Chemistry of Saccharides

Chemistry of SaccharidesRecovery of Sugar from Principal Sources: Sugar CaneLorenz Esperon-Borromeo | 2015BS Chemical Engineering

Introduction:Carbohydrates, sugars and starches are the most widely distributed and abundant organic chemicals on earth.Carbohydrates-polyhydroxy aldehydes or polyhydroxy ketones or substances that yield such compounds on acid hydrolysis.

They; have a central role in the metabolism of plant and animals serve as a basic food act as sweetening agents, gel/paste-forming agents, thickening agents and stabilizers act as precursors for aroma and coloring substances generated within the food by a series of reactions and during handling and processing

SaccharidesBasis of a system of classification for carbohydratesSaccharumLatin word for sugarThe Chemistry of Saccharides

All carbohydrates consist of the following molecules;1. Monosaccharide (simplest sugar)Contains one saccharide moleculeIncludes fructose and glucose (structural isomers)Chemical Formula: C6H12O6

2. DisaccharideUnion of 2 monosaccharides with the loss of 1 molecule waterIncludes Lactose, Cellobiose, Maltose and SucroseSucrose has the formula: C12H22011

2. PolysaccharideCompounds in which the molecules contain many units of monosaccharides joined together by glycoside links.Includes starch and cellulose

StarchMost valuable polysaccharideTree-like, containing 250 to 1000 or more glucose units per molecule joined together through alpha linkages

CelluloseMost abundant polysaccharideFibrous component of a plant cell wallChains of molecules up to 14,000 units of D-glucose

Properties of SugarProduct of photosynthesisOccurs in greatest quantities in sugar cane and sugar beetsCrystallizes from aqueous solution as monoclinic, hemimorphic crystalsMelting point is 188 oC, BUT is indefiniteDensity if 1.5879 g/cm3

Properties of SugarLinear expansion coefficient ranges from 0.028 to 0.050% depending on axisDipole moment is 2.8x10^-29 (8.31D)Sparingly soluble in alcohol but moderately soluble in organic solvents such as dimethyl formamide and pyridine.Specific heat of crystalline sucrose is 415.98J/mol at 20oCPolarization- sucrose in solution rotates a polarized light to the right in equal proportion to the quantity of sucrose present

Raw Sugar Manufacturing: Cane SugarTypical flow diagram for the manufacture of raw sugar from Sugar CaneWashed CaneCutter/ShredderMill/ DiffuserWaterClarifier/ FilterCakeLimeDiffusion JuicerMixer/ JuiceMulti-stage EvaporatorVacuum Pan CrystallizerMolassesRaw Sugar

WashingMechanically harvested cane picks up field, mud, sand, trash and fine dirt during transportation into the factory.To avoid these, cane first goes to a washer. Washing systems vary from a simple system of spraying warm water on a table to a very elaborate system consisting of conveyors with water jets, stripping rolls and baths.

Cutting/ ShreddingThe cane is chopped into short segments (8 to 12 in. long) and the segments are passed through 2 sets of knives.1st Set: Cut the canes into small pieces and acts as a leveler to distribute the cane more evenly on the carrier.2nd Set: Acts as a shredder and thoroughly cuts up and shreds the cane into a fluffy mate of pieces of few cm in length.3rd Set (Special Case of a diffusion): Canes are put through an even finer shredder called a buster. No juice is extracted in the shredder.

MillingThe cut pieces from the shredder then pass through a series of mills, called a tandem or milling trainPrime ObjectivesTo extract the greatest possible amount of sucrose from the sugar cane in juice form.To make the final bagasse (fibrous residue from the cane) as dry as possible so that it will burn readily in the boilers.From 3 to 7 sets of such 3-roller units, described as a 9-roller to 21-roller mill are in use.

A classical combination of 3 rollers arranged in triangular form is the standard milling unit of the sugar industryThe top roller rotates counterclockwise and the bottom 2 rollers clockwise.

After passing through the first mill, the bagasse is carried to the second mill by bagasse carriers by a turn plateCompound Imbibition is used to reduce the sucrose in the fiber by repeated dilution and milling.The juice is collected from the 1st mill and mixed with the juice from the crusher. The mixed juice is then passed through perforated metal screens (1mm diameter) for clarification.