Alkali-Chlorine & Allied Chemicals Course : ACCE-2221 2nd Year : Even Semester Group-A : Chapter-2 30 January 2016 Course Outline 1. Alkali, Chlorine and Allied Chemicals 2. Sodium Chloride as raw material 3. Manufacture of soda ash, Caustic soda, Chlorine. 4. Manufacture of hypochlorite's and bleaching powder. 30 January 2016 Alkali In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. Some authorsalso define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. 30 January 2016 Allied Chemicals Caustic potash Caustic soda Chlorine compressed or liquefied Potassium carbonate Potassium hydroxide Sal soda (washing soda) Sodium bicarbonate Sodium carbonate (soda ash) 30 January 2016 Alkali Metal 30 January 2016 Alkali 30 January 2016 Alkali 30 January 2016 Common properties of Alkali Moderately concentrated solutions (over 10−3 M) have a pH of 7.1 or greater. This means that they will turn phenolphthalein from colorless to pink. Concentrated solutions are caustic (causing chemical burns). Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty substances on the surface of the skin. Alkalis are normally water soluble, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution. 30 January 2016 What is soda ash? Sodium carbonate (also known as washing soda, soda ash and soda crystals), Na2CO3, is a sodium salt of carbonic acid (soluble in water). It most commonly occurs as a crystalline hepta-hydrate, which readily effloresces to form a white powder, the monohydrate. Pure sodium carbonate is a white, odorless powder that is hygroscopic (absorbs moisture from the air), has an alkaline taste, and forms a strongly alkaline water solution. Soda ash is the active ingredient in washing soda. The chemical name for it is sodium carbonate, chemical formula Na2CO3. It is more basic, that is, less acidic, than sodium bicarbonate (baking soda), whose chemical formula is NaHCO3. The purpose of sodium carbonate is simply to increase pH. 30 January 2016 Soda Ash The name "soda ash" is based on the principal historical method of obtaining alkali, which was by using water to extract it from the ashes of certain plants. Wood fires yielded potash and its predominant ingredient potassium carbonate, whereas the ashes from these special plants yielded "soda ash" and its predominant ingredient sodium carbonate. The word "soda" (from the Middle Latin) originally referred to certain plants that grow in salt marshes; it was discovered that the ashes of these plants yielded the useful alkali soda ash. In 1884, the Solvay brothers licensed Americans William B. Cogswell and Rowland Hazard to produce soda ash in the US, and formed a joint venture (Solvay Process Company) to build and operate a plant in Solvay, New York. 30 January 2016 Soda Ash Sodium Carbonate 30 January 2016 Production Process of Na2CO3 1. Le-blanc process 2. Solvay process 3. Hou's process 30 January 2016 Le-blanc Process In 1791, the French chemist Nicolas Leblanc patented a process for producing sodium carbonate from salt, sulfuric acid, limestone, and coal. First, sea salt (sodium chloride) was boiled in sulfuric acid to yield sodium sulfate and hydrogen chloride gas, according to the chemical equation 2 NaCl + H2SO4 → Na2SO4 + 2 HCl Next, the sodium sulfate was blended with crushed limestone (calcium carbonate) and coal, and the mixture was burnt, producing calcium sulfide. Na2SO4 + CaCO3 + 2 C → Na2CO3 + 2 CO2 + CaS The sodium carbonate was extracted from the ashes with water, and then collected by allowing the water to evaporate. NOTE: The hydrochloric acid produced by the Leblanc process was a major source of air pollution, and the calcium sulfide byproduct also presented waste disposal issues. However, it remained the major production method for sodium carbonate until the late 1880s. 30 January 2016 Soda Ash-Solvay Process Solvay process In 1861, the Belgian industrial chemist Ernest Solvay developed a method to convert sodium chloride to sodium carbonate using ammonia. The Solvay process centered around a large hollow tower. At the bottom, calcium carbonate (limestone) was heated to release carbon dioxide: CaCO3 → CaO + CO2 At the top, a concentrated solution of sodium chloride and ammonia entered the tower. As the carbon dioxide bubbled up through it, sodium bicarbonate precipitated: NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl The sodium bicarbonate was then converted to sodium carbonate by heating it, releasing water and carbon dioxide: 2 NaHCO3 → Na2CO3 + H2O + CO2 30 January 2016 Soda Ash-Solvay Process Meanwhile, the ammonia was regenerated from the ammonium chloride byproduct by treating it with the lime (calcium hydroxide) left over from carbon dioxide generation: CaO + H2O → Ca(OH)2 Ca(OH)2 + 2 NH4Cl → CaCl2 + 2 NH3 + 