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Tuesday, 24 December 2013

6 Methods used in sodium hydroxide, caustic soda manufacturing, production

SINGAPORE: Sodium hydroxide, also known as caustic soda or lye, is an inorganic compound with the chemical formula NaOH. It is a white solid, and is a highly caustic metallic base and alkali salt. It is available in pellets, flakes, granules, and as prepared solutions at a number of different concentrations.
Sodium hydroxide is industrially produced as a 50 per cent solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water.
Various methods of preparation of sodium hydroxide are -
Castner - Kellener Process
Principle - In castner-kellner method NaOH is prepared by the electrolysis of aqueous solution of NaCl (Brine).
Castner-kellner cell - It is a rectangular tank of steel. Inside of tank is lined with ‘ebonite.’ Anode is made of titanium. Flowing layer of mercury (Hg) at the bottom of tank serves as cathode.
Ionization of NaCl  - 2NaCl e- 2Na+ + 2Cl-
When electric current is passed through brine, +ve and -ve ions migrate towards their respective electrodes. Na+ ions are discharged at mercury cathode. The sodium deposited at mercury forms Sodium Amalgam. Chlorine produced at the anode is removed from the top of the cell.
Reaction at cathode
2Na+ +2 e- à 2Na
(Na forms amalgam)
Na + Hg à Na/Hg
 Na+ ions are discharged in preference to H+ ions due to high over voltage.
Reaction at anode
2Cl-  à Cl2 + 2e-
Formation of NaOH
Amalgam moves to another chamber called ‘denuder,’ where it is treated with water to produce NaOH which is in liquid state. Solid NaOH is obtained by the evaporation of this solution.
2Na/Hg + 2H2à 2NaOH + H2 + 2Hg
NaOH obtained is highly pure and the process is very effeicient.
Nelson Diaphragm Cell
Principle: Electrolyte used in this process is aqueous NaCl (Brine).
Procedure: Porous diaphragm of asbestos or metal oxide with polymer separates anode and cathode compartments. Diaphragm prevents hydroxide ions entering anode compartment and prevents chloride ions entering cathode compartment. Saturated brine enters anode compartment where chlorine gas is produced.
Anode (positive electrode): carbon (graphite) or titanium coated with Ru-Ti oxide.
Cathode (negative electrode): steel mesh
Reaction at anode(oxidation):
2Cl(aq) àCl2(g) + 2e
Cathode reaction (reduction):
2H2O (l) + 2e à H2(g) + 2OH-(aq)
Na+ migrates across diaphragm to cathode compartment combining with OH- to form NaOH.
Overall cell reaction (showing Na+ spectator ions):
2H2O (l) + 2Cl- (aq) + 2Na+ (aq) -----> 2Na+(aq) + 2OH-(aq) + H2(g) + Cl2(g)
Product contains sodium chloride and sodium hydroxide. NaOH(s) can be crystallised out.
Loewig’s process
Loewig’s process for caustic soda preparation depends on the formation of sodium ferrate (Na2Fe2O4), which is then decomposed with water. The soda liquors are mixed with ferric oxide, and the mass evaporated to dryness and calcined at a bright red heat, usually in a revolving furnace. By the calcination, a reaction between the sodium carbonate and the iron oxide is brought about, carbon dioxide escaping and sodium ferrate remaining in the furnace. The mass is washed with cold water until all soluble matter is removed; then water at 900 C is run over the sodium ferrate, by which it is decomposed, caustic soda formed, and iron oxide regenerated; the last is returned to the calcining process. The ferric oxide used is a natural iron ore, very clean and free from silica or other impurities; that made by calcining a precipitated ferric hydroxide is not well adapted to the process, as it gives a product difficult to lixiviate.
White liquor oxidation process
In the white liquor oxidation process, the nitrogen sulfide (Na2S) in the white liquor is oxidized by air to polysulfides, which are used in the digestion process. The digestion process is where cellulose and semi-cellulose (polysaccharide) are separated from the chips which serve as the wood material for making pulp. White liquor being a chemical such as Na2S, NaOH etc.
This air-oxidation process is situated in between the caustification process and the digestion process. The white liquor that is to be air-oxidized is taken from the line that connects the caustification to the digestion process, and the polysulfides generated are channeled back into process. This means that no modification to the existing system is necessary. The air-oxidation process is comprised mainly of a white-liquor filtration device and an oxidation reactor. The upper-current type is used in order for the filter to efficiently remove the SS, the major components being CaCO3 and other substances
generated during the caustification process. The oxidation reactor is filled with oxidation catalysts, then air supplied via a blower keeps the oxidation reaction going.
The NaOH generated along with the polysulfides in the reaction is used effectively in the digestion process, which also serves to reduce the load placed on the caustification process.
Carmichael method
In Carmichael’s apparatus, an asbestos diaphragm, impregnated with Portland cement, is used. The diaphragm rests horizontally on the cathode at the bottom of the cell; above it is a bell to collect the hydrogen given off. On anode is a grating of copper rods, covered with hard rubber, through which platinum points project into the brine. This anode is suspended in the top of the cell, and the chlorine set free is thus only momentarily in contact with the liquid. The salt solution is fed into the cell at the top, in a rapid stream of drops while the mixture of caustic soda and salt flows continuously from the bottom. The supply of brine is so regulated that the caustic formed at the cathode is drawn off before it has time to diffuse through the liquid. The solution drawn from the cell contains about 20 per cent of caustic soda, and about 75 per cent of the salt is decomposed. The reaction is carried on at a temperature of about 80° C in the top of the cell near the anode, while the region around the cathode is kept as cool as possible.
Being removed from the immediate action of the chlorine, the diaphragms are very durable.
LeSueur’s process
The process uses Lunge’s apparatus. The cathode, of iron wire gauze is placed in a slanting position. On it rests the diaphragm, consisting of two parts, a sheet of parchment paper and it double sheet of asbestos cemented together by blood albumin, coagulated and hardened by treatment with potassium bichromate. An earthenware bell enclosed the anode, which was made of lead, carrying carbon rods dipping into the salt solution. Caustic soda is formed in the solution outside the bell, and owing to the inclined position of the cathode, the hydrogen was expected to escape readily, thus preventing polarization. But it proved in practice that the earthenware bells were disintegrated by the caustic soda solution, while the hydrogen set free. The diaphragms are rapidly destroyed, lasting only from 24 to 48 hours. The anodes are consumed more slowly, lasting about six weeks. The process yields a solution of caustic containing 10 per cent NaOH.
© Worldofchemicals Media

