JP2009011886A - Halide absorbing agent and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a halide absorbing agent having impact resistance and high performance of removing a halide. <P>SOLUTION: The sodium aluminate synthesized from a mixture of an alumina sol with sodium carbonate and a glass fiber of 1-50 wt.% of the halide absorbing agent as a strength increasing/adding material are incorporated in the halide absorbing agent so that the halide absorbing agent has high performance of absorbing the halide and high impact resistance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a halide absorbent and a method for producing the halide absorbent for application to a halogen removal system for removing halides such as hydrogen chloride and hydrogen fluoride contained in a high-temperature gas.

  In recent years, there has been a demand for effective use of resources and reduction of waste, and it is considered that raw material gas produced from biomass and waste is used as fuel gas for power generation equipment (fuel cells and gas engines). The raw material gas produced from biomass and waste contains halides such as hydrogen chloride and hydrogen fluoride as impurities, so it must be used as a fuel gas for power generators such as fuel cells and gas engines. In order to maintain the performance and reduce the impact on the environment, it is necessary to remove halides on the order of several ppm.

  As a technique for removing a halide in a gas, a dry system using a chemical reaction with an alkaline solid substance by using the fact that the halide is an acidic substance is considered. The dry system processes gas at a high temperature, so that there is little reduction in energy efficiency, and a simple system that does not require heat exchangers and drainage equipment for adjusting the temperature.

  However, the halide removal performance in dry systems depends on the reaction characteristics of the substance that reacts with the halide. For this reason, it is indispensable to develop an absorbent containing an absorbent material corresponding to the composition, temperature, pressure, and halide removal concentration level of the target raw material gas.

  Conventional techniques relating to absorbents for removing halides in source gases include activated alumina using an alkali metal as a promoter (for example, Patent Document 1), alumina containing sodium oxide (for example, Patent Documents 2 and 3). ), An inorganic silicate impregnated with an alkaline aqueous solution (for example, Patent Document 4) is known. However, these techniques are intended for use at room temperature or at temperatures below 150 ° C.

  On the other hand, there has been proposed a technique for removing halide contained in a raw material gas to a very low concentration in a dry condition under a temperature condition of a gas temperature of 200 ° C. or higher, further 400 ° C. or higher (for example, Patent Document 5). The technique disclosed in Patent Document 5 is in the form of a powder containing, as a reaction component, alkali aluminate that removes halide contained in a high-temperature source gas to a low concentration for the purpose of using the source gas as a fuel gas for a fuel cell. This is a method for producing an absorbent. Here, alumina sol is used as an aluminum source, and sodium carbonate, which is a sodium source as an alkali, is mixed as an aqueous solution, thereby making it possible to convert all of the raw material sodium carbonate into sodium aluminate.

  When removing the halide in the raw material gas, it is necessary to consider the pressure loss of the packed bed of the absorbent in order to distribute the raw material gas to be removed to the halide removing device filled with the halide absorbent. It is necessary to use the absorbent in the form of granules, spheres, cylinders, honeycombs or the like. In addition, the molded article of the absorbent requires resistance to impact during transportation or when filling the halide removing device.

  At present, it has been found that an absorbent containing sodium aluminate as a reaction component has high purification performance against halides, and it is possible to accurately remove halides by a dry method that does not lower the gas temperature below the dew point. Yes. However, the fact is that there is no halide absorbent that can be easily molded into a molded body considering the pressure loss of the packed bed and that has sufficient resistance to impact and high halide removal performance.

Japanese translation of PCT publication No. 7-506048 Japanese National Patent Publication No. 9-508855 JP-A-6-190274 JP 60-187335 A JP 2000-15091 A

  The present invention has been made in view of the above situation, and an object thereof is to provide a halide absorbent having impact resistance and high halide removal performance.

  Another object of the present invention is to provide a method for producing a halide absorbent which has impact resistance and high halide removal performance and can easily obtain a molded product. And

  In order to achieve the above object, the halide absorbent of the present invention according to claim 1 contains alkali aluminate, which is a composite oxide of aluminum and an alkaline substance, and contains a strength reinforcing additive. To do. That is, the halide absorbent of the present invention is a molded body containing an alkali aluminate and a strength reinforcing additive.

  In the present invention according to claim 1, halide absorption performance can be enhanced by containing alkali aluminate, which is a composite oxide of alumina sol and alkaline substance, and impact resistance can be achieved by containing strength reinforcing additive. Can increase the sex.

