1. CITRIC ACID

2. Citric acid Citric acid is a weak organic acid
found in citrus fruits(lemon).
It is a good, natural preservative
and is also used to add an acidic
(sour) taste to foods and soft drinks.
More than million tonnes are
produced every year by fermentation.

3. Properties At room temperature, citric acid is a white
crystalline powder.
It can exist either in an anhydrous (water-
free) form or as a monohydrate.
The anhydrous form crystallizes from hot
water, whereas the monohydrate forms
when citric acid is crystallized from cold
water. The monohydrate can be converted
to the anhydrous form by heating above
78 °C.
Citric acid also dissolves in absolute
(anhydrous) ethanol at 15 °C.
When heated above 175 °C, it decomposes
through the loss of carbon dioxide and 
water.

4. Occurrence
Citric acid exists in greater than trace amounts in a variety of fruits and
vegetables, most notably citrus fruits.
Lemons and limes have particularly high concentrations of the acid; it can
constitute as much as 8% of the dry weight of these fruits (about 47 g/L in
the juices).
The concentrations of citric acid in citrus fruits range from0.005 mol/L for
oranges and grapefruits to 0.30 mol/L in lemons and limes.

5. Discovery
The discovery of citric acid has been credited to the 8th century
Muslim alchemist Jabir Ibn Hayyan (Geber).
Citric acid was first isolated in 1784 by the Swedish chemist 
Carl Wilhelm Scheele, who crystallized it from lemon juice. 
Industrial-scale citric acid production began in 1890 based on the
Italian citrus fruit industry.
In 1893, C. Wehmer discovered Penicillium mold could produce
citric acid from sugar. However, microbial production of citric
acid did not become industrially important until World War I 
disrupted Italian citrus exports.

6. In 1917, the American food chemist James Currie discovered
certain strains of the mold Aspergillus niger could be efficient
citric acid producers, and the pharmaceutical company 
Pfizer began industrial-level production using this technique
two years later, followed by Citrique Belge in 1929.

7. Citric Acid Production by Aerobic Bioprocesses
Wikipedia

8. Industrial Production of Citric acid
Microorganism: Aspergillus niger (mainly), Candida yeast (from carbohydrates or n-alkanes)
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
- Temperature: 30oC

9. Industrial Production of Citric acid
Bioreactor: batch or fed-batch (100m3)
×106 A. niger spores/L may be introduced to the fermentor.
- Aeration is provided to the fermenter by air sparging (
vvm)
- Temperature is controlled by cooling coil.
- Agitation: rpm 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
Limitation of nitrogen and phosphate provoke an overflow in metabolism that results in an overproduction of citric acid.

10. Industrial Production of Citric Acid
Separation:
- The biomass is separated by filtration
- The liquid is transferred to recovery process:
- Separation of citric acid from the liquid: precipitation
calcium hydroxide is added to obtain calcium citrate
tetrahydrate → wash the precipitate→ dissolve it with
dilute sulfuric acid, yield citric acid and calcium
sulfate precipitate → bleach and crystallization →
anhydrous or monohydrate citric acid.

11. Industrial Production of Citric Acid
Microorganism: S. cerevisae for hexose
Candida sp. for lactose or pentose
Genetically modified E. coli
Ethanol production is growth-associated with S. cerevisae.
Medium requirements for high production
- Carbon source: sugar cane, starch materials (e.g. corn, wheat), cellulosic materials (?!). yield: 0.51 g ethanol/g glucose.
- N, P, minerals.
- Anaerobic
- 100g/L glucose are inhibitory for yeast.
- 5% (v/v) of ethanol are inhibitory for yeast.
- pH:4-6 for oC.

12. Industrial Production of Citric Acid
Bioreactor: batch, continuous or with cell recycle
95% conversion of sugars with a residence time of
40 h in batch reactor
21 h in continuous reactor without cell recycle
1.6 h in continuous reactor with cell cycle
By-products: glycerol, acetic acid, succinic acid.
Separation:
- Distillation to obtaining 95% (w/w) of ethanol-water mixture, followed by
- Molecular sieves to removing water from the mixture to get anhydrous ethanol.

13. 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:
React citric acid with calcium carbonate
Prec
Filter precipitate
ffff
React precipitate with sulfuric acid
Purified Citric Acid
Filter precipitate

14. 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
Kirk 15
Calcium Carbonate, CaCO3
CSTR
Calcium Citrate as a precipitate plus contaminants
Contaminated Citric Acid

15. 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.
Filter
Ex. Plate filter, Rotary presses, rack-and-frame presses
Calcium Citrate as a precipitate plus contaminants
Calcium Citrate, biomass, water

16. Purification of Citric acid
To crack the calcium citrate precipitate, sulfuric acid is needed.
The temperature of this reaction should stay below 60ºC. The
reaction will produce free citric acid and a new precipitate,
calcium sulfate, which will need to be removed later. The
stoichiometric coefficients for this reaction are all one.
Sulfuric Acid, SO4
CSTR
Calcium sulfate as a precipitate, free citric acid, biomass, water
Calcium Citrate, biomass, water

17. Ex. Plate filter, Rotary presses, rack-and-frame presses
Purification of Citric acid
In this filter, the calcium sulfate is washed away from the citric
acid and the leftover biomass is removed. Again, the
contaminants that were present in the fermentation broth can be
removed by additional filtration means, such as microfiltration or
ultra filtration.
Filter
Ex. Plate filter, Rotary presses, rack-and-frame presses
Calcium sulfate as a precipitate, free citric acid, biomass, water
Citric acid, water

18. 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 %
2. Anhydrous
Processed to remove all water from end product
Prepare by dehydrating the monohydrate citric acid product at a temperature above 36.6ºC

19. Purification of Citric acid
Once the product has been brought to the desired purity, it would
be sent to packaging and distribution.
Purification
Citric Acid

20. Applications
Food
Used as flavoring and preservative in food and beverages.
Can be added to e.g. ice cream as an emulsifying agent to keep fats from
separating, to caramel to prevent sucrose crystallization, or to recipes in
place of fresh lemon juice.
Citric acid is used with sodium bicarbonate in a wide range of effervescent
formulae, both for ingestion (e.g., powders and tablets) and for personal
care (e.g., bath salts, bath bombs, and cleaning of grease).
Citric acid is also often used in cleaning products and sodas or fizzy drinks.
Cleaning and Chelating agent
Used to remove scale from boilers and evaporators.
Can be used to soften water, which makes it useful in soaps and laundry
detergents.
In industry, it is used to dissolve rust from steel.
Can be used in shampoo to wash out wax and coloring from the hair.

21. Cosmetics and pharmaceuticals
Citric acid is widely used as a pH adjusting agent in creams and gels of all
kinds.
Citric acid is commonly used as a buffer to increase the solubility of brown 
heroin.
Citric acid is used as one of the active ingredients in the production of antiviral
tissues.
Dyeing
Citric acid can be used in food coloring to balance the pH level of a normally
basic dye.
It is used as an odorless alternative to white vinegar for home dyeing with acid
dyes.
Photography
Citric acid can be used as a lower-odor stop bath as part of the process for
developing photographic film.