ OH → H ₂ + CH ₄ + CO

II. Partial Oxidation of Ethanol (POE) reaction formula: C ₂ H ₅ OH+3/2 O ₂ → 3 H ₂ +2 CO ₂

III. Steam Reforming of Ethanol (SRE) Reaction formula: C ₂ H ₅ OH+3 H ₂ O → 6 H ₂ +2 CO ₂

IV. Oxidative Steam Reforming of Ethanol (OSRE) Reaction Formula: Comprehensive Reaction of POE and SRE

In the above reactions, especially the II, III and IV pathways are the focus of academic research. The temperature of the ethanol steam recombination reaction is about 600 ° C, and the content of carbon monoxide in the product is above 20% ⁽¹⁾ . While the partial oxidation of ethanol has a lower reaction temperature, its ethanol conversion rate does not reach 100% ⁽²⁾ , and usually its hydrogen yield is <3 mole ratio (hydrogen/ethanol).

The ethanol oxidation steam recombination reaction is a combination of ethanol vapor recombination reaction and partial oxidation reaction, and has a theoretical hydrogen yield (>3 molar ratio (hydrogen/ethanol)) which is higher than that of the partial oxidation reaction of ethanol. However, due to different catalysts and reaction conditions, the reaction temperature is still quite high ⁽³⁾ . Therefore, reducing the reaction temperature of hydrogen production by ethanol, reducing the pollution of carbon monoxide in the product, and increasing the hydrogen yield are the current efforts.

(1) Athanasios, NF, Xenophon EV, and Dimitris, K., Chem. Comm. 851-852, (2001); Breen JP, Burch R., and Coleman, HM, Appl. Catal. B, 39, 65- 74 (2002).

(2) Wang, WP, Wang, ZF, Ding, Y., Xi, JY and Lu, GX, Catal. Lett., 81, 63-68, (2002); Wang, WP, Wang, ZF, Ding, Y .and Lu, GX., Chem. Res. Chinese U., 19, 206-210 (2003).

(3) Liguras, DK, Goundani, K. and Verykios, XE, Int. J. Hydrogen Energy, 29, 419-427 (2004); Liguras, DK, Goundani, K. and Verykios, XE, J. Power Sour., 130 , 30-37 (2004); Deluga, GA, Salge, JR, Schmidt, LD, and Verykios, XE, Science, 303, 993-997 (2004).

One of the objects of the present invention is to provide a low-temperature process for hydrogen gas, which can effectively convert ethanol even if the reaction temperature is lowered to 320 ° C, and the hydrogen production rate YH ₂ can still be greater than 3.

Another object of the present invention is to provide a method for producing low-temperature hydrogen gas which can be applied to a fuel cell, using a catalyst composed of platinum, rhodium and an alkali metal supported on zirconia to provide hydrogen gas contaminated with low carbon monoxide. For use in a fuel cell, the support of the above catalyst contains at least zirconia.

A further object of the present invention is to provide a method for recombining oxidizing steam of low temperature ethanol, which can efficiently convert ethanol at a lower reaction temperature so that the consumption per unit of ethanol can have a higher hydrogen production rate.

According to the above object of the present invention, a hydrogen production reaction process for catalytically catalyzing ethanol at low temperature is proposed. First, steam and oxygen of an aqueous ethanol solution are mixed, and then the mixed gas is passed through a catalyst to catalyze the oxidative vapor recombination reaction of ethanol at a temperature of 300 to 420 ° C to produce a hydrogen-containing gas. The catalyst is composed of platinum, rhodium and an alkali metal supported on zirconia, and the content of the alkali metal is 0-1 wt%. This reaction can effectively decompose ethanol to produce a hydrogen-rich gas, the by-product carbon monoxide content is not more than 3%, and the ethanol consumption per mole is greater than 3 moles of hydrogen production.

According to a preferred embodiment of the invention, the source of oxygen may be pure oxygen or air. The catalyst consists essentially of platinum, rhodium and sodium supported on zirconia, and the concentration of the aqueous sodium metal solution added at the time of manufacture is 0-1 wt%.