  Specific examples of the alkali aluminate include sodium aluminate, potassium aluminate, lithium aluminate, magnesium aluminate, calcium aluminate, strontium aluminate, and barium aluminate.

  And the halide absorbent of the present invention according to claim 2 contains the strength reinforcing additive in the amount of 1 to 50% in weight ratio of the absorbent in the halide absorbent of claim 1. It was made to be characterized.

  In the present invention according to claim 2, the presence of the strength reinforcing additive while reinforcing the strength of the absorbent by including the strength reinforcing additive so that the weight ratio of the absorbent is in the range of 1 to 50%. Therefore, it is possible to secure the amount of alkali aluminate, which is a halide-absorbing component, and to combine the strength and removal performance of the absorbent.

  The halide absorbent of the present invention according to claim 3 is the halide absorbent according to claim 1 or 2, wherein the strength reinforcing additive is a needle-like fiber.

  The acicular fiber is a heat-resistant fine fiber, and specifically, glass fiber, potassium titanate whisker, silicon carbide whisker, aluminum silicate whisker, aluminum borate whisker, or the like can be applied.

  According to the third aspect of the present invention, a molded article having high impact resistance can be obtained from the needle-like fibers.

  In order to achieve the above object, the method for producing a halide absorbent according to the present invention according to claim 4 adds needle-like fibers to a mixture containing aluminum and an alkaline substance, performs molding processing, and dries the molding mixture. By firing, aluminum and an alkali are reacted to generate an alkali aluminate to obtain a molded product.

  In the present invention according to claim 4, it is possible to obtain a molded body with improved halide absorption performance by containing alkali aluminate, which is a composite oxide of aluminum and an alkaline substance, and containing a strength reinforcing additive. Thus, a molded body with improved impact resistance can be obtained.

  And the manufacturing method of the halide absorbent of the present invention according to claim 5 is the method of manufacturing a halide absorbent according to claim 4, wherein the raw material aluminum is alumina sol and the alkali is sodium carbonate. The alkali aluminate is sodium aluminate.

  In this invention which concerns on Claim 5, the molded object which improved the absorption capability of the halide can be obtained by containing the alkali aluminate produced | generated from alumina sol and sodium carbonate.

  Specific examples of the alkali aluminate include potassium aluminate, lithium aluminate, magnesium aluminate, calcium aluminate, strontium aluminate, barium aluminate and the like.

  A method for producing a halide absorbent according to a sixth aspect of the present invention is the method for producing a halide absorbent according to the fourth aspect, wherein the needle-like fibers are glass fibers.

  As other examples of the acicular fiber, potassium titanate whisker, silicon carbide whisker, aluminum silicate whisker, aluminum borate whisker, or the like can be applied.

  In this invention which concerns on Claim 6, the strong molded article provided with impact resistance can be obtained with a glass fiber.

  The halide absorbent of the present invention is a halide absorbent having impact resistance and high halide removal performance.

  In addition, the method for producing a halide absorbent according to the present invention has impact resistance and high halide removal performance, and can easily obtain a molded product.

  FIG. 1 shows a process concept for producing a halide absorbent according to an embodiment (example) of the present invention, FIG. 2 shows an appearance photograph of the halide absorbent according to an embodiment of the present invention, and FIG. These are tables showing test conditions for evaluating the hydrogen chloride absorption performance of the absorbent. FIG. 4 is a graph showing the change over time in the hydrogen chloride concentration of the gas after reacting with the halide absorbent, FIG. 5 is a photograph of the appearance of the halide absorbent according to Comparative Example 1, and FIG. The appearance photograph of such a halide absorbent, FIG. 7, shows the relationship between the powdering rate and the chlorine absorption capacity.

  The halide absorbent of the embodiment of the present invention contains sodium aluminate (alkali aluminate) made of a mixture of alumina sol and sodium carbonate as an alkaline substance, and contains glass fiber as a strength reinforcing additive (needle fiber). To do.

  Moreover, you may add base materials, such as an alumina, a silica, and a titania, as an additive. The base material is one in which fine particles of sodium aluminate are highly dispersed in order to increase the reactivity of the produced halide absorbent with the halide. By adding the base material, an absorbent in which sodium aluminate is finely divided and highly dispersed is obtained on the base material, and the absorbent material is finely divided and highly dispersed.

  By adjusting the addition amount of alumina sol and sodium carbonate as raw materials for sodium aluminate, glass fiber as strength reinforcing additive and base material (for example, alumina powder), the content of sodium aluminate is 10% by weight or more and 100%. It is made to become less than weight%. Glass fiber as a strength reinforcing additive (needle fiber) is in the range of 1% to 50% by weight in the produced halide absorbent.

