Essential chemical processes

• Anthraquinone process

hydrogen peroxide is manufactured almost exclusively by the anthraquinone process, which the German chemical company BASF developed and patented in 1939 It begins with the reduction of an anthraquinone (such as 2-ethylanthraquinone or the 2-amyl derivative) to the corresponding anthrahydroquinone, typically by hydrogenation on a palladium catalyst. In the presence of oxygen, the anthrahydroquinone then undergoes autoxidation: the labile hydrogen atoms of the hydroxy groups transfer to the oxygen molecule, to give hydrogen peroxide and regenerating the anthraquinone. Most commercial processes achieve oxidation by bubbling compressed air through a solution of the anthrahydroquinone, with the hydrogen peroxide then extracted from the solution and the anthraquinone recycled back for successive cycles of hydrogenation and oxidation.

• Wet sulfuric acid process

The wet sulfuric acid process is an efficient process for recovering sulfur from various process gases in the form of commercial quality sulfuric acid (H2SO4), with simultaneous production of high pressure steam.

Starting with Hydrogen Sulfide gases The main reactions in the WSA process Combustion: 2 H2S + 3 O2 ⇌ 2 H2O + 2 SO2 + 518 kJ/mol Oxidation: 2 SO2 + O2 ⇌ 2 SO3 + 99 kJ/mol (in the presence of a vanadium (V) oxide catalyst) Hydration: SO3 + H2O ⇌ H2SO4 (g) + 101 kJ/mol Condensation: H2SO4 (g) ⇌ H2SO4 (l) + 90 kJ/mol

The energy released by the above-mentioned reactions is used for steam production. Approximately 2-3 ton high-pressure steam per ton of acid produced.

• Castner-Kellner process

The Castner-Kellner process is the first method of electrolysis on an aqueous alkali chloride solution (usually sodium chloride solution) to produce the corresponding alkali hydroxide.

The apparatus is divided into two types of cells separated by slate walls. The first type uses an electrolyte of sodium chloride solution, a graphite anode, and a mercury cathode. The other type of cell uses an electrolyte of sodium hydroxide solution, a mercury anode, and an iron cathode. The mercury electrode is common between the two cells. This is achieved by having the walls separating the cells dip below the level of the electrolytes but still allow the mercury to flow beneath them.

The reaction at the Graphite anode is: 2 Cl- → Cl2 + 2 e-

The chlorine gas that results vents at the top of the outside cells where it is collected as a byproduct of the process. The reaction at the mercury cathode in the outer cells is Na+ + e- → Na (amalgam)

The sodium metal formed by this reaction dissolves in the mercury to form an amalgam. The mercury conducts the current from the outside cells to the center cell. In addition, a rocking mechanism agitates the mercury to transport the dissolved sodium metal from the outside cells to the center cell.

The anode reaction in the center cell takes place at the interface between the mercury and the sodium hydroxide solution. 2Na (amalgam) → 2Na+ + 2e-

Finally at the iron cathode of the center cell the reaction is 2H2O + 2e- → 2OH- + H2

The net effect is that the concentration of sodium chloride in the outside cells decreases and the concentration of sodium hydroxide in the center cell increases. As the process continues, some sodium hydroxide solution is withdrawn from center cell as output product and is replaced with water. Sodium chloride is added to the outside cells to replace what has been electrolyzed.

Mercury cells are being phased out due to concerns about mercury poisoning from mercury cell pollution and replaced by the Chloralkali process.

• Odda process

The Odda process (also known as the nitrophosphate process) was a method for the industrial production of nitrogen fertilizers. The process involves acidifying phosphate rock with dilute nitric acid to produce a mixture of phosphoric acid and calcium nitrate. Ca5(PO4)3OH + 10 HNO3 → 3 H3PO4 + 5 Ca(NO3)2 + H2O

The mixture is cooled to below 0 °C, where the calcium nitrate crystallizes and can be separated from the phosphoric acid. 2 H3PO4 + 3 Ca(NO3)2 + 12 H2O → 2 H3PO4 + 3 Ca(NO3)2·4H2O

The resulting calcium nitrate produces nitrogen fertilizer. The filtrate is composed mainly of phosphoric acid with some nitric acid and traces of calcium nitrate, and this is neutralized with ammonia to produce a compound fertilizer. Ca(NO3)2 + 4 H3PO4 + 8 NH3 → CaHPO4 + 2 NH4NO3 + 3(NH4)2HPO4

If potassium chloride or potassium sulfate is added, the result will be NPK fertilizer. The process was an innovation for requiring neither the expensive sulfuric acid nor producing gypsum waste.

