WO2007022595A1

WO2007022595A1 - Adsorbent for gases

Info

Publication number: WO2007022595A1
Application number: PCT/AU2006/001238
Authority: WO
Inventors: Oscar Zelayandia
Original assignee: Agriforce Pty Ltd
Priority date: 2005-08-25
Filing date: 2006-08-25
Publication date: 2007-03-01

Abstract

An aqueous precursor formulation for absorbing gases inclusive of carbon dioxide which contains calcium hydroxide, potassium hydroxide or other alkali metal hydroxide, and water. The precursor formulation may have 5-20 g/l of calcium hydroxide; 45-60 g/l of potassium hydroxide or alkali metal hydroxide and optionally 0.3-1.5 g/l of potassium permanganate. The precursor solution is ready for use when diluted by a factor of 0.5-5% and has a pH of 8.0-13.5.

Description

TITLE

"ADSORBENT FOR GASES" FIELD OF THE INVENTION

This invention relates to an adsorbent for absorbing or trapping gases inclusive of carbon dioxide. The adsorbent may also be used for trapping, sulphur dioxide and nitric oxide as well as gaseous emissions or liquids which contain these gases.

BACKGROUND OF THE INVENTION

The production of carbon dioxide in energy generation processes is becoming a world-wide problem and results in reduced radiation from the planet Earth. This causes the temperature on Earth to rise and a number of life-determining processes to be disturbed. This is known as the "greenhouse" effect. The problems of excess carbon dioxide evolution worldwide can be reduced somewhat by limiting the consumption of energy and energy generation by systems which do not evolve carbon dioxide such as the combustion of hydrogen, production of nuclear energy or solar energy. However this is only a limited solution and in reality the problems of excess carbon dioxide evolution can only be overcome by limiting production of carbon dioxide or devising a method to efficiently absorb or trap carbon dioxide. The same applies to evolution of carbon monoxide which if evolved in excess amounts can only cause harm or injury to both humans and animals.

Calcium hydroxide absorbents for absorbing carbon dioxide are described in US Patent Application 20040048742 which comprises 83-97% calcium hydroxide; 5-25% of water; and 0.05-5.0% of a rheology modifier which may include a phosphoric acid or salt thereof. There also may be included 0.1-6.0% of calcium chloride and 0.01-5.0% of a colour indicator dye. This absorbent is in the form of particles having an average length of 1 mm to 10mm and an average width of 0.5-5.0mm.

Reference also may be made to US Patent Application 20040029730 which describes a carbon dioxide absorbent formulation comprising a pharmaceutically acceptable hydroxide such as calcium hydroxide essentially free of sodium, potassium and barium hydroxides; calcium and/or magnesium chloride; a hardening agent selected from alumina silicate, alumino silicate or complex alumino silicate and a non-film forming binding agent comprising derivatised celluloses, gums and starch. The resulting absorbent granules like the particles of US Patent Application 20040048742 can be used in absorbing carbon dioxide in medical anaesthesiology wherein a gas stream containing carbon dioxide is passed through the absorbent granules or particles.

Reference may be made to prior art references which also disclose calcium hydroxide or calcium oxide as a carbon dioxide absorbent. They include US Patent 6,867,165 which refers to particles of a paste containing calcium hydroxide, water and phosphoric acid; US Patent 6,737,031 which refers to solid calcium oxide or calcium carbonate; US Patent 6,228,150 which refers to a solid absorbent containing calcium hydroxide, calcium sulphate hemihydrate and aluminium metal powder; US Patent 5,455,013 which refers to sludge containing calcium hydroxide and US Patent 5,520,894 which refers to calcium oxide and/or magnesium oxide in the presence of calcium carbonate.

Reference may also be made to other solid carbon dioxide absorbents which may comprise a finely ground mixture of potassium carbonate and alumina (US Patent 3,865,924); synthetic meixnerite which is a magnesium- aluminium double hydroxide structure (US Patent 5,887,622); soda lime (US Patent 5,558,088, 5,228,435 and 6,619,789); magnesium oxide, magnesium hydroxide or magnesium hydroxy carbonate (US Patent 5,390,667); (US Patents 6,387,848 and US Patent 6,712,879) lithium zirconate, an alkali metal oxide and/or an alkaline earth metal oxide (US Patent 6,521 ,926) zeolite (US Patent 6,709,485) and cement (US Patent 6,866,702).

However the use of the abovementioned solid carbon dioxide absorbents has disadvantages in that they are mainly based on the use of a granular metal oxide or hydroxide which is converted into a metal carbonate by absorption of carbon dioxide which is converted back into the metal oxide by subsequent removal of the carbon dioxide. This requires use of an expensive engineering plant to achieve this because when the carbon dioxide is released the mechanism for achieving this is use of a furnace which is heated to extremely high temperatures. In US Patent 5,344,627 reference is made to the use of an alkanolamine which is a liquid for absorbing carbon dioxide from flue gas. The carbon dioxide which is absorbed by the liquid is removed from the liquid again at a different point in the liquid cycle and is then liquefied. The liquid cycle together with the necessary absorption and regeneration columns requires a substantial outlay in plant engineering. Similar comments apply to US Patent 5,832,712 which refers to removal of carbon dioxide from exhaust gases using monoethanolamine and to US Patents 5,736,115, 5,909,908, 6,051 ,161 and 6,883,327 which relate to similar subject matter all using an alkanolamine as a carbon dioxide absorbent. US Patent 6,755,892 refers to the use of amine sorbent beads for absorbing carbon dioxide.

