Manufacture of some heavy Inorganic chemicals, Chemistry tutorial


Industrial inorganic chemistry comprises subdivisions of the chemical industry which manufacture the inorganic products on a large scale like the heavy inorganic (that is, chlor-alkalis, sulphuric acid, sulphates) and fertilizers (that is, potassium, nitrogen and phosphorus products) and also the segments of fine chemicals which are employed to produce high purity inorganic on a much smaller scale. Among such are reagents and raw materials employed in high-tech industries, pharmaceuticals or electronics, for illustration, and also in the preparation of inorganic specialties like catalysts, pigments and propellants.

Metals are the chemicals in a certain sense. They are manufactured from ores and purified via most of the similar methods as those employed in the manufacture of inorganic. Though, if they are commercialized as alloys or in their pure form like iron, lead, copper or tungsten, they are considered products of the metallurgical not chemical industry.

The Chemical Industry:

The chemical industry adds up value to raw materials via transforming them to the chemicals needed for the manufacture of consumer products. As there are generally some different methods which can be employed for this aim, the chemical industry is related by the intense competition for new markets. This is made up of companies of various sizes, comprising some giants which are engaged in the transformation of some very fundamental raw materials to final products, and also medium-size or small companies which concentrate on very few of these steps. The closer to the raw material, the bigger the scale of operations; like 'heavy' inorganic chemicals are generally manufactured via continuous processes. At other extreme in terms of scale are the firms which manufacture 'specialties', mostly in batch methods, from 'intermediates' which correspond to chemicals that have already gone via some steps of synthesis and purification.

Fundamental chemicals represent the starting point for the manufacture of inorganic industrial chemicals. They are generally one step away from the raw materials and are generated on a very large scale using continuous processes. The unit price of such products is comparatively low, and producing them cheaply and proficiently is a main concern for the companies which manufacture them. Sulphur, nitrogen, phosphorus and chloralkali industries are the major producers of basic inorganic chemicals, and they will frequently sell them to other industries and also using them in the manufacture of their own end-products. The fundamental principles for their production and main uses are pointed out here for each of such industries.

Inorganic chemicals generated on an industrial scale can be simply identified. Most of today's large companies began as producers of inorganic, however as coal - and particularly petroleum-became significant sources of raw materials and they were integrated to the product chain.

Sources of Inorganic Raw Materials:

There are numerous different sources of raw materials for the manufacture of inorganic chemicals. Some of them are found in their elemental form. Sulphur is a notable exception. It takes place in underground deposits and can be brought to the surface by compressed air after it is melted through superheated steam. Though, increasing quantities of sulphur are recovered from petroleum and natural gas (where they take place as impurities).

Air includes molecular nitrogen and oxygen. They might be separated via liquefaction and fractional distillation all along by inert gases, particularly argon. Salt or brine can be employed as sources of chlorine and at times bromine, sodium hydroxide and sodium carbonate, while metals like iron, aluminum, copper or titanium and also phosphors, potassium, calcium and fluorine are obtained from the mineral ores. Saltpeter was once a significant source of nitrogen compounds, however nowadays most ammonia and nitrates are prepared synthetically from nitrogen gas in the air.

Recovery and recycling provide increasing amounts of some metals. As environmental concerns increase, such operations will probably become a significant source of materials employed in the manufacture of some inorganic chemicals.

Source                               Thousands of Tons          Examples of Uses

Phosphate rock                          37,706                      Fertilizers, detergents

Salt                                            49,723                       Chlorine, alkali production

Limestone                                  20,617                       Soda ash, lime

Sulfur                                         10,144                       Sulphuric acid productions

Potassium compounds                1,323                        Caustic potash, fertilizers

Sodium carbonate                      11,356                       Caustic soda, cleaning


Beginnings of the Chemical Industry:

The origins of chemical industry can be outlined to the Industrial Revolution. Sulphuric acid and sodium carbonate were among the first industrial chemicals. 'Oil of vitriol' (as the former was recognized) played a significant role in the manipulation of metals; however its production on an industrial scale needed the growth of materials which would resist attack. Sodium carbonate was acquired in its anhydrous form, 'soda ash', from vegetable material till the quantities produced could no longer meet up the rapidly expanding requirements of manufacturers of glass, soap and textiles. This led the Royal Academy of Sciences of Paris, in the year 1775, to establish a contest for the discovery of a method based on a rich raw material, sodium chloride and to Nicolas Leblanc's technique for the preparation of soda by transforming salt into sulphate.

