Patent Application
20210188711
Magnesium oxide (MgO)-based cement has over 150 years of history since Sorel cement was invented by Santislas Sorel in 1866. Typically, MgO-based cement is made by mixing calcined MgO powders with various types of concentrated solutions, such as magnesium chloride (MgCl2), magnesium sulfate (MgSO4), and phosphoric acid (H3PO4), and forming the binary hydrated product (such as 5MgO.MgCl2.13H2O). When calcined reactive MgO is mixed with plain water, reactive MgO powder will react with water to form brucite (Mg(OH)2), which has a porous structure and is typically quite low in strength. However, there exists a reawakened interest in MgO—H2O systems as they exhibit the ability to absorb CO2, forming carbonated products as strong as hydrated Portland cement. Recently, various aspects of the carbonation of reactive MgO have been investigated, including carbonation condition, microstructure, additives that enhance hydration and carbonation, durability, and life cycle assessment. MgO—H2O systems hold great promise as low-carbon alternative binders to replace conventional Portland cement in application, including porous blocks, concrete, and ground improvement.
The signs of global warming and climate change, such as melting glaciers, flooding, and heat waves, has sparked significant research efforts towards developing various technologies to stop or slow down the impacts of these climate disasters. Increasing levels of greenhouse gases like carbon dioxide (CO2) in the atmosphere is the primary reason for global warming. Today, concrete is the second most consumed substance in the world after water, and its main ingredient, Portland cement, is the second highest industrial source of CO2 on the planet. If nothing changes in the way cement is manufactured, cement is posed to contribute an even higher percentage of carbon emissions as concrete demand continues to increase, especially in developing countries.
Increased carbon dioxide (CO2) emissions is the most significant environmental challenge of this century. Manufacturing of cement is responsible for about 5˜7 percent of global greenhouse gas emissions. Conventional feedstock for Portland cement manufacturing is limestone (CaCO3), which is excavated and crushed. Then it is sintered with other materials (e.g., clays) at temperatures reaching ˜1450° C. in a cement kiln to produce clinker. This process directly releases CO2 during calcination of CaCO3 (such as via CaCO3→CaO+CO2), which makes up ˜50-60% of the total emissions of Portland cement production.
Several cementitious materials such as alkali-activated materials, reactive belite, and carbonate binders have been developed to lower the carbon footprint of concrete. Carbon dioxide sequestration in concrete has recently been proposed as a potential solution due to the fact that CO2 reacts with cations such as Ca2+, Mg2+, and Li2+ that are present in cement to form highly stable carbonates, which can also improve mechanical properties over time. However, the potential CO2 storage capacity of Portland cement concretes is significantly lower than the CO2 emitted during their production. Therefore, the development and production of eco-efficient alternatives to carbon-intensive Portland cement is important.
Mg-based cements are promising given the high abundance of Mg in the earth's crust and seawater, which can be excavated or precipitated in forms such as magnesite, dolomite, and magnesium hydroxide. Although many forms of Mg-based cements exist, as discussed above, reactive magnesium oxide or magnesia (MgO) is best known for its ability to react with CO2 in the presence of water to form carbonates. The key reactions are as follows:
MgO+H2O→Mg(OH)2 (Brucite)
Mg(OH)2+CO2+2H2O→MgCO3.3H2O (Nesquehonite)
5Mg(OH)2+4CO2→4MgCO3.Mg(OH)2.4H2O (Hydromagnesite)
5Mg(OH)2+4CO2+H2O→4MgCO3.Mg(OH)2.5H2O (Dypingite)
When sourced from magnesite (MgCO3), it has been found that the carbon footprint of the resultant concrete can be higher than that of Portland cement due to the higher energy consumption of producing MgO from MgCO3 than Portland cement clinker (4.096 GJ/ton vs. 2.52 GJ/ton, respectively). Also, similar to the calcination of limestone to produce CaO for Portland cement, calcination of MgCO3 to produce MgO results in the direct release of CO2. From a sustainability perspective, the cement industry is calling for alternative binders that can reduce associated CO2 emissions without compromising performance.
Some embodiments of the present disclosure are directed to a method of making a cementitious composition including providing an aqueous source of metal ions, providing an aqueous demineralized feedstream to an electrochemical device, isolating an alkaline component and an acidic component from the aqueous demineralized feedstream, mixing the aqueous source of metal ions and the alkaline component to form an aqueous mixture, and precipitating metal hydroxides from the aqueous mixture to form a metal hydroxide product and a demineralized alkaline component, the metal hydroxide product including metal ions from the aqueous source of metal ions. In some embodiments, the method includes recycling at least a portion of the demineralized alkaline component to the electrochemical device as the aqueous demineralized feedstream. In some embodiments, the method includes combining the acidic component with at least a portion of the demineralized alkaline component as a demineralized aqueous source product. In some embodiments, the method includes incorporating the metal hydroxide product into a cementitious composition. In some embodiments, the aqueous source includes seawater, brine, brackish water, wastewater, or combinations thereof. In some embodiments, the metal ions include magnesium, calcium, or combinations thereof.