Reference also may be made to US Patent Publication 20050060985 which refers to burning combustion gases including carbon dioxide with a calcareous sorbent such as limestone or calcined dolomite at 650° - 750⁰C wherein the carbon dioxide is trapped within the sorbent. The sorbent is regenerated at a separate sector by calcination. However this process is expensive and uneconomic.

The invention therefore in one aspect relates to a liquid precursor formulation for absorbing carbon dioxide which contains the following components:

(i) calcium hydroxide;

(ii) potassium hydroxide or other alkali metal hydroxide; and

(iii) water.

Preferably the concentration of component (i) is from 5 to 20 g/l, more preferably 5-20 g/l and most preferably 6.5 g/l. The concentration of component (ii) may be from 45 to 60 g/l, more preferably 45 to 50 g/l, and most preferably 46.5 g/l. The precursor solution may have an initial conductivity of 50,000 to 120,000 μS/cm and a specific gravity of 1.0-1.8 and more preferably 1.17. It will also be appreciated that the liquid precursor solution may also contain potassium permanganate for removing other gases from gaseous emissions from boilers or flue gases. Thus such gaseous emissions contain impurities such as sulphur dioxide and nitrogen oxides such as nitric oxide or nitrogen dioxide. The potassium permanganate is useful in facilitating in the removal of such gases from such gaseous emissions. The potassium permanganate when included in the composition may have a concentration of 0.3-1.5 g/l, more preferably 0.5-1.5 g/l and most preferably 1.0 g/l.

The liquid precursor formulation in use is dissolved in water so as to provide a diluted solution which has a pH of 8.0 - 13.5 and more preferably 10.2 - 11.0 and a conductivity of 500 - 60000 μS/cm.

Although the formulation may be diluted in tap water or water around a neutral pH it is desirable that the formulation be dissolved in bore water or sea water which has a high concentration of carbonated salts such as sodium carbonate or bicarbonate as well as sodium chloride which enhances conductivity. In general a dilution factor of the precursor absorbent solution may be from 0.5 - 5.0% although in relation to sea water or bore water this dilution factor may be from 0.5 - 2.5%.

The calcium hydroxide function is to absorb carbon dioxide out of gas streams containing carbon dioxide by reaction with carbon dioxide to form the calcium carbonate. This reaction is favoured by relatively high pH which favours the production of carbonate ion instead of bicarbonate ion. Thus is the purpose of the inclusion of potassium hydroxide.

Potassium permanganate may also be involved in the removal of sulphur dioxide wherein sulphate ion is produced as well as manganese dioxide. However the water itself may assist in efficient removal of sulphur dioxide which may form sulphate anion at high pH.

Nitrogen monoxide or nitric oxide (NO) may also be in the gaseous emissions and the removal of this gas is facilitated by the reaction with permanganate which eventually produces nitrate. The permanganate may be reduced to manganese dioxide.

The high conductivity of the water is desirable because to create a favourable environment for the binding or reaction described above. After the trapping of the carbon dioxide from gaseous emissions which are passed through the diluted solution in use, a solid residue is formed which has a potential use as a road material stabiliser or fertiliser or other application.

When the diluted solution has reached a pH of 6.4 - 6.8, the solid residue will be in the bottom of the container and the water is ready for a reload a new batch of precursor solution. Otherwise, after removal of the solid residue the water remaining can be used for irrigation of crops or further dilution of precursor solution.

When the carbon dioxide is passed through the diluted solution, the gas is bubbled through the solution preferably so that it reaches the bottom of the container so that it is under greater pressure from the weight of the solution so that the pressure will be around 1.5 to 2.5 kilopascal. This pressure results in the carbon dioxide being trapped in the diluted solution and subsequently converted to bicarbonate and subsequently carbonate ion with a subsequent pH drop in the diluted solution to 6.5 to 7.0. There will also be the solid residue as described above which may comprise calcium carbonate, calcium hydroxide and manganese oxide.

The diluted solution of the invention may also be utilised as a method of storage of carbon dioxide, nitric oxide or sulphur dioxide or a combination of these gases for regeneration or disposal as required.

PREPARATION OF PRECURSOR SOLUTION In relation to preparing the precursor solution of the invention, calcium hydroxide at a concentration of 6.5 g/l was mixed with water in a first container and agitated for 15 minutes. The mixture was then allowed to settle and the water separated from the resulting solid residue or sediment.

