Description:Carbon Dioxide Absorbent Bed
Field of the Invention
[1] This invention relates to composition of Carbon Dioxide Absorbent Beds for removal of Carbon dioxide from gas and its method of manufacturing, and method of using, in particular for absorbing low concentrations of carbon dioxide from the environment.
Background of the invention
[2] Carbon dioxide or CO2 is an essential part of the animal and plant life cycle. Without CO2, plants will not survive, causing earth’s biological food chain to collapse.
[3] Carbon dioxide is produced both naturally and by human activities, such as burning gasoline, coal, oil, and wood. Animals and people exhale CO2 which also contributes to CO2 levels in the air. From the research, it is found that an average human being exhales around 0.96 kg of carbon dioxide per day or 0.04 kg per hour.
[4] CO2 becomes a poisonous gas when there is too much of it in the air we breathe. Exposure to ambient CO2 in indoor environments can have harmful effects on the human body. Studies have shown that for every 400PPM increase in CO2, there is a 20% reduction in cognitive performance score. So, high concentration of CO2 in a confined space is bad for human beings to function effectively. At higher levels, carbon dioxide can also cause Drowsiness, Headaches, Trouble concentrating or thinking clearly, Dizziness or disorientation, Shortness of breath, Hyperventilation, Extreme fatigue, dizziness, nausea, and other symptoms. At even higher levels of CO2 can cause asphyxiation as it replaces oxygen in the blood. Exposure to CO2 concentrations of around 40,000 ppm is immediately dangerous to life and health. Therefore, maintaining carbon dioxide concentration at safe level is a matter of prime importance to maintain a healthy ecosystem.
[5] Carbon dioxide can build-up in the rooms in buildings such as bedrooms, meeting rooms, conference rooms, schools, or offices, or in any confined spaces either from the gas being drawn up from the soil or from the human activities inside the building. High levels of carbon dioxide will appear inside the confined spaces if it has poor ventilation, and the indoor air does not circulate properly.
[6] A confined space should therefore be designed so that the carbon dioxide removal rate is proportionate to the number of people within a room and rate of generation of CO2.
[7] Specially, in a confined spaces like enclosed quarters, large amounts of carbon dioxide are generated, which can be dangerous. The increased concentration of CO2 due to continuous breathing in a manned closed space, can be a threat to health and safety. Effective removal of low concentration CO2 from the manned closed space is essential to meet the requirements of long-term space or deep-sea exploration.
[8] There exist several technologies designed for capturing of CO2 at both high and low concentrations of CO2. Examples of these technologies include regenerative and non-regenerative methods. Some regenerative methods include liquid amine and other liquid absorbents, amine/ LiOH/ Ca(OH)2 scrubbers, MEA, Zeolites, ion exchange resins and reactive plastic curtains. Some of the non-regenerative methods include LiOH/NaOH cannisters, LiOH/ NaOH granules, Encapsulated LiOH, LiOH/ Ca(OH)2 Powercube, 6-cube arrangement, NaOH and VOCs with Activated Carbon, etc. Apart from absorption, other technologies being developed include use of cryogenics, biological air purification, hollow-fiber membrane amine-facilitated transport, absorption media tube and electrochemical method of CO2 removal.
[9] there are many disadvantages in the presently available carbon dioxide absorbent bed and systems. Some of the absorbents are complex in form, non-regenerable (absorbent needs to be discarded after one use), moisture in feed degrades absorbent performance (Zeolite), co-absorption of gases along with CO2 is not desired (Zeolite), low absorption rate (NaHCO3), regeneration requires very high temperatures ranges (Soda lime). Absorption-regeneration cycles process requires high-low pressure swings, (Zeolite), state of absorbent is not retained as original form after many cycles.
[10] There is a special requirement of removing CO2 from confined spaces at low CO2 concentrations (as low as 0.05 or 500 PPM).
[11] Clearly there exists a need for an improved composition of material for removal of carbon dioxide from the atmospheric air, particularly suitable for removal of carbon dioxide with lower concentration in a confined environment. Further molding of the composition of various shapes and sizes, which are suitable for specific application, with enhanced life cycle.

Objects of the invention:
[12] The principal object of the present invention is to develop, solid, a reusable Carbon dioxide Absorption bed (CA bed) to remove the carbon dioxide of low concentrations (as low as 500 PPM ) from air present in the atmosphere as well as in the confined spaces, having excellent absorption performance of carbon dioxide in an absorption process and regeneration performance in a regeneration process.
