Citric acid production and importance

1. CITRIC ACID

2. INTRODUCTION
• Citric acid
• Citric acid is a week organic acid found in citrus fruits
• Molecular formula is C6H8O7 and belongs to the carboxylic acids groups
• Stronger acid compared to other typical carboxylic acid. Produced by
fermentation and suitable pH is around 3-6
• Application In Industry
• Beverages
• Food
• Pharmaceutical
• Agriculture
• Metal Industry
Structural Formula of Citric Acid

3. • Citric acid was first commercially-produced in England around 1826
• synthesized from the glycerol
• Wehmer (1893)
• Lemon juice remained the commercial source of citric acid until 1919
• Aspergillus niger started in Belgium
• Molliard (1922)

4. - Microorganism: Aspergillus niger (mainly), Candida yeast
- Citric acid production is mixed growth associated, mainly
take place under nitrogen and phosphate limitation after
growth has ceased.
- Medium requirements for high production
- Carbon source: molasses or sugar solution.
- Na-ferrocyanide is added to reduce Iron (1.3 ppm) and
manganese (<0.1ppm).
- High dissolved oxygen concentration
- High sugar concentration
- pH<2
- 30 oC.
Industrial Production of Citric Acid

5. SOURCE OF RAW MATERIALS
Beet Molasses
• the source of sugar for microbial
production of citric acid
• low cost and high sugar content
• low content of trace metals
• acts as carbon source of the
fermentation
Aspergillus niger
• filamentous fungus
• maintained at pH 4.5 and temperature
at 5 °C
• The best strain for citric acid production
• Scientific classification of A. niger
Domain Eucaryotes
Kingdom Fungi
Phylum Ascomycota
Subphylum Pezizomycotina
Class Eurotiomycetes
Order Eurotiales
Family Trichocomaceae
Genus Aspergillus
Species A.Niger

6. Bioreactor: batch or fed-batch (100m3)
- 5-25X106 A. niger spores/L may be introduced to the fermenter.
- (Aeration is provided to the fermenter by air sparging (0.1-0.4 vvm) v: volume
of air (e.g. liter) ; the second 'v' stands for per unit of medium (e.g. liter); 'm'
stands for per unit of time (e.g. minute)
- Temperature is controlled by cooling coil.
- Agitation: 50-100rpm to avoid shear damage on molds.
- Fed-batch is used to reduce substrate inhibition and prolong the production
phase one or two days after growth cessation.
- Volumetric yield: 130 kg/m3
Industrial Production of Citric Acid

7. Purification of Citric Acid
A typical method used for purification of citric acid from a fermentation
broth involves two major purification techniques:
Precipitation and Filtration. The following schematic displays a generic
citric acid purification scheme.
•ffff
Prec
React citric
acid with
calcium
carbonate
Filter
precipitate
React
precipitate
with sulfuric
acid
Filter
precipitate
Purified Citric
Acid

8. Purification of Citric Acid
The citric acid broth from the production fermenter is highly contaminated by
leftover biomass, salts, sucrose, and water.
First,
the citric acid must be reacted with calcium carbonate to neutralize the
broth and form the insoluble precipitate calcium citrate.
Calcium citrate contains about 74% citric acid. The stoichiometric equation is
as follows:
CaCO3 + Citric Acid → CO2+ Calcium Citrate
Contaminated Citric Acid
CSTR
Calcium Citrate as
a precipitate plus
contaminants
Calcium Carbonate, CaCO3

9. Purification of Citric Acid
The calcium citrate is then washed, heated, and filtered to remove any number of
the contaminants.
Depending on the specific design of the purification scheme, filters can be placed
before the first reaction with calcium carbonate, in series between the two
precipitation reactions or in any other combination that works.
Also, it is important to choose the best kind of filter for what is being removed.
For simplicity, the filters here will remove larger contaminants first (sucrose and
salts) and the smaller contaminants later.
Calcium Citrate as
a precipitate plus
contaminants
Filter
Ex. Plate filter, Rotary
presses, rack-and-
frame presses
Calcium Citrate,
biomass, water

10. Purification of Citric Acid
Further Purification
Citric acid can be produced in two forms
– monohydrate and anhydrous.
These forms may require additional purification steps to reach the desired purity.
1. Monohydrate
• contains one water molecule for every citric acid molecule
• Requires repeated crystallization until water content is approx. 7.5-8.8%
2. Anhydrous
• Processed to remove all water from end product
• Prepared by dehydrating the monohydrate citric acid product at a
temperature above 36.6ºC