Synthesis of layered material from eggshell waste

Abstract

The invention relates to the synthesis of ternary MgCaA1 layered double hydroxides (LDH) from eggshells, functionalization of the synthesized LDHs with different polymers, and the use of these obtained new composites in CO2 capture applications.

Description

[0001] SYNTHESIS OF LAYERED MATERIAL FROM EGGSHELL WASTE

[0002] Technical Field of the Invention

[0003] The present invention relates to the synthesis of layered double hydroxide (LDH) with a ternary MgCaAl layer from eggshell, the functionalization of these said ternary LDHs with different polymers, and the use of the new composites obtained in CO2 capture applications.

[0004] State of the Art (Prior Art) of the Invention

[0005] There are studies in the literature on the solution of the eggshell waste problem and the number thereof is increasing day by day. There are many studies in which eggshells are often used as a source of calcium in the production of hydroxyapatite, especially thanks to the high amount of calcium carbonate (CaCCh) it contains (93-97%).

[0006] On the other hand, the production of layered double hydroxide (LDH) from eggshells has been discussed in recent years, and there are very few studies on this subject.

[0007] Li et al. produced the Ca-Al and Ca-Fe LDH structures from eggshells (Li et al., 2012). In another study, the same group tried Ca-Al LDH, which they synthesized from eggshells, to remove uranium from aqueous solutions (Li et al., 2012).

[0008] Foruzin et al., on the other hand, synthesized NiCaFe-LDH from eggshell and used it in electrochemical water oxidation (Foruzin et al., 2020).

[0009] These studies in the literature have mostly focused on the production of LDH from eggshells and its use in different areas.

[0010] The study on the production of MgCaAl-LDHstructures from eggshell wastes and their use in CO2 adsorption has not been found in the researches. Brief Description and Objects of the Invention

[0011] With the present invention, it is possible to synthesize ternary MgCaAl-LDH from eggshell for the first time in the literature, to obtain new composites by functionalizing the synthesized ternary LDHs with different polymers, and to use the new composites obtained for the first time in CO2 capture applications.

[0012] If the present invention is used in sectors such as iron-steel or cement where carbon storage is mandatory, it is aimed to reduce the rate of carbon dioxide released into the atmosphere.

[0013] The advantages of the present invention are listed as follows.

[0014] With the use of eggshells, which are classified as hazardous waste, as raw material for the first time in the production of ternary MgCaAl LDH, a new usage area is created for waste eggshells, thus both some of the raw materials have been provided free of charge and by contributing to waste management, the negative effects on the environment and human health have been reduced.

[0015] Composite materials can be produced by covalently bonding the obtained ternary MgCaAl LDH surfaces with different polymers, and for the first time in the literature, these composites can be used as solid adsorbents to reduce CO2 emissions.

[0016] Since the amine groups in the structure of the composites to be synthesized show affinity for CO2 molecules and Ca-based LDHs exhibit high reactivity properties with CO2, a new generation material with high CO2 capture performance is produced. Thus, a significant contribution is made to CO2 capture technologies by developing an alternative and more cost- effective and environmentally friendly product to Ca-based LDHs used in existing carbon capture technologies.

[0017] With the present invention, it is envisaged that the evaluation of eggshell waste and the development of new eggshell-based composite materials in the CO2 capture area will contribute to both the literature and Turkey's efforts to reduce CO2 emissions within the scope of the Paris Climate Agreement and to the goals of reducing emissions and minimizing the amount of waste to be realized within the scope of the Green Deal Action Plan. Detailed Description of the Invention

[0018] Ternary layered double hydroxides (LDH) are obtained by adding additional different divalent or trivalent metal ions to binary layered double hydroxides. Binary and ternary LDHs have similar microstructure, while ternary LDHs have superior physicochemical properties due to their complex element components.

[0019] While the current interest in CO2 capture studies is mostly focused on binary LDHs, ternary LDHs can show much higher CO2 adsorption capacities and have been studied less so far.

[0020] Within the scope of the present invention, ternary MgCaAl LDH was synthesized from eggshell, and then these said synthesized ternary MgCaAl LDHs were functionalized separately, preferably with polyethyleneimine (PEI) or polyallylamine (PAA), and composites were obtained to be used as CO2 adsorbents.

[0021] Mg-based binary LDHs, which are frequently studied and well known in the literature, generally exhibit low CO2 capture capacities (Chang et al., 2011). The improved surface basicity of Ca-based LDHs, which have a molecular structure similar to Mg-based LDHs, compared to Mg-based LDHs is due to the higher electronegativity of Ca(II) compared to Mg(II). In this case, since CO2 is an acidic compound, the basic regions in Ca-based LDH facilitate CO2 adsorption and thus lead to an increase in CO2 adsorption capacity. For this reason, in the present invention, a ternary Ca-based layered double hydroxide (LDH) structure is synthesized by using eggshells.

[0022] LDHs are generally expressed in divalent and trivalent metal cations and anionic groups. The general formula of the LDH structure synthesized within the present invention is [MI-X2+Mx3+(OH)2]x+-[Ax / n]n“-mH2O. In the formula, M2+and M3+represent Ca2+, Mg2+and Al3+, respectively, and A"' represents an anion with high activity, such as Cl“, C1O4“, NO3 , CO32, and SO42-.

