Process and recovery

2.  Gluconic acid is used as a mild
acidulant in metal processing,
leather tanning and foods.
 Sodium gluconate is widely used
as a sequestering agent to prevent
the precipitation of lime soap scums
on cleaned products.
 Calcium gluconate is widely used
in calcium therapy.

3.  Gluconic acid is manufactured only by
submerged fermentation process.
 The fungus used is a strain of Aspergilllus
niger. Inoculum consist of either a sporulated
culture or spores germinated in seed tank.
Each type of inoculum has special advantages
not seen in others.
 The acid is quickly neutralised upon
excretion by the fungus. Therefore, the
fermented broth contains either calcium or
sodium gluconate.

4.  The raw materials are D-glucose and oxygen.
 The glucose substrate may be supplied as a solution
of crystalline glucose. Alternatively ,it may be
added as a syrup obtained from starch or crude
starchy matrials by the action of the α-amylase
followed by the amyloglucosidase.
 The glucose concentration that can be handled
depends on whether the sodium or the calcium salt
is to be prepared.

5.  It is necessary to maintain the maximum
concentration of oxygen dissolved in the solution.
 This is achived by the application of vigorous
agitation with a turbomixer or by action of a
cavitator.
 The greater the consumption of power by the
agitator motor,the more dissolution of oxygen.

6. Pressure
(atmospheres)
Weight yield
(%)
1 42.5
3 80.4
4 82.4
5 81.3
6 86.1
Yield of gluconate in relation to air
pressure

7. Operating optimum fermentation conditions in the
manufacture of calcium or sodium gluconate are:
Temperature = 28-300C
Aeration = 1 – 1.5 volumes air/volume
solution/minute
Agitation = vigorous
Initial pH = ~6.5

8.  At the end of the fermentation, fungal
mycelium is filtered off from the solution.
 The mycelium is used for the recovery of
glucose aerodehydrogenase. On the other
hand ,the filtrate is used to recover calcium
or sodium gluconate, gluconic acid, and
glucono-δ-lactone.

9.  Recovery of calcium gluconate is achieved by heating
the filtrate with a slight excess of Ca(OH)2 , then
decolourizing with carbon and filtering. On cooling
to a temperature below 200C and seeding with
calcium gluconate crystals, the compound readily
gets crystallized. A second crop of crystals of
calcium gluconate is obtained by the evaporation of
mother liquors through heating about 10-15 per cent
volume followed by treatment with carbon, filtration
and chilling.

10.  To recover gluconic acid and its delta lactone,calcium
is precipitated by the addition of a stoichiometric
quantity of sulfuric acid.
 Calcium sulfate is filtered off and the filtrateis
decolourized with carbon.
 After the removal of carbon, the acid solution is
subjected to a concentration of 50 per cent acid
strength. The product, thus obtained is a mixture of
free gluconic acid and its γ- and δ-lactones.

11.  Crystals separating from a gluconic acid solution at a
temperature below 300C and preferably near 00C, are
principally of gluconic acid.
 Crystals separating from solution at a temperature
between 30-700C are of δ-lactone. Finally , γ-lactone
crystallizes out at a temperature above 700C.

12. SHUHAIBA .K
2nd yr MFT