In a second container potassium hydroxide having a concentration of 47.5 g/l was mixed with water and agitated for 15 minutes.

In a third container 5OL of the solution from the first container was mixed with 10OL of potassium hydroxide solution from the second container and with gentle agitation potassium permanganate having a concentration

1.0 g/l was added. The precursor solution which resulted was used in the examples referred to hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

SHOWN IN THE DRAWINGS

Preference may be made to preferred embodiments shown in the drawings wherein: FIG 1 shows infrared spectra vs time of the gases emitted from the

4WD vehicle and recorded directly in the FTIR instrument in Example 1 ;

FIG 2 shows infrared spectra vs time of the carbon dioxide emitted from the 4WD vehicle and recorded directly in the FTIR instrument in Example 1 ; FIG 3 shows chemigrams (Areas under the infrared peaks) of the carbon dioxide (CO₂) recorded from the 4WD vehicle (420 units cone.) and Air emissions (~ 0 units cone) having regard to Example 1 ;

FIG 4 shows chemigrams (Areas under the infrared peaks) of the carbon dioxide (CO₂) from the 4WD vehicle and recorded after passing through a solution of sea water and the precursor solution (1), bore water and the precursor solution (2) and just air (3) having regard to Example 1 ;

FIG 5 shows chemigrams of CO₂ from the 4WD after passing through sea water (1), bore water (2) and sea water/precursor solution (3) having regard to Example 1 ; FIG 5A and 5B shows an XPS analysis of the sea water deposit referred to in Table 1 ;

FIG 6 shows XPS spectrum (Survey wide scan) of the solid sample in Example 2;

FIG 7 shows XPS spectrum of the carbon region (C1s) and assignments of the C-peaks discussed in Example 2;

FIG 8 shows XPS spectrum of the Oxygen region (O 1s) and assignments of the obtained peaks after deconvolution and curve fitting of the oxygen spectrum discussed in Example 2; FIG 9 shows XPS spectrum of the calcium region (Ca 1s) and assignments of the Ca-peaks discussed in Example 2;

FIG 10 shows XPS spectrum of the manganese region (Mn 1s) and assignments of the Mn-peaks discussed in Example 2;

FIG 11 shows infrared spectrum of the solid sample in Example 2; FIG 12 shows infrared signals of the solid sample obtained in

Example 2 and calcium carbonate. There are clear similarities between the two spectra, indicating that Calcium Carbonate is the main component present in the solid sample;

FIG 13 shows CO₂ (differential between ambient air and concentration in the chamber) of car exhaust prior to trapping in Example 3;

The plateau of readings represent the maximum possible by the gas analysers used in the experiment;

FIG 14 shows CO₂ levels (differential between ambient air and concentration in the chamber) in the plastic container with the bore water and the absorbent solution, before starting the engine described in Example 3;

FIG 15 shows CO₂ levels (differential between ambient air and concentration in the chamber) while bubbling through the bore water solution described in Example 3; FIG 16 shows CO₂ levels (differential between ambient air and concentration in the chamber) while bubbling through the bore water solution described in Example 3;

Having regard to FIG 16, this jump in CO₂ levels occurred when the vehicle emissions were bubbled through the solution too fast and some CO₂ escaped. After adjusting it down the levels fill to below IOOppm again.

FIG 17 shows CO2 levels (differential between ambient air and concentration in the chamber) of car exhaust prior to trapping as described in

Example 4. Having regard to FIG 17 the plateau of readings represents the maximum possible reading by the gas analysers used in the experiment. The vehicle motor was started 20 seconds after beginning of the experiment;

FIG 18 shows CO₂ levels (differential between ambient air and concentration in the chamber) in the plastic container with the bore water and the absorbent solution, before starting the engine as described in Example 4; FIG 19 shows CO₂ levels (differential between ambient air and concentration in the chamber) while bubbling through the seawater solution as described in Example 4;

Having regard to FIG 19, the first 5 readings taken before vehicle motor was started. Jump happened after CO₂ was bubbled through the solution too fast and excess CO₂ was produced that could not be taken up by the reaction of CO₂ with the diluted aqueous and sorbent solution of the invention. The container was later opened to let the build-up of CO₂ escape and the readings consequently dropped to below 100 ppm again;

FIG 20 shows operation of a boiler whereby emissions from the boiler are passed through the diluted absorbent solution of the invention. EXAMPLE 1

The Polymer Testing Laboratory (PTL) of the Department of Fibre Composites Design and Development (FCDD) of the University of Southern Queensland (USQ) in Toowoomba, Queensland, Australia, was requested to detect and measure the amount of carbon dioxide gas (CO₂) present in the exhaust gases of a 4WD vehicle engine before and after being bubbled through a sample of the carbon dioxide absorbent solution of the invention having the formulation described above. Also a X-ray Photoelectron Spectroscopy (XPS) analysis of the solid precipitate formed after passing carbon dioxide through a solution of sea water/absorbent solution is included.