In another embodiment of the invention, the source of oxygen can be pure oxygen or air. touch The medium consists essentially of platinum, rhodium and potassium supported on zirconia, and the potassium hydroxide aqueous solution added at the time of manufacture has a weight percent concentration of 0.25 wt%.

According to the above, the oxidizing vapor recombination reaction temperature of ethanol can be as low as 320 ° C, so that it can be more easily integrated with the fuel cell. Moreover, the hydrogen content generated by the low temperature process is better, and the carbon monoxide pollutant is not more than 3%, which can reduce the poisoning phenomenon of carbon monoxide on the fuel cell catalyst. Most importantly, the ethanol consumption per mole is greater than 3 moles of hydrogen production, which is higher than the maximum theoretical value of the ethanol partial oxidation (POE) reaction.

In order to get the ideal low-temperature ethanol oxidation steam recombination reaction, I hope to have the following four characteristics:

1. Ethanol conversion rate (C _EtOH ) is high: it can save ethanol feed.

2. The reaction temperature (T _R ) is low: a low reaction temperature can shorten the time required to start the reaction and provide higher safety.

3. High hydrogen production rate (Y _H2 ): that is, the number of hydrogen molecules converted by each ethanol molecule should be as much as possible. Theoretically, the maximum hydrogen production rate of the ethanol oxidation steam recombination reaction is R _H2 =4.

4. The carbon monoxide product distribution rate (P _CO ) is low: carbon monoxide is produced when the oxidation of ethanol is incomplete, and the hydrogen-rich gas is contaminated. The hydrogen-rich gas containing a large amount of carbon monoxide must firstly reduce the carbon monoxide content in the application before it can be fed into a hydrogen fuel cell for fuel, and the device for reducing the carbon monoxide content requires additional configuration space and is expensive. Therefore, the carbon monoxide product distribution rate should be as low as possible to increase convenience and reduce costs.

According to an embodiment of the invention, the platinum, rhodium and alkali metal catalyst supported on the zirconia is used to catalyze the ethanol oxidation steam recombination reaction to produce a hydrogen-rich gas. This catalyst is even at a lower reaction temperature (T _R Below 320 ° C), it still has the advantages of high ethanol conversion (C _EtOH ), high hydrogen production rate (Y _H2 ) and low carbon monoxide product distribution rate (P _CO ).

The product analysis section, ethanol conversion (C _EtOH ), hydrogen yield (Y _H2 ; mol H ₂ /mol Ethanol), and carbon monoxide product distribution rate (P _CO ) are calculated as follows:

Catalyst preparation method

According to an embodiment of the present invention, a catalyst capable of low temperature catalyzing the reorganization of ethanol oxidizing vapor is proposed. The catalyst consists of a support and a metal distributed on the surface of the support. The composition of the metal consists essentially of platinum, rhodium and sodium in an amount of from about 3-4% by weight based on the weight of the catalyst. The support comprises zirconia wherein the zirconia content is from about 96 to about 97 weight percent of the total weight of the catalyst.

An embodiment of the present invention prepares a support catalyst containing at least 3 wt% of platinum rhodium metal and 0-1 wt% sodium metal, respectively, in an incipient wetness impregnation, and contains at least 3 wt% Supportive catalyst for platinum rhodium metal and 0-1 wt% potassium metal. Wherein the support contains about 96 wt% zirconia. The main steps include mixing an aqueous solution containing platinum, ruthenium and an alkali metal with a metal oxide of a catalyst carrier, followed by drying, calcination and reduction to prepare a desired catalyst. The detailed flow of catalyst preparation in this embodiment is as follows:

1. Perform the initial wet point test of the incipient wetness test catalyst carrier: take 1 g of ZrO ₂ powder support, slowly pour pure water into the ZrO ₂ powder support, and stir the support to allow water to be sucked into the hole until When the support is in a clay form, it reaches the initial wet point (that is, when the support is in a clay form), and the amount of pure water is recorded at this time.