[13] Another object of the invention is to develop a CA bed composition that provide good mechanical properties and withstand a greater number of absorption and regeneration cycles.
[14] Another object of the invention is to disclose process of molding CA bed, and post molding treatment of the CA bed.
[15] A further object of the invention is to disclose a process for CO2 absorption and regeneration of CA bed for continued/repetitive application.

Summary of the invention
[16] The present invention discloses a Carbon dioxide Absorption bed (CA Bed), its composition, a method of manufacturing and a method for capturing carbon dioxide as a process of repeating separation of carbon dioxide and regeneration of an absorbent by using an additional heat source after carbon dioxide is captured by a solid absorbent bed.
[17] Aim to remove the CO2 concentration from confined spaces by creating absorbent material which have good absorption capability, have excellent mechanical strength and last for long time periods or a greater number of absorption and regeneration cycles.
[18] Develop reusable material to remove carbon dioxide at low concentrations (as low as 500 PPM) from air present in atmosphere either in confined spaces or open areas - suitable for human beings.
[19] Develop a CA bed which removes CO2 under wide range of CO2 concentrations, tolerate higher levels of relative humidity.
[20] To meet the requirements, in the present invention, carbon dioxide absorption bed (CA Bed) is developed satisfying the physical and chemical requirements of an absorbent having new composition of materials and the specific molding and activation process. The composition of CA bed comprising Potassium Bicarbonate (60-95%), Sepiolite (2.5-20%), and SLA-92 (2.5-20%). Further required amount of distilled water is used to prepare the slurry of the said composition to mold the CA bed of required shape and size, depending on the specific applications.
[21] The disclosed invention provides several advantages over the existing CA beds. The new CA bed comprises active material it is versatile, easy to handle, and economical. CA bed can be molded into desired shape and size, weightless, high durability, low maintenance costs, non-hazardous and fire-resistant. Absorption takes place at ambient conditions, works at both low and high humidity, with low CO2 concentration starting from 500 PPM. There is no co-absorption of other gases, water vapor in the feed air enhances absorption (rather than impeding). Regeneration of KHCO3 can be easily done at atmospheric pressure, at lower temperatures compare to other absorbents and does not require vacuum heating.
[22] present disclosure relates to CA Bed which have high CO2 adsorption capacity, high stability against repeated usage (thermal/aging stability), and high attrition resistance.
Brief description of the drawings
[23] Figure. 1 illustrates exemplary shape of Carbon dioxide Absorbent Bed (CA Bed) for a particular application.
[24] Figure. 2 illustrates exemplary shape of Carbon dioxide Absorbent Bed (CA Bed) for a particular application with exemplary dimensions.

[25] While the invention is described in conjunction with the preferred embodiments given as a way of mere examples. It is to be understood that they are not intended to limit the scope of the present invention to such embodiments. On the contrary, it is intended to cover all possible alternatives, modifications, and/or technical equivalents, with the present invention could be used and may be useful as apparent to a person skilled in the art.
Detailed description:
[26] It shall be observed that systems, composition, components, and methods described in accordance with exemplary embodiments have been represented by known symbols in the figures, showing only specific details that are relevant for an understanding of the present disclosure. Further, details that are readily apparent to those skilled in the art may not have been disclosed.
[27] It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
Composition of CA Bed
[28] An illustrative CA Bed composition comprises an active component Potassium bicarbonate (KHCO3), that acts as active CO2-adsorbent, a support matrix SLA-92, provides structure and porosity for better absorption of CO2, a sepiolite binder provides a good mechanical integrity and strength and distilled water as a solvent to prepare slurry for a molding process of desired shape and size.
[29] The active component Potassium Bicarbonate is an inorganic chemical with the chemical formula KHCO3. It is a white solid powder. It is manufactured by treating an aqueous solution of potassium carbonate with carbon dioxide.
K2CO3 + CO2 + H2O ? 2 KHCO3.
Decomposition of the potassium bicarbonate occurs around 210°C:
2 KHCO3 ? K2CO3 + CO2 + H2O.
[30] Alternatively, in place of Potassium bicarbonate, other active ingredients like Alkali-metal carbonate, alkali-metal oxide, or alkali-metal hydroxide or an alkaline-earth metal compound, such as an alkaline-earth metal carbonate, alkaline-earth metal oxide, or alkaline-earth metal hydroxide, Sodium Bicarbonate, Soda Ash are also can be used.
[31] The Support matrix, SLA-92 is an inert, white granules of Calcium Hexa-aluminate. It has high compressive strength, porosity, surface area and hardness. It is resistant to chemical attack, abrasion, thermal shock. Sepiolite provides mechanical strength and integrity to the bed.
