Carbon dioxide is the major nonhydrocarbon gas found in coal beds, and can range from 0% to 99% of the total gas in coal beds (Rice, 1993).
Related terms:
Carbon Dioxide
S. Goel, D. Agarwal, in Encyclopedia of Toxicology (Third Edition), 2014
Background
Carbon dioxide (CO2) is a naturally occurring colorless and odorless gas. It has a boiling point of −70°C (sublimes), vapor density of 1.53, and is slightly soluble in water. The atmospheric concentration in preindustrial times was 0.028% and in May 2013 was 0.04% recorded at Mauna Loa, Hawaii, USA. It is essential for the survival of most living organisms and cycles in the ecosystem, through respiration (aerobic and anaerobic), photosynthesis, and combustion. Carbon dioxide plays an important role in the regulation of earth's temperature, and is one of the greenhouse gases.
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Carbon Dioxide
Swarupa G. Kulkarni, Harihara M. Mehendale, in Encyclopedia of Toxicology (Second Edition), 2005
Human
Carbon dioxide is a simple asphyxiant that displaces oxygen from the breathing atmosphere resulting in hypoxia. Four stages have been described (depending on the arterial oxygen saturation): (1) indifferent stage, 90% oxygen saturation; (2) compensatory stage, 82–90% oxygen saturation; (3) disturbance stage, 64–82% oxygen saturation; and (4) critical stage, 60–70% oxygen saturation or less.
Following exposure to asphyxiants, cardiovascular effects like tachycardia, arrhythmias, and ischemia are noted. Carbon dioxide exerts a direct toxic effect to the heart, resulting in diminished contractile force. It is also a vasodilator and the most potent cerebrovascular dilator known. Respiratory effects like hyperventilation, cyanosis, and pulmonary edema are also noted. Various neurologic effects like dizziness, headaches, sleepiness, and mental confusion can occur. Prolonged hypoxia may result in unconsciousness; seizures may be seen during serious cases of asphyxia. Gastrointestinal effects, like nausea and vomiting, may occur, but usually resolve within 24–48h following termination of exposure. Decreased vision and increased intraocular pressure may be seen with inhalation of 10% carbon dioxide. Combined respiratory and metabolic acidosis was seen in a serious exposure to dry ice. The Lake Nyos disaster in August 1986 has been postulated to have resulted from the release of carbon dioxide from rising cold deep water producing a deadly cloud of gas. Cough, headache, fever, malaise, limb swelling, and unconsciousness were noted in the victims. Inhalation of carbon dioxide is teratogenic and has caused both male and female adverse reproductive effects in rodents. Increased fetal movements have been noted in humans following inhalation with 5% carbon dioxide in air.
The lowest lethal concentration (inhalation) for humans is 100000ppm for 1min. Carbon dioxide concentrations of 20–30% can cause convulsions and coma within 1min. Unconsciousness may occur when inhaling a concentration of 12% for 8–23min. Inhalation of 6–10% causes dyspnea, headache, dizziness, sweating, and restlessness.
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CARBON DIOXIDE
C.L. Sabine, R.A. Feely, in Encyclopedia of Atmospheric Sciences, 2003
Introduction
Carbon dioxide (CO2) is considered a trace gas in the atmosphere, with contemporary concentrations of approximately 370 parts per million by volume (ppm). Despite its low concentrations relative to those of nitrogen or oxygen, CO2 plays a significant role in the Earth's life cycle and in controlling the global climate.
CO2 is released as a by-product of aerobic respiration. Plants take up CO2 and release oxygen as a part of photosynthesis. Variations in the global balance between photosynthesis and respiration result in seasonal variations in atmospheric CO2 of up to 15ppm. For example, atmospheric CO2 concentrations in the Northern Hemisphere are generally lower in the summer, when many plant species enter a new growth stage and photosynthesis predominates over respiration. CO2 is also a greenhouse gas that absorbs long-wavelength radiation in the atmosphere, attenuating its escape into space. The trapping of radiation by CO2 and other greenhouse gases (e.g. water vapor, methane, nitrous oxide, and chlorofluorocarbons) helps keep the planet warmer than it would be without an atmosphere. It is this greenhouse warming that makes life, as we know it, possible on planet Earth.
Mankind is currently in the process of altering the chemistry of the global atmosphere. Atmospheric CO2 concentrations have been increasing as a direct result of human activities such as deforestation and the burning of fossil fuels (e.g., coal and oil). Over the past 150 years, CO2 concentrations in the atmosphere have increased by as much as 30% (from 280 to 370ppm; Figure 1). This has been accompanied by an increase in global mean surface temperature of between 0.4 and 0.8°C. The present rate of increase in CO2 is unprecedented over the last 20000 years.
