FORM 2
THE PATENTS ACT 1970
(39 of 1970)
& The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10; Rule 13)
1. TITLE OF THE INVENTION:
Lead-Fluoropolymer Double Layer Composite Liner for Transportation Tank / Storage Tank and Processing Equipment for Safe Storage and Handling of Corrosive Chemicals such as Bromine.
2. APPLICANT(S)
(a) NAME: Agrocel Industries Limited
(b) NATIONALITY: An Indian Company
(c) ADDRESS:
Agrocel Industries Limited
4th Floor, Doctor House,
Opp. G K General Hospital,
Bhuj,
Gujarat 370 001,.
INDIA.
3. PREAMBLE TO THE DESCRIPTION:
The following COMPLETE specification particularly describes the nature of this invention and the manner in which it is to be performed.


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LEAD-FLUOROPOLYMER DOUBLE LAYER COMPOSITE LINER FOR TRANSPORTATION TANK / STORAGE TANK AND PROCESSING EQUIPMENT FOR SAFE STORAGE AND HANDLING OF CORROSIVE CHEMICALS SUCH AS BROMINE
FIELD OF INVENTION
This invention relates to a lead-fluoropolymer double layer composite liner for transportation tank / storage tank and processing equipment which provides protection from corrosion to the tank or equipment containing corrosive chemicals such as bromine.
BACKGROUND AND PRIOR ART
Chemicals like bromine are corrosive to common metals and become highly corrosive in presence of moisture. Very few materials such as titanium, fiberglass reinforced plastic (FRP), polyvinylidene fluoride (PVDF) etc. are resistant to bromine. Titanium is expensive and FRP does not last long. Hence PVDF is a preferred choice though it also has limitations.
C C Crump Limited based in UK designs and manufactures either lead or PVDF lined vessels for the transportation of Bromine. BROMAID is a consortium among European bromine companies which prescribes principles and procedures to the participating companies concerned about bromine emergencies and transportation safety. BROMAID has published a handbook covering materials of construction and performance thereof under the actual conditions of use including temperature, pressure and presence of moisture. Use of PVDF lined mild steel is covered in the handbook. However, PVDF lined mild steel has

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limitations. PVDF though resistant to corrosion, it's permeability for bromine increases with pressure. Density of bromine is 3.1 and hence it exerts pressure to the walls of the vessel. The pressure further increases during unloading under pressure with dry air or nitrogen. Further, since the freezing point of bromine is -7.2°C, there is a problem of bromine solidification during transportation in cold countries and the container requires to be heated, which results in increased permeability of PVDF for bromine.
Goslar is the producer of lead-lined steel vessels. Though lead is resistant to dry bromine, in presence of moisture, acid is formed which is corrosive to lead-lined vessels. Corrosiveness of bromine to metals increases if the water content in bromine is above 70 ppm. To overcome this shortcoming, Rudolf et al. (US2670276) invented a method which involves adding an oxidizing agent to bromine to prevent corrosion of lead-lined vessel for bromine. However, adding of oxidizing agent apart from resulting in recurring cost, has disadvantage of carryover traces of oxidizing agent interfering in complex reactions in which bromine is used.
As mentioned in US3375077, stainless steel vessel may be used for dry bromine containing oxides of nitrogen to prevent corrosion. However, it adds NOx to the environment and also recurring cost. Moreover, it is necessary to coat the container from outside because bromine splashes during filling and emptying of the vessel. NOx being volatile, quickly evaporates into atmosphere from splashed bromine. Bromine also comes into contact with moisture and produces acid near openings for transfer, resulting in corrosion.
US Department of Transportation vide its specification 105A300W requires that the bromine tank must have a nickel cladding material on

