Catalyzed sodium sulfite for corrosion prevention. Generally speaking, sulfite is not present in natural water. In boiler feedwater conditioning sodium sulfite is fed to a boiler to remove dissolved oxygen and thus prevent pitting. For the reaction between sulfite and oxygen to proceed rapidly and completely, it is necessary to maintain an excess sulfite concentration at an elevated temperature.
Theoretically, 3.5 Kg of chemically pure sodium sulfite are required to remove approx 400 gram of oxygen. The efficiency of the oxygen removal is estimated at 75 per cent to allow for oxidation in contact with air, blowdown losses, etc. Therefore it is estimated that 4.5 Kg of commercial sodium sulfite are required for 450 Gram of oxygen removed (or 10 ppm sulfite per 1 ppm dissolved oxygen.)
The use of sodium sulfite as a chemical deoxygenator is economical within certain limitations imposed by the dissolved oxygen content of the feedwater. If appreciable quantities of dissolved oxygen are permitted to enter the boiler, costs will be high if sulfite is relied on as the sole means of oxygen removal. Generally, costs are balanced by removal of as much of the oxygen as feasible by mechanical means, e.g. deaerator and by using sulfite to react with the residual oxygen.
To prevent corrosion and pitting in feed lines, closed heaters and economizers, it is desirable to feed the sulfite continuously to the boiler feedwater rather than directly to the boiler feedwater rather than directly to the boiler. Reaction between sulfite and oxygen is not instantaneous and the completion of the reaction is aided by the longer contact times provided by feeding sulfite to the feedwater.
Catalyzed sodium sulfite will, however, react almost instantaneously with dissolved oxygen even at cold water temperatures. Because of this property, catalyzed sulfite has found increased use in the treatment of cooling water, process water, distribution system, etc. for preventing oxygen corrosion.
Sodium sulfite anhydrous is a white granular material with the chemical formula Na2SO3
It is primarily used in pulp and paper industry. It is used in water treatment as an oxygen scavenger agent, in the photographic industry to protect developer solutions from oxidation, in textile industry as a bleaching, as a desulfurising and as a dechlorinating agent and in leather trade for the sulfitisation of tanning extracts. It is used in chemical manufacturing as a sulfonation and sulfomethylation agent. It is used in the production of rubber chemicals, sulfur dyes and other chemical compounds. It is used in other applications including ore flotation, oil recovery, food preservative, making dyes, and detergent.
White, free flowing crystalline Odorless powder
Dose of Sulfite can be controlled by this method ::: Because it readily reacts with oxygen to form sulfate, sulfite is not usually found in natural water systems. In its most common form, sodium sulfite, it is widely used as an oxygen scavenger in feedwater conditioning to prevent pitting in boilers; as a pulping or pulp-bleaching agent by the paper industry; to neutralize residual chlorine in potable water, sewage, industrial effluents, and textile process waters; and as a reducing agent in still other manufacturing processes.
Sample water over 100°F will cause a false-high reading; therefore, quickly cool to room temperature before testing. To prevent a false-low reading caused by the reaction between sulfite and ambient air or dissolved oxygen, water samples should be capped while cooling and then tested without delay. An iodometric drop test is the most popular field method for determining sodium sulfite concentrations.
Reagent packs, containing an instruction and chemicals only, may be purchased for use with buret setups. Note: Sulfide and ferrous iron cause positive interference; copper and nitrite cause negative interference.
The test for sulfite is based on the colour change end point reaction. At the end point reagent combines with the indicator to form a blue color.
Apparatus Required
Buret, automatic, 25 ml - 1 ( Sample Tube, Graduated, 25 mL, plastic w/cap and white dot )
Casserole porcelain, 210 ml - 1
Cylinder, graduated, 50 ml - 1
Measuring dipper (plastic) - 1
Stirring rod, glass - 1
TK - 13 ::: RXSOL-62-5503-002
TK - 14 ::: RXSOL-62-5503-003
TK - 15 ::: RXSOL-62-5503-004 ( 1 ml =0.5 mg SO3 )
The water sample should be freshly obtained with as little contact as possible with air. Do not filter the sample, but cool it to room temperature (70 to 800F).
NOTE:
Sample must be cooled to less than 100ºF (38ºC) to prevent high test results.
Sample must be protected from air contact while cooling to prevent low test results.
1. Measure 50 ml of the water sample with the graduated cylinder . For error free result Collect water to be tested in a clean, preferably large-mouthed, bottle to overflowing. Immediately cap and cool to room temperature.
2. Add three or four drops of TK - 13 ::: RXSOL-62-5503-002 to the sample Swirl to mix. Sample should turn red.
3. Add TK - 14 ::: RXSOL-62-5503-003 Powder a dipper at a time, swirling after each dipper, until color changes from red to colorless. Add 2 more dippers. Swirl until dissolved. ( Note : Use the plastic dipper to add TK - 14 ::: RXSOL-62-5503-003 to the sample. Add only one measure at a time and stir thoroughly between each addition of TK - 14 ::: RXSOL-62-5503-003. All the particle of TK - 14 ::: RXSOL-62-5503-003 may not dissolve and this may create a slight haze in the sample. Continue to add the TK - 14 in this manner until the red color disappears. It is not necessary that the sample solution be exactly neutralized, only that the sample turn colorless. When the sample is colorless, add one additional measure of TK - 14 ::: RXSOL-62-5503-003 and stir. )
4. Add TK - 15 ::: RXSOL-62-5503-004 Reagent dropwise, swirling and counting after each drop, until color changes from colorless to a faint but permanent blue. Always hold bottle in vertical position.
This color change is taken as the endpoint. Record the ml of TK - 15 ::: RXSOL-62-5503-004 solution used.
Using a 50 ml sample, sulfite, in parts per million as SO3 is equal to the ml of TK - 15 ::: RXSOL-62-5503-004 required multiplied by 10.
Limitations of Test :::
This method is rapid and adaptable to field determinations. It is affected by any oxidizable substances in the water such as organic matter sulfides and nitrites. The presence of these interfering substances will cause the sulfite content obtained from this titration to by shown as a higher value than actually exists.