Carbon dioxide, a carbon oxide compound, has a chemical formula of CO2 and a chemical formula of 44.0095. It is colorless and odorless at normal temperature and pressure or colorless and odorless (no smell) The slightly sour gas is also a common greenhouse gas, and it is also a component of air (0.03% -0.04% of the total volume of the atmosphere).
In terms of physical properties, carbon dioxide has a boiling point of -78.5 ° C, a melting point of -56.6°C, a density greater than that of air (under standard conditions), and is soluble in water.
Carbon Dioxide Cycle
In terms of chemical properties, the chemical properties of carbon dioxide are inactive and have high thermal stability (only 1.8% decomposition at 2000°C).
They cannot be burned and generally do not support combustion. They are acid oxides and have the generality of acid oxides. Since carbonic acid is formed by reaction with water, it is an anhydride of carbonic acid.
Carbon dioxide is generally produced by calcining limestone at high temperatures or by reacting limestone with dilute hydrochloric acid. It is mainly used in refrigerated and perishable foods (solid), as a refrigerant (liquid), in carbonized soft drinks (gaseous), and as a solvent for homogeneous reactions ( Supercritical state) and so on.
With regard to its toxicity, studies have shown that low concentrations of carbon dioxide are not toxic, and high concentrations of carbon dioxide can poison animals.
The molecular shape of CO2 is linear, and its structure was once thought to be: O = C = O. However, the carbon-oxygen bond length in CO2 molecule is 116pm, which is between the carbon-oxygen double bond (124pm) and the carbon-oxygen triple bond (113pm), so the carbon-oxygen bond in CO 2 has a certain degree. Three-key feature.
Modern scientists generally considered CO.’S2 central atom of the carbon atoms of the molecules take sp hybridization, two sp hybrid orbital and two oxygen atoms of 2p orbit respectively (containing one electron) formed by superimposing two σ bond, perpendicular to each other on the carbon atoms, The p orbitals then form two large π bonds with the parallel p orbitals of the two oxygen atoms.
Carbon dioxide is a colorless and odorless gas at room temperature and pressure. It is soluble in most organic solvents such as water and hydrocarbons.
Carbon dioxide is one of the oxycarbons. It is an inorganic substance, non-flammable, and generally does not support combustion. It is non-toxic at low concentrations. It is also carbonic anhydrides, are acidic oxide, the acidic oxide having continuity, wherein the carbon valence of +4 valence, the valence of carbon at the highest, so the reduction of carbon dioxide has no oxidation, but oxidation Not strong.
1. The generality of acid oxide
- 1-1. React with water
Carbon dioxide can dissolve in water and react with water to form carbonic acid. Unstable carbon dioxide is easily decomposed into water and carbon dioxide. The corresponding chemical reaction equation is
- 1-2. React with basic oxides
Under certain conditions, carbon dioxide can react with basic oxides to form corresponding salts, such as:
- 1-3. React with alkali
① Reaction with calcium hydroxide
Adding carbon dioxide to the clarified lime water will make the clarified lime water turbid and generate calcium carbonate precipitation (this reaction is often used to test carbon dioxide). The corresponding chemical reaction equation is
When carbon dioxide is excessive, calcium bicarbonate is produced:
The second step:
Due to the large solubility of calcium bicarbonate, when carbon dioxide is passed into the turbid lime water for a long time, it can be seen that the precipitate gradually disappears.
② Reaction with sodium hydroxide
Carbon dioxide deteriorates caustic soda. The corresponding chemical reaction equation is:
When carbon dioxide is excessive, sodium bicarbonate is produced:
The second step:
2. Weak oxidation
- 2-1. Carbon element reduction
Under high temperature conditions, carbon dioxide can react with carbon simple substance to form carbon monoxide . The corresponding chemical reaction equation is:
- 2-2. Elemental magnesium reduction
Under ignition conditions, magnesium bars can burn in carbon dioxide. The corresponding chemical reaction equation is:
- 2-3. Hydrogen reduction
A series of reactions of carbon dioxide and hydrogen to form methanol, carbon monoxide, methane, etc. under the action of a catalyst. The chemical reaction equations of several reactions are:
3. React with peroxide
Carbon dioxide can react with sodium peroxide (Na₂O₂) to form sodium carbonate (Na ₂ CO3) and oxygen (O₂). The corresponding chemical reaction equation is:
4. React with format reagents
Under acidic conditions, carbon dioxide can react with form reagents in anhydrous ether to form carboxylic acids. The corresponding chemical reaction equation is:
Note: In the formula, R is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, X is a halogen, and Etheranhydrous represents anhydrous ether.
