RU2745486C1 - Method for producing high-temperature co2 sorbents - Google Patents

Abstract

FIELD: composite materials.SUBSTANCE: invention relates to the production of composite materials based on calcium oxide and zirconium dioxide and can be used to obtain high-temperature CO2sorbents for cleaning the exhaust gases of industrial enterprises from carbon dioxide. Disclosed is a method of obtaining a powder composite material using a zirconium-containing mineral raw material - baddeleyite concentrate including mixing calcium carbonate with baddeleyite concentrate in the ratio, wt%: baddeleyite concentrate - 11-27, calcium carbonate - 73-89, followed by grinding the mixture to a nanosized state in a bead mill in an aqueous medium using stabilized zirconia beads and heat treatment. As a result of heat treatment in a nitrogen atmosphere at a temperature of 800 °C, a high-temperature regenerating chemisorbent is obtained consisting of calcium oxide and calcium zirconate.EFFECT: preservation of the sorption capacity of the material during high-cycle use.3 cl, 2 dwg

Description

The invention relates to the field of chemical industry, in particular to the production of composite materials based on calcium oxide and zirconium dioxide, and can be used to obtain high-temperature sorbents CO ₂ .

Increasing global energy consumption and associated carbon dioxide emissions in recent decades are driving the development of new and efficient ways to capture and utilize carbon dioxide. The most commonly used methods for the release of CO ₂ liquid absorbents (mono-, di- and triethanolamines), solid adsorbents in the form of oxides (CaO, ZnO, etc.) or mixed oxides of various metals, as well as using selective membranes.

The flue gases generated during the combustion of various fuels usually have a temperature of from 500 to 700 ° C, and therefore the wet separation method is not applicable here, since it is very energy intensive and requires gas cooling. In this regard, the use of new solid high-temperature adsorbents is very important.

Among the most promising carbon dioxide absorbers are zirconates (Li ₂ ZrO ₃ ) and lithium silicates (Li ₄ SiO ₄ ) [1. A. Iwana, H. Stephenson, C. Ketchie; A. Lapkin. High temperature sequestration of CO ₂ using lithium zirconates // Chem. Eng. J. 2009. Vol. 146. Pp. 249-258; 2. SY Shan, MQ Jia, LH Jiang, QC Li, YM Wang, JH Peng. Novel Li ₄ SiO ₄ -based sorbents from diatomite for high temperature CO ₂ capture // Ceram. Int. 2013. Vol. 39. Pp. 5437-5441].

Chemisorption of CO ₂ proceeds according to the following chemical reactions:

Li ₂ ZrO ₃ + CO ₂ = Li ₂ CO ₃ + ZrO ₂

Li ₄ SiO ₄ + CO ₂ = Li ₂ CO ₃ + Li ₂ SiO ₃

H.K. Rusten, H.A. Jakobsen, M.

A. Holmen, D. Chen. Sorption enhanced hydrogen production by steam methane reforming using Li₂ZrO₃ as sorbent: sorption kinetics and reactor simulation // Catal. Today. 2005. Vol. 106. Pp.41-46] предложен способ синтеза Li₂ZrO₃ путем сплавления солей, в результате которого получают высокопористый сорбент. Однако применение литиевых соединений увеличивают затраты на процесс получения сорбента и для удовлетворения потребности промышленности этот способ неприемлем.Currently, lithium zirconates and silicates are considered one of the best sorbents for extracting CO ₂ from flue gases, but this requires a high adsorption temperature (> 500 ° C) and an even higher temperature for CO ₂ desorption. Literature data on the synthesis of zirconates, as well as calcium-doped absorbers, are widely presented. Their synthesis can be carried out by the following methods: fusion of metal salts, sol-gel synthesis, or coprecipitation of precursors in the form of metal salts from their solutions. In the work [E.

HK Rusten, HA Jakobsen, M.

A. Holmen, D. Chen. Sorption enhanced hydrogen production by steam methane reforming using Li ₂ ZrO ₃ as sorbent: sorption kinetics and reactor simulation // Catal. Today. 2005. Vol. 106. Pp.41-46] proposed a method for the synthesis of Li ₂ ZrO ₃ by fusion of salts, as a result of which a highly porous sorbent is obtained. However, the use of lithium compounds increases the cost of the sorbent production process and this method is unacceptable to meet the needs of the industry.

Known patent [US 6271172, B01J 20/04, 07.08.2001], disclosing a method of preparing a high-temperature regenerable absorber based on lithium zirconate. The patent shows that the low rate of CO ₂ absorption by lithium zirconate increases by several tens of times in the presence of alkali metal carbonates. Moreover, a prerequisite for the promoting effect of carbonates is that they must be in a molten state. This invention solves the problem of creating a high-temperature regenerable CO ₂ absorber suitable for removing carbon dioxide in the temperature range of 400-900 ° C, not subject to sintering, having a high dynamic capacity and CO ₂ absorption rate.

The disadvantage of this type of materials is their high tendency to sintering, due to the fact that at temperatures above 710 ° C, lithium silicate is in a molten state. In addition, the cost of lithium zirconate is quite high, which prevents its widespread use.