Carbon dioxide was detected and measured using an integrated TA Instruments/Nicolet NEXUS Evolved Gas Analysis system. This system consists of a Nicolet NEXUS FT-IR spectrometer fitted with a TGA Interface Unit (Gas Cell). Carbon dioxide was detected in the infrared region of 2240 - 2400 cm^"1 wavelength. Spectral data were acquired every 30s as the gas emissions were collected into the Gas Cell. The IR Gas Cell and transfer lines between the engine or the Absorbent solution (2OL volume) and the FT- IR unit were held at 220⁰C to avoid condensation of gases.

Initially the gas emissions from the 4WD vehicle were directly connected through a set of rubber hoses to the transfer line of the Gas Cell of the FTIR Instrument. The infrared spectra of the gases in the 400 to 4000 cm^"1 region were collected every 30 seconds for different periods of time. This was followed by recording a similar set of infrared (IR) spectra of the gas emissions collected at the top of a 2OL solution with a 2% v/v of the precursor absorbent solution. Bore water and sea water were used and the IR signals were collected from solutions with and without. In sea water the diluted solution had a pH of 10.4 and conductively of 51 ,400 μS/cm. In the bore water the diluted solution had a pH of 11.0 and a conductivity of 4000 μS/cm. In these experiments the hoses with the gas emissions from the 4WD vehicle (Toyota 4 runner running on standard unleaded petrol) were directly submerged to the bottom of the 2OL tank. The tank was sealed off at the top and the gases emitted from the solution were collected and transferred to the FTIR Gas Cell by a hose attached to the top side of the plastic tank.

The FTIR Instrument used for the detection and measurement over time of carbon dioxide generated from the 4WD vehicle took measurements before and after carbon dioxide trapping with the absorbent solution. The 3D set of infrared spectra collected directly (without being treated by the absorbent solution) from the 4WD vehicle are shown in Figures 1 and 2.

Carbon dioxide has been assigned to the 2230 -2400 cm^"1 region of the FT-IR spectrum. The plots ("chemigrams") below monitor the peak area of this region of the Infrared spectra during emission of exhaust gases from the 4WD vehicle over a period of 60 minutes. In order to avoid the fast bubbling of gases inside of the 2OL tank, there were put inside of the tank only 2 hoses, living the other 2 hoses open to the air. Figure 3 shows the Chemigrams (areas of the CO₂ infrared peak) taken from the 4WD engine and Air. The gases (and Air) were directly collected into the FT-IR Instrument, without passing through the absorbent solution. In Figure 5 the ¹X' and ¹Y' axes represent time (min) and the arbitrary value of the area under the CO₂ peak, respectively. Therefore, it is important to keep in mind that the area of the CO₂ peak is an arbitrary measurement, it doesn't have any particular units, is only suitable for a comparison of the CO₂ areas of one sample (let say gases collected from bore water without the precursor absorbent solution) and another sample (gases after passing through bore water with the precursor absorbent solution). Therefore, in Figure 5 the relative concentration of CO₂ detected from the 4WD is about 420 times higher than the CO₂ in Air.

In Figure 4 the Areas of the CO2 collected after passing through solutions of bore water (1) and sea water (2), both of them with the precursor solution, are shown. As a comparison the peak of CO2 from air (3), is also included.

Figure 5 shows the Chemigrams of CO₂ coming from the 4WD and collected after passing through the 2OL tank of sea water (1) and bore water (2) without the precursor solution (3). As a comparison, the CO₂ collected from Sea Water with the precursor solution (3) is also included. Figure 5 reveals that initially the CO₂ from the 4WD engine that is flushed through sea and bore water, dissolves up to a saturation point. This point is about 7 minutes and 18 minutes for Sea Water and Bore Water, respectively. Above this point, the water can't dissolve any more CO₂ and therefore the gas reach the maximum value (about 420 units of relative concentration) as generated from the 4WD engine.

An X-ray Photoelectron Spectroscopic (XPS) analysis of the sea water deposit was then carried out and shown in FIGS 5A and 5B and Table 1.

The high concentrations of Ca (13.21 %), Carbon (22.60%) and Oxygen (37.36%), indicated that most of the solid residue is CaCO3 (~ 60 % of the total sample). There is also NaCI (~ 8 %), Mg(OH)₂ (~ 20 %) and the rest (~ 12 %) correspond to other different salt forms of Mg and Ca and

Phosphates.

The results from the XPS analysis compare very well with the analysis of the precursor solution/sea water (done in a different laboratory), where a high concentration of chlorides, Sodium, Calcium and Magnesium are reported. The XPS reveals that after the CO₂ from the 4WD engine passes through the solution of sea water/precursor solution the formed solid residue is mainly CaCO₃, magnesium hydroxide and phosphate salts with NaCI also precipitated. EXAMPLE 2

In a similar manner as reported in Example 1 , PTL was requested to chemically characterise a solid precipitate sample. This sample was obtained from the process as described above in Example 1. Specifically the following tests were performed in the characterization of the chemical composition of the solid residue sample:

• X-Ray Photoelectron Spectroscopic (XPS) Analysis.

