Cairo UniversityFaculty of Engineering

Chemical Eng Department

introduction to chemical engineering

Sugar Industry

November 2008

Outline1. Introduction 2. Photosynthesis 3. Sugar chemistry 4. The sugar industry, basis of operation 5. Raw material preparation 6. Sugar cane processing7. Sugar Beet Processing

1 .Introduction• Most sugars occur naturally in fruits and

vegetables• Sugar is produced in 121 Countries and global

production now exceeds 120 Million tons a year. Approximately 70% is produced from sugar cane, a very tall grass with big stems which is largely grown in the tropical countries. The remaining 30% is produced from sugar beet, a root crop resembling a large parsnip grown mostly in the temperate zones of the north.

2 .Photosynthesis• The process whereby plants make sugars is photosynthesis.

The plant takes in carbon dioxide from the air through pores in its leaves and absorbs water through its roots. These are combined to make sugar using energy from the sun and with the help of a substance called chlorophyll. Chlorophyll is green which allows it to absorb the sun's energy more readily and which, of course, gives the plants' leaves their green colour. The reaction of photosynthesis can be written as the following chemical equation when sucrose is being made:

12 CO2 + 11 H2 O =C12 H22 O11 + 12 O2

• This shows that oxygen is given off during the process of photosynthesis

THE SCALE OF PHOTOSYNTHESIS

Eugene, a biochemist, estimates that each year the green plants on the earth combine a total of 150 billion tons of carbon (from carbon dioxide) with 25 billion tons of hydrogen (from water) and liberate 400 billion tons of oxygen. The plants of the forests and fields on land account for only 10 %, the 90% come from the one-celled plants and seaweeds in oceans.

3 .Sugar chemistry 1

sugar, compound of carbon, hydrogen, and oxygen belonging to a class of substances called carbohydrates. Sugars fall into three groups: the monosaccharides, disaccharides, and trisaccharides. The monosaccharides are the simple sugars; they include fructose and glucose. The disaccharides are formed by the union of two monosaccharides with the loss of one molecule of water. Disaccharides include lactose, maltose, and sucrose

Cont’d. Sugar chemistry

Less well known are the trisaccharides; raffinose is a trisaccharide present in cottonseed and in sugar beets. Sugars belong to two families denoted by the letter d- or l- written before the name of a sugar. The families are related to glyceraldehyde CH2OHCHOHCHO, which can exist in two three-dimensional forms that are mirror images of each other. The isomer of glyceraldehyde that rotates plane polarized light clockwise is labeled d-glyceraldehyde; all natural sugars can be derived from this substance and thus belong the the d family. Although l-sugars can be prepared in the laboratory, they cannot be utilized by animals.

SMALL ATOMIC CHANGES MAKE LARGE DIFFERENCES • The change of location

of 2 hydrogen atoms in the molecule glucose (formula = C6H12O6), can convert it into fructose (ALSO = C6H12O6), a different molecule.

• Our taste-buds can distinguish between this change via the ligand /receptor system.

 

Chemical formula:

4 .The sugar industry, basis of operation

• Maximum sugar content in sugar cane 15% and sugar beet 17%

• Sugar is highly soluble in water• Water as “the universal solvent” is

highly available and inexpensive• The industry exploits above facts to

dissolve the sugar out of the vegetable matter

5 .Raw material preparation• the raw material (cane or beets) enters

the sugar mill straight from the fields• It is unloaded onto chutes belt

conveyor• Raw material is washed using high

pressure water jets• Wash water carrying soil, insecticides,..

is collected as wastewater stream

6 .Sugar cane processing6.1 Crushing: juice (sugar solution) is

squeezed and collected.Discuss:design of the systemhow to achieve maximum sugar extractionthe solid waste ( baggasse ) stream, what to do with it ?

Sugar cane processing

6.2. Clarification: removal of organic acids impurities by adding “milk of lime” (calcium hydroxide in water suspension). This is a neutralization process. Insoluble calcium compounds are precipitated. Boiling is required to enhance the reaction (and kills the bacteria that may be present)

6.3 Filtration: to separate the clear solution from the solid material.Question: what to do with the solid material

Sugar cane processing

6.4. Evaporation: to thicken the sugar solution to the point where it can be taken to a crystallization unit.

Very Important: Study all details

6.5. Crystallization:Very Important: Study all details

A note about the invention of multiple effect evaporators

• Norbert Rillieux is little known today, but his invention, the Multiple Effect Evaporator under Vacuum, revolutionized sugar processing.

• Rillieux, a free African American, patented his invention in the 1840s.

• The basic design is still in use in sugar processing and other industries.

• Rillieux utilized the latent heat produced from evaporating sugar cane juice by employing a series of three or four closed evaporating pans in which vapor was piped out of each pan to heat the juice in the next, with the vapors in the end going to a condenser. At the same time, pressure in the system was reduced by pumps, which created partial vacuums and lowered the boiling point of the liquid.

 

7 .Sugar Beet Processing

Counter current mass transfer operation:Discuss:• Design principle• How to increase the efficiency of

the process• Unit operation inputs and outputs

SIMPLIFIED FLOW DIAGRAM SUGAR CANE INDUSTRY