In earlier post, we have already discussed about the specifications, applications and market potential of Zeolite-A. In present post, we will concentrate ourselves on basic theory and principles to develop most economic production process route and also present basic calculations involved in production of Zeolite-A after analyzing the pros and cons of various process routes using hydrate and bauxite as the basic input material along with sodium silicate.
Process and Involved Reactions:
Zeolite-A is chemically represented as Na12(AlO2)12(SiO2)12.27H2O. It is evident from its chemical formula that one mole of sodium aluminate and one mole of silica will be required along with 27 moles of water for production of one mole of Zeolite-A. In other words, combination of one mole of alumina with one mole of silica will produce one mole of Zeolite-A in presence of sodium hydroxide.
As highlighted in earlier post, bauxite based Zeolite-A plant is more profitable as bauxite is the cheaper source for generating sodium aluminate which in turn result in production of Zeolite–A with aqueous sodium silicate. In this process, alumina present in bauxite forms sodium aluminate on heating with NaOH and reactive silica present in bauxite will get converted to sodium silicate on combination with caustic soda as per following reactions-
Al(OH)3 + NaOH = NaAlO2 + 2H2O.
SiO2 + 2NaOH = Na2SiO3 + H2O.
In further steps, sodium aluminate on reaction with sodium silicate will result in formation of Zeolite-A as shown in following reactions-
12NaAlO2 + 12Na2SiO3 + 12H2O = Na12(AlO2)12(SiO2)12 + 24NaOH
Na12(AlO2)12(SiO2)12 + 27 H2O = Na12(AlO2)12(SiO2)12 .27 H2O
Estimated Input Material Requirement:
The above reactions clearly reveal that twelve moles of hydrated alumina and twelve moles of sodium silicate in aqueous solution produce one mole of Zeolite-A.
Molar mass of Hydrated alumina = 27 + 3*(16+1) = 78 g per mole.
Molar mass of Sodium silicate = 2*23 + 28 + 3*16 = 122 g per mole.
Molar mass of Zeolite-A =12*23+12*(27+2*16)+12*(28+2*16)+27*18 = 2190 g per mole.
∴ Required Hydrate with 10% moisture = (12*78)/(2190*0.90) = 475 kg / t Zeolite-A.
Required Sodium Silicate = (12*122)/2190 = 668 kg/t Zeolite-A.
About 1% physical NaOH and 0.50% occluded NaOH will be lost per tonne of Zeolite-A.
∴ Loss of NaOH with product =1.5%*1= 0.015 t NaOH =15 kg NaOH per tonne of Zeolite-A.
Loss of NaOH with Bauxite residue = 10 kg per tonne of Product.
Chemical losses because of Reactive SiO2 = 30 kg per tonne of product,
Physical losses of NaOH during production = 10 kg NaOH per tonne of Zeolite-A.
Thus total requirement of NaOH=15+10 + 30 + 10 = 65 kg NaOH per tonne of Zeolite-A.
Annual Requirement of Raw materials for 10,000 tpa Zeolite-A Plant:
Hydrate with 10% moisture = 4750 tonnes.
Sodium Silicate = 6680 tonnes,
Caustic soda as NaOH = 650 tonnes.
As such, the above elaborations are brief guidelines for the plant designers of Zeolite-A plant. These are the basic clues based on which development of plant design, basic and detailed engineering activities can be taken up to initiate the execution of project of optimum production capacity.
Trust, you will find these basic inputs as interesting. Please do not take any investment decisions based on the technical inputs published on our blog without carrying out techno-economic feasibility studies. The market for synthetic Zeolite-A is very fluctuating as China is dumping natural Zeolite in nearby countries so you may not get price advantage in present scenario. But for future, Bauxite based Zeolite plant may be a good project having pay back period for investment less than three (3) years.
We will welcome your comments / feed back on the subject for further improvements.