FORM 2
THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003PROVISIONAL SPECIFICATION (See section 10, rule 13)
1. Title of the inventionA SYSTEM AND METHOD FOR MANUFACTURE OF SODA ASH.
2. Applicants)
Name Nationality Address
TATA CHEMICALS LIMITED INDIA BOMBAY HOUSE, 24 HOMI MODI STREET, MUMBAI-400001


3. Preamble to the description
PROVISIONAL SPECIFICATIONThe following specification particularly describes the invention.

The invention relates to the manufacture of soda ash. More particularly the invention relates to a system and method for manufacture of soda ash using sea water.
DESCRIPTION OF RELATED ART
Soda ash or sodium carbonate finds use in a number of industries including manufacture of glass, paper and pulp, detergent, chemicals such as sodium silicates and sodium phosphates and as an alkaline agent in many chemical industries.
Soda ash is prepared either by the purification of naturally occurring trona soda or is manufactured chemically. Industrially soda ash is prepared using a process which involves the conversion of sodium chloride into sodium carbonate using ammonia and limestone.
In the manufacture of soda ash limestone is heated to produce carbon dioxide. This carbon dioxide is bubbled through a concentrated solution of sodium chloride and ammonia to precipitate sodium bicarbonate [NaHCOs] and form ammonium chloride [NH4CI]. The precipitated sodium bicarbonate is then heated to produce sodium carbonate [NaC03]. Ammonia is recovered from the ammonium chloride byproduct by treating it with milk of lime that is obtained from the limestone.
The sodium chloride which is used for this process is in a solution form known as Brine. Raw brine is obtained by dissolving salt in water. Raw brine contains impurities including magnesium and calcium that cannot be tolerated in soda ash making process. These impurities in raw brine are removed by brine purification process wherein the raw brine is treated with Milk of Lime[Ca(OH)2] and soda ash to precipitate magnesium and calcium in the form of magnesium hydroxide[Mg(OH)2] and calcium carbonate[CaCO3]. The resultant brine free of impurities essentially calcium and magnesium is referred to as pure brine and used in soda ash manufacture.


The cost of manufacturing soda ash is affected by various parameters some of which include the cost of obtaining raw water, cost of limestone, cost of purification of brine, cost of effluent and sludge management and the cost of maintenance of plant.
As the process of soda ash manufacture utilizes soda ash itself as a brine purifier, the net amount of soda ash available for sale is reduced.
Milk of Lime, obtained from limestone, is required for the purification of raw brine and for the recovery of ammonia. Impurities present in milk of lime, particularly sulphate, cause scaling and jamming of equipment reducing operational efficiency of the plant.
Effluent from brine purification, ammonia recovery and soda ash manufacture is significant in quantity and requires effective disposal which impacts the effective cost of soda ash manufacture. Large amounts of effluent and sludge generated also raise environmental issues.
The quality and availability of water is often a significant parameter in the manufacture of soda ash. In regions where raw water is not abundantly available, the efficiency and economics of soda ash manufacture is adversely affected.
While seawater is an option for soda ash manufacture, use of the same aggravates the efficiency and economics of the process. This is primarily on account of the impurities present in the seawater that result in an increase in the purification cost of brine while also increasing the effluent and sludge generated.
Known processes for the utilization of sea water in soda ash production such as caustic process, addition of barium chloride /carbonate for removal of sulphate, desalination of sea water using reverse osmosis are not economically efficient and produce large amounts of effluents.
In view of these limitations there is a need to come up with an improved process for the manufacture of soda ash. The process should be such that it allows the use of sea water in soda ash industry. Process should be economical, efficient and should reduce the effluents generated.


SUMMARY
The invention provides for an improved method for the manufacture of soda ash. The invention relates to a method of manufacture of soda ash from brine prepared from sea water comprising of the steps of pretreatment of sea water to remove larger impurities; nano-filtration of the pretreated sea water to remove all divalent ions while retaining the useful chloride ions; preparation of brine solution by dissolving solar salt with nanofiltered sea water; preparation of milk of lime from nano-filtered seawater; treating the raw brine with soda ash and Milk of Lime to obtain pure brine, calcium carbonate, and magnesium hydroxide manufacturing soda ash using the brine prepared from nano-filtered seawater.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serve to explain the principles of the invention. FIG 1 is an illustration of a soda ash production plant in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
1
To promote an understanding of the principles of the invention, reference will be made to the embodiment illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of scope of the invention is thereby intended, such alterations and further modifications in the illustrated system and such further applications of the principles of the inventions as illustrated therein being contemplated as would normally occur to one skilled in art to which the invention relates.


The invention describes a method and system for the production of soda ash. The teaching of this document provides for a method and system of production of soda ash using sea water. The invention includes but is not limited to method and system for the production of soda ash using sea water filtered by a nano-filter.
The nano-filtration of seawater is carried out to remove all divalent ions while retaining useful chloride content. A method for production of brine using the nanofiltered seawater with reduced divalent ions content is included. The document also describes a method for the production of brine such that it is produced in an economically efficient manner with minimum requirement of the end product soda ash. It also describes a method for the brine purification using Milk of lime prepared from nanofiltered seawater with reduced content of divalent ions and limestone. In addition a method for manufacture of soda ash such that it is produced in an economically efficient manner without requiring excessive readjustment to existing plant is included. The document also provides for a method for the utilization of magnesium, calcium and sulphate rich nano-filtration effluent for gypsum production. In addition, the document describes methods for reducing net waste disposed to the environment from a plant.
With reference to the accompanying figure the preferred embodiment for the method and system for improved production of Soda Ash has been illustrated.
Since nano- filtration system is used, pre-treatment of seawater should preferably be carried out to prevent fouling of membrane. Pre-treatment is carried out to achieve a Silt Density Index required to prevent particulate fouling. In a preferred embodiment sea water is pretreated to achieve a silt density index of less than 5. However, the required silt density index will depend upon the type of nano-filtration membrane that is used. To achieve the required Silt Density Index one or several of the following processes may be used: clarification, filtration, microfiltration etc.