[32] In one of the embodiments, the active material can also be used by itself as a Support matric or alternatively supported on a substrate of carbon, alumina, silica, titania, or aluminosilicate. (Examples - diatomaceous earth, gamma-alumina bentonite, montmorillonite, kaolinite, pseudo-bohemite, zirconia, vanadium sulphate, alpha-Al2O3, calcium silicate, magnesia, silica, hydrotalcite, ceria, lanthanum, yttria, and tin oxide, lanthanum aluminate, lanthanum carbonate, molecular sieve 13X, lanthanum acetate, lithium borate, sodium borate and zinc borate).
[33] The Sepiolite binder, is an off-white, naturally occurring fibrous structure made of magnesium silicates. It is light, porous and renders good mechanical integrity and strength due to its rheological properties and microporous structure. It is used in the construction industry for special-purpose purpose ceramics. It is non-toxic and non-hazardous. Sepiolite provides mechanical strength and integrity to the bed.
[34] Alternatively, members of Sepiolite-Palygorskite family/ series, cement, clay, and ceramics can also be used in place of Sepiolite binder.
[35] In the present invention, the CA Bed is be prepared by using different compositions of Potassium Bicarbonate, Sepiolite and SLA-92 based on total weight of the CA bed and by different procedures of making/molding of CA beds.
[36] In one of the embodiments, proportion of the active component, the potassium bicarbonate is preferably 60 to 95% part by weight, based on the total weight of the CA Bed composition, and more preferably, 75 to 85% by weight based on the total weight of the CA Bed composition. If the content of the potassium bicarbonate is less than 65% by weight, the absorption capacity of the CO2 may be reduced. If the content of the potassium bicarbonate is greater than 95% by weight, the physical properties of the CA bed may become weaker for handling and usage with reduced proportions of support matrix SLA-92 and binder Sepiolite.
[37] A proportion of the support matrix SLA-92, is preferably 2.5 to 20% part by weight, based on the total weight of the CA Bed composition, and more preferably 7.5 to 12.5% by weight based on the total weight of the CA Bed composition.
[38] A proportion of the Sepiolite binder, is preferably 2.5 to 20% part by weight, based on the total weight of the CA Bed composition, and more preferably 7.5 to 12.5% by weight based on the total weight of the CA Bed composition.
[39] The Sepiolite binder provides mechanical strength and integrity to the CA bed, whereas SLA-92 support matrix provides porosity to the beds for better absorption of CO2. Proper balance of these raw materials as mentioned above gives a good level of mechanical strength (density), porosity, finish, and absorption capability.
[40] In one of the embodiments of the present invention, after several experimentations with different proportions and testing trials of resulting CA beds and the conditions, the best composition of CA beds has been deduced to be at 80% potassium bicarbonate (KHCO3), 10% Sepiolite and 10% SLA-92. The CA bed with composition of KHCO3(80%), Sepiolite (10%) and SLA-92 (10%) provides best absorption performance and mechanical properties requirement.
Method of manufacturing a CA Bed
[41] The quantity and different ingredients considered herein is for understanding the method of making the CA bed, it in no way meant to constrain or restricts in doing at different volumes for different size and shapes of the CA Beds.
[42] In one of the embodiments, molding of a CA bed of quadrant shape as shown in Fig 1 has been demonstrated. The figure 2. indicates volumetric dimensions of CA bed molded by composition of 2.56 kg of potassium bicarbonate (80%), 0.32 kg of sepiolite (10%), and 0.32 kg of SLA-92 (10%) to make a total weight of 3.2 kg.
The method of manufacturing a CA bed comprises the following process steps
Step 1: Preparation of slurry or wet mix.
[43] Prepare the dry mix by adding ingredients described above, i.e., Potassium bicarbonate (80%), sepiolite (10%), and SLA-92 (10%) in a suitable bowl. Thoroughly dry mix the ingredients using the mixer. Operate the mixer at low RPM to prevent the breaking of Sepiolite fibers. After the dry mixture is prepared and all ingredients are uniformly mixed, add about 400 to 1000 milliliters of distilled water slowly, and continue blending until the slurry or wet mix attains uniformity and sticky, contains just the right amount of water suitable for the molding process.
[44] In one of the embodiments, the amount of water added is 100 to 350 milli liter per Kg of the dry mix to prepare the slurry or the wet mix.