In some embodiments, incorporating the metal hydroxide product into a cementitious composition includes providing a composition of metal hydroxide product and contacting the metal hydroxide product composition with a source of carbon dioxide and a source of H2O. In some embodiments, contacting the metal hydroxide product with a source of carbon dioxide and a source of H2O includes providing H2O to the metal hydroxide product to form a slurry having a water-to-solids ratio of about 0.2 to about 0.3 by mass, compacting the slurry at a pressure to form a compacted slurry, and exposing the compacted slurry to an environment having a concentration of carbon dioxide of at least about 20%. In some embodiments, the pressure is about 3 MPa. In some embodiments, the compacted slurry is exposed to the carbon dioxide for about 2 to about 5 days. In some embodiments, the step of contacting the metal hydroxide product with a source of carbon dioxide and a source of H2O are repeated to additively form a multilayered concrete structural element. In some embodiments, contacting the metal hydroxide product with a source of carbon dioxide and a source of H2O includes pelletizing the metal hydroxide product composition with sprayed water and exposing the pelletized metal hydroxide composition to the source of carbon dioxide.
Some embodiments of the present disclosure are directed to a method of making a cementitious composition including providing an aqueous source of metal ions, providing an aqueous demineralized feedstream to an electrochemical device, isolating an alkaline component and an acidic component from the aqueous demineralized feedstream, mixing the aqueous source of metal ions and the alkaline component to form an aqueous mixture, precipitating metal hydroxides from the aqueous mixture to form a metal hydroxide product and a demineralized alkaline component, the metal hydroxide product including metal ions from the aqueous source of metal ions, heating the metal hydroxide product to form a metal oxide product, and incorporating the metal oxide product into a cementitious composition. In some embodiments, the method includes contacting at least a portion of the demineralized alkaline component with a source of carbon dioxide to form a carbonate product and providing the carbonate product to the slurry.
In some embodiments, incorporating the metal oxide product into a cementitious composition includes mixing the metal oxide product with a source of water to form a slurry and exposing the slurry to a source of carbon dioxide. In some embodiments, exposing the slurry to a source of carbon dioxide includes extruding a first layer of slurry in an environment having a concentration of carbon dioxide of about 20% and extruding at least one subsequent layer of slurry over the first layer of slurry. In some embodiments, incorporating the metal oxide product into a cementitious composition includes pelletizing the metal oxide product with sprayed water and exposing the pelletized metal oxide product to carbon dioxide.
Some embodiments of the present disclosure are directed to a system for making a cementitious composition including an aqueous source of metal ions; a membraneless electrolyzer, including a first input in fluid communication with an aqueous demineralized feedstream, a first outlet stream including an alkaline component, and a second outlet stream including an acidic component; a precipitation tank in fluid communication with the first outlet stream and the aqueous source of metal ions, the precipitation tank including a demineralized alkaline component outlet stream; a neutralization tank in fluid communication with the second outlet stream and the demineralized alkaline component outlet stream, the neutralization tank having a third outlet stream including a demineralized aqueous source product; and a recycle stream in fluid communication with the demineralized alkaline component outlet stream and the first input to provide least a portion of the demineralized alkaline component outlet stream to the membraneless electrolyzer as the aqueous demineralized feedstream.
The drawings show embodiments of the disclosed subject matter for the purpose of illustrating the invention. However, it should be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:
Referring now to
Still referring to
Electrochemical device 104 includes any suitable components to generate alkaline component 104B′ from the aqueous demineralized feedstream and isolate the alkaline component from acidic component 104B″. In some embodiments, electrochemical device 104 includes one or more electrolyzers, electrodialysis cells, or combinations thereof. In some embodiments, electrochemical device 104 is a membraneless electrolyzer. In some embodiments, aqueous source 102 is fed continuously, semi-continuously, as a batch process, or combinations thereof, to electrochemical device 104. In some embodiments, to aid in precipitation of the metal ions from aqueous source 102, additional hydroxide is added to the aqueous source, alkaline component 104B′, or combinations thereof. In some embodiments, the additional hydroxide is NaOH or other suitable hydroxide.
