AU2018247175B2 - Method and system for converting carbon dioxide into solid carbonates - Google Patents

Abstract

A method for converting carbon dioxide into a solid carbonate is disclosed. The method includes contacting aqueous ammonia with carbon dioxide to form an ammonium carbonate solution. The method further includes reacting the ammonium carbonate solution with an ultramafic rock material to form the solid carbonate and regenerate aqueous ammonia, wherein the ultramafic rock material is thermally activated prior to the reacting step.

Description

METHOD AND SYSTEM FOR CONVERTING CARBON DIOXIDE INTO SOLID CARBONATES CROSS-REFERENCE TO RELATED APPLICATION

10011 This application claims the benefit of priority of Singapore Patent Application

No. 10201702474S, filed March 27, 2017, the contents of which being hereby

incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

[0021 The invention relates generally to the conversion of carbon dioxide to solid

carbonates, and in particular, the conversion is carried out at nild conditions such as,

but not restricted to, room temperature and atmospheric pressure. Both methods and

systems for the conversion are disclosed herein.

BACKGROUND

[0031 Mineral carbonation (MC) is a technology thatallows large quantities of carbon

dioxide (C02 ) to be permanently sequestered as solid carbonates. This reaction seeks to

accelerate the rate of natural weathering and is achieved by reacting C02 with minerals

containing alkaline-earth metals such as calcium and magnesium.

[0041 Ultramafic minerals such as olivine and serpentine are suitable raw materials for

MC. For example, in the case of serpentine, the following reaction occurs:

Mg 3 Si20s(OH) 4 + 3CO2 -> 3MgCO 3 + 2SiO2 + 2HO

[0051 The most well-known process for MC is a direct aqueous pressure carbonation

(DAPC) method developed by NETL in the United States. This process involves high

temperatures (> 150 °C) and high pressures (> 115 bar). However, the harsh conditions

mean that the process is costly and energy intensive, and is not easily implemented at

large scales. Economic evaluations of the DAPC processes show that the process costs

I are in the range of USD 315 per ton C02 sequestered, and has an energy penalty (imposed on power plants) of about 235 kWh per ton C02 sequestered.

[006] Therefore, there remains a need to provide for an alternative method and system for the

carbonation process that allows significant reductions in terms of costs and energy

consumption compared to the existing DAPC process and system.

[006a] A reference herein to a patent document or any other matter identified as prior art, is

not to be taken as an admission that the document or other matter was known or that the

information it contains was part of the common general knowledge as at the priority date of

any of the claims.

SUMMARY

[007] It has been surprisingly found that the mineral carbonation process can be conducted at

mild conditions such as, but not restricted to, room temperature and atmospheric pressure, by

reacting heat activated or thermally activated ultramafic minerals with ammonium carbonate.

Techno-economic evaluation of the presently disclosed method based on experimental data

shows a 40 % reduction in costs (> USD 120 per ton C02 sequestered) and large reductions in

energy consumption (78 % less electricity use and 40 % less heat use).

[008] Thus, according to an aspect of the disclosure, there is provided a method for

converting carbon dioxide into a solid carbonate. The method includes contacting aqueous

ammonia with carbon dioxide to form an ammonium carbonate solution, The method further

includes reacting the ammonium carbonate solution with an ultramaic rock material to form

the solid carbonate and regenerate aqueous ammonia, wherein the ultramafic rock material is

thermally activated prior to the reacting step.

[008a] In an aspect, the invention provides a method for converting carbon dioxide into a

solid carbonate, the method comprising: contacting aqueous ammonia with carbon dioxide to

form an ammonium carbonate solution; and reacting the ammonium carbonate solution, which

is already formed, directly with an ultramafic rock material to form the solid carbonate and regenerate aqueous ammonia, wherein the ultramafic rock material is thermally activated prior to the reacting step.

[009] According to another aspect of the disclosure, there is provided a system for converting

carbon dioxide into a solid carbonate. The system includes a carbon dioxide scrubber

configured to contact aqueous ammonia with carbon dioxide to form an ammonium carbonate

solution. The system further includes a reactor in fluid communication with the carbon dioxide

scrubber, wherein the reactor is configured to react the ammonium carbonate solution with an

ultramafic rock material to form the

2a solid carbonate and regenerate aqueous ammonia, wherein the ultramafic rock material is thermally activated prior to the reacting step.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings, like reference characters generally refer to the same parts

throughout the different views. The drawings are not necessarily drawn to scale,

emphasis instead generally being placed upon illustrating the principles of various

embodiments. In the following description, various embodiments of the invention are

described with reference to the following drawings.