2 NaCl + H2SO4 → Na2SO4 + 2 HCl

followed via transformation of the sulphate to soda by charcoal and chalk

Na2SO4 + 2C + CaCO3 → Na2CO3 + CaS + 2 CO2

However he didn't win the prize, Leblanc's method is related by the birth of industrial chemistry.

The industrial production of chemicals was generally based on running reactions which were known to result the desired products on much bigger scales. Success in such endeavors lay much more in the experience and skill of their practitioners than the application of solid chemical principles. This led to severe problems of control and the generation of noxious by-products. The introduction of the Leblanc method in the northwest of England led to a general public outcry against the dark and corrosive smoke which covered the surrounding countryside. The Alkali Act, passed in response in the year 1863, symbolizes the first legislation that established the emission standards.

Sulphuric acid was a necessary chemical for dyers, bleachers and alkali manufacturers. Its production on a large scale needed the growth of lead-lined chambers which could resist the vapors that were formed whenever sulphur was burned by nitrates

SO2 + NO2 + H2O → H2SO4 + NO

NO + 1/2 O2 → NO2

This method was wasteful and emitted the corrosive gases. It enhanced only in the mid-19th century whenever towers to recycle the gases were finally introduced. The transportation of sulphuric acid was dangerous, and alkali manufacturers tended to generate their own as a result. This marked the starting of the diversification and vertical integration which are features of the chemical industry.

Sulphuric acid was as well employed in the preparation of superphosphates that were made as fertilizers on a large scale by the mid 19th century. By that time, a solution was found for the complex engineering problems which had hampered the utilization of the alternative method to produce soda.

NH3 + H2O + CO2 → NH4HCO3

NaCl + NH4HCO3 → NaHCO3 + NH4Cl

2NaHCO3 → Na2CO3 + H2O + CO2

Ernest Solvay, a Belgian chemist, designed a tower in which the carbon-dioxide reacted proficiently with solid salts. The Solvay method had enormous benefits over the Leblanc method: It didn't produce as much waste and pollution; its raw materials, brine and ammonia, were readily available (that is, the latter from gasworks); less fuel was employed, and no sulphur or nitrate was comprised. Despite its higher capital costs, it was quickly adopted and soon became the main source of alkali.

The other main method employed in the manufacture of inorganic chemicals is the catalytic conversion of nitrogen and hydrogen to ammonia. The German chemist Fritz Haber first synthesized ammonia from nitrogen and hydrogen in the year 1909. Four years later, altogether with the other German, Carl Bosch, he changed the method for the commercial production of ammonia. The Haber (or Haber-Bosch) method represented a technological breakthrough as it needed an extremely specialized plant to handle gases at high temperatures and pressures.

Sulphuric Acid and Sulphates:

Sulphuric acid has long been the chemical which is made up in the largest quantities on a world scale. Its production is frequently associated to a country's phase of growth, owing to the large number of transformation method in which it is employed.

Sulphuric acid is made up from elemental sulphur. Mining was the major source for this element, which was obtained from sulphide-containing ores or in extremely pure form from underground deposits by the Frasch method (that is, injection of superheated steam and air to drillings and the separation of the mixture which increases to the surface). The large-scale consumption of petroleum and natural gas has modified this scenario as sulphur takes place as an impurity in most of the fossil fuels and should be eliminated before the fuels are processed. Such fuels are presently the major source of sulphur, and their relative significance tends to increase by more rigorous controls on emissions.

Sulphuric acid is manufactured in three phases:

2 SO2 + O2 → 2SO3

SO3 + H2O → H2SO4

As the reaction of sulphur by dry air is exothermic, the sulphur dioxide should be cooled to eliminate surplus heat and avoid the reversal of reaction.

