Hydrogen sulfide

The hydrogen sulfide , the aqueous solution is Hydrogen Sulfide , is used for monitoring environmental emission control industrial hygiene trace impurity analyzers and as balance gas in some gas mixtures.

Summary

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  • 1 Story
  • 2 Physical properties
  • 3 Sources
  • 4 Destination of atmospheric H 2S
  • 5 Obtaining
  • 6 Applications
  • 7 Toxicity
    • 1 Eliminate Hydrogen Sulfide
  • 8 Common Treatment Options
    • 1 Adding Chlorine
    • 2 Aeration
    • 3 Regulate blood pressure
  • 9 Source

History

Hydrogen sulfide is naturally found in crude oil, natural gas, volcanic gases, and hot springs. It can also be found in swampy waters, ponds or stagnant waters, drains, fishmeal or fish oil ponds, fishing boats and sewers. There have been deaths in stopped lakes or ponds when hydrogen sulfide gurgles from the depths reaching people on its surface. As this acid is denser than water , fractionations by density difference occur. Generally it is by anaerobic decomposition of organic remains.

It can also occur as a result of bacterial degradation of organic matter under anaerobic conditions. It is generated in oil refineries .

Hydrogen sulfide is extremely harmful to health, 20-50 parts per million (ppm) in the air is enough to cause acute discomfort that leads to suffocation and death from overexposure. Due to its toxicity, it is located directly below hydrocyanic acid (HCN). It is common for workers in the port sector to be affected with fatal results when they enter warehouses that have transported products derived from fishing . In this case, the source of the hydrogen sulfide is the sulfurized proteins that degrade releasing the mentioned acid.

Physical properties

  • Molecular Weight: 34.08 g / mol
  • Melting point: -86 ° C
  • Latent heat of fusion (1,013 bar, triple point): 69.75 kJ / kg
  • Liquid density (1,013 bar at boiling point): 914.9 kg / m 3
  • Liquid / Gas Equivalent (1,013 bar and 15 ° C (59 ° F)): 638 vol / vol
  • Boiling point (1,013 bar): -60.2 ° C
  • Latent heat of vaporization (1,013 bar at boiling point): 547.58 kJ / kg
  • Vapor pressure (at 21 ° C or 70 ° F): 18.2 bar
  • Critical Temperature: 100 ° C
  • Critical Pressure: 89.37 bar
  • Gas density (1,013 bar at boiling point): 1.93 kg / m3
  • Gas density (1,013 bar and 15 ° C (59 ° F)): 1.45 kg / m3
  • Compressibility factor (Z) (1,013 bar and 15 ° C (59 ° F)): 0.9915
  • Specific gravity (air = 1) (1,013 bar and 15 ° C (59 ° F)): 1,189
  • Specific Volume (1,013 bar and 21 ° C (70 ° F)): 0.699 m3 / kg
  • Constant pressure heat capacity (Cp) (1 bar and 25 ° C (77 ° F)): 0.034 kJ / (mol.K)
  • Viscosity (1,013 bar and 0 ° C (32 ° F)): 0.0001179 Poise
  • Thermal Conductivity (1,013 bar and 0 ° C (32 ° F)): 12.98 mW / (mK)
  • Solubility in water (1,013 bar and 0 ° C (32 ° F)): 4.67 vol / vol
  • Auto-ignition temperature: 270 ° C

Hydrogen Sulfide (H 2 S) is a flammable, colorless gas with a characteristic odor of rotten eggs . It is commonly known as hydrosulfuric acid or sewer gas. People can detect their odor at very low levels. It is one of the main compounds that causes discomfort due to bad odors. For this reason, different deodorization processes have been developed that eliminate it from the contaminated stream, such as gas treatment processes with amines.

Sources

Natural

Natural state

  • Decomposition of organic matter: Tidal swamps, bogs and mudflats are particularly H 2S emitters .
  • Volcanic eruptions: Volcanic activity generates a certain amount of H 2S, but globally it is negligible when compared to biological decomposition processes.