[0023] The synthesis of ternary MgCaAl-layered double hydroxides (LDH) from eggshells of the present invention, and the production of composite materials by functionalizing these obtained ternary MgCaAl-layered LDHs with different polymers are detailed with the method steps below.

[0024] 1. Synthesis of Ternary MgCaAl LDH from Eggshell

[0025] The synthesis method of ternary MgCaAl layered double hydroxide (MgCaAl-LDH) from eggshell comprises calcination of eggshells, dissolving calcined eggshells, adding magnesium nitrate hexahydrate and aluminum nitrate nonahydrate metal salts to the homogeneous solution formed and then stirring thereof, keeping the precipitate at room temperature for a predetermined period of time, then filtering and washing with water, drying the resulting powder and obtaining ternary MgCaAl layered double hydroxides. The synthesis of ternary MgCaAl LDH from eggshell was carried out with some modifications considering the study of Foruzin et al. (2020). (Foruzin, L. J., Rezvani, Z., Habibi, B., 2020. “New ternary-component layered double hydroxide as a low-cost and efficient electrocatalyst for water oxidation: NiCaFe-LDH from eggshell bio-waste”, Applied Clay Science, 188, 105511. )

[0026] Here, for synthesis, the eggshells calcined at 950°C were first kept in an ultrasonic bath under an inert nitrogen atmosphere in a 6 M nitric acid solution for 1 hour and then completely dissolved at 70°C.

[0027] Magnesium nitrate hexahydrate and aluminum nitrate nonahydrate metal salts were added to the obtained homogeneous solution with molar ratios of Ca+2 / Al+3: 0.15 and Mg+2 / Al+3: 1.3 and stirred for another 1 hour.

[0028] At the end of the period, the pH of the reaction solution obtained was adjusted with NaOH according to the precipitate formation. The pH value at which dense precipitation was observed was recorded as 12.5. Here, precipitation of the reaction solution by pH adjustment is required to obtain LDH. When NaOH was added to the acidic reaction solution, precipitate formation started to occur slowly after pH 10.5 and an intense precipitate formation was observed at pH 12.5. At the point where a dense precipitate was observed, pH adjustment with NaOH was stopped. In general, the optimum pH range in the production of MgAl LDH is between 9-13. In the present invention, the pH was 12.5. Then, the formed precipitate was autoclaved and kept at room temperature for 24 hours, and at the end of the period, it was filtered and washed with warm water. This step is a necessary step for obtaining the final product, a ternary MgCaAl layered double hydroxide. Warm water here is water with a temperature of 35 °C.

[0029] The resulting white powder was dried at 40°C for 12 hours in an incubator.

[0030] 2. Obtaining Composites By Binding Different Polymers to Ternary MgCaAl LDHs

[0031] In this step, composite materials are produced by covalently bonding the surfaces of the ternary MgCaAl LDHs obtained as mentioned above with different polymers. Here, the preferred polymers are polyethyleneimine or polyallylamine.

[0032] Epoxy Silane Grafting of MgCaAl LDHs: Grafting of epoxy silane on the ternary LDH surface was carried out according to the method performed by Kongparakul et al. (Kongparakul et al., 2017). Firstly, LDH was dispersed in 25 ml of dry toluene at a weight ratio with (3- glycidoxypropyl)trimethoxysilane of LDH / (3-glycidoxypropyl)trimethoxy silane: 0.25 and stirred under reflux condenser for 24 hours. At the end of the period, the samples were washed with toluene, centrifuged and epoxy silane-grafted LDH samples were obtained.

[0033] Functionalization of MgCaAl LDH Surface with Polyethyleneimine (PEI): Firstly, PEI (Mn~ 600 by GPC) was dissolved in 20 mL of dioxane and then epoxy silane grafted LDHs were added thereinto at a weight ratio of PEI / Epoxy grafted sample: 2. The resulting mixture was kept in the inert atmosphere at a temperature of 90°C and under reflux condenser for 24 hours. At the end of the period, the samples were centrifuged by washing several times with chloroform in order to remove the unreacted PEIs from the structure, thus obtaining PEI- functionalized composites.

[0034] Functionalization of ternary MgCaAl LDH with polyallylamine (PAA) was performed by two different methods. 1. METHOD

[0035] Methacryl Silane Grafting of MgCaAl LDHs: Grafting of methacryl silane on the ternary LDH surface was carried out according to the method performed by Kongparakul et al. (Kongparakul et al., 2017). Firstly, LDH was dispersed in 25 ml of dry toluene at a weight ratio with methacryl silane of LDH / methacryl silane: 0.25 and stirred under reflux condenser for 24 hours. At the end of the period, the samples were washed with toluene, centrifuged and methacryl silane- grafted LDH samples were obtained.