A known method of producing a refractory material from baddeleyite concentrate with a magnesium-containing stabilizing additive. The method includes mixing the initial components, subsequent heat treatment and further grinding [see. h. EP 0104025 A2, C04B 35/484, 28.03.1984].

The main disadvantage of the known technical solution is the complexity of the technological process associated with the preliminary production of the original magnesium-containing component, purified from impurities.

A known method of producing a composite powder material using zirconium-containing mineral raw materials (baddeleyite concentrate) according to RF patent No. 2167128, IPC S04B 35/482, 05/10/2001. The production method includes mixing baddeleyite concentrate with a magnesium-containing additive, grinding the mixture and its subsequent heat treatment. As a magnesium-containing additive, brucite is used, while maintaining the following ratio of components in the mixture, wt. %:

baddeleyite concentrate 50-95 brucite 50-5.

The disadvantage of such a composite material is its unsuitability as a high-temperature sorbent of carbon dioxide due to its low CO ₂ capacity.

The closest analogue of the claimed invention in terms of its essential features is a method for producing a powder composite material for use as a carbon dioxide sorbent, set forth in US 2010/0196259, class. B01J 20/02, publ. 08/05/2010, clause 8 of the formula. The known method involves mixing calcium carbonate with a hardening additive, for example, zirconium dioxide, in an amount of 25-85 wt. %. The mixture is calcined (activated) at a temperature of 600 to 1050 ° C to obtain calcium oxide and calcium zirconate.

The disadvantages of this method are:

- insufficient sorption capacity for CO _{2 of the} resulting composite material due to the lower sorption capacity of zirconium dioxide in comparison with calcium oxide;

- high cost of raw materials for the manufacture of sorbent

- higher energy costs when processing more zirconium-containing material.

The object of the present invention is to provide a method that eliminates these disadvantages of the prototype.

The task is achieved by the fact that according to the method of obtaining high-temperature sorbents CO ₂ , including mixing calcium carbonate with a strengthening additive, for example, zirconium dioxide, followed by grinding the mixture and its heat treatment, according to the invention, zirconium-containing mineral raw material is used as a strengthening additive - baddeleyite concentrate, joint grinding of powders to a nanoscale state is carried out in a bead mill in an aqueous medium for at least 5 hours using stabilized zirconia beads with a diameter of 1.5 ± 0.1 mm, while maintaining the following ratio of components in the mixture, wt. %:

calcium carbonate 73 - 89, baddeleyite concentrate 11 - 27,

the resulting mixture is activated by heating to 800 ° C and holding at this temperature for 20 minutes in a nitrogen atmosphere with a purity of 99.95% to obtain calcium oxide and calcium zirconate in the composition of a powder composite material.

The ratio of the mass of the composition of powders to the mass of distilled water can be 1: 3, and to the mass of grinding bodies - 1: 10.

After grinding, the mixture of powders of baddeleyite concentrate and CaCO ₃ can be dried at a temperature of 80-90 ° C for a day in a dry heat oven at atmospheric pressure.

The competitive advantages of the method are, firstly, the availability of raw materials - natural calcium carbonate (limestone) and natural zirconium dioxide (baddeleyite) can be used as initial components, and secondly, the use of one of the simplest methods of grinding substances - mechanical grinding and, thirdly, a decrease in energy consumption when obtaining a composite.

To prepare a high-temperature carbon dioxide chemisorbent, CaCO ₃ powder with a purity of more than 99% and a baddeleyite powder with a ZrO ₂ content of more than 99% (JSC Kovdorskiy GOK, Russia) were used as a feedstock. Joint grinding of powders to a nanosized state was carried out in a Pulverisette 7 Premium Line planetary mill (Fritsch, Germany) in an aqueous medium for at least 5 hours using stabilized zirconia beads with a diameter of 1.5 ± 0.1 mm. The ratio of the mass of the composition of powders to the mass of distilled water was 1: 3, and to the mass of grinding bodies - 1:10.

To prepare compositions of powders, weighed amounts of baddeleyite and calcium carbonate were taken so that the chemisorbent contained Zr and Ca in a molar ratio of 0:10, 1:10, 2:10, and 3:10. At these molar ratios, the proportion of baddeleyite in the mixture was 0, 11, 19.75, and 27 wt. % respectively. The thus prepared mixture of ZrO ₂ and CaCO ₃ powders was dried at a temperature of 80-90 ° C for a day in an OV-11 dry heat oven (Jeio Tech Co., Ltd, South Korea) at atmospheric pressure.

The absorption capacity of a composite chemisorbent based on calcium oxide doped with zirconium dioxide with an atomic ratio of zirconium and calcium atoms in the range from 0 to 0.3 in the process of cyclic carbonation-decarbonization was measured by thermogravimetric method using an EXSTAR TG / DTA7200 thermal analyzer (SII Nano Technology Inc. , Japan). The device has two independent gas supply channels with the ability to precisely control the gas flow in the range from 0 to 500 ml / min for each channel. Gases can be supplied both separately and in the form of a gas mixture with a specified volume fraction of each of its components.