Figure 1. CO2 concentrations in Antarctic ice cores (symbols) and annual mean concentrations from direct atmospheric measurements (line) for the past millenium. Prior to the industrial revolution atmospheric CO2 values were very near 280ppm. For the past 150 years atmospheric concentrations have been increasing exponentially. (Adapted from Prentice et al. (2001).)
This article briefly describes the complicated role that CO2 plays on the planet Earth, the different pools where carbon is stored, and the ways in which carbon is transferred between pools over various periods. We will focus on those pools (reservoirs) and transfers (fluxes) with time scales relevant to the human alteration of the natural carbon cycle. In addition, scientific issues relevant to future atmospheric CO2 concentrations will be discussed along with a brief introduction to some of the global policy issues regarding regulation of future CO2 emissions.
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CO2 adsorption by conventional and nanosized zeolites
Ali Bakhtyari, ... Chang-Ha Lee, in Advances in Carbon Capture, 2020
9.1.1 Carbon dioxide, properties, and hazards
Carbon dioxide, also called carbonic acid gas, contains a central carbon atom attached to two oxygen atoms through covalent double bonds. The properties of carbon dioxide are tabulated in Table 9.1.
Table 9.1. Properties of carbon dioxide [1].
| Property | Quantity | Unit |
|---|---|---|
| Molecular weight | 44.009 | kg/kmol |
| Kinetic diameter | 3.30 | Å |
| Polarizability | 29.1×10−25 | cm3 |
| Quadrupole moment | 4.3×10−26 | esucm2 |
| −1.43×1013 | cm2 | |
| Phase change | ||
| Sublimation (at 1atm) | 163.9 | K |
| Boiling point | 194.7 | K |
| Vapor pressure (at 293K) | 57.3 | bar |
| Triple point | 216.58 | K |
| 5.18 | bar | |
| Critical point | ||
| Critical temperature | 304.18 | K |
| Critical pressure | 73.80 | bar |
| Critical density | 478.78 | kg/m3 |
| Compressibility factor | 0.268 | – |
The increasing consumption of hydrocarbons has induced a 30% increase in the concentration of carbon dioxide since the preindustrial period [2]. The concentration of carbon dioxide is predicted to reach about 26billiontons/year in 2100 [2, 3]. Therefore, carbon dioxide capture and reuse are attracting significant attention. The utilization of carbon dioxide as a reactant in manufacturing chemicals also helps reduce the aftereffects of its emission [4]. More information about the utilization and economy of carbon dioxide could be found elsewhere [4–14].
The accumulation of gases released from fossil fuel incineration in the atmosphere results in the trapping of heat within the earth, which is technically referred to as the greenhouse gas (GHG) effect. Carbon dioxide is the most significant GHG. Thus, developing efficient, environmentally friendly, and cost-effective processes for the separation of carbon dioxide is of paramount importance. For this purpose, various separation techniques such as physical/chemical absorption [8, 14–34], membrane-based processes [35–40], and physical/chemical adsorption [2, 41–57] have been developed. Furthermore, developing efficient methods for carbon dioxide storage [7, 8, 47, 58] is of concern to industries. Several separation methods, their advantages, and limitations are well discussed elsewhere [32]. Adsorption-based alternatives have attracted significant attention in relation to commercialization due to their hitherto unprecedented capabilities. The adsorption method shows promise for the separation and storage of carbon dioxide due to its low energy consumption, low capital cost, large adsorption capacity, high carbon dioxide selectivity, easy adsorbent regeneration, facile recovery of adsorbed carbon dioxide, and the durability and stability of adsorbents [2, 41, 47, 51, 52].
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Introduction
William D. Fletcher, Craig B. Smith, in Reaching Net Zero, 2020
What are the greenhouse gases?
Carbon dioxide is the most common greenhouse gas and accounts for about 76% of greenhouse gases. The next largest greenhouse gas is methane, followed by nitrous oxides and fluorinated gases released by industrial processes. Most of the carbon dioxide, 90%, comes from the burning of fossil fuels, namely coal, oil, and natural gas. Coal- and natural gas-fired power plants generate electricity. Oil-based products such as gasoline, diesel fuel, and aviation fuel provide most of the energy used in transportation. Industry also uses fossil fuel to produce power and heat needed by industrial processes. Residential and commercial buildings use electricity for air-conditioning and lighting and oil and natural gas for heating (Photo 1.1).