Friday, 20 December 2013

Michael faraday discovered benzene industrial solvent, carcinogen chemical used in industries

Benzene cyclic hydrocarbon production methods Pyrolysis gasoline, coal tar, Catalytic Reforming

Benzene is considered as simplest form of arene and cyclic hydrocarbon. In 1825 benzene was first isolated by Faraday. Benzene is a natural component of crude oil, and is one of the most elementary petrochemicals. In 1845, Hoffmann isolated benzene from coal-tar.

Benzene molecular formula is C6H6 and benzene structure is having alternative double bonds with hexagon shape. Hydrogens present in the benzene can be replaced by some of the other functional groups. As a result number benzene derivatives will be generated. Derivatives of benzene are ethylbenzene, cumene.

Benzene structure

Benzene ring structure was deduced by Friedrich August Kekule. The carbons present in benzene ring are arranged in a hexagon, and he suggested alternating double and single bonds between them. Each carbon atom has two hydrogens instead of four hydrogens. To satisfy the tetravalency of carbon, the benzene ring consisted of alternate single and double bonds.
August Kekule in dream saw a snake coil up, and grabs its own tail then he proposed benzene might be a ring structure.

Benzene preparation methods

  • Sodium benzoate is heated with soda-lime (NaOH) and when it gets decarboxylated benzene is obtained.
  • Phenol vapors are passed over heated zinc dust, benzene is formed.
  • When ethyne is passed through a red hot copper tube, it polymerizes to benzene
  • Benzene is formed on the reduction of benzene diazonium chloride with sodium stannite or hypophosphorus acid.
  • Benzene sulphonic acid on hydrolysis with superheated steam gives benzene.

C6H5.SO3H + H2O —> C6H6 + H2SO4

Following are the other major processes for production of benzene

  • Catalytic reforming
  • Toluene hydrodealkylation
  • Toluene disproportionation
  • Pyrolysis gasoline
  • Production from coal tar

Pyrolysis gasoline

Pyrolysis gasoline is the by-product of steam cracking of petroleum by products like paraffin gases, naphthas, gas oils. Pyrolysis gasoline contains 5 per cent diolefins. In addition it also contains 60 per cent aromatic compounds, 50 per cent of benzene. Different techniques are applied on diolefins to produce benzene, these are

  • Distillation of diolefins to olefins
  • Saturation of olefins to remove sulfur content
  • Execution of solvent extraction and distillation process to obtain benzene

Production from coal tar

This process improved methods of recovery and purification that coke-oven benzene has been able to withstand the competition of petroleum-derived benzene as well as it has. Production of benzene from coal tar involves recovering benzene from coal tar.

