Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. It is a precursor to almost all fluorine compounds, including pharmaceuticals such as fluoxetine (Prozac), diverse materials such as PTFE (Teflon), and elemental fluorine itself. It is a colourless solution that is highly corrosive, capable of dissolving many materials, especially oxides. Its ability to dissolve glass has been known since the 17th century, even before Carl Wilhelm Scheele prepared it in large quantities in 1771. Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers (although PTFE is slightly permeable to it).

Hydrogen fluoride gas is an acute poison that may immediately and permanently damage lungs and the corneas of the eyes. Aqueous hydrofluoric acid is a contact-poison with the potential for deep, initially painless burns and ensuing tissue death. By interfering with body calcium metabolism, the concentrated acid may also cause systemic toxicity and eventual cardiac arrest and fatality, after contact with as little as 160 cm2 (25 square inches) of skin.

Hydrofluoric acid Acidity

Hydrofluoric acid is classified as a weak acid because of its lower dissociation constant compared to the strong acids. It ionizes in aqueous solution in a similar fashion to other common acids:

HF + H2O ? H3O+ + F?

HF is the only hydrohalic acid that is not considered a strong acid, i.e. it does not fully ionize in dilute aqueous solutions.

When the concentration of HF approaches 100%, the acidity increases dramatically because of homoassociation:

3 HF ? H2F+ + FHF?

The bifluoride (FHF?) anion is stabilized by the very strong hydrogen–fluorine hydrogen bond.

Hydrofluoric acid roduction

Hydrofluoric acid is produced by treatment of the mineral fluorite (CaF2) with concentrated sulfuric acid. When combined at 265 °C, these two substances react to produce hydrogen fluoride and calcium sulfate according to the following chemical equation:

CaF2 + H2SO4 → 2 HF + CaSO4

Although bulk fluorite is a suitable precursor and a major source of world HF production, HF is also produced as a by-product of the production of phosphoric acid, which is derived from the mineral apatite. Apatite sources typically contain a few percent of fluoroapatite, acid digestion of which releases gaseous stream consisting of sulfur dioxide (from the H2SO4), water, and HF, as well as particulates. After separation from the solids, the gases are treated with sulfuric acid and oleum to afford anhydrous HF. Owing to the corrosive nature of HF, its production is accompanied by the dissolution of silicate minerals, and, in this way, significant amounts of fluorosilicic acid are generated.

Hydrofluoric acid Uses

Hydrofluoric acid has a variety of uses in industry and research. It is used as a starting material or intermediate in industrial chemistry, mining, refining, glass finishing, silicon chip manufacturing, and in cleaning.

Hydrofluoric acid Oil refining

In a standard oil refinery process known as alkylation, isobutane is alkylated with low-molecular-weight alkenes (primarily a mixture of propylene and butylene) in the presence of the strong acid catalyst derived from hydrofluoric acid. The catalyst protonates the alkenes (propylene, butylene) to produce reactive carbocations, which alkylate isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a two-phase reaction.

Production of organofluorine compounds

The principal use of hydrofluoric acid is in organofluorine chemistry. Many organofluorine compounds are prepared using HF as the fluorine source, including Teflon, fluoropolymers, fluorocarbons, and refrigerants such as freon.

Production of fluorides

Most high-volume inorganic fluoride compounds are prepared from hydrofluoric acid. Foremost are Na3AlF6, cryolite, and AlF3, aluminium trifluoride. A molten mixture of these solids serves as a high-temperature solvent for the production of metallic aluminium. Given concerns about fluorides in the environment, alternative technologies are being sought. Other inorganic fluorides prepared from hydrofluoric acid include sodium fluoride and uranium hexafluoride.

Hydrofluoric acid Etchant and cleaning agent

Wet etching tanks

In metalworking, hydrofluoric acid is used as a pickling agent to remove oxides and other impurities from stainless and carbon steels because of its limited ability to dissolve steel.[citation needed] It is used in the semiconductor industry as a major component of Wright Etch and buffered oxide etch, which are used to clean silicon wafers. In a similar manner it is also used to etch glass by reacting with silicon dioxide to form gaseous or water-soluble silicon fluorides. It can also be used to polish and frost glass.

SiO2 + 4 HF → SiF4(g) + 2 H2O

SiO2 + 6 HF → H2SiF6 + 2 H2O

A 5% to 9% hydrofluoric acid gel is also commonly used to etch all ceramic dental restorations to improve bonding. For similar reasons, dilute hydrofluoric acid is a component of household rust stain remover, in car washes in "wheel cleaner" compounds, in ceramic and fabric rust inhibitors, and in water spot removers.Because of its ability to dissolve iron oxides as well as silica-based contaminants, hydrofluoric acid is used in pre-commissioning boilers that produce high-pressure steam.

Hydrofluoric acid Niche applications

Because of its ability to dissolve (most) oxides and silicates, hydrofluoric acid is useful for dissolving rock samples (usually powdered) prior to analysis. In similar manner, this acid is used in acid macerations to extract organic fossils from silicate rocks. Fossiliferous rock may be immersed directly into the acid, or a cellulose nitrate film may be applied (dissolved in amyl acetate), which adheres to the organic component and allows the rock to be dissolved around it.