Photo 1.1. Coal burning power plant, Iowa.
Land-use changes, mainly the destruction of forests to clear land for crops and animals, are another source of carbon dioxide. Trees and other plant materials absorb carbon dioxide as part of photosynthesis and naturally remove carbon dioxide from the atmosphere. When forests are destroyed, more carbon dioxide has to remain in the atmosphere or is absorbed by the oceans.
Why is carbon dioxide suddenly a problem? For a long time, probably at least 100 years, few people thought anything about the fact that human beings were now burning increasing amounts of coal and then oil and natural gas. We were too busy enjoying the benefits provided by abundant low-cost energy.
In 1958 a young atmospheric scientist employed by Scripps Institution of Oceanography named Charles Keeling began making measurements from an observatory on the top of Mauna Loa, on the Big Island of Hawaii. This site was selected because it was in the middle of the Pacific Ocean and relatively unaffected by air pollution and other effects from the continents. After several years of measurements, Keeling discovered that the concentration of carbon dioxide in the atmosphere was steadily increasing. He subsequently devoted his life to continuing these measurements and was followed later by his son and other research institutions. As a result, we now know that there has been an ever-increasing concentration of carbon dioxide in the atmosphere. Other measurements indicate that the average temperature of the earth has been increasing simultaneously with the increase in carbon dioxide. In effect, adding carbon dioxide to the atmosphere is equivalent to adding more layers of glass to the greenhouse, causing the earth’s temperature to rise (Photo 1.2).
Photo 1.2. Mauna Loa Observatory, NOAA, Hawaii.
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Membranes, Synthetic, Applications
Eric K. Lee, W.J. Koros, in Encyclopedia of Physical Science and Technology (Third Edition), 2003
III.D.3 Acid Gas Removal
Carbon dioxide, hydrogen sulfide, hydrogen chloride, sulfur dioxide, and some oxides of nitrogen are collectively referred to as acid gases. They are responsible for the “sour” nature of fuel gases from various sources. Carbon dioxide separation was the first large-scale applications developed; it remains one of the most important because of the abundance of carbon dioxide in gas mixtures. Another factor is that membranes exhibiting high permeability toward polar gases were relatively easy to develop based on desalination membrane technology already available.
Large quantities of carbon dioxide have been used in times of high energy costs in conjunction with enhanced oil recovery (EOR). This practice of injecting the gas at high pressure into geological formations to increase oil and natural gas yield, although highly effective, also increases the concentration of carbon dioxide in the natural gas produced and thus reduces its energy value. Moreover, the cost of EOR would be prohibitively high unless the carbon dioxide is reused. Membranes have been used successfully at production wells to separate the carbon dioxide for reinjection while delivering a purified methane stream. Figure 18 shows a multistage process for reducing the carbon dioxide level of natural gas from 7 to 2% while achieving almost 95% methane recovery. Using carbon dioxide, permselective membranes such as cellulose acetate or various polyimides, the product natural gas stream remains at high pressure and requires little recompression for further processing. Such systems have proved to be much more economical to install and operate than diethylamine absorption, the prevailing method of gas treating.
FIGURE 18. Multistage carbon dioxide recovery from natural gas in enhanced oil recovery operation.
Depending on source, geographic location, and the extent of extraction, the acid gas content of fuel gases often exceeds pipeline specifications. Certain natural gases and landfill gases can contain up to 50% carbon dioxide. Bulk removal of both carbon dioxide and hydrogen sulfide from such sources, i.e., the process of “sweetening,” not only improves the fuel value of the gas, but also helps reduce corrosion of pipelines and transmission equipment. Membranes are suitable for this application especially where the scale is relatively small and the economics favor scalable membrane systems.
Sulfur dioxide is a common pollutant found in coal-fired facilities. Various membrane permeation schemes have been proposed but few are competitive with wet scrubbing. More recently, however, bipolar membrane technology (q.v.) has been successfully used to recycle the scrubbing effluent and convert the sulfur into sulfuric acid.
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Karst Geomorphology
J.M. James, in Treatise on Geomorphology, 2013
6.25.3.2 Carbon Dioxide
Carbon dioxide, only a minor gas in the surface atmosphere, is the most studied gas in caves. In well-ventilated caves, carbon dioxide enrichment is only slightly above the average dry surface atmospheric concentration of 0.04%. In poorly ventilated caves, it can have concentrations that outstrip those of oxygen. James (2003a) discussed sources and elevated concentrations of carbon dioxide occurring in caves. Badino (2009) detailed carbon dioxide distribution and movement within caves, both spatially and temporally.