The calcium nitrate mentioned before, can as said be worked up as calcium nitrate fertilizer but often it is converted into ammonium nitrate and calcium carbonate using carbon dioxide and ammonia. Ca(NO3)2 + 2 NH3 + CO2 + H2O → 2 NH4NO3 + CaCO3

Both products can be worked up together as straight nitrogen fertilizer.

• Mannheim process

The Mannheim process is an industrial process for the production of hydrogen chloride and sodium sulfate from sulfuric acid and sodium chloride. The Mannheim furnace is also used to produce potassium sulfate from potassium chloride. The Mannheim process is a stage in the Leblanc process for the production of sodium carbonate.

The process is conducted in a Mannheim furnace, a large cast iron kiln. Sodium chloride and sulfuric acid are first fed onto a stationary reaction plate where an initial reaction takes place. The stationary plate is up to 6 m (20 ft) in diameter. Rotating rabble arms constantly turn over the mixture and move the intermediate product to a lower plate. The kiln portion of the furnace is constructed with bricks that have high resistance to direct flame, temperature, and acid. The other parts of the furnace are heat and acid resistant. Hot flue gas passes up over the plates carrying out liberated hydrogen chloride gas. The intermediate product reacts with more sodium chloride in the lower, hotter section of the kiln producing sodium sulfate. This exits the furnace and passes through cooling drums before being milled, screened and sent to product storage facilities.

The process involves intermediate formation of sodium bisulfate, an exothermic reaction that occur at room temperature: NaCl + H2SO4 → HCl + NaHSO4

The second step of the process is endothermic, requiring energy input: NaCl + NaHSO4 → HCl + Na2SO4 Temperatures in the range 600-700 °C are required.

• The French method

Seashells can also be cooked into lime or wood burned to ashes and then incorporated into a manure pile to lower acidity and help soil bacteria create nitrate salts Niter-beds were prepared by mixing manure with (wood ashes or lime), common earth and organic materials such as straw to give porosity to a compost pile typically 4 feet (1.2 m) high, 6 feet (1.8 m) wide, and 15 feet (4.6 m) long. The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition, then finally leached with water after approximately one year, to remove the soluble calcium nitrate (Ca(NO3)2). The reaction of equal moles of any nitrate salt such as calcium nitrate (Ca(NO3)2) with sulfuric acid (H2SO4) which will cause the sulfate to precipitate out (CaSO4) while leaving behind nitric acid (HNO3) in solution. Distilling this solution to produce the desired level of purity. This procedure can also be performed under reduced pressure and temperature in one step in order to produce less nitrogen dioxide gas.

• Birkeland-Eyde process

The Birkeland-Eyde process was one of the competing industrial processes in the beginning of nitrogen based fertilizer production. It is a multi-step nitrogen fixation reaction that uses electrical arcs to react atmospheric nitrogen (N2) with oxygen (O2), ultimately producing nitric acid (HNO3) with water. An electrical arc was formed between two coaxial water-cooled copper tube electrodes powered by a high voltage alternating current of 5 kV at 50 Hz. A strong static magnetic field generated by a nearby electromagnet spreads the arc into a thin disc by the Lorentz force. The plasma temperature in the disc was in excess of 3000 °C. Air was blown through this arc, causing some of the nitrogen to react with oxygen forming nitric oxide. By carefully controlling the energy of the arc and the velocity of the air stream, yields of up to approximately 4-5% nitric oxide were obtained at 3000 °C and less at lower temperatures. The hot nitric oxide is cooled and combines with atmospheric oxygen to produce nitrogen dioxide. The time this process takes depends on the concentration of NO in the air. At 1% it takes about 180 seconds and at 6% about 40 seconds to achieve 90% conversion. This nitrogen dioxide is then dissolved in water to give rise to nitric acid, which is then purified and concentrated by fractional distillation. The design of the absorption process was critical to the efficiency of the whole system. The nitrogen dioxide was absorbed into water in a series of packed column or plate column absorption towers each four stories tall to produce approximately 40-50% nitric acid. The first towers bubbled the nitrogen dioxide through water and non-reactive quartz fragments. Once the first tower reached final concentration, the nitric acid was moved to a granite storage container, and liquid from the next water tower replaced it. That movement process continued to the last water tower which was replenished with fresh water. About 20% of the produced oxides of nitrogen remained unreacted so the final towers contained an alkaline solution of lime to convert the remaining to calcium nitrate. The process is extremely energy intensive; demanding about 15 MWh per ton of nitric acid, yielding approximately 60 g per kWh.