[0011] FIG. 1 shows a mineral carbonation process conducted at room temperature and

atmospheric pressure according to one example.

[00121 FIG. 2 shows TGA results of solid product compared against starting material

according to one example.

[00131 FIG. 3 shows FTIR analysis ofthe evolved gases from thermal decomposition

of the solid products according to one example.

[00141 Fig. 4 shows the expected cost savings from carbonation at room temperature

and atmospheric pressure based on a process scale of 252,000 ton CO2 per annum and

1,000,000 ton serpentine per annum according to one example.

[00151 FIG. 5 shows the expected energy savings from carbonation at room

temperature and atmospheric pressure based on a process scale of 252,000 ton CO 2 per

annum and 1,000,000 ton serpentine per annum according to one example.

DESCRIPTION

[0016] The following detailed description refers to the accompanying drawings that

show, by way ofillustration,specific details and embodiments inwhich the invention

may be practised. These embodiments are described in sufficient detail to enable those

skilled in the art to practise the invention. Other embodiments may be utilized and structural, chemical, and material changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[00171 In the present disclosure, CO 2 is converted into solid alkaline-earth carbonates

via a reaction with thermally activated ultramafic minerals (also termed asultramafic

rock materials). This is achieved by first capturing the CO2 from flue gas emitted in

power plants, for example, using aqueous ammonia, and then using the resultant

ammonium carbonate to react at room temperature and atmospheric pressure, for

example, with thermally activated ultramafic minerals. The reaction entails the

fonation of a solid carbonate/silica mixture, as well as regeneration of the aqueous

ammonia that is recycled for further CO 2 capture. In other words, the method allows the

recovery of the aqueous animonia that is not lost through absorption or other means into

the product stream.

[00181 The use of ammonium carbonate enables the carbonation reaction to be

conducted at mild conditions such as, but not restricted to, room temperature and

atmospheric pressure, in one step. The properties of ammonia and ammonium carbonate

are exploited to facilitate the carbonation reaction. The method described herein is

distinct from existing carbonation methods in that existing methods require additives

such as sodium-based additives, are non-regenerating, and require much harsher

reaction conditions to carry out the carbonation process.

[00191According to an aspect of the disclosure, there is provided a method for

converting CO2 into a solid carbonate.

[0020] CO2 may be sequestered or captured from flue gas emitted by power plants, for

example. Other sources of large quantities of CO 2 may likewise be applicable.

[0021] The carbonates formed from the conversion are in solid form and may be

alkaline-earth carbonates. The solid carbonates formed may exist in a slurry form, tor

example, and may require further simple separation process.

[00221 The method includes contacting aqueous ammonia (aq. NH 3) with C02 to forn

an ammonium carbonate solution (aq. (NH 4)2COi). For example, flue gas emitted from

power plants is laden with CO2 and may be passed through or bubbled through a

volume of aqueous ammonia. Flue gas passing out from the volume of aqueous

ammonia may now contain a reduced content in C02, to the extent that the flue gas may

be CO 2 free.

100231 The method further includes reacting the aq. (NH 4)2 CO3 with an ultramafic rock

material to form the solid carbonate and regenerate aq. NH 3, wherein the ultramafic

rock material is thennally activated prior to the reacting step. By thermally activiating

the ultramafic rock material, this results in partial or full dehydroxylation of the

ultramafic rock material, and increases the surface area and porosity (and thus

increasing the reactivity) of the ultramafic rock material.

[00241 The reaction between the aq. (N1i 4)2 C03 and the ultramafic rock material may

take place under stirring condition and allowing sufficient time for the reaction to go to

completion, thereby forming the solid carbonate product.

[0025] In various embodiments, the ultramafic rock material may include serpentine

(Mg 3Si 20s(OH) 4), tremolite (MgsCa2SisO22(OH)2), talc (Mg3Si(OH)2), olivine

(Mg2SiO 4), orthopyroxene (MgSiO3:), clinopyroxene ((MgCa)SiO3), and/or any other

types of mineral with sufficiently high alkaline earth metal oxide content (>20% MgO

or CaO) available for reaction.

[00261 In certain embodiments, the ultramafic rock material may include serpentine or

olivine.

