CA3094682A1 - Absorbent and method for preparing the same - Google Patents

Abstract

Client's Docket No.: P55080032CA TT's Docket No.: 9044E-A27040CA/fina1/david/Dean ABSTRACT An absorbent is provided. The absorbent includes calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof, wherein the molar ratio of calcium to iron in the absorbent is between 0.1:1 and 1:1, and the molar ratio of zinc to iron in the absorbent is between 0.1:1 and 1:1. A method for preparing the absorbent is also provided. Date Recue/Date Received 2020-09-28

Description

Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean TITLE
ABSORBENT AND METHOD FOR PREPARING THE SAME
CROSS REFERENCE TO RELATED APPLICATIONS
100011 This Application claims priority of Taiwan Patent Application No.
108147339, filed on December 24, 2019, the entirety of which is incorporated by reference herein.
TECHNICAL FIELD

[0002] The disclosure relates to an absorbent, and in particular it relates to an absorbent prepared from metal-smelting by-products.
BACKGROUND

[0003] Hydrogen sulfide (H2S) gas is a colorless gas with the smell of rotten eggs. It has high toxicity, corrosivity and flammability. When the concentration reaches 5ppm, it causes irritation to the eyes, nose, and throat, and when the concentration exceeds 1,000ppm, it can be fatal. Hydrogen sulfide (H2S) gas exists in various hydrocarbon sources, such as natural gas, biogas, syngas, and even landfills. Depending on the end use, there are strict limits on the content of hydrogen sulfide (H2S) gas in feed gas.

[0004] Based on the cost, efficiency and toxicity of the absorbent, metal oxides such as zinc oxide (Zn0), calcium oxide (CaO) and iron oxide (Fe2O3) are the most commonly used absorbents. However, in a high-temperature (greater than 600 C) reducing atmosphere, zinc oxide (ZnO) is easily reduced to metallic zinc (Zn), which escapes in the form of high-temperature gaseous metal smoke, resulting in a loss of absorbent.

[0005] Therefore, development of an absorbent that has a high absorption rate for hydrogen sulfide (H2S) gas and that can take thermal stability into account is expected.
SUMMARY

[0006] In order to effectively increase the absorption rate for hydrogen sulfide (H2S) Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean gas of absorbents, the disclosure provides an absorbent, by a co-precipitation method, the industrial by-product raw materials are recombined to form zinc ferrite (ZnFe204) and calcium ferrite (CaFe204) with a spinel structure to increase the specific surface area and pore volume of the absorbent.

[0007] In accordance with one embodiment of the disclosure, an absorbent is provided.
The absorbent includes: calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof, wherein the molar ratio of calcium to iron in the absorbent is between 0.1:1 and 1:1, and the molar ratio of zinc to iron in the absorbent is between 0.1:1 and 1:1.

[0008] In accordance with one embodiment of the disclosure, a method for preparing an absorbent is provided. The method includes: mixing a metal-smelting by-product with an acidic solvent to form a first solution, wherein the metal-smelting by-product includes iron, calcium, zinc, or a combination thereof; adding an iron-containing solution to the first solution to adjust the molar ratio of calcium to iron or zinc to iron in the first solution, wherein the molar ratio of calcium to iron in the first solution is between 0.1:1 and 1:1, and the molar ratio of zinc to iron in the first solution is between 0.1:1 and 1:1; adding an alkaline solvent to the first solution to perform a co-precipitation process to form a salt solution; performing a filtration process on the salt solution to obtain a solid filter; and performing a calcination process on the solid filter to prepare an absorbent, wherein the absorbent includes calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof

[0009]

[0010] A detailed description is given in the following embodiments with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure can be more fully understood by reading the subsequent detailed description Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean and examples with references made to the accompanying drawings, wherein:

[0011] FIG. 1 shows an SEM photograph (magnification of 5,000 times) of an absorbent (converted from slag) in accordance with one embodiment of the disclosure;

[0012] FIG. 2 shows an SEM photograph (magnification of 5,000 times) of an absorbent (converted from dust) in accordance with one embodiment of the disclosure;

[0013] FIG. 3 shows an SEM photograph (magnification of 5,000 times) of a slag absorbent;

[0014] FIG. 4 shows an SEM photograph (magnification of 5,000 times) of a dust absorbent;