2 H2O Because the Solvay process recycles its ammonia, it consumes only brine and limestone, and has calcium chloride as its only waste product. This made it substantially more economical than the Leblanc process, and it soon came to dominate world sodium carbonate production. By 1900, 90% of sodium carbonate was produced by the Solvay process, and the last Leblanc process plant closed in the early 1920s. 30 January 2016 Soda Ash-Solvay Process Fig: Flow diagram for Soda Ash Production 30 January 2016 Soda Ash-Solvay Process Fig: Soda ash production process 30 January 2016 Soda Ash- Hou's Process Hou's process Developed by Chinese chemist Hou Debang in the 1930s. The earlier steam reforming byproduct carbon dioxide was pumped through a saturated solution of sodium chloride and ammonia to produce sodium bicarbonate via the following reactions: NH3 + CO2 + H2O → NH4HCO3 NH4HCO3 + NaCl → NH4Cl + NaHCO3 The sodium bicarbonate was collected as a precipitate due to its low solubility and then heated to yield pure sodium carbonate similar to last step of the Solvay process. 2 NaHCO3 → Na2CO3 + H2O + CO2 30 January 2016 Soda Ash 30 January 2016 Properties of Soda Ash PHYSICAL STATE White powder or granules Chemical Name Sodium Carbonate Molecular Weight 105.989 gm./mole 851oC Melting Point 1564oF Specific Gravity 20o/4oC 2.533 gm./cc o 0 C 7 gms Na2CO3 in 100 gms H2O o Solubility 100 C 44.7 gms Na2CO3 in 100 gms H2O o 35.37 C (max.) 49.5 gms Na2CO3 in 100 gms H2O 30 January 2016 Uses of Soda Ash Soda ash is an essential raw material used in many applications such as the manufacture of glass, detergents and soaps, chemicals and many other industrial processes. 30 January 2016 Caustic Soda Sodium hydroxide, also known as caustic soda, or lye, is an inorganic compound with the chemical formula NaOH. It is a white solid and highly caustic metallic base and alkali salt which is available in pellets, flakes, granules, and as prepared solutions at a number of different concentrations. Sodium hydroxide forms an approximately 50% (by weight) saturated solution with water. Sodium hydroxide is soluble in water, ethanol and methanol. This alkali is deliquescent and readily absorbs moisture and carbon dioxide in air. 30 January 2016 Caustic Soda Production Process Historically, sodium hydroxide was produced by treating sodium carbonate with calcium hydroxide in a metathesis reaction. (Sodium hydroxide is soluble while calcium carbonate is not.) This process was called causticizing. Ca(OH)2(aq) + Na2CO3(s) → CaCO3↓ + 2 NaOH(aq) This process was out of date by the Solvay process in the late 19th century, which was in turn supplanted by the chloralkali process which we use today. 30 January 2016 Caustic Soda Production Process Sodium hydroxide is industrially produced as a 50% 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. Solid sodium hydroxide is most commonly sold as flakes, prills, and cast blocks Sodium hydroxide is also produced by combining pure sodium metal with water. The byproducts are hydrogen gas and heat, often resulting in a flame, making this a common demonstration of the reactivity of alkali metals in academic environments; however, it is not commercially viable, as the isolation of sodium metal is typically performed by reduction or electrolysis of sodium compounds including sodium hydroxide. 30 January 2016 Caustic Soda Production Process + − Cathode: 2 H (aq) + 2 e → H2(g) − − Anode: 2 Cl (aq) → Cl2(g) + 2 e Fig: Chlor-Alkali Process for Producing NaOH 30 January 2016 Caustic Soda Production Process + − Cathode: 2 H (aq) + 2 e → H2(g) − − Anode: 2 Cl (aq) → Cl2(g) + 2 e Fig: Chlor-Alkali Process for Producing NaOH 30 January 2016 Sodium Hydroxide Production Process 30 January 2016 Caustic Soda 30 January 2016 Properties of Sodium Hydroxide •The chemical formula for Sodium Hydroxide is NaOH •Molar mass of 39.9971 g/mol •Melting Point: 318'C, 604'F •Boiling Point: 1388'C, 2530'F •Density in Natural State: 2.13 g/cm^3 •Very soluble in water, alcohol, glycerin and methynol •Has an Acidity of 13 •Reacts with Carbon Dioxide to form Sodium Carbonate •Also reacts with other Acids to form pure water and salts •Type of Bond: Ionic •Percentage composition by mass: Sodium: 57.48% Oxygen: 40.00% Hydrogen: 2.52% 30 January 2016 Uses of Sodium Hydroxide 30 January 2016 Chlorine Chlorine is a chemical element with symbol Cl and atomic number 17. Chlorine is in the halogen group (17) and is the second lightest halogen following fluorine. The element is a yellow-green gas under standard conditions, where it forms diatomic molecules. Chlorine has the highest electron affinity and the fourth highest electronegativity of all the reactive elements. For this reason, chlorine is a strong oxidizing agent.