[0027] In preferred embodiments, the ultramafic rock material may include serpentine.

[0028] As mentioned above, the ultramafic rock material is thermally activated prior to

the reacting step. Various manners of thermally activating the ultramafic rock material

may be used.

[00291 In various embodiments, the ultramafic rock material may be grounded prior to

the reacting step. The grinding process may be conducted in a conventional grinding

machine or miller. For example, the ultramafic rock material may be grounded to

between about 50 and about 1,000 microns prior to the reacting step. Any particle size

of the grounded ultramafic rock material within this range may be useful.

[00301 In preferred embodiments, the ultramafic rock material may be grounded to

between about 100 and about 600 microns prior to the reacting step. For example, the

average particle size of the grounded ultramafic rock material may be about 100, 150,

200, 250, 300, 350, 400, 450,500, 550, or 600 microns.

[00311 Alternatively, or additionally, the ultramafic rock material may be thermally

activated by heating at about 500 to 1,000 °C prior to the reacting step. The heating may

be conducted in a conventional furnace. The ultramafic rock material may be heated in

the furnace for a period of time until the average temperature of the ultramafic rock

material reaches between about 500 to 1,000 °C. For example, the ultramafic rock

material may be thermally activated by heating until about 500, 550, 600, 650, 700, 750,

800, 850, 900, 950, or 1,000 'C.

[00321 In preferred embodiments, the ultramafic rock material may include serpentine

and may be thernally activated by heating at about 550 to 750 °C prior to the reacting

step.

[0033] In various embodiments, the ultranafic rock material may be thermally activated

by heating for about 3 to 8 hours.

[00341 In preferred embodiments, the ultramafic rock material may include serpentine

and may be thermally activated by heating at between about 550 and 750 °C prior to the

reacting step for about 4 to 6 hours.

[0035] As mentioned above, the carbonation reaction is carried out at mild conditions

compared to existing methods, thereby achieving a much reduced operating cost.

[0036] Thus, in various embodiments, the reacting step may be carried out at about 20

to 80 °C. In preferred embodiments, the reacting step may be carried out at room

temperature.

[0037 In various embodiments, the reacting step may be carried out at about 1 to 5

atmosphere. In preferred embodiments, the reacting step may be carried out at

atmospheric pressure.

[0038] In various embodiments, the method may further include stirring the aq.

(NH 4) 2CO3 with the thennally activated ultramafic rock material during the reacting

step. Doing so may help in accelerating the rate of conversion reaction.

[0039] After the conversion reaction proceeds to completion, a solid carbonate product

is formed and aq. NH 3 is regenerated. The solid carbonate may exist in a slurry form

with silica. Thus, in various embodiments, the method may further include separating

the solid carbonate from the regenerated aq. NH 3 after the formation.

10040] In preferred embodiments, the solid carbonate may be separated by filtration.

After the filtration, the regenerated aq. NH 3 may be collected for reuse by recycling

back for the contacting step.

[0041] According to another aspect of the disclosure, there is provided a system for

convertingCO 2 into a solid carbonate.

[00421 The system includes a CO 2 scrubber configured to contact aq NI-3 with CO 2 to

form an aq. (NH 4)2 CO 3. The system further includes a reactor in fluidcommunication with the CO 2 scrubber, wherein the reactor is configured to react the aq. (NH4)2CO with an ultramafic rock material to form the solid carbonate and regenerate aq. NH 3

, wherein the ultramafic rock material is thenrally activated prior to the reacting step.

10043] In various embodiments, the system may further include a furnace in fluid

communication with the reactor, wherein the furnace is configured to heat up the

ultramafic rock material at about 500 to 1,000 °C.

[00441 In various embodiments, the system may further include a grinder or mill to

grind the ultramafic rock material to between about 50 and 1,000 incrons.

[00451 In various embodiments, the system may further include a separator in fluid

communication with the reactor, wherein the separator is configured to separate the

solid carbonate from the regenerated aq. NH 3 after formation.

[00461 In various embodiments, the separator may be in fluid communication with the

CO2 scrubber to recycle the regenerated aq. NH3.

[0047 In order that the invention may be readily understood and put into practical

effect, particular embodiments will now be described by way of the following non

limiting examples.

EXAMPLES

[00481 In this example, a mineral carbonation process conducted at room temperature

and atmospheric pressure is illustrated (FIG. 1).