2. 5 g of ZrO _{2 was} placed in a mortar for grinding, and 1.5 wt% of PtCl _{4 (aq)} and 1.5 wt% of RuCl _{3 (aq) were} slowly dropped into a mortar and ground.

3. Rinse the beaker containing PtCl _{4 (aq)} and RuCl _{3 (aq)} with a small amount of deionized water, wash the residual Pt and Ru, and then drip into the mortar, and then grind to the initial wetness point ^(4). dry.

4. It was baked in an oven at 110 ° C for 12 hours, taken out and ground again, and placed in a calciner and calcined at 400 ° C for 4 hours. The sample taken out was named PtRu/ZrO ₂ .

5. 3 g of PtRu/ZrO _{2 was} placed in a mortar and ground, and 0.25 wt% of Na ₂ CO _{3 (aq) was} slowly dropped and ground.

6. Rinse the Na ₂ CO _{3 (aq)} beaker with a small amount of deionized water, wash the residual Na, and then drip into the mortar and grind to dryness.

7. After being baked in an oven at 110 ° C for 12 hours, it was ground and ground, and the ground sample was named PtRuNa _0.25 /ZrO ₂ .

8. Repeat steps 5-7 to replace 0.25 wt% Na ₂ CO _{3 (aq)} with 0.5 wt% Na ₂ CO _{3 (aq)} , 1 wt% Na ₂ CO _{3 (aq)} , 0.25 wt% K ₂ CO _{3 (aq)} , the samples were named PtRuNa _0.5 /ZrO ₂ , PtRuNa ₁ /ZrO ₂ , PtRuK _0.25 /ZrO _{2 , respectively} .

9. Place the calcined catalyst product in a sample vial and store in a dry box.

10. Before the catalyst test, the steps of pressing, crushing and sieving (mesh 60-80) are carried out, and then reduction is carried out for 3 hours by hydrogen at 200 °C.

Description of the effect of active metals in the catalyst

The platinum metal contained in the above catalyst is a catalytic converter center, which catalyzes the oxidizing vapor recombination reaction of ethanol. Since the platinum metal catalyst is susceptible to poisoning by carbon monoxide, a by-product of the oxidizing steam recombination reaction, the catalytic activity is lost. The addition of ruthenium reduces the chance of platinum catalyst being poisoned by carbon monoxide and increases the tolerance of the catalyst to carbon monoxide. The addition of an alkali metal catalyzes the reaction formula of (1), which promotes the reaction of carbon monoxide with water to form carbon dioxide and hydrogen, which can reduce the production of carbon monoxide and increase the productivity of hydrogen.

CO+H ₂ O → CO ₂ +H ₂ (1)

Reaction system for ethanol oxidation steam recombination and method for testing catalytic reaction

In accordance with an embodiment of the invention, a fixed flow of ethanol vapor is passed through a 100 mg catalyst sample positioned in a fixed reactor. The flow rate of ethanol vapor is controlled at 61 ml/min, the flow rate of carrier gas is controlled at 50 ml/min (2.7 ml of oxygen per minute, 47.3 ml of argon per minute), and the molar ratio of oxygen to ethanol (oxygen) The alcohol ratio, x) is controlled by the flow rate of oxygen.

A schematic representation of the reaction system of the process of the present invention is shown in Figure 1. Reactants 100a and 100b, catalyst 200, and product 300 are present in the reaction system. Reactant 100a is an aqueous ethanol solution and 100b is oxygen. The catalyst 200 is filled in a reactor 201 which is a supporting catalyst containing 3 wt% of platinum rhodium metal and 0-1 wt% of an alkali metal. Product 300 comprises carbon dioxide, ethylene, water vapor, acetaldehyde, ethanol, acetone, hydrogen, oxygen, methane, and carbon monoxide. The entire reaction process is to let the reactants 100a and 100b enter the preheater 203, and after heating to 110 ° C, the reactants 100a and 100b are allowed to enter the mixing tank 202 for mixing, and then enter the reactor 201 and touch. The medium 200 is contacted and the reactor temperature is controlled between 300 and 420 °C. The reaction produces product 300, which is then passed into analyzer 301 to analyze the composition of product 300. The catalyst 200 participating in the reaction was used before being reacted with hydrogen at 200 ° C for 3 hours to activate it. The experimental results of changing the cause of change are listed in Table 1.