6. Preparation of diamond (replacement reaction)
At 440 ° C (713.15K) and 800 atmospheres (about 808MPa), carbon dioxide can react with sodium metal to form diamond. The corresponding chemical reaction equation is:
7. The dark reaction of photosynthesis
Carbon dioxide participates in the dark reaction of photosynthesis and is an indispensable raw material for photosynthesis of green plants. The reaction process involved is called “fixation of carbon dioxide”. The corresponding chemical reaction equation is:
The carbon dioxide gas produced during the high-temperature calcination of limestone (or dolomite) is washed with water, removed impurities, and compressed to obtain gaseous carbon dioxide:
Fermentation gas recovery
The carbon dioxide gas produced in the ethanol fermentation process is washed with water, removed impurities, and compressed to obtain carbon dioxide gas.
- By-product gas recovery
In the production of ammonia, hydrogen, and synthetic ammonia, there is often a process of decarburization (that is, removal of carbon dioxide in a gas mixture), so that carbon dioxide in the mixed gas can be absorbed under pressure and heated under reduced pressure to obtain high purity carbon dioxide gas.
- Adsorption expansion method
Generally, the by-product carbon dioxide is used as the raw material gas, and the high-purity carbon dioxide is extracted from the adsorption phase by the adsorption expansion method, and the product is collected by the cryopump. After removing some impurities, high-purity carbon dioxide products can be obtained after rectification.
- Charcoal kiln
Carbon dioxide is obtained by refining the carbon kiln gas and the gas obtained from methanol cracking.
- Prepared by reacting marble with dilute hydrochloric acid
Dioxocarbon, marble and dilute hydrochloric acid. Neither type of soda is used, and the speed is too fast to control.
Without sulfuric acid, magnesium salts are not as cheap as calcium salts. Nitric acid is easy to decompose when it is exposed to light.
Marble or limestone (the main ingredient is CaCO₃) and dilute hydrochloric acid.
Preparation apparatus set
Solid-liquid non-heating type (pictured).
Because the density of carbon dioxide is greater than that of air, it can dissolve in water and react with water, so the upward exhaust method is adopted.
The generated gas was passed into clear lime water, and the lime water became turbid, proving that the gas was carbon dioxide.
A burning wooden stick is placed at the mouth of the gas cylinder (cannot reach into the bottle). If the flame goes out, it is full.
① Hydrogen chloride (HCl) gas that may be volatilized during the reaction can be removed by a saturated sodium bicarbonate (NaHCO3) solution.
② If necessary, the water vapor in the generated gas can be removed by using a scrubbing bottle filled with concentrated sulfuric acid.
③ Can’t use calcium carbonate and concentrated hydrochloric acid to react. Reason: concentrated hydrochloric acid is easy to volatilize a large amount of hydrogen chloride gas, so that sodium bicarbonate cannot be completely removed, and the purity of the carbon dioxide produced will decrease.
④ is marble (CaCO in the laboratory ₃ reaction) dilute hydrochloric acid and carbon dioxide from the system.
⑤ Do not use Na ₂ CO ₃ (soda) and NaHCO ₃ instead of CaCO ₃ (baking soda) to react with hydrochloric acid to make carbon dioxide. Reason: Na ₂ CO ₃ and NaHCO ₃ react too quickly with hydrochloric acid, and the carbon dioxide produced is very fast. Escape, difficult to control, and easy to operate.
⑥ Dilute sulfuric acid cannot be used instead of hydrochloric acid. Reason: The reaction of dilute sulfuric acid with marble (CaCO ₃ ) will generate slightly dissolved calcium sulfate (CaSO ₄ ) on the surface of the marble, preventing the reaction from proceeding and making The response is very slow.