  • Extraction of lowest boiling point fractions
  • Applying of caustic soda for the removal of tar acids
  • Crude oil distillation
  • Crude oil purification through hydrodealkylation

Toluene Hydrodealkylation

  • Toluene hydrodealkylation reaction takes place is as follows
  • Mixing of toluene with aromatics or paraffins
  • At specific pressures these mixtures are heated in the presence of hydrogen gas
  • The steam which is formed in previous step then moved to reactor containing dealkylation catalyst
  • In this reactor toluene reacts with hydrogen as a result, benzene and methane products will form
  • At high pressures benzene is separated from methane
  • Then methane also removed from reactor
  • Here in this step benzene can be recovered from fractionalization column and then be stored.

Catalytic Reforming

Catalytic reforming involves the dehydrogenation of naphthenes to aromatics, or the isomerizatoin of alkylnaphthenes and it follows dehydrogenation process. The feed for this process is naptha.

  • First the naptha is hydrotreated to remove sulfur contaminant.
  • Recycled hydrogen is then added, mixed and heated.
  • Conversion of paraffins to aromatic compounds in catalytic reactors and in this reactors platinum or rhenium chloride is acts as catalyst.
  • In further step a stream is formed which is rich in aromatic compounds.
  • Then stream is sent to separation section to separate hydrogen and this hydrogen recycled as basic feedstock.
  • Liquid portion of stream fed to a stabilizer which separates hydrocarbons from liquids.
  • The liquid is then sent to a debutanizer
  • Benzene, toluene and xylenes are then extracted using glycol and sulfonate solvents

10 Industrial applications of Hydrochloric acid

SINGAPORE: Hydrochloric acid (HCl) is a clear, colorless, highly pungent solution of hydrogen chloride in water. It is an extremely important product of the chemical industry and used in many industrial processes. Here are some of the important applications and uses of hydrochloric acid.
Steel Pickling: This is a process whereby rust and scale is removed from steel sheet or coil with the use of a dilute solution of hydrochloric acid. The metal can then be processed. Hydrochloric acid is used in pickling operations for carbon, alloy and stainless steels. Pickling is required for steel products that undergo further processing such as wire production, coating of sheet and strip, and tin mill products. Hydrochloric acid is used primarily for continuous pickling operations in which hot-rolled strip steel is passed through a countercurrent flow of acid solution.
Used in manufacture of organic compounds: HCl is used to manufacture organic compounds such as vinyl chloride and dichloroethane which are used to produce polyvinyl chloride (PVC).
HCl as cleaning agent: One of the strongest commercially available cleaners today is hydrochloric acid. Hydrochloric acid is extremely powerful and is recommended as a cleaner. Industrial strength hydrochloric acid, is commonly used on masonry; however, the acid can be used to clean any product that can withstand its effects.
Used to neutralise water in swimming pools: HCl is used to neutralize water in making it safe for bathers. Most often the pH level is high; the best way to lower pH is by slowly pouring hydrochloric acid directly into the deep end of the pool while the pool pump is on and the water is circulating.
Used to regulate pH level: HCl is used to regulate the pH level in a wide range of manufacturing and treatment processes including the production of drinking water, pharmaceuticals, beverages and foods. It is used in the processing of additives for the food industry including fructose, citric acid and hydrolyzed vegetable protein.
Cleans up accumulated algea, zebra mussels on pontoon boats: Aluminum pontoons on pontoon boats accumulate algea, zebra mussels, etc and become badly fouled in one or two seasons. Low odour hydrochloric acid cleans it up very well. Apply with pump up garden sprayer (all plastic) and wash off after 5 - 10 minutes with water or pressure washer. Very expensive cleaners are sold for this same purpose and do not work any better.
To regenerate ion exchangers: High-quality hydrochloric acid is used in the regeneration of ion exchange resins. HCl is very efficient and does not cause precipitations in the resin bed. Cation exchange is widely used to remove ions such as Na+ and Ca2+ from aqueous solutions, producing demineralized water. The acid is used to rinse the cations from the resins. Na+ is replaced with H+ and Ca2+ with 2H+.
Used in activating oil wells: HCl is used in a process known as oil-well acidization. This process involves injecting the acid into the cavities of oil wells to dissolve away sections of rock, leaving an open column behind. Ultimately, the method serves to accelerate oil production from the well.
Production of inorganic compounds: Numerous products can be produced with hydrochloric acid in normal acid-base reactions, resulting in inorganic compounds. These include water treatment chemicals such as iron(III) chloride and polyaluminium chloride (PAC).
Fe2O3  + 6 HCl → 2 FeCl3 + 3 H2O
(ferric oxide)              (ferric chloride)    
Both iron(III) chloride and PAC are used as flocculation and coagulation agents in wastewater treatment, drinking water production, and paper production.
pH control and neutralization: Hydrochloric acid can be used to regulate the basicity (pH) of solutions.
OH + HCl → H2O + Cl
In industry demanding purity (food, pharmaceutical, drinking water), high-quality hydrochloric acid is used to control the pH of process water streams. In less-demanding industry, technical quality hydrochloric acid suffices for neutralizing waste streams and swimming pool treatment.