[0015] FIG. 5 shows the absorption effect of an absorbent on hydrogen sulfide (H2S) gas in accordance with one embodiment of the disclosure;

[0016] FIG. 6 shows a thermogravimetric analysis chart of an absorbent (converted from slag) in accordance with one embodiment of the disclosure;

[0017] FIG. 7 shows a thermogravimetric analysis chart of an absorbent (converted from dust) in accordance with one embodiment of the disclosure;

[0018] FIG. 8 shows a thermogravimetric analysis chart of a slag absorbent;
and

[0019] FIG. 9 shows a thermogravimetric analysis chart of a dust absorbent.
DETAILED DESCRIPTION

[0020] The following description is of the best-contemplated mode of carrying out the disclosure. This description is made for the purpose of illustrating the general principles of the disclosure and should not be taken in a limiting sense. The scope of the disclosure is determined by reference to the appended claims.

[0021] In accordance with one embodiment of the disclosure, an absorbent is provided.
The absorbent includes calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof The molar ratio of calcium to iron in the absorbent is between about 0.1:1 and Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean about 1:1. The molar ratio of zinc to iron in the absorbent is between about 0.1:1 and about 1:1.

[0022] In one embodiment, the calcium ferrite (CaFe204) and the zinc ferrite (ZnFe204) may include a spinel structure.

[0023] In one embodiment, the absorbent further includes, for example, magnesium oxide (MgO), aluminum oxide (Al2O3), silicon oxide (SiO2), sulfur oxide (SO3), calcium oxide (CaO), manganese oxide (MnO), iron oxide (Fe2O3), zinc oxide (Zn0), or a combination thereof In one embodiment, the magnesium oxide (MgO) is about 0-5 parts by weight, the aluminum oxide (A1203) is about 0-4 parts by weight, the silicon oxide (SiO2) is about 0-20 parts by weight, the sulfur oxide (SO3) is about 0-3 parts by weight, the calcium oxide (CaO) is about 1-25 parts by weight, the manganese oxide (MnO) is about 1-parts by weight, the iron oxide (Fe2O3) is about 25-75 parts by weight, and the zinc oxide (ZnO) is about 1-40 parts by weight, based on 100 parts by weight of the absorbent.

[0024] In one embodiment, the calcium ferrite (CaFe204) has a characteristic peak value of 20=33.64 , 33.57 and 61.41 . In one embodiment, the zinc ferrite (ZnFe204) has a characteristic peak value of 20=29.92 , 36.92 and 62.24 .

[0025] In one embodiment, the absorbent has a specific surface area of about 1-80m2/g.
In one embodiment, the absorbent has a pore volume of about 0.01-0.5cm3/g.

[0026] In accordance with one embodiment of the disclosure, the composition of the metal-smelting by-products meets the following condition (S-0) or condition (D-0).

[0027] Slag (S-0): 0.1wt% to 3wt% of magnesium oxide, 1 wt% to 6wt% of aluminum oxide, 12wt% to 25wt% of silicon oxide, 0.1wt% to 3wt% of sulfur oxide, 15wt%
to 25wt% of calcium oxide, lwt% to 6wt% of manganese oxide, 25wt% to 50wt% of iron oxide, and 2wt% to 8wt% of zinc oxide, based on the total weight of the absorbent; and dust (D-0): 0.1wt% to 3wt% of magnesium oxide, 0.1wt% to 3wt% of aluminum oxide, Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean lwt% to 1 Owt% of silicon oxide, 0.1wt% to 4wt% of sulfur oxide, lwt% to 15wt%
of calcium oxide, lwt% to 5wt% of manganese oxide, 35wt% to 60wt% of iron oxide, and 20wt% to 40wt% of zinc oxide, based on the total weight of the absorbent.

[0028] In accordance with one embodiment of the disclosure, before adjusting composition, the metal-smelting by-product (slag (S-0)) has a specific surface area between 0.1m2/g and 5m2/g and a pore volume between 0.01cm3/g and 0.2cm3/g; the metal-smelting by-product (dust (D-0)) has a specific surface area between 0.1m2/g and 5m2/g and a pore volume between 0.01cm3/g and 0.2cm3/g.

