© British Sugar 2010 Chemical reactions Learning objectives: Identify the chemical reactions used in sugar production, both in industry and in the laboratory Identify the physical and chemical changes during the process of extracting sugar from sugar beet Recognise some changes made in industry to increase the yield

© British Sugar 2010 Main differences between a factory and a the laboratory In industry there is: Extra cleaning and separating of raw materials A different shape of the cossettes A more complex filtration process A vacuum used to remove water The use of seed crystals to enhance crystallisation The automated transfer of materials, as opposed to by hand A centrifuge is used to remove crystals

© British Sugar 2010 Experiments to extract sugar Experiment one Diffusion Experiment two Carbonation Experiment three Evaporation and crystallisation

© British Sugar 2010 Experiment one - Diffusion The aim of experiment one is to extract the sugar from the sugar beet to form a sugar solution When the sugar beet is put into warm water the sugar (sucrose) diffuses out of the sugar beet into the water This juice can be called a solution. The sugar has been the solute and the water is the solvent

© British Sugar 2010 Experiment one - Diffusion When the sugar beet is sliced, the cell membrane is denatured allowing the sugar solution to leach out of the cell The sugar beet cell wall is made of cellulose, hemicellulose and pectin The aim of diffusion is to maintain the cell wall, not to denature it. The sugar is already in solution in the vacuole of each parenchymal cell

© British Sugar 2010 Experiment one - Diffusion The cell membrane is semi-permeable allowing free transit of water, but not solutes (including sugar) within the vacuole. In diffusion, the vacuole cell membrane is denatured allowing the sugar solution to leach out. The cell wall, however, is highly permeable and large molecules can pass through unhindered. The cell wall needs to remain intact so the pulp can be pressed. Similar intermolecular forces of attraction allow the water and sucrose molecules to attract, releasing energy and causing the sucrose to remain dissolved. Increased surface area increases the contact between the cells and the water allowing a faster diffusion rate of the sucrose.

© British Sugar 2010 Experiment two - Carbonation The second experiment aims to remove impurities from the sugar juice by adding slaked lime and carbon dioxide Chemical reaction one When the lime is slaked by adding water, the temperature of the mixture rises significantly. This can be described as an exothermic reaction. calcium oxide + water → calcium hydroxide CaO + H 2 O → Ca(OH) 2

© British Sugar 2010 Experiment two - Carbonation Chemical reaction two carbon dioxide + calcium oxide → calcium carbonate CO 2 + CaO → CaCO 3 This can be a reversible reaction. When the rate of the forward reaction is equal to the rate of the backward reaction, it is said to be at equilibrium. calcium oxide + carbon dioxide → calcium carbonate calcium carbonate → calcium oxide + carbon dioxide The first reaction combining calcium oxide and carbon dioxide can occur at room temperature. In the factory very high temperatures and a reducing atmosphere are created in a Lime kiln to drive the reaction to produce calcium oxide and carbon dioxide.

© British Sugar 2010 Experiment two - Carbonation Catalysts increase the rate of reversible reactions. However, in Experiment two, flocculant is added to increase the size of the solid particles. Due to the increased size of solid particles, gravity increases the speed of the reaction. Two different ways to increase the yield of calcium carbonate include: removing the product as it is made increasing the concentration of reactants These are the only chemical reactions in the sugar production process. The remaining processes are physical changes only.

© British Sugar 2010 Experiment three – Evaporation and crystallisation Water OUT Reflux (liebig) condenser Water IN Stillhead To vacuum pump Round bottomed flask Sugar solution GAUZE HEAT

© British Sugar 2010 Experiment three – Evaporation and crystallisation Experiment three aims to remove the excess solvent or water from the juice leaving a concentrated solution of sugar The use of a vacuum when heating the sucrose solution prevents caramelisation, whilst the excess solvent (water) is removed A super saturated concentration must be created before sugar crystals will form

© British Sugar 2010 Experiment three – Raoult’s Law in action? Raoult’s Law describes the method of mixing two solutions when they have different types of intermolecular boiling points. The boiling point of the two mixtures changes. If the bonding is disrupted, the boiling point will lower. Alternatively, if there is additional bonding, the boiling point will rise. Raoult’s Law does not apply in this experiment as sugar (C 12 H 22 O 11 ) and water (H 2 O) have similar types of bonding, as hydrogen is the main source of intermolecular attractions.

© British Sugar 2010 Changes made within industry In contrast with laboratory experiments, steps taken within the industry to improve yield include: A cleaning stage that enhances the removal of sugar and limits the amount of impurities that have to be removed in the purification stage Slicing the sugar beet into V-shaped cossettes, increasing the surface area and the rate of diffusion whilst maintaining an appropriate mechanical strength

© British Sugar 2010 Changes made within industry Close control of microbiological action which can be the greatest cause of sugar loss Acidity is maintained at pH 5.5 to prevent sugar being broken down into glucose and fructose (which occurs if pH falls below 4) Undertaking the process in a vacuum. This reduces the boiling point of the sugar solution, so decreases the temperature. This reduces the risk of caramelisation, a competing reaction Introducing seed crystals to help start the crystallisation and reduce the problem of uncontrolled crystallisation, which results in very small crystal sizes

© British Sugar 2010 Changes made within industry The automation of various processes throughout the factory allows much higher volumes of materials and beet to be transferred around the factory. The size of the factory is so large that it would be impossible any other way The sugar juice is very viscous when at 65% concentration which would make filtering very difficult. Centrifuging spins the mixture with the crystals remaining in the basket whilst the syrup flows through the screen and is pumped to the next stage