Sugar was first manufactured from sugar cane in India, and its manufacture has spread from there throughout the world. Chemically, sugar is the substance sucrose, which can be hydrolysed in acidic solution (i.e. below pH 7) to form the monosaccharides glucose and fructose as follows.
sucrose + H2O → glucose + fructose
The raw sugar is mixed with a saturated syrup and then centrifuged to extract the crystals.
Surface impurities (molasses) dissolve in this syrup and are removed.
The sugar is redissoved and calcium hydroxide and carbon dioxide are added to the solution. These react according to the following equation
Ca(OH)2 + CO2 → CaCO3 + H2O
Colour, gum and amino acid impurities precipitate out with the calcium carbonate.
Activated charcoal is added to the syrup, removing colour and inorganic ash.
The solution is boiled under vacuum and the crystal growth monitored to produce particular sizes of crystal
The sugar is made into a variety of different products (raw sugar, golden syrup, treacle, soft brown sugar, coffee crystals, 1A sugar, castor sugar, liquid sugar) with varying amounts of glucose, fructose and inorganic impurities.
Pollution is minimised by ensuring complete fuel combustion, monitoring liquid and gaseous effluents. The solid mud from carbonatation is buried on site.
Granulated sugar containing 99.93% sucrose and sold as castor sugar (fine crystals) and 1A sugar is the major refined product. Soft brown sugar is a specialty product with a characteristic flavour, produced by crystals used from a selected syrup with a high reducing sugar and ash content. Coffee crystals are made from the same syrup as brown sugar, but are crystallised over a much longer period of time giving much larger crystals.
Several grades are produced in liquid form with quality to meet customer requirements. This sugar is produced at 67o Brix (% solids) at which density it is unlikely to crystallise. Liquidsugar is utilised in industry.
Golden syrup and treacle are produced from selected syrups by inverting1 a portion of the syrup using invertase (an enzyme) or acid hydrolysis to split sucrose into glucose and fructose. Golden syrup contains about 27% sucrose and 47% reducing sugar with 3% ash and 18% water. The high reducing sugar component inhibits crystallisation and allows a table syrup to remain in liquid form. Treacle is produced in the same manner from a similar syrup except that char decolourisation is not used
ROLE OF THE LABORATORY
Most processes are continuous and semi-automatically controlled with direction from a process control laboratory. Important criteria for control are density, pH and impurity content (reducing sugars and inorganic ash), temperature and production rate.
Pollution control is given a high priority in the refining process. Atmospheric emission from the boiler station is strictly controlled using air/fuel ration mixing equipment to ensure complete combustion with continuous monitoring of smoke emission density. It is anticipated that natural gas fuel will eventually replace the fuel oil presently used, thus eliminating sulfur oxide emission.
Carbonation mud is used as dry land fill on the refinery grounds. The material has little recycling potential. Liquid effluent is closely monitored by laboratory staff.