[0029] In accordance with one embodiment of the disclosure, the composition of the metal-smelting by-product meets the condition(slag (S-0)), and the weight ratio of the iron ions in the iron-containing compound (such as ferric chloride) to the metal-smelting by-product is 1:10 to 1:5 (for example, 1:9, 1:8, 1:7 or 1:6). In addition, the composition of the metal-smelting by-product meets the condition (dust (D-0)), and the weight ratio of the iron ions in the iron-containing compound to the metal-smelting by-product is 1:20 to 1:10 (for example, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12 or 1:11).

[0030] In accordance with one embodiment of the disclosure, a method for preparing an absorbent is provided. The method includes the following steps. First, a metal-smelting by-product and an acidic solvent are mixed to form a first solution. The metal-smelting by-product includes iron, calcium, zinc, or a combination thereof In one embodiment, the first solution is weakly acidic, and its pH value is, for example, 5-6.

[0031] Next, an iron-containing solution is added to the first solution to adjust the molar ratio of calcium to iron or zinc to iron in the first solution. Since the main components and ratios of metal-smelting by-products generally obtained are diverse (the ratio of calcium to iron or zinc to iron is different), the disclosure adjusts the molar ratio of calcium to iron or zinc to iron in the first solution by adding the iron-containing solution to Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean fall within the applicable range of the disclosure. In one embodiment, the molar ratio of calcium to iron in the first solution is between about 0.1:1 and about 1:1. In one embodiment, the molar ratio of zinc to iron in the first solution is between about 0.1:1 and about 1:1. Next, an alkaline solvent is added to the first solution to perform a co-precipitation process to form a salt solution. In one embodiment, the salt solution is weakly alkaline, and its pH value is, for example, greater than or equal to 7.

[0032] Next, a filtration process is performed on the salt solution to obtain a solid filter.
Next, a calcination process is performed on the solid filter to prepare an absorbent. The absorbent includes calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof The calcium ferrite (CaFe204) has a characteristic peak value of 20=33.64 , 33.57 and 61.41 . The zinc ferrite (ZnFe204) has a characteristic peak value of 20=29.92 , 36.92 and 62.24 .

[0033] In one embodiment, the metal-smelting by-product may include slag or dust. In one embodiment, the iron in the iron-containing solution may include ferric chloride, ferric sulfate, ferric nitrate, ferric phosphate, ferric citrate, ferric oxalate, or ferric carbonate. In one embodiment, the acidic solvent may include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, oxalic acid, or carbonic acid. In one embodiment, the alkaline solvent may include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or ammonia. In one embodiment, the calcination process has an operation temperature that is lower than about 300 C.

[0034] The absorbent of the present disclosure can be applied to reduce the concentration of hydrogen sulfide (H2S) gas in the syngas to avoid the sulfur-containing substances in the syngas causing corrosion of the delivery pipeline/equipment and poisoning of the downstream catalyst bed. The syngas may include, for example, gas produced by gasification of coal, waste, or biomass.

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean

[0035] The present disclosure recombines iron oxide (Fe2O3) and zinc oxide (ZnO) in industrial by-products (i.e. metal-smelting by-products, such as slag or dust) by a co-precipitation method to form zinc ferrite (ZnFe204) with a spinel structure, and recombines iron oxide (Fe2O3) and calcium oxide (CaO) to form calcium ferrite (CaFe204) with a spinel structure. In addition to enhancing the thermal stability and mechanical properties of the absorbent, the recombined compound also has a higher specific surface area and pore volume than the raw material, which contributes to increase the contact area of the absorbent with hydrogen sulfide (H2S) gas, and increase the absorption rate of the absorbent for hydrogen sulfide (H2S) gas and the utilization rate of the absorbent. The present disclosure can be applied to the field of gas purification technology, enhance the application value of such industrial by-products, achieve the purpose of new energy development and resource reuse, and construct a complete circular economy system.