Diluted hydrofluoric acid (1 to 3 %wt.) is used in the petroleum industry in a mixture with other acids (HCl or organic acids) in order to stimulate the production of water, oil, and gas wells specifically where sandstone is involved.

Hydrofluoric acid is also used by some collectors of antique glass bottles to remove so-called 'sickness' from the glass, caused by acids (usually in the soil the bottle was buried in) attacking the soda content of the glass.

Offset printing companies use hydrofluoric acid to remove unwanted images from printing plates. Felt-tip markers called "deletion pens" are available to make the process safer for the worker.

Hydrofluoric acid Health and safety

A hydrofluoric acid burn of the hand

left and right hands, two views, burned index fingers

HF burns, not evident until a day after

In addition to being a highly corrosive liquid, hydrofluoric acid is also a contact poison. It should therefore be handled with extreme care, using protective equipment and safety precautions beyond those used with other mineral acids. Owing to its low acid dissociation constant, HF as a neutral lipid-soluble molecule penetrates tissue more rapidly than typical mineral acids. Because of the ability of hydrofluoric acid to penetrate tissue, poisoning can occur readily through exposure of skin or eyes, or when inhaled or swallowed. Symptoms of exposure to hydrofluoric acid may not be immediately evident, and this can provide false reassurance to victims, causing them to delay medical treatment.[9] Despite having an irritating odor, HF may reach dangerous levels without an obvious smell. HF interferes with nerve function, meaning that burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury. Symptoms of HF exposure include irritation of the eyes, skin, nose, and throat, eye and skin burns, rhinitis, bronchitis, pulmonary edema (fluid buildup in the lungs), and bone damage.

Once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. Burns with areas larger than 160 cm2 (25 square inches) have the potential to cause serious systemic toxicity from interference with blood and tissue calcium levels. In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity.[12] In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel or special rinsing solutions.However, because it is absorbed, medical treatment is necessary; rinsing off is not enough. Intra-arterial infusions of calcium chloride have also shown great effectiveness in treating burns.

Hydrogen fluoride is generated upon combustion of many fluorine-containing compounds such as products containing Viton and polytetrafluoroethylene (Teflon) parts.[19] Hydrofluorocarbons in automatic fire suppression systems can release hydrogen fluoride at high temperatures, and this has led to deaths from acute respiratory failure in military personnel when a rocket-propelled grenade hit the fire suppression system in their vehicle. Hydrofluoric acid can be released from volcanoes, sea salt aerosol, and from welding or manufacturing processes.

Hydrofluoric acid is also a highly reactive compound and must be stored carefully to prevent dangerous reactions, though it is not flammable. It reacts with bases, acids, and oxidants and attacks glass, ceramics, concrete, some forms of plastic, rubber, and coatings. When combined with methanesulfonic acid or polymerizing cyanogens, it produces explosive gases.

While the acid’s body-dissolving effects were grossly exaggerated in the TV series, hydrofluoric acid, or HF, does indeed need to be stored and used in plastic containers as it slowly dissolves many materials, including the fibreglass many modern bathtubs are made of. HF slowly dissolves silicon dioxide – the major component of most types of glass – by forming water-soluble hexafluorosilicic acid and gaseous silicon tetrafluoride. Chemists use the acid’s ability to etch glass for removing particularly stubborn stains from laboratory glassware and it is an invaluable tool in the semiconductor industry for cleaning silicon wafers

There are certainly stronger acids than HF – with a pKa of only 3.2 it is weaker than other hydrohalide acids and a long way off superacidic fluoroantimonic acid with its extraordinary pKa of -25. The reason for HF’s meagre acidity is the strong bond between the hydrogen and the fluorine atom, resulting in only partial ionisation in dilute solutions. As is the case with other hydrogen halides, hydrofluoric acid is the aqueous solution of the colourless gas hydrogen fluoride. Commercial hydrofluoric acids contain about 50% HF, the most concentrated ones up to 75%. Interestingly, when the HF concentration approaches 100%, something curious happens: in a process called homoassociation, polyatomic ions such as HF2- and free protons form, leading to a dramatic increase in acidity.

Swedish pharmaceutical chemist Carl Scheele discovered hydrofluoric acid in 1771, when he investigated the composition of a mineral called fluorspar: Calcium fluoride. At a time when the element fluorine was unknown and all acids were thought to contain oxygen, Scheele noticed the glass-etching properties of the fumes that developed when heating fluorspar in sulfuric acid. Leading the fumes into water, he was the first to make large quantities of hydrofluoric acid. The exposure to HF – along with Scheele’s bad habit of tasting and smelling the substances he discovered – might have been one of the causes for his death at the age of just 43.

