Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing element or inorganic compound except carbon dioxide
Reexamination Certificate
2001-02-07
2004-11-02
Marx, Irene (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing element or inorganic compound except carbon dioxide
C435S257100, C435S256800, C435S262000, C435S170000, C210S601000
Reexamination Certificate
active
06812011
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved process for the removal of calcium ions from the brine by marine cyanobacteria.
The salt recovered from the brine in which the calcium is reduced has the applications (i) in chlor-alkali industry employing membrane cell or mercury cell technology for the manufacture of caustic soda and chlorine, (ii) in the manufacture of soda ash which has applications in preparation of many inorganic chemicals and detergents, (iii) in preparation of various other grades of high purity salt like, IP grade, AR grade, Dairy salt, etc., and (iv) in food industries as preservative where low calcium containing salt is desirable.
BACKGROUND OF THE INVENTION
Reference may be made to M. H. Vyas et al. (Indian Patent No. 315Del/95) wherein a method has been described for the preparation of sodium chloride containing low calcium impurity (Ca 0.16%) from sea brine using activated starch solution. Moreover the starch solution is heated prior to addition in sea brine solution. The limitation of this method is that the method is applicable to sea brine and not to subsoil brine. Besides, heating starch solution requires energy (power) which make the process uneconomical and unfeasible.
A. G. Bayer, in his paper “The importance of electrolyte quality to chlor-alkali cells, Unde Chlorine Symposium, 1995 has described the use of amino-phosphoric resin to remove calcium ions from the brine in the concentration range 4-10 g/L in presence of greater than 102 g/L of Sodium ions. The drawback associated with this process is the regeneration of resin; bringing it to the required cationic form; washing etc. makes the process more complicated, time-consuming and costly. Monitoring of this column involves additional manpower.
D. W. Kaufman in his book “Sodium chloride”, Reinhold Publication Co., New York (1960), describes the use of (i) precipitants like calcium hydroxide and sodium carbonate to precipitate magnesium and calcium, and (ii) flocculent like poly-acrylamide to enhance the settling rate of the precipitates in the treatment of brine. The drawback of this process is that, the brine requires a prior chemical treatment to reduce the calcium and magnesium content. Moreover, the process also imbibes raises the problem of sludge disposal.
Z. Rant: Die Erzeugung von soda nach dem solvay verfahren, F. Enke-verlag, Stuttgart 1968 and H. Borger, Bergban Rundschau 4, 1952 described the purification of the brine which should be as near saturation as possible to achieve optimum sodium utilization, it is best carried out by the lime-soda process, which yields the precipitation of magnesium hydroxide and calcium as calcium carbonate. The reagents used in this precipitation are prepared by dissolving soda ash or milk of lime in brine (Na
2
CO
3
concentration: 65-80 kg/m
3
, Ca(OH)
2
concentration: 170-185 kg/m
3
). Moreover, he has described that reaction times and settling rates are enhanced if the brine with the added reagent solution is mixed with recycled seed slurry. Under the described condition the precipitation of Mg(OH)
2
& CaCO
3
can be produced with settling rate upto 1 m/h and in some cases even 3 m/h. The drawback of the process is it needs chemicals for the precipitation of impurities like calcium and magnesium from the brine, which is costlier, and it also generates sludge and therefore disposal of the sludge creates environmental problems.
J. D. Adhiya et al., in Membrane Technology in Encyclopedia of Chemical Processes & Design, Marcel Dekker Inc., New York, Vol.29 (1988), in his paper, he said that International Salt Co., Salt Lake City, Utah, USA has described a mechanical method based on selectively heating (the resin bed on conveyor belt) and separating the salt and impurities in crushed rock salt. In this process, iron impurities are removed simultaneously by applying electromagnets. The drawbacks of the process are (i) an additional mechanical device is required to separate impurities from salt which adds to the cost of the product, (ii) besides, the separation is to be carried out at higher temperature; therefore energy (power) consumption increases. He has also disclosed the use of monovalent selective ion-exchange type membranes to concentrate the brine solution and remove the bivalent impurities viz. calcium, magnesium and sulphate. The concentrated brine solution is then subjected to evaporation process in order to crystallize salt with greater than 99.5% purity. The drawback of the process is, it needs a special preparation for monovalent selective membranes. The simultaneous removal of divalent cations and anions to prevent the clogging of membranes also needs special monitoring and washing.
A. I. Postornko et al. In U.S. Pat. No. 537,027-A (1976) has studied the dissolution kinetics of sodium chloride containing calcium sulphate as an impurity. In this process the flow rate and the contact time are so adjusted that highly soluble sodium chloride along with minor proportion of calcium sulphate is separated. The major proportion of calcium sulphate is recovered separately (undissolved). The drawback of the process is the accurate adjustment of flow rate and contact time is difficult which is to be maintained for a longer period. The disposal of sludge containing gypsum also involves an environmental problem.
R. F. Chambers et al. in U.S. Pat. No. 4,227,447-A (1981) and Toa GO Sci Chem. Ind. J. P. S7-106, 520-A2, K. Suzuki, R. Nagai, H. Goto (1982) has described the use of sodium bicarbonate or phosphoric acid in the treatment with saturated salt solution (brine) to reduce the calcium content. The author has revealed a recrystallization method for preparing pure salt from rock salt and sea salt. The process is based on solubility difference of sodium chloride and calcium carbonate at different temperatures. The author claims that under specified condition salt is soluble and insoluble calcium sulphate is removed by filtration. The filtered saturated salt solution is pumped to flash chamber where salt is crystallized. The drawback associated with this process is that the unit operation is increased which will eventually increase the time of completion of a specific batch. Besides, equal amount of investment is required, which would increase the capital investment. The process requires more energy (power).
D. Bayer, EZ709,728-C2 (R.Scharfer) (1983) and K. Maycock et al., SCI Chlorine Symposium, London (June, 1997) has described the calcium sulphate removal and K. Haycock et al., has removed calcium using ion exchange process or by membrane nanofiltration. The drawback of the process is it requires a huge plant, increasing investment and power.
A. U. Hamidani and J. R. Sanghavi, in their paper entitled “Improvement in the quality of salt from inland brine of Kharaghoda area”, Salt Research & Industry, Vol.37, March 1992, India have explained the method of reducing the calcium content in sub-soil brine, by establishing a common ion effect in the saturated solution. The addition of MgSO
4
or Na
2
SO
4
to the saturated solution in adequate amount creates a common ion effect and thereby the calcium sulphate is knocked out of the system. The drawback of the method is that by creating a common ion effect, calcium content is reduced, but the magnesium content is increased which is undesirable. The addition of Na
2
SO
4
reduces the calcium but the sulphate content is increased which is also not desirable.
G. C. Jain et al., in their paper “Mixing of bitterns with weak brines in salt manufacture” in Salt Research & Industry, Vol.4, No.4, October 1967, India has described the process wherein the bittern is mixed with brine of less sodium chloride concentration in the condensers of the salt farms. In this mixing, due to the common ion effect the calcium sulphate is thrown out of the system. The drawback of the process is that it is difficult to accurately maintain the ratio of bittern to brine in the field, which does not give consistent result. Moreover the pumping of higher density bittern to weaker brine against the gravity results
Bhatt Ajoykumar Murlidhar
Chauhan Shantibhai Amritlal
Gandhi Mahesh Ramniklal
Ghosh Pushpito Kumar
Mishra Sandhya
Council of Scientific & Industrial Research
Marx Irene
Wenderoth , Lind & Ponack, L.L.P.
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