Interesting facts about Hydrochloric acid, Hydrochloric acid uses, hazards

SINGAPORE: Hydrochloric acid is a colourless and odourless solution of hydrogen chloride and water; with chemical formula HCl. Once commonly referred to as muriatic acid or spirit of salt, this acid is a highly corrosive chemical compound with several applications in industry. Here are some of the interesting properties of HCl –
Chemical properties of HCl: Hydrochloric acid is a clear, colourless, highly pungent solution of hydrogen chloride (HCl) in water. It is a highly corrosive, strong mineral acid with many industrial uses. The molar mass being 36.46 g/mol, compound has a density of 1.18 g/cm3 .
HCl can dissociate (ionize) only once to give up one H+ ion (a single proton). In aqueous hydrochloric acid, the H+ joins a water molecule to form a hydronium ion, H3O+.The other ion formed is Cl−, the chloride ion. Hydrochloric acid can therefore be used to prepare salts called chlorides, such as sodium chloride. Hydrochloric acid is a strong acid, since it is essentially completely dissociated in water.
Present in digestive acids: HCl exists naturally within gastric acid which is one of the main elements that works in the intestinal tract to digest food and get rid of secretions in human beings. The gastric acid comprises primarily of hydrochloric acid which acidifies the stomach contents. Chloride and hydrogen ions are secreted separately in the stomach section which sits at the top of the stomach by parietal cells of the gastric mucosa into a secretory network known as canaliculi prior to entering the stomach lumen. After exiting the stomach, the hydrochloric acid of the chyme is dissolved in the duodenum by sodium bicarbonate. The intestinal tract is protected from the strong acid by the secretion of a thick, protective mucus layer, and by secretin induced buffering with sodium bicarbonate. If hydrochloride is sent to the oesophagus, it can aggravate the lining of the oesophagus and lead to the sensation like peptic ulcers or heartburn.
Fatal at certain concentrations (HCl hazards): concentration of 600 molar of HCl can kill a person. The concentration of 50 – 150 molar can make a person blind.
Used in activating oil wells: HCl is used in a process known as oil-well acidization. This process involves injecting the acid into the cavities of oil wells to dissolve away sections of rock, leaving an open column behind. Ultimately, the method serves to accelerate oil production from the well.
HCl as cleaning agent: One of the strongest commercially available cleaners today is hydrochloric acid. Hydrochloric acid is extremely powerful and is recommended as a cleaner. Industrial strength hydrochloric acid, is commonly used on masonry; however, the acid can be used to clean any product that can withstand its effects.
Hydrochloric acid safety: Concentrated HCl is highly corrosive. In laboratories, it is advisable to apply a barrier cream to the hands prior to use. Keep it away from any heat source such as burners, ovens, sunlight etc. Keep containers closed and in an upright position when not in use. For dilute HCl add the acid to water and store the diluted acid solution in a reagent bottle (never add the water to the acid). On industrial scale, label the product, chemical name and chemical formula. Name the ingredients and formulation details where relevant. Follow the first aid and emergency procedures. Provide the details of manufacturer, reference to MSDS and expiry date.

Thursday, 19 December 2013

sodium hydroxide industrial applications, uses, as cleaning, sanitization agent, chromatography methods

Sodium hydroxide is the principal strong base used in the chemical industry. In bulk it is most often handled as an aqueous solution, since solutions are cheaper and easier to handle. Sodium hydroxide is also used for the manufacture of sodium salts and detergents, for pH regulation, and for organic synthesis.