It is natural to expect hydrofluoric acid to be corrosive, but to make things worse, HF is also a strong contact poison. The acid readily penetrates the outer layers of the skin and interferes with nerve function – burns might not be immediately visible and can even remain painless, meaning accidental exposure can remain unnoticed for hours. At the body’s neutral pH, hydrofluoric acid dissociates and produces a flood of fluoride ions, which react with the abundant calcium and magnesium ions, forming insoluble salts. Alkaline metal ions are essential for the body’s proper function; their loss stops muscles working and corrodes bones. Even relatively small HF burns, about the size of the palm of your hand, can cause an array of unpleasant medical effects such as pulmonary oedema (fluid accumulation in the lungs) and life threatening cardiac arrhythmia (decreased or irregular heartbeat). Doctors treat HF poisoning with calcium gluconate injections or calcium chloride infusions to remove the fluoride ions before they devour the body’s own calcium and magnesium.

Sometimes, such as in the case of an unfortunate Australian technician, the acute fluoride poisoning can be fatal. Dissolving rock samples with hydrofluoric acid, the technician spilled a medium-sized beaker of 70% HF onto his lap – an area of about 10% of his body’s total surface. Despite immediately hosing himself and receiving treatment an hour later, the man became unconscious and died of multi organ failure two weeks later.

However, as nasty as HF might sound, a world without hydrofluoric acid would be pretty bleak. It is industry’s main source of fluorine – pharmaceuticals, refrigerants and fluoropolymers such as Teflon all rely on hydrofluoric acid.

Hydrofluoric acid poisoning

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Hydrofluoric acid is a very strong inorganic acid. This article discusses poisoning from swallowing, breathing in, or touching hydrofluoric acid.

Hydrofluoric acid poisoning can have direct effects on the heart. It can lead to irregular, and sometimes life-threatening, heartbeats.

People who come into contact with this poison are likely to have a combination of the symptoms listed.

Hydrofluoric acid is especially dangerous. The most common accidents involving hydrofluoric acid cause severe burns on the skin and hands. The burns may be extremely painful. People will have a lot of scarring and some loss of function in the area involved.

Swallowing this poison can have severe effects on many parts of the body. Extensive damage to the mouth, throat, and stomach are possible. Holes (perforations) in the esophagus and stomach may cause serious infections in the chest and abdominal cavities, which may result in death.

Hydrofluoric acid Pathophysiology

The 2 mechanisms that cause tissue damage are corrosive burn from the free hydrogen ions and chemical burn from tissue penetration of the fluoride ions. Fluoride ions penetrate and form insoluble salts with calcium and magnesium. Soluble salts also are formed with other cations but dissociate rapidly. Consequently, fluoride ions release, and further tissue destruction occurs.

Anhydrous hydrogen fluoride and hydrofluoric acid are extremely corrosive to all tissues of the body. Skin contact results in painful deep-seated burns that are slow to heal. Burns from dilute (<50%) HF solutions do not usually become apparent until several hours after exposure; more concentrated solutions and anhydrous HF cause immediate painful burns and tissue destruction. HF burns pose unique dangers distinct from other acids such as HCl and H2SO4: undissociated HF readily penetrates the skin, damaging underlying tissue; fluoride ion can then cause destruction of soft tissues and decalcification of the bones.

Hydrofluoric acid and HF vapor can cause severe burns to the eyes, which may lead to permanent damage and blindness. At 10 to 15 ppm, HF vapor is irritating to the eyes, skin, and respiratory tract. Exposure to higher concentrations can result in serious damage to the lungs, and fatal pulmonary edema may develop after a delay of several hours. Brief exposure (5 min) to 50 to 250 ppm may be fatal to humans. Ingestion of HF can produce severe injury to the mouth, throat, and gastrointestinal tract and may be fatal. Hydrofluoric acid is a clear, colorless liquid, miscible with water, with an acrid, irritating odor. It is an extremely corrosive liquid and vapor that can cause severe injury via skin and eye contact, inhalation, or ingestion.

Hydrofluoric acid has not been reported to be a human carcinogen. No acceptable animal test reports are available to define the developmental or reproductive toxicity of HF. The OSHA Permissible Exposure Limit is 3 ppm (as fluoride). Anhydrous HF has a vapor pressure of 775 mm Hg at 20℃, while Hydrofluoric acid has a vapor pressure of 14 mm Hg at 20℃ C.

Hydrofluoric acid corrosivity

Hydrofluoric acid attacks glass, concrete, and many metals. It also attacks carbonaceous natural material such as woody materials, leather, and rubber.

Some materials resist the corrosive action of the acid, such as platinum, wax, polypropylene, polyethylene, and Teflon. In contact with metals with which it will react, hydrogen gas is liberated and the danger exists of a spark or flame resulting in an explosion. HF is used in many labs and in the glass shop on a regular basis. It should always be stored in plastic bottles. Containers of HF should be stored in secondary containers made of polyethylene in areas separate from incompatible materials. All work with hydrofluoric acid should be conducted in a fume hood to prevent exposure by inhalation. Splash goggles and Neoprene gloves as well as laboratory coats should be worn at all times to prevent eye and skin contact.