Carbon dioxide hydrates and hydrolyzes in water to form the weak acid – carbonic acid. It is a critical component in both the solution of limestone bedrock and precipitation of calcite speleothems:
In the above equilibrium equation, the red arrows show the forward reaction, which represents the solution of limestone (CaCO3). A high concentration of carbon dioxide in the cave air will induce a high concentration of carbon dioxide in solution, thus enhancing its corrosive power. The blue arrows show the reverse reaction, which represents the formation of calcite speleothems by the degassing of carbon dioxide. If the concentration of carbon dioxide is lower in cave air than in the calcium carbonate-saturated water, the water will degas carbon dioxide and calcite precipitation takes place. As the differential between the atmospheric and aqueous carbon dioxide is reduced, the precipitation reaction slows. If the concentration of carbon dioxide becomes higher in the air than in the water, the reverse reaction cannot take place and solution will occur.
Hill and Forti (1997a) reviewed the large number of calcite speleothems that need an air–water interface to form. In Tommy Grahams, a Nullarbor cave, a core was taken from a calcite mass at a depth of –22m in a completely flooded passage. The core (Figure 10) was found to have laminar calcite above a mass of calcite rafts. Formation of calcite rafts requires an air–water interface and a still-water surface. A deposit of subaqueous laminar calcite directly above the rafts gave an age of 80±5ka using uranium series dating. The calcite rafts must have formed before this and when there was air in the cave passage. Water levels in the Nullarbor Caves are maintained by sea level in the Great Australian Bight (Lowry and Jennings, 1974). Hence, prior to 80ka ago, there was a period of low sea level in the Bight allowing the cave to drain and provide an air space suitable for raft formation (Contos, 2001).
Figure 10. A core from Tommy Grahams, Nullarbor karst, Australia. The core contained a mass of calcite rafts below laminar mixing zone calcite. Photo by Julia M James.
James et al. (1998) studied automobile emissions in the 165-m-long Grand Arch at Jenolan Caves (Figure 1). The road through the Grand Arch takes hundreds of vehicles a day. Carbon dioxide is the major combustion product of automobile fuel. Calculations have shown that if all the automobile carbon dioxide is retained in the Grand Arch, its concentration would be more than the double that of the surface atmosphere. The excellent ventilation of the Grand Arch removes the carbon dioxide and its experimental concentrations were found to be slightly above atmospheric.
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Gasification Technologies and Their Energy Potentials
Yaning Zhang PhD, ... Roger Ruan PhD, in Sustainable Resource Recovery and Zero Waste Approaches, 2019
Carbon Dioxide Gasification
Carbon dioxide gasification would also result in a high CGE because (1) it avoids N2 dilution and (2) it produces rich CO and H2 (mainly through the dry reforming reaction: CH4+ CO2→ 2CO+2H2, the Boudouard reaction: C+CO2→ 2CO, steam reforming methanization: CH4+ H2O → CO+3H2, and water gas reaction: C+H2O → CO+H2). However, it would yield a low CGE if the gasification agent (carbon dioxide) is not efficiently or completely consumed (the carbon dioxide in syngas dilutes the LHV of syngas).
Generally, carbon dioxide gasification would result in a high CGE. Table14.8 shows the CGEs of carbon dioxide gasification of different biomass feedstocks at different gasification temperatures and CO2/C ratios. It is observed that the CGEs are between 50% and 87%. These values (50%–87%) are generally higher than the CGEs of air gasification (36%–84%) and oxygen gasification (28%–85%). This is mainly because more CO is produced during the carbon dioxide gasification process, and the mechanism involved is mainly the Boudouard reaction (C+CO2→ 2CO).
Table14.8. CGEs of Biomass Carbon Dioxide Gasification.
| Biomass | CGE (%) | Temperature, CO2/C Ratio | References |
|---|---|---|---|
| Rice straw | 50 | 700°C, 0.25 | [46] |
| Pine sawdust | 58 | 700°C, 0.25 | [46] |
| Rice straw | 61 | 1000°C, 1 | [46] |
| Rice straw | 68 | 1000°C, 0 | [46] |
| Rice straw | 71 | 1000°C, 0.5 | [46] |
| Rice straw | 75 | 1100°C, 0.25 | [46] |
| Pine sawdust | 75 | 1000°C, 1 | [46] |
| Pine sawdust | 79 | 900°C, 0.25 | [46] |
| Pine sawdust | 82 | 1000°C, 0.5 | [46] |
| Pine sawdust | 87 | 1000°C, 0.25 | [46] |
CGE, cold gasification efficiency.