[0036] Functionalization of MgCaAl LDH Surface with Polyallylamine (PAA): The LDH samples grafted with methacryl silane were weighed at the weight ratio of LDH grafted with methacryl silane / allylamine: 0.13 and stirred under nitrogen atmosphere, and then 0.1 g / ml aqueous solution of ammonium persulfate was added. The mixture was stirred under a nitrogen atmosphere at 40°C for 24 hours. At the end of the period, the pH of the mixture was adjusted to 2-3 with HC1. It was centrifuged with 1% HC1 solution 2 times and then washed with water, filtered and dried at 100°C.

[0037] 2. METHOD

[0038] Epoxy Silane Grafting of MgCaAl LDHs: Grafting of epoxy silane on the ternary LDH surface was carried out according to the method performed by Kongparakul et al. (Kongparakul et al., 2017). Firstly, LDH was dispersed in 25 ml of dry toluene at a weight ratio with (3- glycidoxypropyl)trimethoxysilane of LDH / (3-glycidoxypropyl)trimethoxy silane: 0.25 and stirred under reflux condenser for 24 hours. At the end of the period, the samples were washed with toluene, centrifuged and epoxy silane-grafted LDH samples were obtained.

[0039] Functionalization of MgCaAl LDH Surface with Polyallylamine (PAA): PAA covalent binding on epoxy silane-grafted LDH was carried out according to the method performed by larikov et al. (larikov, et al., 2014). Firstly, a 10% polyallylamine hydrochloride (PAH) aqueous solution was prepared and the pH of the solution was adjusted with 1 M NaOH to 11. Epoxy-grafted LDH sample was added to this solution and kept at 75°C for 36 hours. At the end of the period, the sample was filtered and washed twenty times with distilled water to neutral pH. Afterwards, the sample was kept in water in an ultrasonic bath for five minutes to remove PAA that was not covalently bonded to the surface from the structure and was filtered again and left to dry under vacuum.

[0040] Since it is important to bind amines to the adsorbent by covalent modification methods in order to obtain amine-modified materials with high stability under steam conditions, in the present invention, PEI and PAA polymers are bonded to the LDH surface by covalent bonding.

[0041] In addition to these, PEI and PAA polymers were preferred due to the high number of amines. Thus, it is predicted that the CO2 capture capacities of samples modified with PEI and PAA polymers will be higher than the capacity of samples previously modified with polymers or aminosilanes in the literature.

[0042] With the present invention, it is expected that the CO2 capture capacity of ternary MgCaAl layered double hydroxides obtained from eggshells and composites obtained by bonding with polyethyleneimine or polyallylamine at low pressure (1 bar) will be in the range of 0.75-1.25 mmol.g1. The CO2 capture capacity at high pressure (50 bar) is expected to be more than 2 mmol.g1.

[0043] Within the scope of the present invention, a new generation composite material with high CO2 capture performance is synthesized by combining the superior physicochemical properties of the ternary LDH structure, the affinity of amine groups in polymer-functionalized LDH with CO2 molecules, and the high reactivity properties of Ca-based LDHs with CO2. In addition, the target value of more than 2 mmol.g-1is achieved via the source of Ca+2metal obtained from waste eggshells, not by adding an extra-costly metal source.

Claims

CLAIMS1. A synthesis method of ternary MgCaAl layered double hydroxide (MgCaAl-LDH), characterized by the steps of: i. calcination of eggshells, ii. dissolving calcined eggshells, iii. adding magnesium nitrate hexahydrate and aluminum nitrate nonahydrate metal salts to the homogeneous solution formed and then stirring thereof, iv. precipitation of the resulting acidic reaction solution with pH adjustment, v. after keeping the formed precipitate at room temperature for a predetermined period of time, filtering and washing with water, vi. drying the obtained powder to obtain ternary MgCaAl layered double hydroxide.

2. The synthesis method according to claim 1, characterized in that in step i., the calcination of eggshells is carried out at 950°C.

3. The synthesis method according to claim 1, characterized in that in step ii., the eggshells are completely dissolved at 70°C by keeping them in an ultrasonic bath for 1 hour under an inert nitrogen atmosphere in a 6 M nitric acid solution.

4. The synthesis method according to claim 1, characterized in that magnesium nitrate hexahydrate and aluminum nitrate nonahydrate metal salts were added to the homogeneous solution obtained in step iii. with molar ratios of Ca+2 / Al+3: 0.15 and Mg+2 / Al+3: 1.3 and stirred.

5. The synthesis method according to claim 1 , characterized in that in step iv. , the precipitation process is carried out by adding NaOH to the acidic reaction solution.

6. The synthesis method according to claim 1, characterized in that in step v., the precipitate is kept at room temperature for 24 hours, then filtered and washed with water.

7. The synthesis method according to claim 1, characterized in that in step vi., the white powder is dried at 40°C for 12 hours in the incubator to obtain a ternary MgCaAl layered double hydroxide.

8. A ternary MgCaAl-layered double hydroxide (MgCaAl-LDH) obtained by the synthesis method according to any of the preceding claims.

9. A composite containing MgCaAl-LDH according to claim 8.

10. The composite according to claim 9, characterized in that it is modified with polyethyleneimine or polyallylamine.

11. The CO2 adsorbent made of the composite according to claim 9 or 10.

12. Use of the composite according to claim 9 or 10 as a CO2 adsorbent.