Artificial

Artificial State

  • Incomplete combustions: When combustion is carried out with an oxygen deficiency, the sulfur in fossil fuels is transformed into H 2S, at the same time as carbon in CO.
  • Industrial processes: Such as kraft paper processing, sewage plants, coking ovens, and steel fabrication.

Destination of the atmospheric H 2 S

2 S is emitted into the atmosphere by natural sources in large quantities. H 2 S rapidly oxidizes to SO 2 . In fact, of all the SO 2 molecules present in the air at any given time, up to 80% were initially emitted as H 2 S and then transformed into SO 2 . H 2 S can be oxidized by atomic and molecular oxygen and by ozone. Ozone is both a natural component of the stratosphere and a component of urban atmospheres.

The oxidation reaction of H 2 S, considered to be the most important, is the one that occurs between H 2 S and O 3 :

2 S + O 3 = H 2 O + SO 2

This reaction is very slow in the gas phase, but it can be much faster on the surface of the particles present in the air . The life of 1 ppb of SH 2 exposed to 0.05 ppm O 3 in the presence of 15000 particles / cm 3 is estimated to be 2 hours.

The rate of oxidation of H 2 S in mist or cloud droplets is very fast.

In general, the life of a H 2 S molecule before transforming into SO 2 is on the order of a few hours.

Obtaining

Hydrogen sulfide can be conveniently generated in the laboratory by reaction of hydrochloric acid with ferrous sulfide FeS. Another method is heating a mixture of paraffin with elemental sulfur. In industry, hydrogen sulphide is a by-product of natural gas or biogas cleaning that usually accompanies concentrations of up to 10%.

Applications

Hydrogen sulfide is traditionally used in the cation run to precipitate group II heavy metal cations from the analytical run, which are then separated by other methods. Amorphous precipitates can be black or white . The conjugated salt, sodium sulfide, is used as an aging agent for bronzes (padlocks, goldsmiths). Also sodium sulfide is used, for example, in the manufacture of leather.

Recent studies have successfully induced hibernation in mice by applying hydrogen sulphide.

Hydrogen sulfide is responsible for the blackening of some paints based on lead carbonate due to the formation of black lead (II) sulfide. In some cases this can be remedied by applying lead (II) hydrogen peroxide to white lead (II) sulfate. It is a starting compound in some organic syntheses.

Toxicity

The toxicity of hydrogen sulfide is similar to that of hydrocyanic acid. The reason why, despite the more mass presence of this compound, there are relatively few deaths is the bad smell with which it is accompanied. However, after 50 ppm it has a narcotic effect on the receptor cells of smell and the affected people no longer perceive the stench.

After 100 ppm, death can occur. As the density of the hydrogen sulfide is greater than that of the air, it usually accumulates in low places such as wells, etc. where it can cause victims. Often several people are affected, a first victim falls unconscious and then all the others who come to their rescue without the necessary protective equipment are also affected. Hydrogen sulfide seems to act above all on the metal centers of enzymes, blocking them and thus preventing their operation. For a treatment it is recommended to take the affected person as quickly as possible to fresh air and apply pure oxygen. Furthermore, the sulfide ion combines with hemoglobin in the same way that oxygen precipitates the suffocation of the organism.

Exposure to low levels of hydrogen sulfide can cause irritation of the eyes, nose or throat. It can also cause breathing difficulties in asthmatic people. Brief exposures to high concentrations of hydrogen sulfide (over 500 ppm) can cause unconsciousness and possibly death. In most cases, people who lose consciousness seem to recover without suffering other effects. However, some people seem to experience permanent or long-term effects such as headache, poor ability to concentrate, poor memory, and poor motor function. No health effects have been detected in people exposed to hydrogen sulfide at concentrations typically found in the environment (0.00011-0.00033 ppm).

Scientists do not have information that shows the death of people poisoned by ingesting hydrogen sulfide. Pigs that ate food containing hydrogen sulfide suffered from diarrhea for several days and lost weight even after 105 days.

Scientists have little information about what happens when a person is exposed to hydrogen sulfide through the skin. However, it is known that care needs to be taken with hydrogen sulfide in the form of a compressed liquid, as it can cause frostbite of the skin.