Wt _M %: weight percentage of alkali metal in the catalyst

The analysis method of the product was analyzed by gas chromatography (Gas Chromatography; GC). The reaction is carried out in parallel using two chromatography columns, wherein the Porapak Q column is used to separate carbon dioxide, ethylene, water, acetaldehyde, ethanol and acetone in the product, and hydrogen, oxygen and methane in the product. Carbon monoxide is separated by another MS-5A column. The separated products, hydrogen, oxygen, methane, and carbon monoxide, were quantitatively analyzed by Thermal Conductivity Detector (TCD).

All reactions were started from low temperature, and the product analysis was carried out after one hour of stabilization at a preset temperature, and then the temperature was raised to the next reaction temperature.

Effect of Alkali Metal Content on Recombination Reaction of Ethanol Oxidation Steam

Experiment 1 of Table 1 is the experimental control group. The catalytic effect of PtRu/ZrO ₂ catalyst on ethanol vapor was tested without adding alkali metal. It was found that the catalytic effect was best at 360 ° C, and the hydrogen generation rate Y _H2 was 3.35. However, the carbon monoxide distribution rate is slightly higher, reaching 2.96%. Experiments 2~4 were carried out to observe the catalytic effect of PtRuNa _x /ZrO ₂ catalyst on ethanol vapor under different sodium contents. It was found that in Experiment 2, when the concentration of sodium solution added was 0.25 wt%, it was produced at 320 °C. The best catalytic effect, Y _H2 is 3.76, and the carbon monoxide concentration is below the detection limit. In Experiment 3, when the concentration of the added sodium solution was raised to 0.5 wt%, the temperature at 340 ° C, the Y _{H2 was} increased to 3.83, but the carbon monoxide distribution rate was also increased to 1.26%. The results of Experiment 4 show that if the concentration of the added sodium solution is further increased to 1 wt%, Y _H2 is lowered to 3.43, and the carbon monoxide distribution rate is 1.08%. The results of Experiment 5 showed that when 0.25 wt% of the added sodium solution was replaced by a 0.25 wt% potassium solution, Y _{H2 was} lowered to 3.22, and the carbon monoxide distribution rate was 1.42%.

Catalyst use cycle test

Figure 2 shows the effect of PtRuNa _0.25 /ZrO ₂ catalyst product distribution, ethanol conversion rate and hydrogen yield as the ethanol oxidation steam recombination time increases. After 120 hours of reaction, the ethanol conversion (C _EtOH ) was still 100%, the hydrogen yield (Y _H2 ) was still maintained at 3.2, and the product distribution rate (P _CO ) of carbon monoxide approached 0%.

In summary, the ethanol oxidation steam recombination reaction described in the examples of the present invention can obtain a relatively high hydrogen yield (Y _H2 >3.0) by adjusting the reaction conditions. Compared to the theoretical hydrogen production rate of the partial oxidation reaction of ethanol (Y _H2 = 3.0), the hydrogen yield is higher and a hydrogen-rich gas of less than 1000 ppm of carbon monoxide can be obtained. The reaction temperature (~600 ° C) and the carbon monoxide product distribution rate (>20%) compared to the steam reforming reaction of ethanol have a lower reaction temperature (300-420 ° C) and a lower carbon monoxide product distribution rate. (<1000 ppm). The low carbon monoxide hydrogen-rich gas can be used as a fuel for a hydrogen fuel cell after undergoing a further carbon monoxide oxidation treatment step.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and retouched without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

100a‧‧Reactive substance a

100b‧‧‧Reaction b

200‧‧‧ catalyst

201‧‧‧Reactor

202‧‧‧ mixing tank

203‧‧‧Preheating zone

300‧‧‧ products

301‧‧‧ analyzer

1 is a schematic view showing the structure of a reaction system for recombination reaction of ethanol oxidizing vapor according to an embodiment of the present invention.