⑦ Can’t use MgCO ₃ (magnesium salt) instead of CaCO ₃ (calcium salt). Reason: Although MgCO ₃ and hydrochloric acid and CaCO₃ and hydrochloric acid react similarly, but because there are fewer sources of MgCO ₃, it is not as cheap and easily available as CaCO₃.
⑧ Nitric acid cannot be used instead of hydrochloric acid. Reason: Nitric acid is easily decomposed by light
If in place of hydrochloric acid and nitric acid, the resulting CO.’S ₂ in will be a small amount of NO₂ and O₂. In addition, nitric acid is more expensive than hydrochloric acid, so nitric acid is usually not used instead of hydrochloric acid.
⑨Because carbon dioxide can extinguish a fire, you can place a burning match at the mouth of a gas cylinder for inspection. If the flame goes out, it proves that carbon dioxide has filled the gas cylinder.
- Decomposed from sodium bicarbonate by heating
After the sodium bicarbonate is sufficiently dried, it is filled into a rigid glass tube, and the tube mouth is filled with glass wool, and then closed, and a vacuum pump is used to evacuate. Then, the sodium bicarbonate is decomposed by heating.
The carbon dioxide that originally occurred can be released. The gas produced by the decomposition needs to be introduced into an ice-cooled duct to condense the water vapor in the gas, and then the gas is successively introduced into a U-shaped tube containing calcium chloride and phosphorus pentoxide, respectively, to be dried. At 100 ° C, the decomposition pressure of sodium bicarbonate was 97.458kPa, and at 120 ° C it was 166.652kPa.
High-purity carbon dioxide is mainly used in the electronics industry, medical research and clinical diagnosis, calibration gas for carbon dioxide lasers, testing instruments, and other special mixed gas preparations. It is also used as a regulator in the polymerization of polyethylene.
Solid carbon dioxide is widely used in refrigerated dairy products, meat, frozen foods, and other perishable foods in transit. It is used as a refrigerant in many industrial processes, such as crushing heat-sensitive materials, rubber polishing, metal cold processing, shrink assembly of mechanical parts, Vacuum cold trap, etc.
Gaseous carbon dioxide is used for carbonized soft drinks, pH control of water treatment processes, chemical processing, food preservation, inert protection of chemical and food processing processes, welding gases, plant growth stimulants, used in hardening molds and cores in casting and for Pneumatic device, also used as a thinner for germicidal gas (that is, a mixed gas of ethylene oxide and carbon dioxide is used as sterilization, insecticide, fumigant, widely used in sterilization of medical devices, packaging materials, clothing, fur, bedding , Bone meal disinfection, fumigation of warehouses, factories, cultural relics, books).
Liquid carbon dioxide is used as a refrigerant, low temperature tests for aircraft, missiles and electronic components, to improve oil well recovery, rubber polishing, and to control chemical reactions. It can also be used as a fire extinguishing agent.
Carbon dioxide in the supercritical state can be used as a solvent for dissolving non-polar, non-ionic and low molecular weight compounds, so it is widely used in homogeneous reactions.
- Environmental hazards
Natural greenhouse effect: Greenhouse gases such as carbon dioxide in the atmosphere can radiate longer-wavelength longer-wavelength radiation to the ground after strongly absorbing long-wave radiation from the ground, which acts as thermal insulation for the ground.
Enhanced greenhouse effect: Since the industrial revolution, human activities have emitted a large number of greenhouse gases such as carbon dioxide, which has caused the concentration of greenhouse gases in the atmosphere to rise sharply, resulting in an increasing greenhouse effect.
According to statistics, the global average annual atmospheric carbon dioxide concentration before industrialization was 278ppm (1ppm is one millionth), and in 2012, the global average annual atmospheric carbon dioxide concentration was 393.1ppm. By April 2014, the atmosphere in the northern hemisphere. The average carbon dioxide concentration exceeded 400 ppm for the first time.
Global warming: The increasing intensification of the greenhouse effect of the atmosphere has led to global warming and a series of global unpredictable global climate problems.