Hydrofluoric acid acid strength:

In this paper, from the view of structure to discuss the problem of HF acid strength, think system of fluorine ion in H2O in the solvent system and HF deep agent system is lead to different states and properties of hydrogen fluoride as solute and as a solvent system is the main factor of different acidity.

Compared with other hydrogen halide, HF acid has many special place, such as the polarity of the largest hydrofluoric acid is a weak acid, pure liquid hydrogen is a kind of strong acid, strong acid such as nitric acid in the liquid hydrogen fluoride becomes accept protons alkali. How to explain the hf acid is not yet well settled up a problem. The order of the strength of halogen acid as chemical materials widely used chemical thermodynamics analysis, think the hydrofluoric acid weak acid is due to H - F key button is too big and strong hydrogen bonds between HF and water (solvent) effect. As for HF concentrated solution of strong acid, general explanation for the HF has two balance in aqueous solution.

However, on the basis of thermodynamic calculation to "explain" the characteristics of HF acid has certain limitations, because it will just Δ G,Δ H and Δ S overall value to the assumptions of process (such as a bond dissociation energy, ionization energy, electron affinity, hydration energy and entropy of hydrate etc.), and the points of the process itself is experimental observations, it is difficult to calculate from the very beginning. Of strong solution thermodynamics calculation is unwise, because by concentration and calculate the ionization constants of concentrated solution acidity and based on the indicator and reflect the effect of acidity.

In conclusion, the F - ions in H2O in the solvent system and HF solvent system is lead to different states and properties of hydrogen fluoride as solute and as a solvent system is the main factor of different acidity.

The classification of high purity hydrofluoric acid:

High purity hydrofluoric acid, the formula for HF, the molecular weight is 20.01. Colorless transparent liquid, relative density 1.15 ~ 1.18, the boiling point of 112.2 ℃, smoke in the air stream, stimulating odour, highly toxic. With general metal, metal oxide and hydroxide, generate the various salts. Strong causticity, erosion and silicate glass can generate gaseous silicon tetrafluoride. Soluble in water, alcohol, soluble in other organic solvents.

High purity hydrofluoric acid as acid cleaning, etch, with nitric acid, glacial acetic acid and hydrogen peroxide and ammonium hydroxide configuration USES, mainly used in integrated circuit (IC) and very large scale integrated circuit (VLSI) chip cleaning and corrosion, the microelectronics industry is one of the key basic chemical material in the production process, also can be used as analytical reagent preparation of high purity and containing fluorine chemicals. At present, in China is basically used as etching agent and cleaning agent in the microelectronics industry, less dosage of other aspects.

SEMI International (Semiconductor Equipment and Materials International) standardization organization according to the actual development of high-purity reagent in the worldwide scale, classified according to the varieties, each species incorporated into a guidance standard, including multiple level for different process technology. The domestic some high purity reagent production enterprises have their own standards, among them, BV series standards are common, the standard is divided into seven levels.

At present, due to the different standards for the microelectronics manufacturing enterprise of high purity hydrofluoric acid, it can be divided into four levels: (1) low-grade products, used in > 1.2 mu mIC technology of production; (2) the medium product, suitable for 0.8 ~ 1.2 mu mIC technology of production; (3) in high-grade products, suitable for 0.2 ~ 0.6 mu mIC technology of production; (4) a high grade product, suitable for 0.09 ~ 0.2 microns and < 0.09 mu m IC technology.

High purity hydrofluoric acid preparation method and process:

Common purification technology for the preparation of high purity hydrofluoric acid at home and abroad are: distillation, distillation, and boiling distillation, gas absorption technology, such as the purification techniques have different characteristics, different. Some purification techniques such as the boiling distillation technology can only be used for the preparation of the product quantity is little, and some purification techniques such as gas absorption technology can be used in mass production. Therefore, when choosing technology route should be depending on the actual situation. In addition, because the hydrofluoric acid has strong corrosion resistance, the use of distillation process of the distillation equipment used in general need platinum, gold, silver and other precious metals or teflon etc. The capability of corrosion resistance of materials to manufacturing.

High purity hydrogen production unit process arrangement to give priority to with vertical flow, anhydrous hydrofluoric acid raw materials and high pure water in the upper, the purification of hydrofluoric acid in the middle, filtration, packaging and stored in the ground floor. Because the raw material (anhydrous hydrofluoric acid and high pure water) and intermediate can rely on gravity flow from top to bottom, avoid using pump to save energy, reduce the production cost. Here is a kind of distillation, absorption of combining the production technology of producing high purity hydrofluoric acid.

The anhydrous hydrofluoric acid after chemical pretreatment through feeding pump into the high slot, again through flow control into the rectification column, refined after hydrogen fluoride gas is obtained by distillation operation, and turn it into the absorption tower, rectifying column residual liquid made industrial emissions and hydrofluoric acid on a regular basis. In the absorption tower, by adding after measurement, the high pure water, make the distillation of high purity hydrogen fluoride gas formation after hydrofluoric acid, and can be used to control methods such as spray density, gas liquid ratio make further purification, high purity hydrofluoric acid crude product. Then after super clean filtering process, make the product mix and get further filtering, guarantee the particles of qualified products. Finally in purifying indoor packing for final product - high purity hydrofluoric acid.