Most of the plants make use of reactors with different phases in order to cool the stream for the catalytic step. Conversion via a vanadium pentoxide catalyst deposited on a silicate support is the vital step in the method, in which the gaseous stream is passed over the successive layers of catalyst. The gas mixture is then passed via an absorption tower. Oleum, the product, is a concentrated solution of sulphuric acid having surplus sulphur trioxide.

As the inexpensive source of acid, a huge amount of the sulphuric acid which is produced is employed for the preparation of other mineral acids. This is as well employed to produce sulphates, like ammonium sulphate (that is, a low-grade fertilizer), sodium sulphate (that is, employed in the production of paper) and aluminum sulphate (that is, employed in water treatment), and also organic sulphates (employed as surfactants). Sulphuric acid is as well a good catalyst for numerous reactions, comprising the transformation of ethanol to ethylene or ethyl ether.

Nitrogen Compounds:

In common, chemicals having nitrogen are prepared from ammonia produced via the Haber method.

As molecular nitrogen is inert, its reaction by hydrogen needs very severe conditions and a catalyst. The iron catalyst is employed. High pressure prefers the formation of products; however an increase in temperature will shift the equilibrium in the opposite direction. Plants will therefore operate under conditions which represent the most favorable balance between the operating costs and capital investment.

Energy consumption is extremely high and its cost is a significant component all along by the starting materials. Nitrogen is simply obtained from air and hydrogen and can be generated by the shift reaction.

CO + H2O → CO2 + H2

Or from the hydrocarbon reforming

CH4 + 2H2O → CO2 + 4H2

Further phases are needed to make sure the conversion and to take away carbon-dioxide or carbon monoxide from the gas mixture. The mixture of ammonia and synthesis gas (CO + H2) results from the reaction by nitrogen as a result the two should be separated and the synthesis gas recycled.

Most of the ammonia which is produced is utilized as fertilizer or employed to manufacture other fertilizers, like urea, ammonium sulphate, ammonium nitrate or diammonium hydrogen phosphate. Ammonia is as well employed in the Solvay method, and it is a starting material for the preparation of cyanides and nitriles (that are employed to make polymers like nylon and acrylics) and also aromatic compounds having nitrogen, like aniline and pyridine.

The other source of nitrogen compounds in the chemical industry is nitric acid, acquired from the oxidation of ammonia

4NH3 + 5O2 → 4NO + 6H2O

3NO + 3/2O2 → 3NO2

3NO2 + H2O → 2HNO3 + NO

The primary reaction is run over platinum-rhodium catalysts at around 900°C (1,652°F). In the second and third phases, a mixture of nitric oxide and air circulates via condensers, where it is partly oxidized. The nitrogen dioxide is absorbed in the tower, and nitric acid sinks to the bottom. Nitric acid is mostly employed to make ammonium nitrate, most of it for fertilizer however it as well goes to the production of explosives. Nitration is employed to manufacture explosives like nitroglycerine and trinitrotoluene (TNT) and also many significant chemical intermediates employed in the pharmaceutical and dyestuff industries.

Phosphorus Compounds:

The world's main source of phosphorus is apatite, a class of phosphate minerals. Commercially, the most significant is fluoroapatite, a calcium phosphate which comprises fluorine. This fluorine should be eliminated for the formation of phosphoric acid; however it as well can be employed to form hydrofluoric acid and fluorinated compounds.

Phosphoric acid is the starting material for most of the phosphates which are produced industrially. This is obtained from the reaction of the apatite mineral by sulphuric acid.

Silica is present in the mineral as the impurity, and it reacts by hydrofluoric acid to result silicon tetrafluoride that can be transformed to fluorosilicic acid, a significant source of fluorine. More than half of the phosphoric acid which is generated by the reaction of phosphates by sulphuric acid is transformed directly to sodium or ammonium phosphates to be employed as fertilizer; therefore, purity is not a concern.

For products which need high purity, like detergents and food-stuffs, phosphoric acid is formed from elemental phosphorus (at around four times the cost). The electric furnace operating at 1,400 to 1,500°C (2,552 to 2,732°F) is employed to form a molten mass of apatite and silica which reacts by coke and decreases the phosphate mineral.

