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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
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