Impurity arsenic is the need to control an important impurities in high purity hydrofluoric acid, arsenic in hydrofluoric acid raw materials generally exists in the form of three valence, and AsF3 differ with the boiling point of hydrofluoric acid is not big, so only by distillation for the separation effect is not ideal. For arsenic removal of impurities, can be in the process of distillation, adding suitable amount of strong oxidizer (such as potassium permanganate, etc.) will be three valence state of arsenic oxide, make it in the deposit on the tower in the process of distillation kettle and be removed.

Facilities of hydrofluoric acid:

1, Analysis, control and product testing:

With the continuous development of the microelectronics industry production technology of high-purity hydrofluoric acid requirements are also getting higher and higher - required to control the particle size getting smaller and smaller, the requirements of metal and non-metallic impurities getting low (impurity Trace Trace  is even ppm or even ppb / ppt / ppc level), which requires manufacturers must have the ability to analyze control and product testing to match. However, these analyzes control and product testing equipment is expensive, highly specialized technical operation and high requirements, general management and small and medium enterprises is difficult to bear, so that the final products are generally identified or directly to users through the authorized testing center test use and identification, in order to obtain customer acceptance.

Preparation of high purity hydrofluoric acid the test instruments are as follows: (1) high-frequency inductively coupled plasma mass spectrometry (ICP-MS); (2) by inductively coupled plasma atomic emission analyzer (IeP-AES); (3) Atomic Absorption spectrophotometer; (4) the oxygen atom flameless atomic absorption analyzer; (5) ion chromatographic analyzer; (6) laser light scattering particle counter liquid; (7) meter and impurity analysis system; (8) to the original force between microscope; (9) optical microscope particle counter; (10) scanning electron microscope; (11) and the optical film thickness measuring surface profiling instrument; (12) surface tension tester; (13) in air dust particle analyzer; (14 ) water resistivity meter.

2, High purity water--essential raw material to produce hydrofluoric acid

High purity water is an indispensable raw material for the production of high purity hydrofluoric acid, but also the packaging container of cleaning agent, which will directly affect the purity of the product quality high-purity hydrofluoric acid. The main control targets are high water resistivity and solid particles, other auxiliary indicators total oxidizable carbon (TOC), bacteria, dissolved silica, ion concentration. Currently, high purity water production technology is more mature, more common is the first by an ion exchange column and micro filter to give ordinary water, then using reverse osmosis, electrodialysis and other membrane technology for further processing, with the final sterilization and ultrafiltration can obtain high purity water.

3,The package of high-purity hydrofluoric acid:

High-purity hydrofluoric acid is highly corrosive, because the higher quality requirements in the IC production industry, so the packaging technology requirements more stringent. First, the containers must have a corrosion resistance, and secondly to prevent the products appear secondary pollution. Currently the most widely used material is a high density polyethylene (HDPE), tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE).

4, Environment of hydrofluoric acid factory

Factory workshop, analysis room, warehouses and other closed environments, to achieve a certain degree of cleanliness, typically 10000 (hydrofluoric acid with high purity product grade and improve); to maintain a certain temperature (22.2 ± 2.5 ℃, the specific operation site control 22.2 ± 0.11 ℃), about humidity (40%, not less than 30%, not more than 50%).

Here we make a detailed introduce of the current market situation and current production situation for hydrofluoric acid in China, look back the history evolution for hydrofluoric acid technology development in China. Summarize and compare the current technology process for hydrofluoric acid, give a relative introduction about current research process for sulphate acid-fluorite other processes.

Put emphasis on introducing several process technology harvests for using Fluosilicate acid to hydrofluoric acid, consider that there has a great strategic significance for hydrofluoric acid industry and technology developing in China when fluorine resource of fluosilicate acid be utilized efficient. The late 1950s, the need for national defense industry, began developing hydrofluoric acid production technology. Since the relative abundance of fluorite resources, coupled with hydrofluoric acid applications ranging from military defense to expanding refrigeration and air conditioning, aerospace, automotive, textile, chemical, pharmaceutical industry and so on, increasing demand; and because many foreign businessmen have come to China Sourcing hydrofluoric acid, resulting in a significant increase in the two major domestic and international market demand for hydrofluoric acid, promote the vigorous development of the production of hydrofluoric acid.

Hydrofluoric acid is the foundation of modern fluorine chemical industry, is making element fluorine, a variety of fluorine refrigerant, fluorine and new materials, inorganic fluoride salts, various organic fluorides of basic raw materials. So explore efficient energy consumption, environmental protection and sustainable development of hydrogen fluoride production technology has a very important significance and far-reaching impact on the fluorine chemical industry.

First aid measures of hydrofluoric acid burns:

1, Before the operation of hydrofluoric acid, please carefully check for leaks latex gloves, wash their hands after each operation.