During the tests, the mass of the samples was recorded as a function of time. The absorption capacity of the chemisorbent in each cycle was calculated as the quotient of dividing the amount of CO ₂ absorbed by the chemisorbent during carbonation by the weight of the chemisorbent before carbonization. The obtained value was expressed in mmol / g. To measure the absorption capacity of the chemisorbent, weighed portions weighing 6 - 8 mg were taken. The chemisorbent was preliminarily activated in the same thermal analyzer by heating to 800 ° C, followed by holding at this temperature for 20 min in a nitrogen atmosphere of 99.95% purity to decompose the initial calcium carbonate. As a result, the initial calcium carbonate passed into calcium oxide, and zirconium dioxide, reacting with a part of the formed calcium oxide, formed calcium zirconate (CaZrCO ₃ ).

The scheme of thermal effects on the chemisorbent within the cycle was as follows:

1. Cooling from 800 ° C to 700 ° C at a rate of 10 ° C / min and holding at 700 ° C for 30 min in a gaseous environment containing 70 vol. % nitrogen with a purity of 99.95%) and 30 vol. % carbon dioxide with a purity of 99.95%;

2. Heating up to 800 ° C at a rate of 20 ° C / min and holding at 800 ° C for 20 min in a nitrogen atmosphere with a purity of 99.95%).

There were 50 such cycles.

FIG. 1 shows the change in the mass of the chemisorbent during a typical single carbonation-decarbonization cycle, i.e. a single cycle of interaction of calcium oxide with carbon dioxide with the formation of calcium carbonate and the subsequent decomposition of calcium carbonate with the formation of calcium oxide and the release of carbon dioxide. FIG. 2 shows the dependences of the specific capacity of chemisorbent with different content of ZrO ₂ for CO ₂ on the number of carbonization-decarbonization cycles. From the graph in FIG. 2 that with an increase in the content of Zr atoms in the chemisorbent, the value of its initial (achieved during the first absorption of CO ₂ ) specific capacity decreases from 12.7 mmol / g for a molar ratio of Zr and Ca 1: 10 to 8.6 mmol / g for 3 :ten. The observed decrease in the specific capacity of the chemisorbent is due to a decrease in the fraction of the active substance (CaO) in the chemisorbent due to the formation of CaZrO ₃ , the content of which in the chemisorbent increases with an increase in the amount of ZrO ₂ introduced into it.

After the carbonization process in cycle 50, the specific capacity of the chemisorbent with a molar ratio of Zr and Ca 3: 10 exceeds that for the case of 1: 10-6.2 mmol / g versus 4.6 mmol / g. If the chemisorbent is not doped with Zr atoms, then its initial the specific capacity is 16.1 mmol / g, which is close to the maximum value of 17.9 mmol / g, calculated stoichiometrically. However, after 3 cycles, it begins to decrease sharply, reaching 1.0 mmol / g in cycle 50.

Thus, the introduction of Zr atoms into the chemisorbent composition leads to a decrease in the absolute value of its specific capacity, but, on the other hand, ensures its stability over time. This is due to the formation of an inert matrix of CaZrO ₃ , which prevents the sintering of chemisorbent particles during carbonization-decarbonization.

From FIG. 2, it follows that a chemisorbent with a molar ratio of Zr and Ca 2: 10 is better suited for high-cycle use than a chemisorbent with a molar ratio of Zr and Ca 3: 10, since in the first case, the value of the specific capacity of the chemisorbent, established after repeated carbonization-decarbonization, is greater than in the second, 8.5 mmol / g and 6.2 mmol / g, respectively.

The developed high-temperature regenerating chemisorbent of carbon dioxide can be used to clean the exhaust gases of industrial enterprises from carbon dioxide.

Claims (5)

1. A method of obtaining high-temperature sorbents CO ₂ , including mixing calcium carbonate with a hardening additive, for example zirconium dioxide, followed by grinding the mixture and its heat treatment, characterized in that zirconium-containing mineral raw material is used as a hardening additive - baddeleyite concentrate, joint grinding of powders to The nanosized state is carried out in a bead mill in an aqueous medium for at least 5 hours using stabilized zirconia beads with a diameter of 1.5 ± 0.1 mm, while maintaining the following ratio of components in the mixture, wt%: calcium carbonate 73-89 baddeleyite concentrate 11-27, the resulting mixture is activated by heating to 800 ° C and holding at this temperature for 20 minutes in a nitrogen atmosphere with a purity of 99.95% to obtain calcium oxide and calcium zirconate in the composition of a powder composite material. 2. The method according to claim 1, characterized in that the ratio of the mass of the composition of powders to the mass of distilled water is 1: 3, and to the mass of grinding bodies 1:10. 3. The method according to claim 1, characterized in that after grinding the mixture of powders of baddeleyite concentrate and CaCO _{3 is} dried at a temperature of 80-90 ° C during the day in a dry-heat oven at atmospheric pressure.

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