Despite the high toxicity of hydrogen sulfide gas to mammals, there are many microorganisms that tolerate high concentrations of this gas or even feed on it. Thus there are theories that associate the metabolization of hydrogen sulfide gas, such as exists for example near sub-volcanic volcanic sources, with the development of life on Earth.

Eliminate Hydrogen Sulfide

The presence of hydrogen sulfide in drinking water in homes is not a health hazard, but it is a common nuisance pollutant, with a distinct “rotten egg” odor that makes you want water treatment. Various treatment methods are available, and frequently hydrogen sulfide can be treated and removed using the same process and equipment used to remove iron and manganese .

Common Treatment Options

Most methods of treating sulfide rely on oxidation of the hydrogen sulfide gas to an elemental sulfide, a solid. Oxidation is the process by which soluble or dissolved contaminants are converted into soluble and insoluble derived products that can be filtered. This process changes the chemistry and physical properties of the reagents. Hydrogen sulfide can be oxidized by various methods. If concentrations exceed 6.0 mg / l, oxidation such as disinfection with chlorine is recommended. If concentrations do not exceed 6.0 mg / l and the pH is above 6.8, a filter such as the Manganese Greensand filter can be used.

Adding Chlorine

The addition of chlorine is an effective and widely used method to oxidize hydrogen sulfide, especially if the pH of the water is 6.0-8.0. Chlorine is regularly administered as sodium hypochlorite, which reacts with sulfide, hydrogen sulfide, and bisulfite to form compounds that do not cause unpleasant tastes or odors in drinking water.

The amount of hypochlorite to be used depends on the concentration of hydrogen sulfide in the water supply, however a dose of 2.0 mg / l of chlorine is recommended for every 1.0 mg / l of hydrogen sulfide. The chlorine should be added to the system before mixing in the tank, and should provide sufficient storage to allow the water is in contact with chlorine for twenty minutes. Treated water may have odors and flavors left by the formation of certain by-products or chlorine residues. After the required contact time, therefore, water must be passed through an activated carbon filter to remove any remaining suspended sulfur or chlorine.

Chlorination systems are available as a drop-shaped pellet unit or a liquid chemical feeder. The ball-shaped drop system automatically dispenses a measured amount of chlorine through the borehole cover or into the holding tank during the pump cycle. The chemical feeder system has the characteristic of the liquid feeder connected to the well pump.

Aeration

Another common sulfide water treatment is aeration. Hydrogen sulfide is physically removed by stirring the water through bubbling or cascading and then separating or “pickling” the hydrogen sulfide in a container. Unwanted hydrogen sulfide is removed as a volatile gas by blowing it into a waste pipe or outside. Aeration is more effective when concentrations are lower than 2.0 mg / l. At higher concentrations, this method may not remove all of the unpleasant odor unless air is used to chemically oxidize the hydrogen sulfide which is then filtered.

In a typical aeration system, ambient air is introduced into the water using a compressor or heater. Well-designed aeration tanks keep an air bag in one-third or one-half of the tank. If the tank does not have an air bag, the sulfur smell may return. Most supply sources contain less than 10 mg / l sulfur, in which case the aeration tank is almost the same size as the filter tank (10 “x 54”) works well. When sulfide levels exceed 10 mg / l, aeration tanks, re-pressurize systems, chlorination systems may be needed. Aeration is not always the most practical water treatment, especially if the concentrations of hydrogen sulfide exceed 10 mg / l, because this requires very acidic conditions (pH 4.0-5.0), extended contact times and water to mix, and usually wide space requirements. In addition, treated water may need to be re-pressurized for distribution within the home and extremely unpleasant odors must be removed by venting the gas outside.

Regulate blood pressure

To the finding that hydrogen sulfide , or H 2 S, is produced in the thin lining of blood vessels formed by endothelial cells, is added that H2S regulates blood pressure by relaxing these vessels. This messenger molecule, the newest member of the gasotransmitter family, is similar in function to the chemical signals represented by nitric oxide, dopamine, and acetylcholine, which transmit signals between nerve cells and excite or restrain brain activity.

Since gasotransmitters are present in all mammals, it is logical to suppose that the findings of this research could have numerous applications in the field of human physiology and medicine.

 

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