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Chlorine Chemistry
What is the
History of Chlorine?
Chlorine was first discovered in the sixteenth
century, and today is one of the most produced chemicals in the US, finding its way into a
multitude of products. Chlorine is so deeply inter-twined into industry that finding
alternatives would indeed change our daily lives.
How Chlorine is Made?
Chlorine is produced the electrolysis of salt water. When electricity is passed through 2NaCl (salt) and 2H20 (water), the atoms dissociate
into Cl2 (chlorine) + 2NaOH (sodium Hydroxide) + H2 (Hydrogen). Cl2 is isolated in its
gaseous form, and used to create other chlorine compounds used for sanitizing, bleaching
and production of plastics and related products.
How Does Chlorine Work to Sanitize?
When chlorine is added to water, another
dissociation occurs. When we add Cl2 (chlorine) + H2O (water), we get a reaction which
leaves us with HOCl (hypochlorous acid) + HCl (hydrochloric acid). Hypochlorous acid is
the active, killing form of chlorine. This is what does the real sanitizing work. The
chlorine molecule or ion kills microorganisms by slashing through the cell walls and
destroying the inner enzymes, structures and processes. When this occurs, the cell has
been deactivated, or oxidized. The hypochlorous molecule continues this slash & burn
until it combines with a nitrogen or ammonia compound, becoming a chloramine, or it is
broken down into its component atoms, becoming de-activated itself.
Is Chlorine Dangerous and Unhealthy?
No doubt about it, chlorine certainly is a hazardous
product, with some forms of it being more dangerous for the handler and the environment
than other forms. Chlorine in a solution of water at levels found in swimming pools pose
no danger for swimmers. Allergic reactions to chlorine are rare, however some individuals
may experience skin irritation. Chloramines, sometimes found in poorly balanced water, are
the cause of occasional red eyes when swimming. Extremely high levels of chlorine in the
water could possibly release enough gas off of the surface in certain conditions to render
breathing difficulties. The main hazard is towards the person in charge of
adding the chlorine to the pool. Use caution and always read the directions. Always use
care when opening a container of chlorine. Breathing in chlorine gas can knock you right
out, and could be fatal. Always wear protective handling gear such as eye protection and
rubber gloves. If chlorine touches your skin, you should wash it off to prevent
irritation. If chlorine splashes in the eye, irrigate with
water and contact a physician right away. The label on the chlorine container will also tell you never, never, never
mix chlorine with any other chemical. You could produce something of a bomb or even
napalm. This includes mixing two different types of chlorine, or chlorine and bromine. KABOOM! Dirt, debris or any foreign substance (like algaecides, alkalis, acids, etc.) can
cause spontaneous combustion when mixed with chlorine. FIRE! See our page on
Chemical Safety for more info.
As for the environment; pools have a small impact. Being closed systems, pools just don't contact nature very much. There could be some
hazard involved with waste water from the pool that has either extremely high chlorine
levels or extremely low pH levels. It is unlikely that the amount of water expelled during
backwashing your filter could pose much harm, but large amounts of D.E. Powder can choke a
stream if pumped directly into it. Impacts have been seen on drain and clean jobs, when
acid water is pumped into nearby streams. Pool water is very similar in make up to the
city water right out of the tap. Many people water their lawns with higher chlorine and
lower pH than is found in their pool. There are certain industrial uses of chlorine
chemistry which are detrimental to the environment, but in a swimming pool environment,
the potential hazards are much lower, even non-existent. There has been much publicity and
controversy over chlorine in recent years, with some organizations calling for bans on its
use. You decide if chlorine chemistry is right for you and your pool.
What
different types of Chlorine are there?
In its elemental state chlorine exists as a gas. Gas is available for swimming pool sanitation. It is very cheap, and is the purest form of
chlorine with no binders or carriers. The percentage of available chlorine is 100%. It is also
extremely dangerous and restricted in its use. It is rare to find a pool using gas as it's
sanitizer, and those that do are usually very old, very large public pools that have (we
hope) enacted strict safety procedures. Gas is very acidic, with a pH close to muriatic
acid, so these pools using it add a lot of base to counteract this.
Liquid chlorine is another type which is created by
bubbling the chlorine gas through a solution of caustic soda. The yellow liquid (stronger,
but chemically identical to bleach) has 10 - 15% available chlorine, and has a pH on the
other end of the scale at 13. Liquid Chlorine is called Sodium Hypochlorite (NaOCl), and
because it is already in solution, sodium-hypo produces hypochlorous acid instantly when
it contacts water. The liquid can be poured directly into the pool but it is recommended
to use a diaphragm or peristaltic pump. The use of liquid chlorine is more dominant in
larger commercial pools which have it delivered into 55 gallon vats. For most residential
pools, the lower cost seems to be outweighed by its difficulty in use and the amount of
acid required to counteract its pH of 13. Use care when handling as this chemical is
corrosive to just about everything.
Tri-chlor is a tablet form of chlorine and is short
for Trichloro-s-triazinetrione, a stabilized form of chlorine that has achieved a great
amount of use in the last ten years. "Stabilized" means that it has cyanuric
acid pressed into the tablet. Cyanuric, also called stabilizer or conditioner, is like
sunscreen for the chlorine molecule; an extender. Tri-chlor is created by
combining the salts of cyanuric acid and chlorine gas into a tablet or stick and is 90%
available chlorine. The pH is somewhat low at 3, so the pH in your pool may gravitate
downward. This form is slow dissolving so it works well in floaters or in-line
erosion feeders. Using tablets in the skimmer is not recommended because of the corrosive
nature of the chemical contacting metal pipes and equipment. This becomes more of a
problem when the filter pump is operated on a timer. Tablets have been known to strip out the
copper inside of a heater. They are an effective, yet expensive, means of controlling
algae. Tablets should also not be thrown
directly into the pool, they can stain and etch plaster and bleach and deteriorate vinyl.
Another member of the chlorinated iso-cyanurate
family is Di-chlor; Sodium
Dichloro-s-triazinetrione. Di-chlor is made in roughly
the same manner as tri-chlor; however, the product is much different. The pH is a very
acceptable 7, and it is manufactured in the form of granules, so it dissolves rapidly and
goes right to work on contaminants. Di-chlor has less chlorine, pound per pound, at only 62%
available chlorine. Because it contains cyanuric acid, it lasts longer than other un-stabilized forms of granular chlorine. It can be used as a shock treatment oxidizer or
for normal sanitation. Di-chlor's main drawback is it's
cost per pound of available chlorine. It
is perhaps the most expensive form of
chlorine available. (continued......)
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