In a preferred embodiment sea water first passes though a clarifier to remove suspended solids. Moreover coagulants and/or flocculants may be added to seawater to facilitate removal of suspended solids. Suspended solids are discharged as slug. The clarified seawater is then passed through a series of multimedia filters. This filtered seawater is finally passes through a cartilage filter. The cartilage filter used should be such that 5 micron filtration is carried out. For the pre-treatment of water each of these methods can be used individually or in combination.
The pre-treated seawater (1) is pumped to a nano-filtration (NF) membrane (2). The nano-filtration membrane has a high degree of selectivity for some ions. That is some ions pass easily through the membrane than other ions. The nano-filtration membrane selected for such an application has a high rejection rate for all divalent ions. In particular, the nano-filtration membrane has high rejection rate for divalent ions such as magnesium, calcium and sulphate as compared to chloride ions. Moreover, the nano-filtration membrane that is used should be such that it retains the useful chloride content. The nano-filtration membrane selected for this application should be such that the rejection rate for sulphate is especially high.
Any commercially available nano-filtration membrane having high divalent ion rejection characteristics may be used. In a preferred embodiment a polysulphone membrane having high rejection rate for divalent ions as compared to chloride is used.
Pre-treated seawater (1) is pumped through the nano-filtration unit (2). The pre-treated seawater is pumped through the nano-filtration unit at a relatively low pressure compared to reverse osmosis.
The solution that passes through the nano-filtration unit is known as the nano-filtrate permeate (3). The solution that does not pass through the membrane and is retained in the nano-filtration unit is known as the nano-filtrate retentate (4). The nano-filtration process used is such that the nano-filtrate permeate has reduced content of divalent ions such as sulphate, magnesium and calcium, while the nano-filtration retentate is rich in divalent ions such as sulphate, magnesium and calcium.


For example in an experiment seawater with a composition of 0.5gpl calcium, 1.5gpl magnesium, 2.9gpl sulphate and 22gpl chloride was passed through a nano-filtration such that the nano-filtration permeate has a composition of 0.15gpl calcium, 0.22gpl magnesium, 0.23gpl sulphate and 17.5gpl chloride. Thus the nano-filtration is carried out such that 70% calcium, 80% magnesium and 90% sulphate is rejected.

Inlet Sea Water, gpl NF product, gpl Rejection %
Calcium 0.5 0.15 >70
Magnesium 1.5 0.22 >80
Sulphate 2.9 0.23 >90
Chloride 22 17.5 <20
The retentate (4) which is seawater rich in sulphate, magnesium and calcium may be discharged as an outflow or sent to a minerals recovery process to extract materials such as gypsum. In a preferred embodiment nano-filtration retentate (4) is sent to solar pond to facilitate gypsum formation.
The nano-filtration permeate (3) that is, sea water with reduced content of divalent ions is used as a feed for preparation of brine. Brine can be prepared from nanofiltered water using any brine preparation method. In a preferred embodiment brine is prepared by dissolving sea salt in nanofiltered water with lower divalent ion content. Solar salt is added to the nanofiltered sea water and dissolved using a static dissolver to form raw brine (5).
The raw brine (5) with reduced divalent ion content is then sent for further processing in accordance with the teaching of this document. The raw brine with reduced divalent ion content is purified to remove magnesium and calcium which cannot be tolerated by the soda ash industry. In a preferred embodiment magnesium is removed from raw brine solution as magnesium hydroxide by adding milk of


lime. Moreover the milk of lime used for brine purification is such that it is prepared from nano-filtered water with reduced divalent ion content especially reduced sulphate content. Calcium is removed from raw brine solution by adding soda ash to form calcium carbonate. This brine is then filtered to remove the magnesium hydroxide and calcium carbonate. On account of the reduction in the magnesium and calcium content in the nano-filtered water the quantities of soda ash and milk of lime that are required for brine purification are significantly reduced. Thus the method and system as described increases the net amount of soda ash for sale. It also significantly reduces the amount of limestone required for milk of lime production for use in the soda ash industry. This filtrate which is rich in magnesium hydroxide and calcium carbonate with very little pure brine is discharged as effluent (6). Similarly on account of the reduced magnesium and calcium content in the nano-filtered water the effluent discharged during brine purification is reduced. The pure brine (7) is sent to the soda ash plant for manufacture of soda ash.
Nano-filtered water (3) with reduced content of divalent ions like sulphate, magnesium and magnesium, is sent as a feed for the preparation of milk of lime. Milk of lime is prepared by dissolving limestone in nano-filtered water. Moreover the milk of lime prepared from nano-filtered water is such that it has reduced sulphate content. Milk of lime with reduced sulphate content is used for brine purification and for ammonia recovery. The use of brine and milk of lime with reduced sulphate content reduces the scaling and jamming of the plant which reduces the routine cleaning requirement hence increasing the efficiency of the soda ash plant.
Nano-filtration permeate(3) is also used as a source of water in auxiliary processes in the soda ash industry.
The method and system as described above does not require any substantial modification to the existing soda ash manufacture plant besides the addition of a nano-filtration section. In addition the method


and system so described reduces the effluents that are generated in the manufacture of soda ash which increases the efficiency of the plant by reducing effluent management costs.
It will readily be appreciated by those skilled in the art that the present invention is not limited to the specific embodiment herein shown. Thus variations may be made within the scope and spirit if the accompanying claims without sacrificing the principle advantages of the invention.