2, Contaminated by hydrofluoric acid, do not panic, timely reporting and department heads immediately with plenty of cold running water for 15-30 minutes, then the affected area is immersed in a saturated solution of magnesium sulfate; easy to immerse immersed saturated magnesium sulfate with a clean dressing after the solution was wet, cold packs placed on top of the best. Every 10 minutes for a dressing.

3, Continuous immersion or cold compresses to the affected area four hours after the magnesium sulfate solution blisters or swelling, should be kept cold state to the professional hospital for disposal.

4, The affected area can not be damaged soaked in magnesium sulfate solution, go to the hospital after the rinse water for disposal.

Hydrofluoric acid reactor:

Hydrofluoric acid, hydrofluoric acid production line reactor is the most important equipment, due to the bulky, heavy weight, the production line is the most difficult to install equipment. Hydrofluoric acid reactor is the largest volume of the whole plant equipment, the total length of the reactor 30 m, a diameter of 3 m, the cylinder on the total weight 140.3 t, with the last round cylinder weight 10.3 t, is the construction process of the project most important and difficult one.

Anhydrous hydrogen fluoride production, crude hydrogen fluoride gas generated by the reactor has a high temperature, highly toxic, highly corrosive properties, and a certain amount of entrained dust. These features give the selection pipeline, piping, and etc. made high design requirements.

Anhydrous hydrofluoric acid production process hazardous factors:

Anhydrous hydrofluoric acid is an extremely corrosive acid. Its physical characteristics are wide liquid temperature range, high conductivity, polar, boiling point, freezing point, low viscosity and surface tension, chemical properties of fluorocarbon chains having active and strong chemical activity, with almost all types of organic or inorganic compounds bind. China is emerging as the work of fluorinated fine chemical industry, anhydrous hydrofluoric acid can be widely used in industrial, civil and national defense industries. E.g. fluorine plastic widely used, fluorine rubber, fluorine refrigerants, fluorine-containing coating, fluorine-containing surfactant and a fluorine-containing pharmaceutical products.

Hydrofluoric acid: Pumps and compressors category:

Chemicals used in many types of pumps and compressors, the present production process commonly used in conventional centrifugal pump, vortex pump, liquid hydrocarbon pumps, gear pumps, metering pumps, etc., as well as corrosion-resistant diaphragm pump, pump anti-corrosion lining, shielding pumps, pump and other alloys. There used to transport sulfuric acid, made larger flow pump fuming sulfuric acid, anhydrous hydrogen fluoride, etc., have for the recovery of by-product hydrochloric acid, fluorosilicic acid, hydrofluoric acid and neutralized with caustic circulation pump, but also a small amount of resistance for injection polymerization inhibitor triethylamine and special metering pumps polymer additives and the like. Most of these materials are highly corrosive, and some have some toxicity, should be attention during operation and maintenance. Their common precautions such as: outlet valve is not open or opening is too small, so that the resistance increases, causing the outlet pressure exceeds a predetermined generating material in the joint or leak at the valve. Pump rotating parts of the seal is also very easy problem areas should be checked regularly to ensure they are in good sealed state.

Organic fluorine used in the production of raw materials, intermediate products, finished products, many are "dangerous chemicals in China" (2002 Edition), GB 13690-1992 "commonly used classification of dangerous chemicals and signs", GB 12268-1990 "dangerous goods items watch "and" highly toxic chemicals directory "(2002 edition) and other standards identified as toxic and inflammable and explosive materials or corrosive materials. In the production, storage, transportation, use and other processes, often due to accidental leaks, improper operation, faulty contact and the risk of accidents caused. Especially in the production process, the greater the possibility of danger. Of anhydrous hydrogen fluoride, and chlorine-containing perfluorinated tetrafluoroethylene isobutylene distillation residue, which is widely distributed in both the production process equipment, and stored in cylinders. Since the cylinder was pressurized state, during storage and transportation within and outside the plant vulnerable to leaks. Hydrogen fluoride and chlorine gas moisture or water will generate highly corrosive inorganic acids; organic fluorine containing olefin residue in the water is also very easy to generate an organic acid, which is more big possibility of damage to equipment and piping. Other typical dangerous chemicals have been: sulfuric acid, fuming sulfuric acid, fluorosilicic acid, hydrofluoric acid, water, sodium hydroxide (caustic soda), chloroform (chloroform), hydrochloric acid, antimony trichloride, antimony pentachloride , tetrafluoroethylene, hexafluoropropylene, triethylamine, persulfate or organic peroxide.

Fluorine chemical industry, almost all production units are inseparable from the basic raw material of anhydrous hydrogen fluoride, anhydrous hydrogen fluoride and the production of the main raw material to concentrated sulfuric acid and oleum are highly corrosive mineral acids, more due to corrosion and leaks the most likely to cause injury is a pipe weld, flange interface, valves, pumps, seals, and also more likely to occur when splashing or ejection during sampling and inspection, must pay attention to protect your face and exposed skin. The production process of the finished product containing unreacted sulfuric acid, hydrofluoric acid products, as well as a mixture of fluorine acid and the like, which is highly corrosive mixture of inorganic acids in the operation also need to pay attention to not touch the body.