• Wood lye production

Take any large wooden or steel container, cut holes in its bottom and put in a layer of pebbles. Place two or three inches of straw or dried grass on top of the little rocks and then fill the barrel almost full with hardwood ashes from the fire. Tamp the ashes down as you fill the container and leave a small depression in the top. Support the barrel about three or four feet off the ground and place a sloping trough under the keg to catch and funnel into a bucket the lye that seeps out. When you have the apparatus set up, fill the depression in the barrel with water. Slowly, that water will seep down through the ashes and after six to eight hours a solution of lye will begin to trickle (not run) down the trough. Don’t get anxious and try to speed the process by adding more water up above until the depression in the ashes is empty. When it comes to leaching out lye, patience is a decided virtue. The first run will be strong enough to cut grease, but succeeding runs of lye will have to be poured through your processer twice. The finished solution is finished, though, since the leaching barrel produces the same results you’d get by boiling the wood ashes.

Hickory, sugar maple, ash, beech and buckeye are the best producers of lye. Most hardwood ashes will do. White ashes from a hardwood fire are what contain the lye.

• Fischer-Tropsch process

The Fischer-Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen or water gas into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150-300 °C (302-572 °F) and pressures of one to several tens of atmospheres. n the usual implementation, carbon monoxide and hydrogen, the feedstocks for FT, are produced from coal, natural gas, or biomass in a process known as gasification. The Fischer-Tropsch process then converts these gases into a synthetic lubrication oil and synthetic fuel.

• charcoal manufacture

Charcoal can be made from anything containing carbon. Traditionally wood has been the raw material used to make charcoal. Charcoal is made by removing the hydrogen and oxygen in the wood while leaving just the carbon.

Making charcoal consists of 4 steps.

1.) Drying the wood to be made into charcoal.

2.) Heating the wood in an oxygen limited environment. At 100°C the chemical bonds begin to break. 100° to 200°C, noncombustible products, such as carbon dioxide, traces of organic compounds and water vapor, are produced. Above 200°C the celluloses break down, producing tars and flammable volatiles. If these are mixed with air and heated to the ignition temperature, combustion reactions occur. Above 200°C the lignin in the wood starts to breakdown in an exothermic reaction.

3.) The wood should continue to be heated to between 450- 500°C. A temperature of 500°C gives a typical fixed carbon content of about 85% and a volatile content of about 10%. The yield of charcoal at this temperature is about 33% of the weight of the oven dry wood.

4.) The wood is allowed to cool in an oxygen limited environment to prevent the oxidation (combustion) of the remaining carbon.

Traditionally this was done by piling dry wood into a dome shaped mound. The mound was then covered with smaller branches, leaves and finally dirt. Covering the mound limited its exposure to oxygen. A flue was left open in the middle of the mound to introduce hot coals and start the mound to smoldering. The shape of the mound is important because as the wood transforms to charcoal it shrinks in size. This shrinking inevitably causes holes in the outer covering of dirt which allows more oxygen into the mound. These holes have to be plugged quickly or the mound will catch fire and all the potential charcoal will go up in smoke. Planning for the shrinking of the mound helps to minimize the work in plugging holes as they appear. The key is to keep the entire mound smoldering but not burning. This requires constant attention. It might take two men three weeks to build the mound of 700kg (1500lbs) which will then burn for 12-18 days. The charcoal burner must spend the entire time by the mound tending to it as it smolders.

A more modern method (and one that requires less attention) is to seal up the wood in a fireproof container with a small hole in it so that it can vent the gasses that are produced and then place the container in a fire or kiln. This allows more attention to be paid to the fire that is providing the heat without having to worry that the wood being charred is being exposed to too much oxygen.

The process of driving off the hydrogen and oxygen by thermal decomposition is called pyrolysis. Pyrolysis is the same process that is used to turn coal into coke. It is also used to make carbon fiber.