• Infrared Spectroscopy (FT-IR) of the solid sample in KBr tablets.

This example details the results of these tests, conducted on the solid residue.

The sample used for analysis was obtained by filtration of the solid residue at the bottom of a liquid absorbent solution. The filtrate was dry until constant weight in the oven at 60 ⁰C. Techniques used for analysis and findings

3.1. X-Ray Photoelectron Spectroscopy (XPS)

Description of the XPS Technique:

X-Ray Photoelectron Spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA) is routinely used to obtain detailed chemical analysis of organic and inorganic samples. In XPS x-rays hit the sample producing photoelectrons whose energy is measured. The energy is specific to each element and is used to identify all elements (except hydrogen and helium) present in the outer 100 A of the surface (detection limits ca. 0.1 atomic percent). In summary, XPS provides information on a) Surface concentrations of elements present, b) The bonding state (molecular environment) and/or oxidation state for most atoms, c) Aromatic

or unsaturated structures from shake-up (π → %^*) transitions, d) Surface

electrical properties from charging studies, e) Surface heterogeneity using non-destructive depth profiling and assessment using angular dependent ESCA. f) Underlying surface layers by destructive depth profiling using argon etching (for inorganics samples), g) Functional groups on surfaces by positive identification through the use of derivatization reactions.

Figures 6 to 10 show the XPS spectra of the solid sample (Survey), Carbon, Oxygen, Calcium and Manganese regions, respectively. The assignments of the different peaks present in each spectral region are included and the Tables with the values of Atomic Mass and relative concentrations (Atomic Cone. And Mass Cone, %) of the chemical species present in the sample.

3.2. Fourier Transform Infrared Spectroscopy (FT-IR)

FT-IR is a technique used to characterise the chemical structure of materials. In this technique, a beam of (infrared) light is shone on a material and the way in which this light is absorbed as a function of the light frequency is monitored. This absorption versus frequency spectrum provides a "fingerprint" of the material and can be used to infer its chemical structure.

FT-IR spectra were collected using FCDD's Nicolet Nexus FT-IR spectrometer in a Transmission mode, via mixing of the sample (2 % w/w) with Potasium Bromide (KBr) salt, which provides the background of the Infrared spectra. FT-IR spectra in the mid-IR region of the spectrum (4000 cm^"1 to 700 cm^'1) were taken, as shown in Figure 11. Figure 12 shows the Infrared signal of the sample and the Infrared spectrum of Calcium Carbonate. The similarity of both spectra indicates that most of the Infrared signal of the solid sample corresponds to Calcium Carbonate (CaCOs), confirming the results obtained from the XPS analysis. The large peak at 3446 cm-1 corresponds to the stretching vibrations of the O-H groups present in Ca(OH)₂ and from any residual moisture (H₂O) still present in the sample. The peak at 2362 cm-1 corresponds to CO₂ present in the environment during the scanning of the sample. According to the above presented XPS and Infrared analysis of the solid sample, the relative concentration (%) of the different chemical species are shown in Table 4. EXAMPLE 3

Quantification of CO₂ gas in exhaust of 4WD vehicle after 'trapping' with the precursor solution diluted in bore water (ie. "bore water solution").

1. Aim of the experiment

This experiment aimed at quantifying the CO₂ (carbon dioxide) levels in the emissions from a 4WD vehicle, after 'trapping' them in the bore water solution. The absorbent solution is designed to consume most of the CO₂ emitted from combustion engines in a chemical reaction that takes place inside 'salty' bore water. Water from many Australian bores is high in carbonated salts eg sodium carbonate or calcium carbonate. In the absorbent solution, CO₂ from a combustion engine is bubbled through bore water to which a chemical solution was added.

The levels of CO₂ before and after bubbling through the absorbent solution are to be quantified.

2. Material and Methods

To prove that most of the CO₂ is, indeed, extracted from the emissions, the exhaust from a 4WD vehicle before and after 'trapping' was connected to a chamber that is normally used to measure plant CO₂ uptake in photosynthesis. The CO₂ chamber (BIOSYSTEMS ENGINEERING,

Queensland) was connected to the gas analysers of a Licor-6400 portable photosynthesis system (LI-COR, Nebraska). This system is designed to measure CO₂ concentration inside a chamber and compare that with the CO₂ concentration of ambient air. The readings quoted here are therefore, the difference between ambient air CO₂ (usually around 379 ppm) and the CO₂ concentration in our chamber. Because the gas analysers are designed to measure very small CO₂ concentration differentials typical for plant CO₂ fluxes, their detection range has a maximum of approx. 3000 ppm OfCO₂. As a combustion engine's output is much higher than 3000 ppm, we could only show how quickly the maximum reading was reached when the exhaust was attached to the chamber without running through the absorbent solution. These gas analysers, however, were very capable of detecting any CO₂ present in the sample while the reaction was taking place.