2Ca3(PO4)2 + 6SiO2 + 10C → P4 + 6CaSiO3 + 10CO

Concentrating phosphoric acid leads to the polyphosphoric acid, a mixture of some polymeric species, a good catalyst and dehydrating agent. Polyphosphate salts are employed as water softeners in the detergents or as buffers in food. Small quantities of elemental phosphorus are employed to form matches, and phosphorus halides to make specialty chemicals for the pharmaceutical and agrochemical industries.

Chlor-Alkali Compounds:

Industries manufacturing chlorine, sodium hydroxide (as well termed as caustic soda), sodium carbonate (or soda ash) and its derivatives and compounds based on the calcium oxide (or lime) are generally comprised under this category. As both sodium hydroxide and chlorine encompass a common raw material, sodium chloride, they are generated in quantities that reflect their equivalent molar ratio, irrespective of the market for either product. As they are produced via electrolysis, they need a cheap source of brine and electricity.

2NaCl + 2H2O → 2NaOH + Cl2 + H2

Most of the methods are based on the electrolysis of a sodium chloride solution; however some of the plants operate by the molten salt. Three various cell kinds are employed in electrolysis in water: mercury cells, diaphragm cells and membrane cells. Membrane cells are substituting the other two kinds in modern units; however it might not be economically feasible to transform older plants.

Sodium carbonate and Sodium hydroxide are the alternative sources of alkali, and their utilization has followed the availability of raw materials and also the effectiveness of methods developed for their production. Both need sodium chloride and energy and, whenever limestone deposits are as well available, sodium carbonate might be formed by the Solvay method. Limestone comprises mostly of calcium carbonate and can be employed to produce calcium oxide (or quicklime) and calcium hydroxide (or slaked lime); the oxide might be obtained via heating (1,200 to 1,500°C, or 2,192 to 2,732°F) limestone, whereas the hydroxide that is more well-situated to handle, is obtained by adding water to the oxide

CaO + H2O → Ca(OH)2

Its main principal use is in steelmaking; however it as well goes to the manufacture of chemicals, water treatment and pollution control. In the Solvay method, calcium carbonate and sodium chloride are employed to form calcium chloride and sodium carbonate with ammonia (that is recycled) as a medium for dissolving and carbonating the sodium chloride and calcium hydroxide for precipitating the calcium chloride from the solution.

As sodium carbonate might be mined directly, its utilization might be favored over a manufactured product. It is mainly employed in the glass industry. Sodium silicates might be derived from the sodium carbonate and in their finely divided form, silica gel, might be employed in soaps and detergents.

Sodium hydroxide has numerous different uses in the chemical industry. Considerable amounts are employed in the preparation of paper and to form sodium hypochlorite for use in disinfectants and bleaches. Chlorine is as well employed to generate vinyl chloride, the starting material for the formation of polyvinyl chloride (PVC) and in water purification. Hydrochloric acid might be made by the direct reaction of chlorine and hydrogen gas or via the reaction of sodium chloride and sulphuric acid. It is employed as a chlorinating agent for the metals and organic compounds.

In several regions of the world, there are salt deposits or brines which have been enriched via bromine. Commercially, bromine might be extracted via treating the brines by chlorine and eliminating it by steam.

2 Br- + Cl2 → Br2 + 2Cl-

Bromine is mainly utilized in water disinfection; bleaching fibers and silk; and in the formation of medicinal bromine compounds and dyestuffs.

Titanium Dioxide:

Titanium dioxide is by far the most significant titanium compound. This can be purified via dissolving in sulphuric acid and precipitating the impurities. The solution is then hydrolyzed, washed and calcinated. On the other hand, ground rutile is chlorinated in the presence of carbon and the resultant titanium tetrachloride is burned in oxygen to form the chloride.

Titanium dioxide is mainly found in nature in three crystal forms: anastase, brookite and rutile. Its extreme brightness and whiteness and its high index of refraction are responsible for its extensive use as a white pigment in paints, floor covering, lacquers, paper, plastics, rubbers, textiles, ceramics and cosmetics.

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