Sodium hydroxide is employed to digest tissues, such as in a process that was used with farm animals at one time. This process involved placing a carcass into a sealed chamber, then adding a mixture of sodium hydroxide and water. This eventually turns the body into a liquid with coffee-like appearance and the only solid that remains are bone hulls, which could be crushed between one's fingertips.

Surfactants can be added to the sodium hydroxide solution in order to stabilize dissolved substances and thus prevent redeposition. A sodium hydroxide soak solution is used as a powerful degreaser on stainless steel and glass bakeware. It is also a common ingredient in oven cleaners.

Sodium hydroxide is widely accepted for cleaning, sanitizing, and storing chromatography media and systems. The advantages of sodium hydroxide as a cleaning and sanitation agent are

  • Efficacy
  • Low cost
  • Ease of detection
  • Removal
  • Disposal

Sodium hydroxide has been shown to be effective in removing proteins and nucleic acids. It is also effective for inactivating

  • Viruses
  • Bacteria
  • Yeasts
  • Fungi
  • Endotoxins

It is common practice in industrial manufacturing to save time by adding a salt, such as sodium chloride, to the sodium hydroxide solution to combine cleaning with sanitization.

During restrictive inspections, producers of biopharmaceuticals and biological products usually give attention to cleaning and cleaning validation of chromatography resins and multiuse purification systems. Chromatographic resins must either be disposed of or sufficiently cleaned to ensure reproducibility in subsequent cycles.

Over the years, varied cleaning agents have been proposed. Once evaluating a new cleaning agent for a resin, make sure it is compatible with system components as well. Destruction of O-rings and other column components by a cleaning agent is a risk to a process.

For resins, the foremost cleaning agent is sodium hydroxide. Some reports indicate that heated sodium hydroxide is an excellent cleaning agent. Even without the heating, high concentrations of sodium hydroxide require facility and equipment evaluation and use of safety equipment to protect workers.

Sodium hydroxide is frequently used as an industrial cleaning agent where it is often called "caustic". It is added to water, heated, and then used to clean process equipment, storage tanks, etc. It can dissolve grease, oils, fats and protein based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties.

As a cleaning agent, sodium hydroxide saponifies fats and dissolves proteins. In general, it can solubilize precipitated proteins. Its hydrolyzing power is enhanced by the presence of chlorine.

Chromatography columns can become contaminated by a variety of protein and nonprotein species during a purification process. Consequences of chromatography column contamination include

  • Increase in backpressure
  • Loss of signal resolution
  • Altered product yield
  • Medium discoloration

Common chromatographic contaminants include

  • Residual proteins
  • Proteins
  • Nucleic acids
  • Lipids
  • Viruses
  • Bacteria
  • Yeast
  • Fungi
  • Prions
  • Endotoxins
  • Metal ions

Sodium hydroxide for proteins removal

Sodium hydroxide has been used extensively to get rid of proteins from ion exchange, hydrophobic interaction, and gel filtration media. The ability of sodium hydroxide to remove proteins from chromatography media depends on the following factors

  • Nature of the media
  • Nature of sample
  • Sample contaminants

These factors may interfere with the cleaning efficiency of sodium hydroxide. A higher concentration of sodium hydroxide may be required if lipids are bound to a protein.

Sodium hydroxide for nucleic acids removal

Nucleic acids can bind tenaciously to anion exchangers of chromatography equipment. 1 M sodium hydroxide and 3 M sodium chloride, with a total contact time of one hour, effectively removes radiolabelled calf thymus DNA from a weak anion exchanger.

Since it is a bacteriostat it is recommended for the removal of bacteria from chromatography equipment sodium hydroxide should be added along with ethanol. Sodium hydroxide may not completely eliminate bacterial spores alone in further good manufacturing process required to complete the process.

Endotoxins are effectively removed by using sodium hydroxide sanitizing agent.

When sodium hydroxide used for sanitization of chromatography media, the ability to withstand stringent sanitizing conditions depends on the following factors

  • Functional groups
  • Attachment chemistries
  • Stability of base matrices to alkaline conditions

Other applications

Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel coloring production, poultry scalding, soft drink processing, and thickening ice cream. Olives are often soaked in sodium hydroxide to soften them, while pretzels and German lye rolls are glazed with a sodium hydroxide solution before baking to make them crisp.

Sodium hydroxide has been used to straighten hair


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