Chemistry in Technology

1. Chemistry in Technology The LeBlanc and Solvay Processes

2. Learning Goals • Understand how stoichiometry and percentage yield are applied in Industry • Understand the multi-step industrial processes used to make chemicals • Understand the environmental and energy issues related to chemical production

3. Success Criteria • Understand the Leblanc and Solvay processes involved in making sodium carbonate • Understand that most industrial chemical processes require several steps • Understand the terms – raw materials, intermediate products, byproducts, products and net reaction • Understand the historical importance of this process.

4. The Science of Glass-making • Glass is formed by heating a mixture of: Sand + sodium carbonate + calcium oxide Sand (Silica) = SiO2 (the largest component of glass) Sodium Carbonate (Soda Ash) = Na2CO3 (catalyst – lowers the temperature at which sand melts (1425 - 1600℃) Calcium Oxide (Lime) = CaO (strengthens the glass and makes it more water-resistant)

5. Glass production • Sodium carbonate is added to silica (silicon dioxide - quartz) to make sodium silicate which is then reacted with more silica and lime (CaO) to make an amorphous (no crystal structure) solid of silica, sodium and calcium. The glass is actually a super-cooled solid

6. Modern Glass Production • The molten glass is poured on molten tin (which has a low melting point) in order to form perfect flat surfaces • YouTube Video: http://www.youtube.com/watch?v=-z1P2cK9Rro and http://www.youtube.com/watch?v=64JCYGIrFEE

7. Glass • Actually a “super-cooled” liquid • A solid that retains its liquid structure • Can almost be considered an extremely viscous liquid that flows incredibly slowly • Glass is Amorphous – no crystal structure – glass is cooled so quickly that there is no time for a crystal structure to form • Glass is formed in nature when molten magma is cooled rapidly when erupted from a volcano - Obsidian

8. Making Glass before 1700 • Sand (even very pure sands needed to make colourless glass) were easy to find. • Lime was relatively easy to produce (by heating limestone) (CaCO3 ⇒ CaO + CO2) • BUT sodium carbonate is a rare mineral and there was no way to produce it synthetically • GLASS was expensive to make and was only available to the rich!

9. The LeBlanc Process • Used during the 1700 and 1800’s to make sodium carbonate. An example of early Chemical Engineering • From the 1700s, sodium and potassium carbonate were in great demand to produce glass, soap and textiles. • Frenchman, Nicholas Le Blanc, invented a method for converting sea salt into sodium carbonate which was in widespread use by 1810. • However, the process produced hazardous by-products including hydrochloric acid, nitrogen oxides, sulphur and chlorine gas. (See the fumes around this early 1800’s sodium carbonate factory in England)

10. The LeBlanc Process • NaCl(s) + H2SO4(l) ====⇒ NaHSO4(s) + HCl(g) • NaHSO4(l)+ NaCl(s) ====⇒ Na2SO4(s) + HCl(g) • Na2SO4(s)+CaCO3(s)+2C(s) ==⇒ Na2CO3(aq)+CaS(s)+2CO2(g) Things to notice: • Waste products • The amount of heat energy required • The number of solids involved in the reactions (very inefficient) and unusable by-products like CaS Heat (from coal) Heat (from coal) Heat (from coal)

11. PROBLEMS!!! • Harmful to the environment (release of HCl(g) into the air) • High energy use (burning of coal for heat which also uses a lot of energy) • Inefficient – low percentage yield • By-products are useless and were often dumped (into waterways) causing pollution • THIS IS A DIRTY, INEFFICIENT PROCESS!

12. Sodium Carbonate and Health • Alkali compounds are needed to make soap. Thus a cheap source of sodium carbonate made the industrial production of soap inexpensive in the 1800’s. • Cheap soap led to great improvements in hygiene and subsequent lowering of the spread of infectious diseases. • Sodium Carbonate is still a key component in soap making (YouTube – 49 seconds - http://www.youtube.com/watch?v=7I-ugF8Sf7U ) • Or http://www.youtube.com/watch?v=54n0tLU7TEg(how to make soap in the lab)

13. The Solvay Process • Enest Solvay (1838 – 1922) began the study of a cheaper way to produce sodium carbonate. • The cost of this process was 1/3 of the cost of the LeBlanc process. • It took time for companies to switch production methods (which) is expensive, but they were eventually convinced not only by the cost savings, but also by the CLEANER, more efficient process.

14. The Solvay Process Copy these 6 steps into your notebook: • CaCO3(s) ==⇒ CaO(s) + CO2(g) • CO2(g) + NH3(aq)==⇒ NH4HCO3(aq) • NH4HCO3(aq) + NaCl(aq) ==⇒ NH4Cl(aq) + NaHCO3(s) • NaHCO3(s) ==⇒ Na2CO3(aq)+H2O(l) +CO2(g) • CaO(s)+ H2O(l)==⇒ Ca(OH)2(s) • Ca(OH)2(s) + NH4Cl(aq)==⇒ NH3(aq) + CaCl2(aq) +H2O(l) Note that the Solvay process has 6 steps (vs. 3 for the LeBlanc Process). Heat (small amount) Heat (small amount)

15. The Solvay Process Intermediate products: products created at one step that are used up in another. The remaining compounds are the Net Reaction: Write the net reaction for the Solvay Process. The reactants of the net reaction are known as the Raw Materials (they must be purchased) The target product is the primary product (in this case – sodium carbonate) Other products are known as by-products (sometimes they can be sold, sometimes they are waste)

16. The Solvay Process Intermediate products: Circle these in green and place a slash through them Write the Net Reactionfor the Solvay Process underneath the 6-step reaction. Raw Materials: Circle these in black Primary product: Circle this in red By-products: Circle this in blue

17. The Solvay Process Get out your green, black, red and blue pens! • CaCO3(s) ==⇒ CaO(s) + CO2(g) • CO2(g) + NH3(aq)==⇒ NH4HCO3(aq) • NH4HCO3(aq) + NaCl(aq) ==⇒ NH4Cl(aq) + NaHCO3(s) • NaHCO3(s) ==⇒ Na2CO3(aq)+H2O(l) +CO2(g) • CaO(s)+ H2O(l)==⇒ Ca(OH)2(s) • Ca(OH)2(s) + NH4Cl(aq)==⇒ NH3(aq) + CaCl2(aq) +H2O(l) ------------------------------------------------- What is the net reaction? Heat (small amount) Heat (small amount)

18. What are the advantages of the Solvay process over the LeBlanc process? THINK ABOUT: • Environment Concerns (do any products become waste pollutants? How much energy is needed?) • Cost • Efficiency (Aqueous reactions require less energy (heat) and have higher percentage yields) • By-products? (Can they be sold?) (CaCl2 can be used as road salt or as a dessicant (drying agent)