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the inside surface comprising at least 20% of the total thickness, or it should be lined with at least 3/16 inch (4.7 mm.) thick lead. Such tank also has disadvantages as mentioned above.
Thus, there is a need for a means to protect from corrosion of transportation tank /storage tank and processing equipment which will overcome abovementioned disadvantages of the prior art. Present invention provides an effective solution for the same.
OBJECTS OF INVENTION
Main object of invention is to provide a lead-fluoropolymer double layer composite finer for transportation tank /storage tank and processing equipment for safe storage & handling of chemicals such as bromine.
Another object of invention is to provide a transportation tank /storage tank and processing equipment for safe storage & handling of chemicals such as bromine, wherein corrosion of said tank or equipment is prevented by using the lead-fluoropolymer double layer liner.
Another object of invention is to provide a transportation or storage tank and processing equipment with lead-fluoropolymer double layer liner which has reduced permeability to chemicals such as bromine even at elevated pressure.
Another object of invention is to provide a transportation or storage tank and processing equipment lined with lead-fluoropolymer double layer composite liner which is cost-effective.
Another object of invention is to provide a transportation or storage tank and processing equipment for chemicals such a_s bromine, wherein the

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need for drying bromine or carrier gas is obviated and moisture above 70 ppm can be tolerated.
Another object of invention is to provide a transportation or storage tank and processing equipment for chemicals such as bromine with enhanced safety.
Another object of invention is to provide a transportation or storage tank and processing equipment for chemicals such as bromine, which is more durable than conventional tanks.
STATEMENT OF INVENTION
The present invention provides a corrosion resistant lead-fluoropolymer double-layer composite liner for transportation tank /storage tank & processing equipment for safe storage and handling of corrosive chemicals such as bromine, a transportation or storage tank & processing equipment lined with said liner, and a process for lining a transportation tank /storage tank & processing equipment with said liner.
DETAILED DESCRIPTION OF INVENTION
Fluor op olymers commonly used in lining include polytetrafluoro ethylene
(PTFE), polyvinylidenefluoride (PVDF), ethylene-chlorotrifluoroethylene
(ECTFE), ethylene-tetrafluoroethylene (ETFE), fluorinated
ethylenepropylene (FEP), perfluoroalkoxytetrailuoroethylene (PFA) etc. PTFE, FEP and PFA are fully fluorinated fluoropolymers whereas ECTFE, ETFE and PVDF are partially fluorinated fluoropolymers.

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A liner must be resistant to chemicals and at the same time, it should
also have good tensile strength and abrasion resistance. While fully
fluorinated fluoropolymers are more resistant to chemicals and exhibit
higher thermal stability compared to partially fluorinated fluoropolymers,
partially fluorinated fluoropolymers on the other hand have greater
tensile strength and abrasion resistance. Fluoropolymers also differ in
permeability to various chemicals. Thus, if fully fluorinated
fluoropolymers are chosen for lining material, corrosion of tank can be avoided but tensile strength and abrasion resistance are compromised. On the other hand, if partially fluorinated fluoropolymers with good tensile strength are used in liners, they are more permeable to the chemicals especially at elevated pressure, resulting in corrosion of the tank.
Lead-fluoropolymer double layer composite liner of the present invention overcomes abovementioned shortcomings of the liners of prior art. The double layer liner is bonded to the wall of the tank or process equipment in such a manner that fluoropolymer side of the double layer liner facing towards inside of the tank/equipment and lead side of the layer is bound to the wall.
Lead-fluoropolymer double layer liner of the present invention is not a mere arrangement or rearrangement of known devices functioning independently of each other. Though lead liners and fluoropolymer liners are known in the art, a "composite" double layer prepared by the process described herein, by virtue of which said two layers are bonded to form a composite double layer which has superior performance compared to a system comprising two layers merely kept together, loosely one above the other. Such a system does not address problems of abrasion, permeability and cohesion simultaneously.