• Portland cement

In the early 19th century, a bricklayer named Joseph Aspdin in Leeds, England first made Portland cement by burning powdered limestone and clay in his kitchen stove. The secret to Portland cement are the compounds belite (Ca2SiO4) and alite (Ca3O·SiO4). When they are mixed with water (hydrated) they form crystals that grow like tiny rock-hard fingers wrapping around the sand and gravel creating concrete. The compounds responsible for this are created by heating a mixture of ground limestone and clay (or shale) to temperatures between 1400-1450 °C.

A modern manufacturing process consists of three stages:

1.) Grinding a mixture of limestone and clay or shale to make a fine "rawmix. The limestone contributes calcium carbonate while the clay or shale provides the silicon and aluminum oxides needed to form belite and alite. Limestone with some impurities is preferred to limestone that is pure calcium carbonate.

2.) Heating the rawmix to a sintering temperature of (1400-1450 °C) This fuses the rawmix into lumps or nodules which is called “clinker”. The clinker once cooled is relatively stable and can be stored.

3.) Grinding the resulting clinker to make cement The grinding is usually done with gypsum to facilitate the grinding and to prevent flash setting (premature loss of workability or plasticity of cement paste) of the cement

Grinding the limestone to a fine enough powder before mixing it with clay would be difficult without modern grinding technology. Traditionally the method was:

1. Comminute the limestone by

   a) Burning the limestone into quick lime.

   b) After it has cooled, the quicklime would be combined with water to form slaked lime. This slaked lime would be combined with the clay or shale to form the raw mix and then steps 2 and 3 would be resumed.

In the second stage as the rawmix is heated, these chemical reactions take place as the temperature of the rawmix rises: 70 to 110 °C - Free water is evaporated. 400 to 600 °C - clay-like minerals are decomposed into their constituent oxides; principally SiO2 and Al2O3. Dolomite (CaMg(CO3)2) decomposes to calcium carbonate, MgO and CO2. 650 to 900 °C - calcium carbonate reacts with SiO2 to form belite (Ca2SiO4). 900 to 1050 °C - the remaining calcium carbonate decomposes to calcium oxide and CO2. 1300 to 1450 °C - partial (20-30%) melting takes place, and belite reacts with calcium oxide to form alite (Ca3O·SiO4).

Alite is the characteristic constituent of Portland cement. Typically, a peak temperature of 1400-1450 °C is required to complete the reaction. The partial melting causes the material to aggregate into lumps or nodules, typically of diameter 1-10 mm. This is called clinker.

The clinker once ground with gypsum is a hydraulic cement than can then be used to create concrete.

• Leblanc process

The Leblanc process was an early industrial process for the production of soda ash (sodium carbonate) that replaced kelp which was harvested, dried, and burned. The ashes were then "lixivated" (washed with water) to form an alkali solution. This solution was boiled dry to create the final product. The sodium carbonate concentration in soda ash varied very widely, from 2-3 percent for the seaweed-derived form ("kelp"), to 30 percent for the best barilla produced from saltwort plants in Spain. Plant and seaweed sources for soda ash, and also for the related alkali "potash", became increasingly inadequate by the end of the 18th century, and the search for commercially viable routes to synthesizing soda ash from salt and other chemicals intensified.

It involved two stages: production of sodium sulfate from sodium chloride, followed by reaction of the sodium sulfate with coal and calcium carbonate to produce sodium carbonate.

Due to the serious pollution issues that it causes, it was replaced by the Solvay process.

Step 1

The sodium chloride is initially mixed with concentrated sulfuric acid and the mixture exposed to low heat. The hydrogen chloride gas bubbles off and was discarded to atmosphere before gas absorption towers were introduced. This continues until all that is left is a fused mass. This mass still contains enough chloride to contaminate the later stages of the process. The mass is then exposed to direct flame, which evaporates nearly all of the remaining chloride.

Step 2

The coal used in the next step must be low in nitrogen to avoid the formation of cyanide. The calcium carbonate, in the form of limestone or chalk, should be low in magnesia and silica. The weight ratio of the charge is 2:2:1 of salt cake, calcium carbonate, and carbon respectively. It is fired in a reverberatory furnace at about 1000 °C.

