Citric Acid Report (details of Production Processes)

Citric Acid Report (details of Production Processes)

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. Wikipedia
Citric Acid Production by Aerobic Bioprocesses

6. 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: 30
o
C
Industrial Production of Citric acid

7. Bioreactor: batch or fed-batch (100m
3
)
- 5-25×10
6
A. niger spores/L may be introduced to the fermentor.
- Aeration is provided to the fermenter by air sparging (0.1-0.4
vvm)
- 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/m
3
Industrial Production of Citric acid

8. 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.
Industrial Production of Citric Acid

9. -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 30-35
o
C.
Industrial Production of Citric Acid

10. 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.
Industrial Production of Citric 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.

11. •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
Purification of Citric acid

12. •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:
CaCO
3
+ Citric Acid → CO
2
+ Calcium Citrate
Kirk 15
Calcium Carbonate,
CaCO
3Contaminated Citric
Acid
Calcium
Citrate as a
precipitate
plus
contaminants
CSTR
Purification of Citric acid

13. •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
Purification of Citric acid

14. 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,
SO
4
Calcium sulfate
as a precipitate,
free citric acid,
biomass, water
CSTR
Calcium
Citrate,
biomass,
water
Purification of Citric acid

15. 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.
Calcium sulfate
as a precipitate,
free citric acid,
biomass, water
Citric acid,
water
Filter
Ex. Plate filter, Rotary
presses, rack-and-
frame presses
Purification of Citric acid

16. 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
•Prepare by dehydrating the monohydrate citric acid product at a
temperature above 36.6ºC
Purification of Citric acid

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

18. 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.

19. 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. 

20. Food Industry Uses
Jellies and jams Gelling agent, tartness and flavour
Soft drinks and syrupsAcidulant , Natural fruit flavour, tartness
Frozen fruits Inactivation of oxidative enzymes,
protects ascorbic acid by inactivating trace metals
Animal fats and oilsShows Synergism with other antioxidants,
Sequestrant
Dairy products emulsifier, acidifying agent in many cheese products
Antioxidant
Cosmetics pH adjustment, antioxidant, buffering agent
Wines and ciders Prevents turbidity, prevents browning in some white
wines
adjusts pH, inhibits oxidation.
Fruits and vegetable
juices
Stabilizer
Pharmaceuticals Antioxidant, anticoagulant, acidulants