Still referring to
Mg2++2OH−→Mg(OH)2(s) Kspo=5.61×10−12 M3
where Kspo is the solubility product constant at 25° C. Consistent with Le Chatelier's principle, increasing pH shifts equilibrium of this reaction to the right, leading soluble Mg2+ to rapidly convert into insoluble Mg(OH)2 particles. Thus, by splitting the aqueous demineralized feedstream into reduced-pH acidic component 104B′ and elevated-pH alkaline component 104B′ via an electrolysis process and subsequent mixing of the alkaline component with aqueous source 102, system 100 is able to induce precipitation of metal ions from that source, e.g., in the form of Mg(OH)2 from the aqueous mixture with the Mg component coming from aqueous source 102, which can then be collected as a product and repurposed.
As discussed above, in some embodiments, outlet stream 104B includes alkaline component 104B′. Alkaline component 104B′ is provided to precipitation tank 106, raising the pH and causing metal ions to convert to insoluble compounds and precipitate out of solution, forming a precipitated product and a demineralized stream, e.g., demineralized alkaline component outlet stream 106B. In some embodiments, the precipitated product is separated from the demineralized stream via a separation module. The separation module can have any suitable configuration to isolate the precipitated product from the demineralized stream. In some embodiments, the separation module is integrated with precipitation tank 106. In some embodiments, the separation module is a component of system 100 separate from precipitation tank 106. In some embodiments, the separation module includes a rotary drum filter. In some embodiments, the precipitated product is removed from precipitation tank 106 continuously, semi-continuously, in a batch process, or combinations thereof. In some embodiments, precipitation tank 106 includes a product stream 106A for removing the precipitated product from the tank. In some embodiments, the precipitated product includes one or more compounds including metal ions from aqueous source 102. In some embodiments, the one or more compounds include metal hydroxides. In some embodiments, the metal hydroxides are incorporated into a cementitious composition, further processed for use in a cementitious composition, or combinations thereof, as will be discussed in greater detail below.
Referring again to
As discussed above, the precipitated product produced by system 100 is suitable for use in the production of cement. In an exemplary embodiment, metal hydroxides from precipitation tank 106 can be used as a substitute for limestone and other traditional feedstocks in the production of cement, which can help cut the carbon footprint by more than half while still utilizing existing plant infrastructure and mixing/building standards. In other exemplary embodiments, metal hydroxide and/or metal oxide products can be used as binders of inert aggregate for the formation of concrete and concrete structural elements having desired conformations. In some embodiments, at least a portion of carbon dioxide effluent stream 108D is reused in processing of the precipitated product into cementitious compositions and/or concrete structural elements, as will be discussed in greater detail below.
Referring now to
At 216, the metal hydroxide product is incorporated into a cementitious composition. While the exemplary embodiments of the present disclosure describe incorporating metal hydroxide and metal oxide products that have been isolated from aqueous sources into cementitious products, the present disclosure is not limited in this regard, as other embodiments of systems and methods of the present disclosure incorporate metal hydroxide and metal oxide products from other sources, including, e.g., reagent grade products generally available to the public from a variety of providers. In some embodiments, both reagent grade metal hydroxide and metal oxide products and aqueous solution-sourced metal hydroxide and metal oxide products are incorporated into the cementitious composition. As discussed above, the metal hydroxide products, e.g., those produced via steps 202-210, are highly useful in the production of cements and concretes. In some embodiments, Ca(OH)2 is substituted for limestone in the production of traditional Portland cement. Without the need to utilize limestone in the traditional process, the CO2 generated in the calcination of limestone to CaO is eliminated, reducing the overall carbon cost of producing Portland cement.
Referring now to
In some embodiments, other additives are incorporated into the slurry at steps 216B, 216C, 216D, or combinations thereof In an exemplary embodiment, inert aggregate is included in the slurry which, upon curing, forms a concrete structural element. In some embodiments, steps 216A-216D are repeated to form multilayered concrete structural elements. In these embodiments, a first layer of slurry is provided and cured as discussed above. Then, additional layers of slurry can be provided and cured on the first layer. Layer-by layer, a concrete structural element can be formed progressively, resulting in a densified structure with enhanced strength and transport properties and substantially uniform carbon curing throughout the resulting multilayered element.