Step 2: Molding of a CA Bed
[45] The mold may be of any shape, size, with or without holes, as needed for an application. For the purpose of illustration, the CA bed of shape and size as shown in Fig 1 has been produced with unique mold set up. The 3.2Kg of composition in the form of slurry has been used.
[46] The prepared slurry or wet mix or the composition is poured uniformly into the mold with open top. The pressure is exerted over the open top of about 100-200kg/m2 to attain the desired density of the composition.
[47] In one of the embodiments, the slurry may be added in one or more stages, with equal proportion of the slurry in each stage, with equal height and exerting the pressure at each stage, to achieve uniform density, without any cavities formed in the CA Bed.
[48] In one of the embodiments as shown in exemplary Fig1. the circular holes are provided in each bed to increase the diffusion area, and these holes are oriented in perfect alignment with air to flow through them from one end to other smoothly.
[49] Once the molding process over, and the desired strength is achieved for handling/transportation. The CA bed is transported to furnace with or without bottom support plate for further process.
[50] In one of the embodiments, the CA mold can be of any shape and size, may be in single or assembled with two or more CA beds to meet the specific requirement and application.

Step-3: Activation of a CA Bed (one time process after molding)
[51] Initially the CA bed molded as described above is made up of 80% potassium bicarbonate (2KHCO3). it is a combination of Potassium carbonate(K2CO3), carbon dioxide (CO2) and water. The CO2 of the potassium bicarbonate must be removed to make the CA bead ready for absorption of CO2 from the atmosphere. The decomposition of CO2 from the potassium bicarbonate (2KHCO3) is the one-time activation process on a newly molded CA bed, as explained in the following paragraphs.
[52] The freshly molded CA bed is heated gradually in a ventilated oven or muffle furnace from ambient temperature (15-45°C) to about 300-550°C. (preferably about 400°C, as at very high temperatures of < 550°C, the raw materials tend to lose their chemical and mechanical properties, and at low temperatures up to 300oC, the mold does not cure well, achieve good mechanical strength and surface finish) at a heating rate of 2-5°C per minute (preferably at 3°C per minute). Once the temperature reaches to about 400°C, the same temperature is to be maintained until the overall heating time completes six hours. The heating time of six hours includes the raising the temperature from ambient to 400°C and maintaining the temperature at 400°C.
[53] At higher temperatures, more than 550°C, the CA bed material becomes hard resulting in poor CO2 absorbent capabilities. The heating rate must be maintained to ensure consistent integrity of the CA bed. Very fast heating can lead to rapid evaporation of gases leading to internal cracks and slow heating rate will increase the process time.
[54] After heating duration of six hours is complete, allow the CA bed to cool down to the ambient temperature naturally.
[55] In the heating process the CA bed is activated for absorption process by decomposition of active ingredient, the Potassium bicarbonate to potassium carbonate, water, and Carbon dioxide by following chemical action.
Activation Process: 2KHCO3 ? K2CO3 + CO2 +H2O
[56] The released CO2 gas and H2O vapor may be allowed to escape into the atmosphere or may be collected and disposed of, depending the set up developed for the purpose.
[57] The activation process is a one-time activity, after the molding process is done. The activated CA bed is ready for CO2 absorption process. The bed is subjected to subsequent absorption-regeneration cycles. As consistent absorption results (product concentration and amount of CO2 absorbed) remain same, we can assure that the regeneration has been complete.
[58] The prepared beds which are not being used must be stored carefully. Each bed needs to be individually shrink-wrapped as soon as they are heated and cooled leaving no part of the bed exposed to the atmosphere due to its deliquescence behavior. All the shrink-wrapped beds are to be stored in a cool, dry environment preferably in a pantry/ storage area.
Method of using a CA Bed: Absorption process
[59] During the absorption process, the Potassium carbonate absorbs the carbon dioxide in the presence of humid air, and convert back to Potassium bicarbonate as exhibited in the following chemical equation
Absorption process: K2CO3 + CO2 + H2O ? 2KHCO3
[60] The absorption process takes place at ambient pressure, ambient temperature, at relative humidity range of 10-90% and CO2 concentration of as low as 500 PPM (The absorption process performance and mechanical strength of the CA bed is best at relative humidity range of 45-70%. At higher humidity, absorption rate increases and mechanical strength decreases while at lower humidity, absorption rate decreases and mechanical strength increases). The absorption parameters are indicated by CO2 sensors measurement which will indicate if absorption is saturated or not. The process can be adjusted according to desired level of product concentration.