[0036] Examples/Comparative Examples

[0037] Example 1

[0038] Preparation of the absorbent (converted from slag)

[0039] First, 100g of slag (a metal-smelting by-product, provided or manufactured by Taiwan Steel Union Co., Ltd.) and 180g of 36% hydrochloric acid (an acidic solvent) were mixed and stirred. After filtration, a filtrate was obtained. The main components of the slag included 39.6 parts by weight of iron oxide (Fe2O3), 19.4 parts by weight of calcium oxide (CaO), and 19.3 parts by weight of silicon oxide (5i02) (based on 100 parts by weight of the slag). After that, 100g of 35% ferric chloride aqueous solution was added to the filtrate to adjust the molar ratio of calcium to iron in the filtrate to about 1:2.
Next, 200g of 35%
sodium hydroxide aqueous solution (an alkaline solvent) (a precipitating agent) was added to the filtrate to perform a co-precipitation process to form a salt solution.
After that, a filtration process was performed on the salt solution to obtain 75g of solid filtrate. Next, a Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean calcination process with a temperature of about 300 C was performed on the solid filter for about 8 hours, and the absorbent (S-1) of this embodiment was prepared. After that, the chemical composition and physicochemical properties (such as specific surface area and pore volume) of the absorbent were analyzed. The analysis results are shown in Table 1 below. The prepared absorbent was photographed by SEM (magnification was 5,000 times), as shown in FIG. 1, to observe the microstructure of the absorbent. In accordance with the X-ray diffraction spectrum of the absorber in this embodiment, its main component was calcium ferrite (CaFe204), and the characteristic peak value thereof was 20=33.64 , 33.57 and 61.41 . It can be seen that through the process described in Example 1, the slag has been recombined to form a spinel structure, and the mechanical properties of the absorbent have also been improved.

[0040] Example 2

[0041] Preparation of the absorbent (converted from dust)

[0042] First, 100g of dust (a metal-smelting by-product) and 150g of 35%
hydrochloric acid (an acidic solvent) were mixed and stirred. After filtration, a filtrate was obtained. The main components of the dust included 53.0 parts by weight of iron oxide (Fe2O3) and 32.1 parts by weight of zinc oxide (ZnO) (based on 100 parts by weight of the dust). After that, 65g of 35% ferric chloride aqueous solution was added to the filtrate to adjust the molar ratio of zinc to iron in the filtrate to about 1:2. Next, 75g of 35% sodium hydroxide aqueous solution (an alkaline solvent) (a precipitating agent) was added to the filtrate to perform a co-precipitation process to form a salt solution. After that, a filtration process was performed on the salt solution to obtain 95g of solid filtrate. Next, a calcination process with a temperature of about 300 C was performed on the solid filter for about 8 hours, and the absorbent (D-1) of this embodiment was prepared. After that, the chemical composition and physicochemical properties (such as specific surface area and pore volume) of the Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11david/Dean absorbent were analyzed. The analysis results are shown in Table 1 below. The prepared absorbent was photographed by SEM (magnification was 5,000 times), as shown in FIG. 2, to observe the microstructure of the absorbent. In accordance with the X-ray diffraction spectrum of the absorber in this embodiment, its main component was zinc ferrite (ZnFe204), and the characteristic peak value thereof was 20=29.92 , 36.92 and 62.24 . It can be seen that through the process described in Example 2, the dust has been recombined to form a spinel structure, and the mechanical properties of the absorbent have also been improved.

[0043] Comparative Example 1

[0044] Analysis of the chemical composition and physicochemical properties of the slag absorbent

[0045] The chemical composition and physicochemical properties (such as specific surface area and pore volume) of the provided slag absorbent (S-0) were analyzed. The analysis results are shown in Table 1 below. The slag absorbent was photographed by SEM
(magnification was 5,000 times), as shown in FIG. 3, to observe the microstructure of the slag absorbent.

[0046] Comparative Example 2

[0047] Analysis of the chemical composition and physicochemical properties of the dust absorbent

[0048] The chemical composition and physicochemical properties (such as specific surface area and pore volume) of the provided dust absorbent (D-0) were analyzed. The analysis results are shown in Table 1 below. The dust absorbent was photographed by SEM
(magnification was 5,000 times), as shown in FIG. 4, to observe the microstructure of the dust absorbent.
Table 1 Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean Examples/ Comparative Example 1 Comparative Example 2 Comparative Example 1 (S-1) Example 2 (D-1) Examples (S-0) (D-0) (Absorbent code) Composition analysis (parts by weight) MgO 0.7 0.5 1.0 0.6 A1203 3.2 0.8 0.4 0 5i02 19.3 0 3.5 0 SO3 2.3 0.5 2.2 0.4 CaO 19.4 23.8 3.6 1.0 MnO 3.8 2.1 2.2 1.6 Fe2O3 39.6 70.2 53.0 64.7 ZnO 6.7 2.1 32.1 31.7 Analysis of physicochemical properties Specific surface 1.7 14.65 2.7 34.19 area (m2/g) Pore volume 0.01 0.09 0.016 0.19 (cm3/g)