  In adjusting the content of sodium aluminate, the necessary amount of sodium aluminate is secured by appropriately adjusting the addition amounts of the strength reinforcing additive and the base material. The halide absorbent of the present invention utilizes the high reactivity of sodium aluminate, and when the content of sodium aluminate is lowered, the absorption capacity of the halide is reduced and the removal performance is lowered. On the other hand, when the content of sodium aluminate is increased, the contents of the strength reinforcing additive and the base material are decreased, and the molded absorbent is inferior in strength. For this reason, the content of sodium aluminate is set to be 10 wt% or more and less than 100 wt%.

  A method for producing the above-described halide absorbent will be described with reference to FIG.

After the sodium carbonate (Na ₂ CO ₃₎ was dissolved in water (H ₂ O), alumina sol were mixed (Al ₂ O _3), base (e.g., alumina: Al ₂ O ₃₎ and reinforcement additives (e.g. Add glass fiber) and mix. Before, during or after the addition of the base material and the strength reinforcing additive, the raw materials are sufficiently mixed and the water content is adjusted in order to ensure the moldability in the subsequent process.

  A mixture obtained by adjusting the moisture and sufficiently stirred is molded to obtain a molded product. For forming, a method of extruding the mixture is generally used, but the method is not limited to this. For example, the mixture can be obtained by mold filling or rolling. Any shape can be used as long as the gas flow is not hindered.

  The molded product obtained by the molding operation is used as a halide absorbent that has been dried and fired and molded (molded halide absorbent). Drying is performed, for example, in a temperature range of 20 ° C. to 120 ° C., and the time is set according to the moisture content of the molded product and the processing conditions (temperature, heater capacity, air circulation rate, molded product amount / shape, etc.). . Baking subsequent to drying is performed, for example, in a temperature range of 200 ° C. to 900 ° C., and the time is set according to the reaction amount of the molded product (described later) and processing conditions. Drying and firing are usually about 1 to 24 hours.

By baking sodium carbonate and (Na ₂ CO ₃₎ a mixture of alumina sol (Al ₂ O _3),
Na ₂ CO ₃ + Al ₂ O ₃ → 2NaAlO ₂ + CO ₂ (1)
Through this chemical reaction, sodium aluminate (NaAlO ₂ ) is synthesized.

In this case, the molding process is performed in an unreacted state in which sodium carbonate (Na ₂ CO ₃ ) and alumina sol (Al ₂ O ₃ ) are mixed and roughly dried to adjust the water content. By firing the molded product, the formation reaction of sodium aluminate (NaAlO ₂ ) represented by the formula (1) proceeds, and a molded halide absorbent containing sodium aluminate (NaAlO ₂ ) is obtained.

The above-mentioned halide absorbent has excellent halide absorption performance by containing sodium aluminate (NaAlO ₂ ) composed of a mixture of alumina sol (Al ₂ O ₃ ) and sodium carbonate (Na ₂ CO ₃ ). However, the impact resistance of the absorbent can be increased by adding a strength reinforcing additive (for example, glass fiber) thereto.

  The results of the performance test of the halide absorbent described above will be described with reference to FIGS.

The halide absorbent according to the embodiment shown in FIG. 2 is obtained by adding 15% by weight of glass fiber as a strength reinforcing additive for improving the bonding strength between particles. It is a cylindrical pellet having a diameter of 3.4 mm and a length of 6 to 10 mm, and the packing density into the reaction vessel is 0.62 g / cm ³ . From the crystal structure analysis, it is confirmed that the main component of the halide absorbent is sodium aluminate, and the sodium content is 21.8 wt% and the aluminum content is 27.2 wt%.

  The strength of the halide absorbent was evaluated from the pulverization state (powdering ratio) when the halide absorbent was dropped. Assuming an impact when filling the halide removing device, it was naturally dropped from a height of 2 m and made to collide with a stainless steel plane. The collected halide absorbent was classified with a sieve having an opening of 2 mm, and the halide absorbent under the sieve that was crushed and powdered by the impact of dropping was weighed. The weight ratio of the sample under the crushed and pulverized comb to the evaluated halide absorbent is defined as the pulverization rate and used as an evaluation index for strength.