Referring now to
Referring now to
NaOH+CO2→NaHCO3 (pH<8)
2NaOH+CO2→Na2CO3+H2O (pH>10)
The sodium carbonate and/or sodium bicarbonate can then be provided to the slurry. These carbonates are beneficial in that they can accelerate the hydration of the metal oxides, forming additional reaction products that can provide strength gains in the structural elements made from the cementitious compositions of the present disclosure. In some embodiments, the source of water is liquid H2O, gaseous H2O, i.e., water vapor, or combinations thereof. In some embodiments, the slurry has a liquid-to-solids, e.g., water-to-solids, ratio of about 0.1 to about 0.5 by mass. In some embodiments, the slurry has a liquid-to-solids ratio of about 0.2 to about 0.3 by mass. In some embodiments, the slurry has a liquid-to-solids ratio of about 0.3 by mass.
The slurry is contacted with a source of carbon dioxide. The source of carbon dioxide can be any source having a suitable concentration of carbon dioxide therein. In some embodiments, at least a portion of the carbon dioxide is sourced from the acidic component. In some embodiments, the source of carbon dioxide is waste effluent from an industrial process. In some embodiments, the source of carbon dioxide has a CO2 concentration of about 10% to about 30%. In some embodiments, the source of carbon dioxide has a CO2 concentration of about 20%. In some embodiments, the slurry is cured for greater than about 2 days. In some embodiments, the slurry is cured to about 2 days to about 5 days. In some embodiments, the temperature during step 314B is generally maintained at about 25° C. In some embodiments, the relative humidity in the environment around the slurry during step 314B is generally maintained at about 75% to about 85%.
In some embodiments, other additives are incorporated into the slurry at steps 314B. As discussed above, in an exemplary embodiment, inert aggregate is included in the slurry which, upon curing, thus forms a concrete structural element. In some embodiments, steps 314A-314B are repeated to form multilayered concrete structural elements. In these embodiments, a first layer of slurry is provided and cured as discussed above. Then, additional layers of slurry can be provided and cured on the first layer. In some embodiments, the layers are extruded. Layer-by layer, a concrete structural element can be formed progressively, resulting in a densified structure with enhanced strength and transport properties and substantially uniform carbon curing throughout the resulting multilayered element.
When exposed to moisture, the metal oxide product hardens as oxides hydrate to form hydroxides. In the embodiments utilizing carbonate additives, this hydration is accelerated. When exposed to CO2, hydroxides convert to hydrated carbonates in various forms, e.g., hydromagnesite and/or nesquehonite in the case of magnesium, which can provide strength gain. Several studies have shown that MgO cement can capture 1.1 ton of CO2 per 1 ton of MgO during accelerated CO2 curing. Thus, embodiments of method 300 produce CO2-negative concrete considering zero CO2 emission during the harvesting and calcination of Mg(OH)2, and carbon curing to form the final solid MgO binder.
In some embodiments, the metal oxide and/or metal hydroxide products are incorporated into a cementitious composition by pelletizing the products with sprayed water. In these embodiments, the metal oxide and/or metal hydroxide products are combined with water as it is sprayed on a surface, such as a pelletizer disc. Product powder particles stick to each other and start to agglomerate during the pelletizing process. In exemplary embodiments with a pelletizer disc , the rotation of the disc can be maintained until the aggregates reach the desired particle size. The particles are then exposed to a carbon dioxide consistent with the embodiments described above. The result is cementitious pellets including carbonates which are lightweight and advantageous for use as aggregate replacement in concrete structural elements.
Seawater-derived Mg(OH)2 was obtained by precipitation using 4.86 g NaOH per L of seawater and rinsed 2 times with 48 L of deionized water. The seawater-derived Mg(OH)2 was compared to reagent grade Mg(OH)2 (Sigma Aldrich) via TGA and XRD in
The precipitated Mg(OH)2 formed a dried filter cake and was crushed into a fine powder that was white in color, as shown in the inset in
From a TGA scan of the seawater-derived cement, the presence of Mg(OH)2 is observed. However, besides the dominant peak associated with Mg(OH)2, smaller peaks associated with residual water and an unidentified peak were also observed. Consistent with TGA results, XRD patterns taken of the seawater-derived precipitate match brucite Mg(OH)2 (PDF #44-1482). The only non-Brucite reflection is associated with a minor peak around 2θ=29.5°, which is consistent with CaCO3 (Calcite, PDF #05-0586). The unidentified peak in the TGA was thus confirmed to be CaCO3. The composition of raw Mg-cement by weight was then determined to be: ˜84.1% Mg(OH)2, ˜3.5% water, and ˜9.3% CaCO3. Without wishing to be bound by theory, the expected inert nature of CaCO3 in a carbon dioxide environment implies it will exist as an impurity and will effectively reduce the “active” proportion in the cement—the brucite. This may lead a lower strength as compared to purer Mg(OH)2.