According to the International Climate Change Economics Report, if humans have maintained their current lifestyle, by 2100, the global average temperature will be 50% likely to rise by 4 ° C. If the global temperature rises by 4 ° C, glaciers on the north and south poles of the earth will melt, and sea levels will rise accordingly.
Over 40 island nations and the world ’s most populous coastal cities will face the danger of flooding. Tens of millions of people worldwide Life will face a crisis, and even produce a global ecological balance disorder, eventually leading to large-scale migration and conflicts around the world.
Low-carbon life: Minimize the energy used in daily life, thereby reducing carbon dioxide emissions, reducing atmospheric pollution, and slowing ecological degradation.
CCS technology: CCS technology, or Carbon Dioxide Capture and Storage (CCS) technology, is one of the most important technologies to address global climate change in the short term. It refers to the use of carbon capture technology to The carbon dioxide produced by the energy industry is separated, and then stored and transported to a place isolated from the atmosphere, such as the seafloor or underground.
Studies have shown that when the concentration of carbon dioxide in the air is less than 2%, there is no obvious harm to people. Exceeding this concentration can cause damage to the human respiratory organs, that is, carbon dioxide is generally not a toxic substance, but when the concentration of carbon dioxide in the air exceeds a certain limit, It can cause the body to be poisoned, and high concentrations of carbon dioxide can cause suffocation.
Animal experiments have proven that in the air with normal oxygen content (20%), the higher the concentration of carbon dioxide, the higher the mortality of the animal. At the same time, pure carbon dioxide caused animal deaths to occur more rapidly due to lower oxygen.
In addition, some people think that under low oxygen conditions, carbon dioxide at a concentration of 8% to 10% can cause the death of humans and animals in a short time.
The high concentration of carbon dioxide itself has a stimulating and anesthetic effect and can cause hypoxia to suffocate the body.
Symptoms of poisoning
Mild: General discomfort such as dizziness, headache, muscle weakness, and general weakness.
Moderate: Dizziness will fall to the ground, chest tightness, nasal and sore throat pain, tight breathing, chest compressions and suffocation, severe headache, tinnitus, muscle weakness, redness of the skin, increased blood pressure, fast pulse And strong.
Severe: Sudden dizziness cannot support and fell to the ground, belching, dyspnea, palpitations, unconsciousness, coma, bruising of the skin lips and nails, blood pressure drop, pulse is too weak to reach, pupil dilated. The light reflection disappears, the whole body is soft, the glottis is enlarged, and the breathing and heartbeat are stopped successively to death. Some symptoms may include drowsiness and memory loss after the acute period.
① Quickly remove the poisoned person from the high-concentration carbon dioxide environment, go to fresh air, loosen the collar of the poisoned person, artificially assist breathing to make it inhale oxygen as soon as possible, and treat with hyperbaric oxygen if necessary, rescuers should wear effective breathing Protector.
② Injection of respiratory stimulants, antibiotics for secondary infections; decreased carbon dioxide binding capacity should be intravenously infused with sodium bicarbonate or sodium lactate, limb spasm can take larger doses of sedatives, long-term high fever and convulsions can be used as sedatives, others such as lungs Treatment of symptoms such as edema and cerebral edema.
Before entering a work area with a high concentration of carbon dioxide, check whether the carbon dioxide concentration in the air exceeds 2%. If it exceeds, you need to take effective safety measures, such as:
① ventilate and detoxify, replace the workplace air, and make the carbon dioxide concentration in the air. Not more than 2%.
② wear a ventilation mask, self-suction catheter gas mask, oxygen respirator, and other commonly used gas masks.
Precautions for storage
Carbon dioxide is suitable for storage in a cool, ventilated warehouse for non-combustible gases, and is suitable for shipment in liquid or solid form. When storing and transporting carbon dioxide, the following points should be paid attention to:
① Keep away from fire and heat sources, and the storage temperature should not exceed 30 ℃.
② Store separately from flammable materials, and avoid mixed storage.
③ The storage area should be equipped with emergency treatment equipment for leakage.