Chemicals Based
Technologies - Synthetic Hydrotalcite
Introduction
Synthetic hydrotalcites (SHT), also
known as anionic clays or layered double hydroxides
are rarely found in nature. They are functionally akin
to zeolites. The structure of SHT is very similar to
brucite, Mg (OH)2. Magnesium is octahedrally surrounded
by six oxygens in the form of hydroxides; the octahedral
units then, through edge sharing, form infinite sheets.
The sheets are stacked on top of each other through
hydrogen bonding. When some of the magnesium in the
lattice is isomorphously replaced by higher charged
cation, e.g. Al3+, then the resulting overall single
Mg2+ – A13+ - OH Layers gains a positive charge.
Sorption of an equivalent amount of hydrated anions
render the structure electrically neutral. The anion
is frequently found to be carbonate. A typical hydrotalcite
may be represented by formula such as MG4.5 A12 (OH)13
CO3 3H2 O. Many modification of this structure can be
made by changing the A1 to Mg ratio.
SHT finds application in pharmaceutical
industry as an antacid. SHT has also replaced heavy
metal based heat stabilizers for PVC. SHT like compounds
are imported under the trade name like DHT-4A, L-55R-II
and Alcamizer. They are used as halogen scavenger in
plastic processes such as the production of polypropylene.
It deactivates the residual quantities of acidic substances
associated with acid catalysts used in producing polymers.
CSMCRI has developed processes to prepare pharmaceutical
grade and halogen scavenger grade SHT.
SCOPE
Major quantum of SHT is imported in
India at very high price. There is no production of
SHT from indigenous raw materials like bittern –
a waste mother liquor remained after separation of salt
from sea brine. There are number of novel applications
of SHT like in catalysis, as adsorbents, as fire retardant,
as anion exchangers etc. In view of these, there is
an excellent scope to produce SHT and holds tremendous
potential for the export.
Process
Bittern and soda ash are reacted to
make magnesium precursor. Aluminium sulphate and soda
ash solutions are reacted to make aluminium precursor.
These precursors are blended and subjected to hydrothermal
treatment under optimized process conditions. The slurry
is filtered, dried, pulverized and sieved to obtain
pharmaceutical grade SHT. To prepare halogen scavenger
grade SHT, the slurry is treated with surface modifier
to make the material hydrophobic prior to filtration.
The cake is washed, dried, pulverized and sieved to
obtain halogen scavenger grade SHT.
Halogen Scavenger
Grade Synthetic Hydrotalcite Specification of Raw Materials
And Utilities
Basis – 100 kg/day
Raw Materials.
S.No.
Raw material
Specification
Required/day
1.
Bittern
30o Be'
700 liters
2.
Aluminium Sulphate
Non ferric, technical grade
140 kg
3.
Soda Ash
Technical grade, BIS
240 kg
4.
Caustic Soda
Technical grade
75 kg
5.
Surface Modifier
Technical grade
6 kg
Utilities
S.No.
Utility
Required/day
1.
Electricity
60 KWH
2.
Steam
2.2 Ton
3.
DM water
8 kl
4.
Water
4 kl
Product Specifications
Specification of CSMCRI Product
(SHT) and that of imported product DHT-4A are as under.
Properties
CSMCRI SHT
DHT-4A
Molar ratio MgO/A12 O3
4.2
4.0 - 5.0
Specific surface area (BET) m2/gm
12
5 - 15
Loss on drying (1052 C, 1hr, %wt)
0.4
0.5 max.
Heavy metals (as pb)
<100 ppm
100 ppm max.
Particle size distribution (by number)
Mean particle size (surface weighted)
0.45
0.4 - 0.7
Under 1 µm
90%
85% min.
Over 5 µm
None
None
pH of suspension
[2%(w/v)C2 H5 OH:H2O (1:1]
9.1
9.0 ± 0.5
Bulk density gm/c.c
0.3
0.33 (0.06m3/20kg bag)
List Of Major Equipments
a) Solution
preparation tanks
b) Jacketed reactor, S.S.
c) Plate @ frame filter press
d) Agitated nutsche filter
e) Autoclave, S.S. with stirrer
f) Boiler
g) Pulverizer
h) Sieve Separator
i) Dryer
j) Pumps
Advantages of Indian technologies:
Low capital investment
High employment potential
Maximum use of local raw materials
and manpower resources
Adaptable levels of sophistication
For further information please contact
:
National Research Development Corporation
( A Government of India Enterprise )
20-22, Zamroodhpur Community Center
Kailash Colony Extension
New Delhi 110 048. India
Tel: 91-11-26419904, 26417821, 26480767, 26432627
Fax: 011-26231877, 26460506, 26478010
Website: www.nrdcindia.com