Figure 2 shows the effect of increasing the reaction time of ethanol oxidation steam on the distribution of PtRuNa _0.25 /ZrO ₂ catalyst product, ethanol conversion rate and hydrogen yield.

100a‧‧Reactive substance a

100b‧‧‧Reaction b

200‧‧‧ catalyst

201‧‧‧Reactor

202‧‧‧ mixing tank

203‧‧‧Preheating zone

300‧‧‧ products

301‧‧‧ analyzer

Claims (16)

A low-temperature catalytic ethanol hydrogen production reaction process comprises: mixing steam and oxygen in an aqueous ethanol solution, the molar ratio of the oxygen to the ethanol is 0.26; and passing a mixed gas of steam and oxygen of the aqueous ethanol solution through a catalyst. Catalyzing the oxidative vapor recombination reaction of ethanol at 300-420 ° C, wherein the catalyst consists essentially of platinum, rhodium and alkali metals supported on zirconia, wherein the total content of platinum and rhodium is 3 wt%, alkali metal The content is 0-1 wt%. The hydrogen production reaction process for low temperature catalytic ethanol according to claim 1, wherein the alkali metal is sodium or potassium. The hydrogen production reaction process of the low temperature catalytic ethanol according to the second aspect of the patent application, wherein the alkali metal is sodium. The hydrogen production reaction process for low temperature catalytic ethanol according to claim 1, wherein the source of the oxygen is pure oxygen or air. The hydrogen production reaction process for low temperature catalytic ethanol according to claim 1, wherein the concentration of the aqueous ethanol solution is about 40 vol%. A catalyst capable of low-temperature catalyzing hydrogen production of ethanol for catalyzing a oxidative vapor recombination reaction of ethanol at 300-420 ° C, wherein the catalyst consists essentially of platinum, rhodium and an alkali metal supported on zirconia. The catalyst for low-temperature catalyzed hydrogen production of ethanol as described in claim 6 wherein the total content of platinum and rhodium is at least 3 wt%. The catalyst for low-temperature catalyzed hydrogen production of ethanol as described in claim 6 wherein the alkali metal content is 0-1 wt%. The catalyst for low-temperature catalyzed hydrogen production of ethanol as described in claim 6 wherein the alkali metal is sodium or potassium. The catalyst for low-temperature catalyzed hydrogen production of ethanol as described in claim 9 wherein the alkali metal is sodium. The invention relates to a method for preparing a catalytic catalyst for hydrogen production of ethanol at a low temperature, wherein the catalyst is basically composed of platinum, rhodium and an alkali metal supported on zirconia, and comprises: adding an aqueous solution of a platinum metal salt and a cerium metal salt solution to oxidation. In the zirconium powder, after grinding to dryness, it is calcined at 400 ° C to prepare a zirconia powder containing platinum and ruthenium metal; and the alkali metal salt aqueous solution is added to the zirconia powder containing platinum or ruthenium metal, After drying at 110 ° C, the catalyst is prepared, and the total content of platinum and rhodium in the catalyst is at least 3 wt%. Low temperature catalytic ethanol as described in claim 11 A method for producing a hydrogen reaction catalyst, wherein the platinum metal salt aqueous solution has a concentration of 0.15 wt%. The method for preparing a low temperature catalytic ethanol hydrogen production reaction catalyst according to claim 11, wherein the concentration of the cerium metal salt aqueous solution is 0.15 wt%. The method for preparing a low-temperature catalytic ethanol hydrogen production reaction catalyst according to claim 11, wherein the alkali metal salt aqueous solution concentration is 0.25-1 wt%. The method for preparing a low-temperature catalytic ethanol hydrogen production reaction catalyst according to claim 11, wherein the alkali metal salt aqueous solution is a sodium metal salt aqueous solution or a potassium metal salt aqueous solution. The method for preparing a low-temperature catalytic ethanol hydrogen production reaction catalyst according to claim 15 , wherein the alkali metal hydrazine aqueous solution is a sodium metal hydrazine aqueous solution.