A byproduct of fluorosilicic acid and hydrofluoric acid are corrosive acids, especially in the open valves and pumps, the system pressure is too high and do not cause leakage. When by-product packaging, often using artificial filling, the other handling, weighing, also commonly used by hand, more prone to accidents.

Under normal production conditions, the entire process system of harmful substances (besides hydrogen fluoride, also have sulfuric acid, fuming sulfuric acid and so on) is not going to leak out, but when any abnormal operation caused by pressure fluctuations when it material leakage may occur. In addition, the maintenance system of the prior inadequately treated, remaining in the equipment and piping dead toxic gases may escape. Storage container of anhydrous hydrogen fluoride or anhydrous hydrogen fluoride there since the pipeline run, run, drip, leak, leak may occur. Another type of valve is fitted with an extreme case of anhydrous hydrogen fluoride vessel and on the pipe, parts suddenly due to corrosion damage, or accidental impact damage, a large number of hydrogen fluoride to escape, causing serious poisoning.

The typical case of danger of hydrofluoric acid:

In 1991 a factory in Hubei anhydrous hydrogen fluoride finished tank, due to the observation level sight glass suddenly broken, a lot of liquid hydrofluoric acid tank discharge, resulting in one dead and one seriously injured.

1991 anhydrous hydrogen fluoride large tank factory in Guangdong Huiyang, liquid outlet pipe valve failure and maintenance, the operator inadvertently forgot to cut off the pipeline, the inner tube remains liquid hydrofluoric acid, but not required to wear protective supplies, hydrofluoric acid also caused the discharge, the same result one person was killed and one seriously injured.

Anhydrous hydrogen storage tank in a specific factory replacement level timing, although according to regulations prior to open the vent valve venting pressure relief valve may be due to the opening was not big enough, the discharge time is not long, and pressure not drained. Unchecked operator test, then disassemble the level gauge, causing the liquid discharge, resulting in two deaths.

Overview on electronic grade hydrofluoric acid:

By the end of 2011, the national electronic-grade hydrofluoric acid production capacity of about 80,000 tons, but production is less than 50,000 tons. Electronic grade hydrofluoric acid has four levels (PPT level, UP-S grade, UP level, EL grade), packaging with bottles of high density polyethylene material, tons of barrels and tankers. Products are mainly used in integrated circuits, solar photovoltaic, liquid crystal displays, LED semiconductor industry.

Currently used for producing an electronic grade hydrofluoric acid purification technology at home and abroad have distillation, distillation, sub-boiling distillation, vacuum distillation, gas absorption technology, these purification technologies have their own characteristics. Such as sub-boiling distillation technique can only be used to prepare a small amount of product, gas absorption technology for large-scale production. Further, since the highly corrosive hydrofluoric acid, the use of corrosion at high temperature distillation process will be more serious, so the distillation apparatus used is generally required platinum, gold, silver and other precious metals such as polytetrafluoroethylene or corrosion resistance capacity than strong material to make. Closely related to the electronic-grade hydrofluoric acid production plant design and process layout, the vertical arrangement of the flow of raw materials (anhydrous hydrofluoric acid and high purity water) and the intermediate product can flow by gravity from top to bottom, in the middle of the preparation of high purity hydrofluoric acid, the product filtration, bottling and storage at the bottom. This arrangement can reduce the pump delivery, save energy, reduce production costs, while avoiding secondary pollution pump products.

Dangers of Hydrofluoric Acid

Hydrofluoric Acid is one of the most dangerous acids known. It needs to be treated differently than even strong acids like Sulfuric and Hydrochloric.

Hydrofluoric Acid is an acid like no other. It is so potent that contact with it may not even be noticed until long after serious damage has been done. Even very strong acids, and mixtures of acids, like Aqua Forte and Aqua Regia, do not have the power to cause death and injury in the way that Hydrofluoric Acid can.

Why is Hydrofluoric Acid so Dangerous?

Hydrofluoric Acid has two mechanisms that cause tissue damage:Corrosive Burns from free hydrogen ions Chemical Burns from tissue penetration of the fluoride

ion.Fluoride ions penetrate and form insoluble salts with calcium and magnesium.

Soluble salts are also formed with other cations but dissociate rapidly. Consequently, fluoride ions release, and further tissue destruction occurs.

Hydrofluoric Acid vs Other Acids

Hydrofluoric acid (HF) differs from other acids because the fluoride ion readily penetrates the skin, causing destruction of deep tissue layers,including bone. Pain associated with exposure to solutions of HF (1-50%) may be delayed for 1-24 hours. If Hydrofluoric Acid is not rapidly neutralized and the fluoride ion bound, tissue destruction may continue for days and result in limb loss or death.

Hydrofluoric Acid is similar to other acids in that the initial extent of a burn depends on the concentration,the temperature, and the duration of contact with the acid.