That is, the powdering rate (%) is (weight of the crushed and pulverized halide absorbent under the comb) / (weight of the dropped halide absorbent) × 100 (%)
Is calculated by It can be evaluated that the smaller the pulverization rate, the smaller the proportion of the pulverized / pulverized halide absorbent, and the higher the strength of the absorbent. Assuming that the allowable value of the powdering rate of the absorbent that can be applied to the halide removing device is 0.25%, if it is less than this value, it is determined that the absorbent has practical strength. The pulverization rate of 0.25% is a value obtained by evaluating a commercially available catalyst used in a large reactor of a fixed bed system.

  The powdering rate of the halide absorbent of the embodiment shown in FIG. 2 is as small as 0.11%, and has a strength that can be applied to a large-sized halide removing apparatus as it is.

  The halide absorbent shown in FIG. 2 was filled in a fixed bed type reaction tube, and a gas containing hydrogen chloride (HCl) at a concentration of 500 ppm as a halide to be removed was circulated to evaluate the absorption performance.

As shown in FIG. 3, the main components of the gas are as follows: H ₂ is 25%, CO is 17%, CO ₂ is 8.5%, H ₂ O is 28.0%, N ₂ is in the balance state, HCl is 500 ppm. This gas condition simulates a raw material gas produced from woody biomass. The reaction temperature was 300 ° C., the filling volume of the halide absorbent was 20 cm ³ , and the flow rate of the simulated gas was 1000 ml / min, so that the superficial velocity similar to the practical condition was 3000 h ⁻¹ .

Removal of hydrogen chloride (HCl) consumes sodium aluminate (NaAlO ₂ ) in the halide absorbent, and the hydrogen chloride concentration at the outlet of the reaction tube gradually increases. When all of the sodium aluminate reacts, hydrogen chloride contained in the reaction tube inlet gas is not removed, and as a result, it flows out to the reaction tube outlet at a concentration almost equal to the inlet concentration. In an actual halide removal apparatus, the halide absorbent is replaced before the halide concentration reaches the allowable value of the power generation equipment using the purified gas. For this reason, the removal target was set to 20 ppm, and the circulation time until the chlorine concentration at the outlet reached 20 ppm was evaluated. The results are shown in FIG.

  As shown by the solid line in FIG. 4, it can be seen that the halide absorbents of the examples maintain the state in which the chlorine concentration at the outlet is below 20 ppm over a circulation time of about 2460 minutes.

From the crystal structure analysis of the halide absorbent after use, sodium aluminate present before the reaction disappeared, and sodium chloride (NaCl) was detected instead. From this result, the halide absorbent of the example is
2NaAlO ₂ + 2HCl → 2NaCl + Al ₂ O ₃ + H ₂ O (2)
It was confirmed that hydrogen chloride (HCl) in the simulated gas could be absorbed and removed to the order of several ppm by the progress of the reaction shown in FIG.

FIG. 5 shows a halide absorbent containing no strength reinforcing additive as Comparative Example 1 and FIG. 6 as Comparative Example 2. Comparative Example 1 is a halide absorbent containing alumina as a base material, and is a cylindrical pellet having a diameter of 3.8 mm and a length of 10 to 40 mm. The packing density of the reaction vessel is 0.60 g / cm ³ . The main component of the halide absorbent is sodium aluminate, having a sodium content of 16.4 wt% and an aluminum content of 38.0 wt%. Comparative Example 2 is a halide absorbent aimed at increasing the content of sodium aluminate by reducing alumina as a base material, and is a cylindrical pellet having a diameter of 4.0 mm and a length of 6 to 10 mm. The packing density is 0.55 g / cm ³ . The main component of the halide absorbent is sodium aluminate, with a sodium content of 19.6 wt% and an aluminum content of 33.7 wt%.

  The powdering rate of the halide absorbent shown in FIGS. 5 and 6 is as large as 2.3% in Comparative Example 1 and 0.55% in Comparative Example 2, and is used as it is by filling it in a large-sized halide removing device. Can not. On the other hand, in the halide absorbent of the example (see FIG. 2) to which glass fiber was added as the above-mentioned strength reinforcing additive, the powdering rate was 0.11%, and the strength was greatly improved. The content could be increased to 21.8 wt%.