In Table14.8, carbon dioxide gasification of rice straw showed the lowest CGE (50%) because the lower gasification temperature (700°C) resulted in a lower carbon conversion efficiency (78%). Carbon dioxide gasification of pine sawdust showed the highest CGE (87%) due to the facts that (1) the optimal CO2/C ratio (0.25) resulted in the highest carbon conversion efficiency (98%) and (2) the high gasification temperature (1000°C) was also conducive to the carbon conversion efficiency.
The CGE of carbon dioxide gasification process is significantly varied by the gasification temperature. Yu etal. [46] studied the carbon dioxide gasification of rice straw and pine sawdust at different gasification temperatures. The results showed that the CGE of pine sawdust was increased from 58% to a maximum of 87% (50% increase) when the gasification temperature was increased from 700 to 1000°C (43% increase) and that the CGE of rice straw was increased from 50% to a maximum of 75% (50% increase) when the gasification temperature was increased from 700 to 1100°C (57% increase).
The CGE of the carbon dioxide gasification process is varied also by the CO2/C ratio. Yu etal. [46] studied the carbon dioxide gasification of rice straw and pine sawdust at different CO2/C ratios. The results showed that the CGE of rice straw was increased from 68% to 71% (4% increase) when the CO2/C ratio was increased from 0 to 0.5, whereas the CGE of pine sawdust was decreased from 87% to 75% (13.8% decrease) when the CO2/C ratio was increased from 0.25 to 1 (300% increase). These also indicate that the CGE of a carbon dioxide gasification process is varied by the biomass feedstock.
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ESSENTIAL OILS
R.P.W. Scott, in Encyclopedia of Analytical Science (Second Edition), 2005
Supercritical carbon dioxide extraction
Supercritical carbon dioxide extraction is a relatively recent process and yields products of extremely high quality. The process is, however, relatively expensive due to high cost of liquid carbon dioxide. The critical temperature of carbon dioxide is 31°C and the critical pressure just over 1000psi. Critical carbon dioxide is an excellent solvent for essential oils. Due to the relatively low temperature of the extraction, it can easily handle thermally labile oils without degradation and in addition it is chemically very inert and so does not react with any of the essential oil components. The essential oil is easily recovered from the extract by reducing the pressure in a controlled manner and allowing the carbon dioxide to evaporate. The extraction is carried out in a pressurized container constructed from heavy duty stainless steel at ∼35°C and ∼1000psi. The equipment can also be very expensive.
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An Overview of In-Situ Burning
Merv Fingas, in Oil Spill Science and Technology, 2011
23.7.4.5 Combustion Gas Measurement
Combustion gases of concern include carbon dioxide, carbon monoxide, sulphur dioxide, and nitrogen oxides.
Carbon Dioxide—Carbon dioxide is the end result of combustion and is found in increased concentrations around a burn.99,185 Normal atmospheric levels are about 300 ppm, and levels near a burn can be around 500 ppm, which presents no danger to humans. The three-dimensional distributions of carbon dioxide around a burn have been measured. Concentrations of carbon dioxide are highest at the 1-m level and fall to background levels at the 4-m level. Concentrations at ground level are as high as 10 times that in the plume, and distribution along the ground is broader than for particulates. Carbon dioxide can be measured in a number of ways, real-time instruments generally measure it using an infrared technique, discrete samples can be taken and quantified by gas chromatography ,and infrared open-path instruments can provide real-time measurement.
Carbon Monoxide—Carbon monoxide levels are usually at or below the lowest detection levels of the instruments and thus do not pose any hazard to humans. The gas has only been measured when the burn appears to be inefficient, such as when water is sprayed into the fire. Carbon monoxide appears to be distributed in the same way as carbon dioxide. Measurements of carbon monoxide can be done using similar techniques as for carbon dioxide.
Sulphur Dioxide—Sulphur dioxide per se is usually not detected at significant levels or sometimes not even at measurable levels in the area of an in-situ oil burn. Sulphuric acid, or sulphur dioxide that has reacted with water, is detected at fires, and levels, though not of concern, appear to correspond to the sulphur content of the oil. Sulphur dioxide itself, though not detected, can be measured using specialized sensor-type instruments or reactive tape instruments. Sulphuric acid aerosols can be measured by titrating caustic solutions through which the sample air was drawn (impinger method) or using a reactive tape instrument.
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