Hydrofluoric Acid Mortality/Morbidity

Local effects include tissue destruction and necrosis. Burns may involve underlying bone.Systemic fluoride ion poisoning, from severe burns is associated with hypocalcemia (low

calcium levels), hyperkalemia (high potassium levels), hypomagnesemia (low magnesium levels) and sudden death.

Deaths have been reported from concentrated acid burns involving as little as 2.5% Body Surface Area (BSA).

Storing Hydrofluoric Acid

Store in a cool, dry place away from incompatible materials. HF reacts with many materials therefore avoid contact with glass,concrete, metals, water, other acids, oxidizers,

reducers, alkalis, combustibles, organics and  ceramics.

Store in containers made of polyethylene or fluorocarbon plastic, lead, or platinum. Place storage bottles in polyethylene secondary containment trays.

Never store HF in glass containers.

Spills

Ensure all areas where HF is used are equipped with proper spill response equipment. Small spills can be neutralized by covering with magnesium sulfate (dry) and absorbed with spill control pads or other absorbent materials. Add sodium bicarbonate or magnesium oxide to an absorbent and place in a plastic container for disposal. Wash the spill site with a sodium bicarbonate solution. Or use a commercial spill kit. Call EHS (4-5084) to dispose of spill clean-up materials. All spill clean-up materials must be placed in a plastic container.

3M's Universal Sorbent is recommended, as it does not react with HF. Organic spill kits that contain Floor-Dri, kitty litter, vermiculite or sand should not be used because HF reacts with silica to produce silicon tetrafluoride, a toxic gas.

If the spill is large, in a confined space, or in an area where there is not adequate ventilation, or if the acid is concentrated evacuate the room and immediately report the spill to EHS (4-5084) or after hours call 911.

Fire and Explosion Hazard

Hydrogen fluoride is non-combustible, but may create irritating and corrosive fumes of fluorides when heated or in combination with steam or water. Since hydrogen fluoride does not burn,use an extinguishing agent suitable for surrounding fire. Use water to absorb fumes and keep containers cool. Heat released when water or steam combines with hydrogen fluoride or hydrofluoric acid could be hazardous. For fires involving hydrofluoric acid, apply water in flooding quantities. Hydrofluoric acid and various metals may form hydrogen (extremely flammable gas) creating a fire hazard.

Symptoms of Hydrofluoric Acid Burns

The Hydrogen Fluoride molecule is so mobile that it may easily pass through the skin.Because Fluorine has an extremely high affinity for Calcium, bones will be attacked,

and this may result in hypocalcaemia. There may be no pain immediately after the burn,leading the injured person to believe that they are not in danger.

Symptoms of Exposure

CONCENTRATIONS LESS THAN 20% -Erythema (skin redness) and pain may be delayed up to 24 hours, often not reported until tissue damage is extreme. In one study,7% HF produced symptoms in 1 to several hours, 12% Hydrofluoric Acid in less than one hour, and 14.5% Hydrofluoric Acid immediately.

CONCENTRATIONS 20 TO 50% - Erythema and pain may be delayed from 1 to 8 hours,and is often not reported until tissue damage is extreme.

CONCENTRATIONS GREATER THAN 50% -Produces immediate burning, erythema, and tissue damage.

Decontamination and First Aid

Immediately remove all exposed clothing taking necessary precautions to prevent self-exposure(wear gloves) while washing all exposed areas with copious amounts of water.

Application of 2.5 to 33% calcium gluconate or carbonate gel or slurry, either placed into a surgical glove into which the affected extremity is then placed, or rubbed into the burn, is recommended.

Use calcium gluconate for dermal treatment only.DO NOT USE CALCIUM CHLORIDE – Calcium chloride is irritating to the tissues and may cause injury.

Hydrofluoric Acid EXPOSURE KIT

Before beginning work involving Hydrofluoric Acid an exposure kit must be available and located in the laboratory area. The exposure kit must contain the following items:

Container of calcium gluconate gel This gel must be inspected before each use of HF or at least monthly to ensure the gel has not been removed or has not reached the expiration date. If a tube of the gel has been opened, a new container must be purchased and the old container discarded.No work with HF can be done with an expired tube of calcium gluconate gel.

Hydrofluoric Acid EXPOSURE KIT cont.

2 pairs of Neoprene or Nitrile (22mil) gloves 1 heavy-duty polyethylene bag to be used for items contaminated by HF 1 HF Contaminated Waste Label Copy of CHP and MSDS to take to the emergency room Calcium Carbonate (antacid tablets)

First Aid for Inhalation Exposure

If a large volume of Hydrofluoric Acid gas is inhaled:Immediately remove the victim to clean air. Call 911 Inform 911 operator of Hydrofluoric Acid exposure and instruct them to notify hospital of person in transport Inhalation of Hydrofluoric Acid fumes may cause swelling in the respiratory tract up to 24 hours after exposure. Persons who have inhaled Hydrofluoric Acid vapors may need prophylactic oxygen treatment and must be seen by a physician as soon as possible