  FIG. 4 shows the concentration of hydrogen chloride (HCl) in the outlet gas when the halide absorbents of Comparative Examples 1 and 2 are filled in a reaction vessel and a gas simulating a raw material gas produced from woody biomass is circulated. Also shown. The circulation time until the outlet chlorine concentration of Comparative Example 1 and Comparative Example 2 reached 20 ppm was able to maintain the outlet chlorine concentration below 20 ppm for about 1280 minutes and 2020 minutes, respectively. Since the superficial velocity was adjusted in the evaluation test, the longer the time for maintaining the state below 20 ppm, the higher the performance of the absorbent. Therefore, it can be seen that the halide absorbents of the examples to which the strength reinforcing additive is added have excellent removal performance by increasing the use of sodium.

  FIG. 7 shows a situation in which the absorption amount of hydrogen chloride (HCl) up to 20 ppm breakthrough of the halide absorbents of Examples and Comparative Examples 1 and 2 was calculated, and the relationship with the powdering rate was combined. It is. In the figure, ◯ marks are the halide absorbents of the examples, and Δ and □ marks in the figures are the halide absorbents of Comparative Examples 1 and 2.

  As can be seen from the figure, the halide absorbents of the examples (circles in the figure) have a pulverization rate lower than the target value of 0.25%, impact during transportation and impact when filling the reaction vessel. It can be seen that it has sufficient impact resistance to withstand. Further, the absorption capacity of chlorine is 4.0 mmol / g or more in the examples, and a high absorption capacity is obtained.

  Compared to the halide absorbers of Comparative Example 1 and Comparative Example 2 that do not contain a strength reinforcing additive (glass fiber) (△ mark and □ mark in the figure), the strength of the halide absorbent added with the strength reinforcing additive is greatly increased. It has been confirmed that it has increased. Further, the halide absorbent to which the strength reinforcing additive is added has increased the absorption capacity of hydrogen chloride (HCl) by about 2 times due to the proper sodium content, in other words, hydrogen chloride (HCl). As a result, it was confirmed that the absorption time that can be removed to a low concentration was extended about twice.

  Therefore, it is possible to obtain a halide absorbent having impact resistance and high halide removal performance. By having impact resistance, it is possible to use a large-sized halide removing device that maintains excellent shape without being crushed and pulverized even if it has excellent handling properties. In addition, since it has a high absorption capacity, the amount of the absorbent used to absorb the halide is reduced, and a highly practical halide absorbent can be obtained.

  As an application example of the halide absorbent of the present invention, a fuel cell obtained by purifying a raw material gas obtained by gasifying a fuel composed of biomass, waste, etc., that is, a raw material gas containing various impurities as impurities. It is a power generation facility used as fuel gas for gas engines, and is used as an absorbent for a halide removing device that removes halides such as hydrogen chloride and hydrogen fluoride to a low concentration of several ppm or less. In addition to the purification of fuel gas, for example, it can be used as an absorbent in a halide removing device for combustion gas or sample gas.

  INDUSTRIAL APPLICABILITY The present invention can be used in the industrial field of halide absorbents and methods for producing halide absorbents for application to halogen removal systems that remove halides such as hydrogen chloride and hydrogen fluoride contained in high-temperature gas. it can.

It is a process conceptual diagram for manufacturing the halide absorber which concerns on the Example of this invention. It is an external appearance photograph of the halide absorber which concerns on the Example of this invention. It is a table | surface which shows the test conditions which evaluate the hydrogen chloride absorption performance of a halide absorber. It is a graph showing the time-dependent change of the hydrogen chloride density | concentration of the gas after reacting with a halide absorber. It is an external appearance photograph of the halide absorber of the comparative example 1 of this invention. It is an external appearance photograph of the halide absorber of the comparative example 2 of this invention. It is a graph showing the relationship between the powdering rate of a halide absorber, and a chlorine absorption capacity.

Claims (6)

  A halide absorbent comprising alkali aluminate, which is a composite oxide of aluminum and an alkaline substance, and a strength reinforcing additive.   2. The halide absorbent according to claim 1, further comprising a strength reinforcing additive in an amount ranging from 1 to 50% by weight of the absorbent.   3. The halide absorbent according to claim 1, wherein the strength reinforcing additive is a needle-like fiber.   Add a needle-like fiber to a mixture containing aluminum and an alkali substance, perform molding, and dry and fire the molding mixture to react aluminum and alkali to produce an alkali aluminate to obtain a molded product A process for producing a halide absorbent characterized by the above. In the manufacturing method of the halide absorber of Claim 4,
A method for producing a halide absorbent, characterized in that the starting aluminum is alumina sol and the alkali is sodium carbonate, and the produced alkali aluminate is sodium aluminate.   6. The method for producing a halide absorbent according to claim 4 or 5, wherein the needle-like fibers are glass fibers.

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