Prior to 'trapping', the exhaust from the 4WD vehicle was connected directly to the chamber with the gas analysers. During the 'trapping', the exhaust was connected to a sealed 20 L plastic container holding the mixture of bore water and the absorbent solution. The plastic container itself was connected with the chamber via a hose. Before the engine was started, the CO₂ levels in the 20 L container containing the bore water were measured. The bore water was tested for conductivity and pH before and after

'trapping'.

3. Results

After connecting the exhaust directly to the CO₂ chamber, the CO₂ levels very quickly rose to a maximum reading of approximately 3600 ppm as shown in FIG 13.

We then connected the CO2 chamber to the container with the 20 L of bore water. The bore water used had a pH of 7.5 and an electrical conductivity of 3.6 mS. After adding 100 ml of the precursor solution to the 20 L of bore water the pH rose to 11.3 and the EC measured 4.0 mS.

The CO2 levels in the plastic container with the bore water and the absorbent solution, before connecting to the vehicle emissions, were around 15 ppm as shown in FIG 14.

After connecting the 4WD exhaust to the absorbent solution the CO₂ levels were consistently below 100 ppm for as long as the vehicle emissions were passed through the bore water and the chemical reaction was taking place as shown in FIGS 15 and 16.

This experiment was designed to run until the salty water solution is exhausted. In a 20 L container this normally takes at least one hour. For the purpose of this experiment where the main emphasis was on CO₂ levels, we stopped the reaction after 25 minutes. The pH then measured 8.1 and the

EC measured 3.7 mS. In a later trial where the reaction was run for the full hour, the same bore water ended up with a pH of 6.5 and an EC of 2.3 mS.

After the chemical reaction takes place, white sediment becomes visible at the bottom of the container and the bore water looks clear instead of cloudy.

Conclusions

These experiments show that CO₂ is taken out of the emissions of the exhaust of a combustion engine when bubbled through salty bore water combined with the diluted absorbent solution. Compared to the high readings that were measured shortly after connecting the engine exhaust to the chamber, constant readings of below 100 ppm of CO2 (differential between ambient air and concentration within the chamber) are extremely low and would indicate that the absorbent solution is very efficient at removing CO₂ from the emissions. Because the portable photosynthesis system is normally used to measure plant CO₂ uptake (very low range), it is extremely sensitive and therefore very reliable at detecting any CO₂ left in the system.

According to the theory behind the absorbent solution, the carbonates present in the bore water have 'used up' the CO₂ from the engine emissions in a chemical reaction and the product of this reaction has precipitated to the bottom of the container. EXAMPLE 4

Quantification of CO₂ gas in exhaust of 4WD vehicle after 'trapping' with the precursor solution in seawater

1. Aim of the experiment

The aim of this experiment was to test the efficiency of the precursor solution in 'trapping' the CO₂ (carbon dioxide) emissions from a 4WD vehicle using seawater. The previous experiment in Example 3 to quantify the levels of CO₂ before and after bubbling through the absorbent solution was repeated, but instead of salty bore water, seawater was used. 2. Material and Methods

The same experimental set-up as described in the first report was used for this experiment with the exception of using seawater instead of bore water. The exhaust from a 4WD vehicle was directly connected to a chamber that is normally used to measure plant CO₂ uptake in photosynthesis. The CO₂ chamber (BIOSYSTEMS ENGINEERING, Queensland) was connected to the gas analysers of a Licor-6400 portable photosynthesis system (Ll- COR, Nebraska). This system is designed to measure CO₂ concentration inside a chamber and compare that with the CO₂ concentration of ambient air. The readings quoted here are therefore, the difference between ambient air CO₂ (usually around 379 ppm) and the CO₂ concentration in our chamber. Because the gas analysers are designed to measure very small CO₂ concentration differentials typical for plant CO₂ fluxes, their detection range has a maximum of approx. 3000 ppm of CO₂. As a combustion engine's output is much higher than 3000 ppm, we could only show how quickly the maximum reading was reached when the exhaust was attached to the chamber without running through the absorbent solution. These gas analysers, however, were very capable of detecting any CO₂ present in the sample while the reaction of carbon dioxide with the absorbent solution was taking place.

Prior to 'trapping', the exhaust from the 4WD vehicle was connected directly to the chamber with the gas analysers.

During the 'trapping', the exhaust was connected to a sealed 20 L plastic container holding the mixture of seawater (collected from Moreton Bay) to which 100ml of the absorbent solution was added. The plastic container itself was connected with the chamber via a hose.

The seawater was tested for conductivity and pH before and after 'trapping' and a sample each of the water before and after treatment was sent away for a full laboratory analysis.