[0049] In Comparative Example 1, the main components of the slag absorbent (No.: S-O) were 39.6 parts by weight of iron oxide (Fe2O3), 19.4 parts by weight of calcium oxide (CaO), and 19.3 parts by weight of silicon oxide (5i02). In Comparative Example 2, the main components of the dust absorbent (No.: D-0) were 53.0 parts by weight of iron oxide (Fe2O3) and 32.1 parts by weight of zinc oxide (Zn0). According to the analysis results of the physicochemical properties in Table 1, whether it is the slag absorbent (S-0) of Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean Comparative Example 1 or the dust absorbent (D-0) of Comparative Example 2, it is a material with low specific surface area and non-porous. In Example 1, the molar ratio of calcium to iron in the absorbent (S-1) converted from slag was about 0.48, which was close to 0.5. In Example 2, the molar ratio of zinc to iron in the absorbent (D-1) converted from dust was about 0.475, which was also close to 0.5, so it can be seen that the products prepared in Examples 1 and 2 were in line with the target products of calcium ferrite (CaFe204) and zinc ferrite (ZnFe204). Furthermore, according to the analysis results of the physicochemical properties of Table 1, the specific surface area and pore volume of the calcium ferrite (CaFe204) absorbent (S-1) of Example 1 and the zinc ferrite (ZnFe204) absorbent (D-1) of Example 2 are significantly higher than their raw materials (slag or dust), which indicates that the surface properties of the absorbent prepared by the methods of Examples 1 and 2 can thus be effectively improved, beneficial to improvement of absorption efficiency.

[0050] In addition, according to the SEM microstructure photos (magnification of 5,000 times) of FIGS. 1 to 4 (the absorbents S-1, D-1, S-0 and D-0), it can be seen from the appearance that the surface of the slag absorbent (S-0) (as shown in FIG. 3) and the dust absorbent (D-0) (as shown in FIG. 4) are smooth and free of pores. However, the surface of the absorbent (S-1) converted from slag (as shown in FIG. 1) of Example 1 is composed of a large number of spherical particles with a particle diameter of less than 100nm, and there are pores. In Example 2, the absorbent (D-1) converted from dust (as shown in FIG. 2) is composed of a foil-like substance, and the appearance is very different from the dust raw material. According to the comparison of the SEM microstructure photos in FIGS. 1 to 4, the analysis results shown in Table 1 that the specific surface area and pore volume of the absorbent of the present disclosure are significantly improved compared to the surface properties of its raw materials can be verified.

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean

[0051] Example 3

[0052] Test of absorption effect of the absorbent on hydrogen sulfide (H2S) gas

[0053] The calcium ferrite (CaFe204) absorbent (S-1) prepared in Example 1, the zinc ferrite (ZnFe204) absorbent (D-1) prepared in Example 2, the slag absorbent (S-0) provided in Comparative Example 1 and the dust absorbent (D-0) provided in Comparative Example 2 were selected for the test of the absorption effect of the absorbents on hydrogen sulfide (H25) gas. At 400 C, the inlet concentration of hydrogen sulfide (H25) gas was set at 1,000 ppm, and the process was continuously performed for 30 hours. During the period, the reacted gas was collected according to the set time (sampling every 30 minutes, and 6 minutes per sampling), and the outlet concentration of hydrogen sulfide (H25) gas was detected using a hydrogen sulfide (H25) gas detection tube (Gastec Piston Pump). The relationship between the outlet concentration of hydrogen sulfide (H25) gas over time is shown in FIG. 5.

[0054] It can be seen from FIG. 5 that after the calcium ferrite (CaFe204) absorbent (S-1) prepared in Example 1 and the zinc ferrite (ZnFe204) absorbent (D-1) prepared in Example 2 were operated for 7 hours, the measured outlet concentration of hydrogen sulfide (H25) gas approached zero (less than 2ppm). At this time, the absorption effect of the absorbent (S-1) and the absorbent (D-1) on hydrogen sulfide (H25) gas is obviously the same as that of the slag absorbent (S-0) of Comparative Example 1 and the dust absorbent (D-0) of Comparative Example 2 on hydrogen sulfide (H25) gas. However, when the absorbent (S-1) and the absorbent (D-1) were continuously operated for 21 hours, the measured outlet concentration of hydrogen sulfide (H25) gas was merely 200 ppm and 120 ppm respectively, which is much lower than the results (about 1,000 ppm) of the slag absorbent (S-0) and the dust absorbent (D-0) after they were continuously operated for 20 hours.