[00491 In this process, a C02-.Iaden gas stream (i.e. flue gas from power plants) is

contacted with an aq. NH 3 . The contacting results in the formation of an aq. (NH 4 )2CO 3:

H 2 0() CO2(g) + 2 NH3aq) - (NH4)2CO3(aqg

[00501 The aq. (NH4)2CO3 then transferred to a reactor where it comes into contact with

a thermally activated ultramafic mineral, for example, serpentine.

10051] Parallel to the CO 2 capture step using aq. NH 3 , the ultramafic mineral is also

ground into small particle sizes, for example, up to 100 microns. The grounded

ultramafic mineral is then fed into a furnace where it is heated to between 600 and 700

°C for several hours (usually around 4 hours). This results in partial or full

dehydroxylation of the ultramafic mineral, and increases the surface area and porosity

(and thus increasing the reactivity) of the ultramafic mineral.

[0052] The carbonation reaction is conducted by stirring the aq. (NH 4 )2 CO3 and

activated ultramafic mineral at room temperature and atmospheric pressure for a

sufficient time, thereby allowing the reaction to go to completion.

[0053] The carbonation reaction ideally proceeds as follows:

Mg 3Si 20 5(OH)4()+ 3(NH4)2C03(,q) - 3MgCOi(S)+ 2SiO 2 (s)+ 5H2 0) + 6NHa q)

[0054] In the carbonation reaction, a solid mixture of magnesium carbonate (MgCO 3

) and silica (SiO 2) is forced. The aq. (NH 4 ) 2 CO3 is also regenerated into aq. NH 3 , and is

further recycled to capture more CO2 in the flue gas scrubbing step. The recycling is

done by filtering the slurry to obtain a solid carbonate/silica mixture, and the liquid aq.

NH 3 .

100551 The net reaction is as follows:

Mg3SizOs(OH) 4 3CO2 - 3MgCO3 +2SiO 2 + 2H 20

[0056] The solid products were analyzed using TGA-FTIR to determine the amount of

CO2 sequestered in the ultramafic mineral and also to detennine whether there was any

adsorbed or chemically bound ammonia in the product.

[00571 TGA analysis (FIG. 2) of the carbonated activated serpentine indicates that

roughly 12 wt% of the solid product is CO, which corresponds to a carbonation

efficiency of about 40 to 45 %(compared to about 60 to 80 % for conventional DAPC).

[00581 Based on the TGA profile, the formed carbonate is mainly hydromagnesite

(Mg 5(C03)4(OH)2-4H 2 0).

[00591 FTIR analysis (FIG. 3) of the evolved gases from thermal decomposition of the

solid products (obtained after filtration) showed that there was no adsorbed or

chemically bound ammonia. This implies that full recovery of the ammonia is possible

and practically achievable.

[0060] In a lab-scale experiment, 10 g activated serpentine was reacted with 100 ml I

M (NH4)2CO3 solution at room- temperature and atmospheric pressure overnight. The

slurry was filtered and the solids were washed with water thrice to remove any

unreacted (NH 4 )2 CO 3 . The washed solids were then subject to an acid test, where HCl

was added to the solids to test for presence of carbonates. Vigorous fizzling/bubbling

was observed upon addition of acid, suggesting presence of solid carbonates (MgCO 3 or

its hydrated forms) in the residue. The liberated NH 3 may be further recycled to a flue

gas scrubber to capture more C02 as (NH 4 ) 2 CO3 reacts with incoming activated

serpentine.

[0061] Fig. 4 shows the expected cost savings from carbonation at room temperature

and atmospheric pressure based on a process scale of 252,000 ton CO2 per annum and

1,000,000 ton serpentine per annum.

[0062] The costs associated with high pressure carbonation can be brought down

significantly if the reaction can be conducted at room temperature and atmospheric

pressure. This avoids the use of expensive pressure reactors and compressors.

[00631 FIG. 5 shows the expected energy savings from carbonation at room

temperature and atmospheric pressure based on a process scale of 252,000 ton CO 2 per

annum and 1,000,000 ton serpentine per annum.

[0064] Significant energy savings can be achieved by conducting the carbonation

reaction under room temperature and atmospheric pressure conditions, Carbonation at

low temperature and pressure will also avoid significant electrical energy penalties on

power plants.

[00651 By "comprising" it is meant including, but not limited to, whatever follows the

word "comprising". Thus, use of the term "comprising" indicates that the listed

elements are required or mandatory, but that other elements are optional and may or

may not be present.