The black-ash product of firing must be lixiviated right away to prevent oxidation of sulfides back to sulfate. In the lixiviation process, the black-ash is completely covered in water, again to prevent oxidation. To optimize the leaching of soluble material, the lixiviation is done in cascaded stages. That is, pure water is used on the black-ash that has already been through prior stages. The liquor from that stage is used to leach an earlier stage of the black-ash, and so on.

The final liquor is treated by blowing carbon dioxide through it. This precipitates dissolved calcium and other impurities. It also volatilizes the sulfide, which is carried off as H2S gas. Any residual sulfide can be subsequently precipitated by adding zinc hydroxide. The liquor is separated from the precipitate and evaporated using waste heat from the reverberatory furnace. The resulting ash is then redissolved into concentrated solution in hot water. Solids that fail to dissolve are separated. The solution is then cooled to recrystallize nearly pure sodium carbonate decahydrate.

• lead chamber process

lead chamber process was an industrial method used to produce sulfuric acid in large quantities. This allowed the effective industrialization of sulfuric acid production and, with several refinements, this process remained the standard method of production for almost two centuries. So robust was the process that as late as 1946, the chamber process still accounted for 25% of sulfuric acid manufactured. Sulfur dioxide is introduced with steam and nitrogen dioxide into large chambers lined with sheet lead where the gases are sprayed down with water and chamber acid (62-70% sulfuric acid). The sulfur dioxide and nitrogen dioxide dissolve, and over a period of approximately 30 minutes the sulfur dioxide is oxidized to sulfuric acid. The presence of nitrogen dioxide is necessary for the reaction to proceed at a reasonable rate. The process is highly exothermic, and a major consideration of the design of the chambers was to provide a way to dissipate the heat formed in the reactions.

Early plants used very large lead-lined wooden rectangular chambers (Faulding box chambers) that were cooled by ambient air. The internal lead sheathing served to contain the corrosive sulfuric acid and to render the wooden chambers waterproof. Around the turn of the nineteenth century, such plants required about half a cubic meter of volume to process the sulfur dioxide equivalent of a kilogram of burned sulfur. In the mid-19th century, French chemist Joseph Louis Gay-Lussac redesigned the chambers as stoneware packed masonry cylinders. In the 20th century, plants using Mills-Packard chambers supplanted the earlier designs. These chambers were tall tapered cylinders that were externally cooled by water flowing down the outside surface of the chamber.

Sulfur dioxide for the process was provided by burning elemental sulfur or by the roasting of sulfur-containing metal ores in a stream of air in a furnace. During the early period of manufacture, nitrogen oxides were produced by the decomposition of niter at high temperature in the presence of acid, but this process was gradually supplanted by the air oxidation of ammonia to nitric oxide in the presence of a catalyst. The recovery and reuse of oxides of nitrogen was an important economic consideration in the operation of a chamber process plant.

In the reaction chambers, nitric oxide reacts with oxygen to produce nitrogen dioxide. Liquid from the bottom of the chambers is diluted and pumped to the top of the chamber, and sprayed downward in a fine mist. Sulfur dioxide and nitrogen dioxide are absorbed in the liquid, and react to form sulfuric acid and nitric oxide. The liberated nitric oxide is sparingly soluble in water, and returns to the gas in the chamber where it reacts with oxygen in the air to reform nitrogen dioxide. Some percentage of the nitrogen oxides is sequestered in the reaction liquor as nitrosylsulfuric acid and as nitric acid, so fresh nitric oxide must be added as the process proceeds. Later versions of chamber plants included a high-temperature Glover tower to recover the nitrogen oxides from the chamber liquor, while concentrating the chamber acid to as much as 78% H2SO4. Exhaust gases from the chambers are scrubbed by passing them into a tower, through which some of the Glover acid flows over broken tile. Nitrogen oxides are absorbed to form nitrosylsulfuric acid, which is then returned to the Glover tower to reclaim the oxides of nitrogen.

Sulfuric acid produced in the reaction chambers is limited to about 35% concentration. At higher concentrations, nitrosylsulfuric acid precipitates upon the lead walls in the form of 'chamber crystals', and is no longer able to catalyze the oxidation reactions.

Until this process was made obsolete by the contact process, oleum had to be obtained through indirect methods. Historically, the biggest production of oleum came from the distillation of iron sulfates at Nordhausen, from which the historical name Nordhausen sulfuric acid is derived.