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11clavid/Dean

[0055] It can be seen from the test results in FIG. 5 that the absorption capacity (or removal rate) for hydrogen sulfide (H2S) gas of the absorbent (S-1) and the absorbent (D-1) of the present disclosure is far superior to that of the slag absorbent (S-0) and the dust absorbent (D-0). After the reaction, the absorbent (S-1) and the absorbent (D-1) were collected and the sulfur content thereof was analyzed, it can be known that the absorption capacity (or removal rate) for hydrogen sulfide (H25) gas of the absorbent (S-1) and the absorbent (D-1) was 0.25g hydrogen sulfide/g absorbent and 0.31g hydrogen sulfide/g absorbent respectively, which is far superior to that of the slag absorbent (S-0) and the dust absorbent (D-0) for hydrogen sulfide (H25) gas (i.e. 0.14g hydrogen sulfide/g absorbent and 0.18g hydrogen sulfide/g absorbent, respectively). This test result shows that the absorbents prepared by the methods of Example 1 and Example 2 have a specific surface area superior to that of its raw material, so the effective contact area between the active material in the absorbent and hydrogen sulfide (H25) gas is increased. In addition, the reduction in the size of the particles in the absorbent or the formation of a foil structure are conducive to improving the efficiency of the absorbent, and its ability to absorb hydrogen sulfide (H25) gas is significantly improved.

[0056] Example 4

[0057] Analysis of thermal stability of the absorbent

[0058] The calcium ferrite (CaFe204) absorbent (S-1) prepared in Example 1 was selected for thermogravimetric analysis to evaluate its thermal stability.
With a thermogravimetric analyzer (TGA), the test temperature was set to around 1,000 C, and the weight loss of the absorbent (S-1) at that temperature was analyzed. The analysis results are shown in FIG. 6. It can be seen from the analysis results in FIG. 6 that the thermogravimetric loss of the calcium ferrite (CaFe204) absorbent (S-1) can be reduced to below 4 wt%, which means that the absorbent (S-1) has excellent thermal stability.

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT ' s Docket No.: 9044E-A27040CA/fina11clavid/Dean

[0059] Example 5

[0060] Analysis of thermal stability of the absorbent

[0061] The zinc ferrite (ZnFe204) absorbent (D-1) prepared in Example 2 was selected for thermogravimetric analysis to evaluate its thermal stability. With a thermogravimetric analyzer (TGA), the test temperature was set to about 1,000 C, and the weight loss of the absorbent (D-1) at that temperature was analyzed. The analysis results are shown in FIG. 7.
It can be seen from the analysis results in FIG. 7 that the thermogravimetric loss of the zinc ferrite (ZnFe204) absorbent (D-1) can be reduced to below 4 wt%, which means that the absorbent (D-1) has excellent thermal stability.

[0062] Comparative Example 3

[0063] Analysis of thermal stability of the absorbent

[0064] The slag absorbent (S-0) provided in Comparative Example 1 was selected for thermogravimetric analysis to evaluate its thermal stability. With a thermogravimetric analyzer (TGA), the test temperature was set to around 1,000 C, and the weight loss of the absorbent (S-0) at that temperature was analyzed. The analysis results are shown in FIG. 8.
It can be seen from the analysis results in FIG. 8 that the thermogravimetric loss of the slag absorbent (S-0) reaches 16 wt%, which means the thermal stability of the absorbent (S-0) is poor.

[0065] Comparative Example 4

[0066] Analysis of thermal stability of the absorbent

[0067] The dust absorbent (D-0) provided in Comparative Example 2 was selected for thermogravimetric analysis to evaluate its thermal stability. With a thermogravimetric analyzer (TGA), the test temperature was set to around 1,000 C, and the weight loss of the absorbent (D-0) at that temperature was analyzed. The analysis results are shown in FIG. 9.
It can be seen from the analysis results in FIG. 9 that the thermogravimetric loss of the dust Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina11david/Dean absorbent (D-0) reaches 20wt%, which means the thermal stability of the absorbent (D-0) is poor.