The Mg(OH)2 powder was mixed with water to yield a water-to-solids ratio of 0.3, then cast in cylindrical molds (1 in×1 in). Each cylindrical specimen was compacted at 3 MPa for two minutes, then demolded and cured in a carbon-rich environment (20% CO2 concentration, 25° C.±1° C. operation temperature, and 80%±5% relative humidity). The cylinders were subjected to compression loads to observe their performance and were later processed for characterization.
Referring now to
The presence of carbonates was confirmed via XRD in both the seawater and standard Mg(OH)2 (see
The compressive strength of mixtures composed of standard Mg(OH)2 subjected to carbonation curing for 3 hours, 2 days and 5 days were obtained. Additionally, compressive strength after 2 days carbonation curing was compared between mixtures composed of standard and seawater-derived Mg-cement. Each tested mix had a water-to-binder ratio of 0.3.
The mass, and density, of the cylinders were obtained prior to carbonation curing and were found to be comparable: 1.49 g/cm3 for commercial brucite and 1.44 g/cm3 for seawater-derived precipitated Mg(OH)2. The mass change over 2 days was found to be the same at +13%. For the standard Mg-cement, the compressive strength increased with time, where the strength was 23 MPa at 3 hours, 33 MPa at 2 days, and reached 71 MPa at 5 days. The compressive strength of seawater specimens at 2 days was 23 MPa. Without wishing to be bound by theory, this may have occurred due to the properties of both the raw material and the carbonated material, namely, a difference in particle size distribution may affect packing behavior during compaction, which in turn may affect permeability for carbonation. Additionally, the PSD and particle morphology also affect the surface area available for products to form. CO2 curing also leads to formation of different carbonates and these have distinctly different morphologies. Further, the strength of the binding matrix depends on product morphologies. For instance, rosette like structures are more favorable for strength, i.e., better integrity, than needle like structures. The strength observed in the exemplary embodiments described above is strong enough considering the early compressive strength of ordinary Portland cement concrete. With longer curing durations, the strength of the seawater magnesium samples should continue to enhance considering the compressive strength development results of standard magnesium hydroxide groups.
The methods and systems of the present disclosure are advantageous in that they utilize carbonated metal hydroxides and oxides to produce compositions with compressive strengths suitable for use as construction materials. The metal hydroxides and oxides are carbonated through a curing process to sequester environmental carbon dioxide, reducing or eliminating the carbon footprint associated with traditional methods of cement and concrete manufacturing. Additionally, the produced compositions reach compressive strengths comparable to those of traditional, reactive metal oxide fabrication techniques, but with reduced water demand and elimination of highly energy intensive calcination steps. By way of example, conventional limestone feedstock for Portland cement manufacturing is excavated, crushed, and then sintered with other materials at temperatures reaching ˜1450° C. in a cement kiln to produce clinker. This traditional process directly releases CO2 during calcination of CaCO3 (CaCO3→CaO+CO2), which makes up ˜50-60% of total emissions of cement production. The systems and methods of the present disclosure can produce an electrochemically harvested Ca(OH)2 powder that is fed into existing cement plants/kilns through partial to full replacement of the limestone. By using Ca(OH)2 as a feedstock, indirect CO2 emissions associated with the harvesting or direct CO2 emissions during the calcination process to obtain CaO can be eliminated.
Finally, the systems and methods are advantageous in that the metal hydroxides and oxides used as construction materials can be sourced from mineralized aqueous solutions. Importantly, the production of these metal hydroxide/oxide products via electrolysis can be carried out without any CO2 emissions if the electricity used to power electrolysis is generated by renewable solar and wind. Hydroxides generated by electrolysis can then be calcined to produce oxide products as necessary, releasing steam in the process. Obtaining the metal hydroxide/oxide product has the added benefit of evolving low pH demineralized streams as a byproduct, which can be recycled to help create yet more product, or can be neutralized for use in parallel water desalination systems and processes, or for return to the sea.
Although the disclosed subject matter has been described and illustrated with respect to embodiments thereof, it should be understood by those skilled in the art that features of the disclosed embodiments can be combined, rearranged, etc., to produce additional embodiments within the scope of the invention, and that various other changes, omissions, and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.
This application claims the benefit of U.S. Provisional Application Nos. 62/953,251, filed Dec. 24, 2019, 63/083,311, filed Sep. 25, 2020, and 63/129,110, filed Dec. 22, 2020, which are incorporated by reference as if disclosed herein in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 62953251 | Dec 2019 | US | |
| 63083311 | Sep 2020 | US | |
| 63129110 | Dec 2020 | US |