Method of using a CA Bed: Regeneration process
[61] The CO2 absorbed CA bed is subjected to regeneration process for subsequent absorption process. In the regeneration process the CA bed is reactivated for subsequent absorption process by decomposition of active ingredient, the Potassium bicarbonate to potassium carbonate, water, and Carbon dioxide by following chemical action,
Regeneration process: 2KHCO3= K2CO3 + CO2 + H2O
[62] The CO2 absorbed CA bed is heated to about 100 to 250°C, (preferably 210°C as most of the KHCO3 will decompose completely to K2CO3 by this temperature) where it should reach 210°C within 15-20 minutes and needs to last at 210°C at least around 2 hours. With increase in temperature, the potassium bicarbonate (2KHCO3) decomposes in to Potassium carbonate (K2CO3), Carbon Dioxide (CO2) and water. Higher temperature yields faster regeneration. and is allowed to cool naturally to ambient temperature in the heating equipment. It can also be cooled faster by forced ambient air circulation in the heating equipment.
[63] The CO2 absorption by the CA bed and regeneration and cooling of regenerated CA bed is a batch process. The timings for each of the absorption, regeneration and cooling may vary, depends on the field of application.
[64] The CA Bed disclosed in the present invention is efficiently works for upto 800 absorption and regeneration cycles, consisting of absorption, regeneration, and cooling steps. Beyond 800 cycles, the bed might not perform.
[65] It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
, Claims:We claim
1. Composition of a carbon dioxide absorbent bed (CA Bed) comprises:
an active component, that acts as active CO2 absorbent;
a support matrix provides structure and porosity for absorption of CO2;
a binder provides a good mechanical integrity and strength with catalytic advantage (due to presence of alumina) to improve the overall strength of the absorbent bed;
a solvent to prepare slurry for a molding process of desired shape and size.
2. The carbon dioxide absorbent bed of claim 1, wherein the active component is a potassium bicarbonate.
3. The carbon dioxide absorbent bed of claim 1, wherein the support matrix is SLA-92.
4. The carbon dioxide absorbent bed of claim 1, wherein the binder is a sepiolite.
5. The carbon dioxide absorbent bed of claim 1, wherein the solvent is a distilled water
6. The carbon dioxide absorbent bed of claim 1, wherein the carbon dioxide bed comprises 60 to 95 parts by weight of active component; 2.5 to 20 parts by weight of support matrix; and 2.5 to 20 parts by weight of binder.
7. Method of manufacturing of a CA bed comprises a process with a steps of:
step 1. preparing a dry mixer by adding an active component of 60-95 parts by weight, a support matrix of 2.5-20 parts by weight, a binder of 2.5-20 parts by weight;
step 2. stirring dry mixer of active component, support matrix, and binder to distribute uniformly;
step 3. preparing wet mix or slurry adding a solvent slowly, and blending until the slurry or wet mix attains uniformity and sticky, contains just the right amount of solvent suitable for the molding process;
step 4. preparing the carbon dioxide absorbent bed of desired shape and size with suitable mold by pouring the wet mix or slurry in to the mold, exerting the suitable pressure to attain desired density.
8. Method of activation of a CA bed comprises a process with a steps of:
step 1. heating of the freshly molded CA bed gradually in a ventilated oven or muffle furnace up to about 350-550°C. (preferably about 400°C) at a heating rate of 2-5°C per minute (preferably at 3°C per minute);
step 2. maintaining the desired temperature (350-550°C), the until the overall heating time of six hours, with increase in temperature the potassium bicarbonate (2KHCO3) decomposes in to Potassium carbonate (K2CO3), Carbon Dioxide (CO2) and water, as per the chemical equation, and become ready for CO2 absorption;
2KHCO3= K2CO3 + CO2 + H2O
step 3. allowing the CA bed to cool down to the ambient temperature naturally
9. Method of absorption by a CA bed comprises process with a step of absorbing of Carbon dioxide (CO2) by the active component potassium carbonate in the presence of humid air, and convert back to Potassium bicarbonate as per the following chemical equation
K2CO3 + CO2 + H2O = 2KHCO3.
10. Method of regeneration of a CA bed comprises a process with a steps of:
step 1. heating the carbon dioxide absorbed CA bed to about 100 to 250°C, (preferably 210°C) with increase in temperature the potassium bicarbonate (2KHCO3) decomposes in to Potassium carbonate (K2CO3), Carbon Dioxide (CO2) and water, as per the chemical equation
2KHCO3= K2CO3 + CO2 + H2O
step 2. allowing to cool naturally or faster by forced ambient air circulation to ambient temperature in the heating equipment