3. Results

After connecting the exhaust directly to the CO₂ chamber, the CO₂ levels very quickly rose to a maximum reading of approximately 3600 ppm as shown in FIG 17. The CO₂ chamber was then connected to the container with the 20 L of seawater. The seawater used had a pH of 8.28 and an electrical conductivity of 4.96 mS. After adding 100 ml of the precursor solution to the

20 L of seawater the pH rose to 9 and the EC measured 5.24 mS.

The CO₂ levels in the plastic container with the bore water and the absorbent solution before connecting to the vehicle emissions were measured in the first experiment and were around 15 ppm as shown in FIG

18.

After connecting the 4WD exhaust to the absorbent solution, the CO₂ levels were consistently reduced from 3600 ppm to around 100 ppm for as long as the vehicle emissions were passed through the seawater and the chemical reaction was taking place as shown in FIG 19.

The experiment was stopped after one hour and at that point the pH of the water measured 9.8 with an EC of 5.1 mS. 4. Conclusions

These experiments show that the reduction of CO₂ emissions of the exhaust of a combustion engine when bubbled through the absorbent solution can also be achieved by using seawater. Compared to the high readings that were measured shortly after connecting the engine exhaust to the chamber, constant readings of below 100 ppm of CO₂ (differential between ambient air and concentration within the chamber) are extremely low and would indicate that the absorbent solution is very efficient at removing CO₂ from the emissions even when using seawater.

It will be noted from this Example as well as previous Examples 1-3 that manganese dioxide was a component of the solid residue and this resulted from the diluted absorbent solution trapping of nitric oxide present in the exhaust emissions which were not monitored. Sulphur dioxide absorbed in the diluted absorbent solution also was not monitored. EXAMPLE 5

In FIG 20 is shown an example of the absorbent solution of the invention in use in relation to trapping carbon dioxide from gases from a boiler 10. Water is heated in the boiler 10 to generate high pressure steam whose passage in conduits 11 is shown by the arrows in full outline for activating a turbine 12 as shown. The water is heated in the furnace chamber 13 as shown and emissions from the boiler through conduit 14 are passed through a fabric filter 15 to filter out any fly ash before the resulting smoke is discharged from the emission stack 16. A certain amount of such emissions (e.g. 30-50%) is passed through one of containers 17A and 17B which contain the diluted absorbent solution of the invention. A precipitate from the absorbent solution may be reused as required. Two containers 17Aand 17B are shown one of which can be used as a changeover container as required. The resulting "clean" water with carbon dioxide removed is then returned to the to the boiler as shown through conduit 18.

Water to boiler 10 is transported through conduit 19 and reheated steam is passed to turbine 12 through conduit 20 . Furnace ash is passed from furnace chamber 13 through conduit 21 for ultimate disposal from conduit 22. There is also fly ash from fabric filter 15 also passed into conduit 22 as shown. Air plant 23, coal bunker 24 and pulverising mill 25 are also shown. Coal 26 is passed into bunker 24 along conveyors 27 from storage container 28.

In another aspect of the invention there is provided a method of trapping gaseous emissions containing carbon dioxide, nitric oxide or sulphur dioxide or combinations thereof which includes the step of passing said gaseous emissions through a diluted absorbent solution of the invention. EXAMPLE 6

An experiment in relation to the absorbent solution of the invention was carried out at Tarong Power Station, Queensland, Australia. The flue gas of the power station was reduced to 4 kilopascal pressure and a flow rate was produced of 12 litres per minute at 21⁰C. The detection apparatus utilised could read the presence of sulphur dioxide, nitric oxide, nitrogen dioxide, carbon dioxide and the presence of particulate matter. The experiment referred to dissolving the precursor solution used in Examples 1- 5 in containers of water i.e. (i) residual water for cooling used at the power station; (ii) bore water and (iii) "ash recycled water" from the power station. A control (iv) was utilised using dam water which did not include the aqueous precursor solution. For containers (i) (ii) and (iii) a 2% solution of the precursor solution was made i.e. dissolving 1.2 I of the precursor solution in 60 I or water. This is shown in Tables 5, 6, 7 and 8 attached herewith. Table 5 refers to water type (i). Table 6 refers to water type (ii). Table 7 refers to water type (iii) and Table 8 refers to the control. The containers for each of (i), (ii) and (iii) were sealed. The results are shown graphically in FIGS 21 and 22 and it will be appreciated that the results for the control have to be subtracted from the results obtained in Tables 5, 6 and 7. The majority of the gas reductions seen for the first 15-20 minutes in each of Tables 5, 6, 7 and 8 are due to dilution of the flue gas in water. However, for carbon dioxide there is shown 23.3% removal at the end of 30 minutes for example in relation to cooling water. There is also shown a corresponding reduction of 6.4% in NOX.

Table 1.

Concentration of the atomic species detected in the solid residue after flushing of CO₂ through sea water in Example 1.