[0066] By "consisting of' is meant including, and limited to, whatever follows the

phrase "consisting of'. Thus, the phrase "consisting of' indicates that the listed

elements are required or mandatory, and that no other elements may be present.

[0067] The inventions illustratively described herein may suitably be practiced in the

absence of any element or elements, limitation or limitations, not specifically disclosed

herein. Thus, for example, the tens "comprising", "including", "containing", etc. shall

be read expansively and without limitation. Additionally, the terms and expressions

employed herein have been used as terms of description and not of limitation, and there

is no intention in the use of such tens and expressions of excluding any equivalents of

the features shown and described or portions thereof, but it is recognized that various

modifications are possible within the scope of the invention claimed. Thus, it should be

understood that although the present invention has been specifically disclosed by

preferred embodiments and optional features, modification and variation of the

inventions embodied therein herein disclosed may be resorted to by those skilled in the

art, and that such modifications and variations are considered to be within the scope of

this invention.

II

[0068] By "about" in relation to a given numerical value, such as for temperature and

period of time, it is meant to include numerical values within 10% of the specified

value.

[0069] The invention has been described broadly and generically herein. Each of the

narrower species and sub-generic groupings falling within the generic disclosure also

form part of the invention. This includes the generic description of the invention with a

proviso or negative limitation removing any subject matter from the genus, regardless of

whether or not the excised material is specifically recited herein.

[00701 Other embodiments are within the following claims and non- limiting examples.

In addition, where features or aspects of the invention are described in terms of

Markush groups, those skilled in the art will recognize that the invention is also thereby

described in terns of any individual member or subgroup of members of the Markush

group.

Claims (18)

The claims defining the invention are as follows:

1. A method for converting carbon dioxide into a solid carbonate, the method comprising:

contacting aqueous ammonia with carbon dioxide to form an ammonium carbonate

solution; and

reacting the ammonium carbonate solution, which is already formed, directly with an

ultramafic rock material to form the solid carbonate and regenerate aqueous ammonia,

wherein the ultramafic rock material is thermally activated prior to the reacting step.

2. The method of claim 1, wherein the reacting step is carried out at 20 to 80 °C.

3. The method of claim 2, wherein the reacting step is carried out at room temperature.

4. The method of any one of claims 1 to 3, wherein the reacting step is carried out at 1 to

5 atmosphere.

5. The method of claim 4, wherein the reacting step is carried out at atmospheric

pressure.

6. The method of any one of claims1 to 5, wherein the ultramafic rock material

comprises serpentine (Mg 3Si2O 5(OH)4), tremolite (Mg5 Ca2Si 8O22(OH)2), talc

(Mg3 Si4O(OH)2), olivine (Mg2SiO4), orthopyroxene (MgSiO3), clinopyroxene ((MgCa)SiO3),

and/or a mineral with an alkaline earth metal oxide content having more than 20% MgO or

CaO.

7. The method of claim 6, wherein the ultramafic rock material comprises serpentine.

8. The method of any one of claims 1 to 7, wherein the ultramafic rock material is

grounded prior to the reacting step.

9. The method of claim 8, wherein the ultramafic rock material is grounded to between

50 and 1,000 microns prior to the reacting step.

10. The method of claim 9, wherein the ultramafic rock material is grounded to between

100 and 600 microns prior to the reacting step.

11. The method of any one of claims 1 to 10, wherein the ultramafic rock material is

thermally activated by heating at 500 to 1,000 °C prior to the reacting step.

12. The method of claim 11, wherein the ultramafic rock material comprises serpentine

and is thermally activated by heating at 550 to 750 °C prior to the reacting step.

13. The method of any one of claims 1 to 12, wherein the ultramafic rock material is

thermally activated by heating for 3 to 8 hours.

14. The method of claim 13, wherein the ultramafic rock material comprises serpentine

and is thermally activated by heating at between 550 and 750 °C prior to the reacting step for 4

to 6 hours.

15. The method of any one of claims 1 to 14, further comprising stirring the ammonium

carbonate solution with the thermally activated ultramafic rock material during the reacting

step.

16. The method of any one of claims 1 to 15, further comprising separating the solid

carbonate from the regenerated aqueous ammonia after the formation.

17. The method of claim 16, wherein the solid carbonate is separated by filtration.

18. The method of any one of claims 1 to 17, wherein the regenerated aqueous ammonia is

collected for reuse.