[0068] While the disclosure has been described by way of example and in terms of embodiments, it should be understood that the disclosure is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Date Recue/Date Received 2020-09-28

Claims

Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina1/david/Dean What is claimed is:
1 1. An absorbent, comprising:

calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof, wherein a molar ratio of calcium to iron in the absorbent is between 4 0.1:1 and 1:1, and a molar ratio of zinc to iron in the absorbent is between 0.1:1 and 1:1.
1 2. The absorbent as claimed in claim 1, wherein the calcium ferrite 2 (CaFe204) and the zinc ferrite (ZnFe204) comprise a spinel structure.
1 3. The absorbent as claimed in claim 1, further comprising magnesium 2 oxide (Mg0), aluminum oxide (A1203), silicon oxide (Si02), sulfur oxide (S03), calcium oxide (Ca0), manganese oxide (Mn0), iron oxide (Fe203), zinc oxide (Zn0), 4 or a combination thereof 1 4. The absorbent as claimed in claim 3, wherein the magnesium oxide 2 (Mg0) is 0-5 parts by weight, the aluminum oxide (A1203) is 0-4 parts by weight, the silicon oxide (Si02) is 0-20 parts by weight, the sulfur oxide (S03) is 0-3 parts by weight, the calcium oxide (Ca0) is 1-25 parts by weight, the manganese oxide (MnO) 5 is 1-5 parts by weight, the iron oxide (Fe203) is 25-75 parts by weight, and the zinc 6 oxide (ZnO) is 1-40 parts by weight, based on 100 parts by weight of the absorbent.
1 5. The absorbent as claimed in claim 1, wherein the calcium ferrite 2 (CaFe204) has a characteristic peak value of 20=33.64 , 33.57 and 61.41 .
1 6. The absorbent as claimed in claim 1, wherein the zinc ferrite 2 (ZnFe204) has a characteristic peak value of 20=29.92 , 36.92 and 62.24 .
1 7. The absorbent as claimed in claim 4, wherein the absorbent has a 2 specific surface area of 1-80m2/g.

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina1/david/Dean 1 8. The absorbent as claimed in claim 4, wherein the absorbent has a pore 2 volume of O. 01 -0.5 cm3/g.
1 9. A method for preparing an absorbent, comprising:
2 mixing a metal-smelting by-product with an acidic solvent to form a first 3 solution, wherein the metal-smelting by-product comprises iron, 4 calcium, zinc, or a combination thereof;
adding an iron-containing solution to the first solution to adjust the molar ratio 6 of calcium to iron or zinc to iron in the first solution, wherein the 7 molar ratio of calcium to iron in the first solution is between 0.1:1 and 8 1:1, and the molar ratio of zinc to iron in the first solution is between 9 0.1:1 and 1:1;
adding an alkaline solvent to the first solution to perform a co-precipitation 11 process to form a salt solution;
12 performing a filtration process on the salt solution to obtain a solid filter; and performing a calcination process on the solid filter to prepare an absorbent, 14 wherein the absorbent comprises calcium ferrite (CaFe204), zinc ferrite (ZnFe204), or a combination thereof 1 10. The method for preparing an absorbent as claimed in claim 9, wherein 2 the metal-smelting by-product comprises slag or dust.
1 11. The method for preparing an absorbent as claimed in claim 9, wherein 2 the acidic solvent comprises hydrochloric acid, sulfuric acid, or phosphoric acid.
1 12. The method for preparing an absorbent as claimed in claim 9, wherein 2 the calcium ferrite (CaFe204) has a characteristic peak value of 20=33.64 , 33.57 and 3 61.41 .
1 13. The method for preparing an absorbent as claimed in claim 9, wherein 2 the zinc ferrite (ZnFe204) has a characteristic peak value of 20=29.92 , 36.92 and 3 62.24 .

Date Recue/Date Received 2020-09-28 Client's Docket No.: P55080032CA
TT's Docket No.: 9044E-A27040CA/fina1/david/Dean 1 14. The method for preparing an absorbent as claimed in claim 9, wherein 2 the alkaline solvent comprises sodium hydroxide, sodium carbonate, or ammonia.
1 15. The method for preparing an absorbent as claimed in claim 9, wherein 2 the calcination process has an operation temperature that is lower than 300 C.

Date Recue/Date Received 2020-09-28