Peak Posxtion FHHH Rau Rrea RSF Htonic Rtotiic Mass

BE (eV) <eV> (CPS) Hass Cone % Cone %

C Is 282.000 3.348 85600.0 0.278 12.011 33.79 22.60

0 Is 529.000 3.680 293680.0 0.780 15.999 41.92 37.36

Ca 2p 348.000 7.702 98780.0 1.833 40.078 5.92 13.21

Mg 2s 86.000 3.183 16950.0 0.252 24.312 7.39 10.00

P 2p 130.000 3.105 17250.0 0.486 30.974 3.90 6.73

Cl 2p 19G.O0O 3.358 25095.0 0.891 35.460 3.09 6.11

Na Is 1069.000 2.838 21550.0 1.685 22.990 1.75 2.24

N as NOS 404.000 2.953 3820.0 0.477 14.007 0.88 0.69

H as orgaπo N 397.000 2.888 5920.0 0.477 14.007 1.36 1.06

Table 2.

Different elements and the relative concentration (%) detected in the XPS analysis in Example 1.

Peak Position FMHH Rau Rrea RSF Htonic Htonic Hass

BE (eV> (eV) (CPS) Hass Cone % Cone %

C Is 282.000 2.904 110355.0 0.278 12.011 43.78 29.07 0 Is 529.000 3.226 294005.0 0.780 15.999 42.18 37.31 Ca 2p 344.000 2.894 138310.0 1.833 40.078 8.33 18.46 Hn Ep 640.000 4.153 99450.0 2.659 54.938 4.31 13.08 Ha Is 1068.000 2.963 12210.0 1.685 22.990 0.99 1.26 Cl 2B 196.000 3.882 3333-0 0.891 35.460 0.41 0.81

Table 3.

Different chemical species and their relative concentrations detected in the XPS spectra of the carbon and oxygen regions.

Peak Position FMHH Raw Rrea RSF Rtonic Rtonic Hass

BE teV) (eV) (CPS) Mass Cone % Cone /i

Oxide 529.610 1.300 1739.0 0.780 15.999 8.21 9.31

0 en Carbonate 531.109 1.300 8067.6 0.780 15.999 38.09 43.15

0 organic 532.388 1.573 1408.0 0.780 15.999 6.64 7.53

C-C 281.807 1.150 1935.9 0.278 12.011 28.35 24.11

C-O 286.144 1.150 239.2 0.278 12.011 3.50 2.98

C=O 287.494 1.150 37.8 0.278 12.011 0.55 0.47

C03 289.308 1.176 1002.6 0.278 12.011 14.65 12.4G

Table 4.

Relative concentration of chemical specifications of the solid sample in Example 2.

Table 5

Table 6

Table 7

Table 8

Substitute Sheet (Rule 26^ RO/ATT

Claims

CLAIMS:

1. An aqueous precursor formulation for absorbing gases inclusive of carbon dioxide which contains the following components:

(i) calcium hydroxide; (ii) potassium hydroxide or other alkali metal hydroxide; and

(iii) water.

2. An aqueous precursor formulation as claimed in claim 1 which also contains (iv) potassium permanganate.

3. An aqueous precursor formulation as claimed in claim 2 wherein component (i) has a concentration of 5-20 g/l component (ii) has a concentration of 45-60 g/l; and component (iii) has a concentration of 0.3-1.5

g/l.

4. A liquid precursor formulation as claimed in claim 3 wherein the concentration of component (i) is 5-12 g/l; the concentration of component (ii) is 45-50 g/l; and the concentration of component (iii) is 1.0 g/l.

5. An aqueous formulation as claimed in claim 4 wherein the concentration of component (i) is 6.5 g/l; the concentration of component (ii) is 46.5 g/l and the concentration of component (iii) is 1.0 g/l.

6. An aqueous precursor solution as claimed in any preceding claim having a conductivity of 50,000-120,000 μs/cm.

7. An aqueous precursor solution as claimed in any one of claims 1-5 further diluted in water by a factor of 0.5-5.0% and having a pH of 8.0-13.5.

8. A diluted aqueous solution as claimed in claim 7 having a pH of 10.2- 11.0.

9. A diluted aqueous solution as claimed in claims 7 or 8 having a conductivity of 500-60,000 μs/cm.

10. An aqueous precursor solution as claimed in any one of claims 7-9 further diluted in water by a factor of 2.5-5.0%.

11. An aqueous solution for absorbing carbon dioxide which has: (i) 5-20 g/l of calcium hydroxide;

(ii) 45-60 g/l of potassium hydroxide or other alkali metal hydroxide;

(iii) a pH of 8.0-13.5; and (iv) a conductivity of 50,000-120,000 μs/cm.

12. An aqueous solution as claimed in claim 11 having (v) 0.3-1.5 g/l of potassium permanganate.

13. An aqueous solution as claimed in claim 11 or 12 wherein the pH is 10.2-11.0.

14. A method of trapping gaseous emissions containing carbon dioxide and nitric oxide which includes the step of passing said gaseous emissions through a diluted aqueous solution as claimed in any one of claims 7-10.

15. A method as claimed in claim 14 wherein said diluted aqueous solution is placed in a container in fluid communication with said gaseous emissions and said gaseous emissions are passed through the container leaving behind a solid residue for use as a road stabiliser.