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Sheets of fluoropolymer are used for making a layer of fluoropolymer on lead. Fluoropolymer sheets are first bonded on lead with the help of resin binder and then said sheets are welded at the adjacent borders to form a continuous fluoropolymer layer.
Optimum thickness of lead layer is around 6+2 mm and that of fluoropolymer layer is around 4+2 mm. However, it can be varied depending on the requirement, which may be estimated by conducting hydraulic test as described in paragraphs below.
As per one embodiment of the present invention, a steel tank with wall thickness of 10 mm and about 10 ton capacity to carry liquid bromine is first lined with lead by a conventional method wherein the inner metal surface of the tank or equipment is first cleaned by sand-blasting to remove impurities. The surface is then washed with dilute hydrochloric acid and then with water and dried. On the dry. surface, tin chloride or zinc chloride flux is applied uniformly using a torch to melt and apply the material. Lead lining is then applied by melting lead using the torch and applying it on the surface. Desired thickness of lead lining is built up in several phases. Around 6 mm thick lead-lining is optimum. The lining is then inspected for pin holes or other flaws by dye penetration test.
After lead lining is completed, fluoropolymer PVDF sheets of around 4 mm thickness are pasted on lead surface using Bisphenol A -epichlorohydrin epoxy resin binder (average molecular wt.<700) containing a hardener. The hardener is made from a mixture comprising Bisphenol A 5% wt/wt, triethylenetetramine 2% wt/wt, barium sulfate 50% wt/wt, diethylenetriamine 4% wt/wt, N-(3-dimethylaminopropyl)-1,3-propylenediamine 5% wt/wt, reaction product of C18 fatty acid dimmer with poly ethyl en epoly amide [68410-23-1] and bentonite. The

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resin-binder and hardener are taken in a ratio of 4:1 wt/wt to make a binder paste. Fluoropolymer sheets are pasted on lead lining using the binder paste in such a manner so as to cover the lead lining completely with iluoropolymer. Curing time is 4-24 hrs. at room temperature. Adjacent fluoropolymer sheets are joined by welding. The lead-fluoropolymer double layer composite liner thus obtained is then stiffened from inside with four axial and four radial stiffeners made from 12 mm thick fluoropolymer sheet.
The lining is then inspected by 20KV spark test to check weld joints. Then hydraulic test is conducted at 6 kg/cm2 pressure which is maintained for 2 hrs and then released. The tank is then emptied, dried and observed for de-bonding, if any, near weld joints. Then final spark test is conducted to check whether there is any leakage at weld joints after applying pressure.
The transportation tank / storage tank is thus lined with the lead-fluoropolymer double layer composite liner in such a manner that fluoropolymer side of the said double layer liner faces towards inside of the tank and the lead side of the layer is towards the wall of the tank.
Lead-fluoropolymer double layer composite liner obtained as mentioned above has corrosion resistance as well as strength to withstand pressure and it is most suitable for tank/ equipment for transportation/storage/processing of corrosive chemicals such as bromine. A tank with a double layer composite liner of present invention has been proven to be effective without any problem for more than five vears.

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WE CLAIM:
1. Lead-fluoropolymer double layer composite liner for transportation tank /storage tank and processing equipment, said liner comprising a lead layer and a fluoropolymer layer bonded together to form a composite double layer liner.
2. A transportation tank / storage tank or processing equipment lined with a lead-fluoropolymer double layer liner claimed in claim 1, and lined in such a manner that fluoropolymer side of the said double layer composite liner faces towards inside of the tank or processing equipment and the lead side of the layer is towards the wall of the tank or processing equipment.
3. A process for lining a transportation tank / storage tank and processing equipment with composite double layer liner claimed in claim 1, comprising following steps: (1) lining the tank or processing equipment first with lead; (2) applying binder paste and fixing fluoropolymer sheets on lead lining to fully cover lead lining with fluoropolymer; (3) welding adjacent fluoropolymer sheets to form a continuous fluoropolymer layer bonded to lead layer to form a composite double layer liner.
4. A process as claimed in claim 3, wherein said composite double
layer liner is stiffened with radial and axial stiffeners made
preferably from fluoropolymer sheets.