Aerosoles

Analysis of the environmental impact of aerosol spray

Rafael Vidal Picho

Introduction

Some history about aerosol cans

The first aerosol sprays were invented in USA during the 1940s . It was used to protect american soldiers against some diseases caused by insects near the pacific. As a lot of units were produced , the stock was quite big and a big portion of this units went back to the north-american market .

As many of the inventions during the history, a military invention evolved in a non-military one. During the 50s and 60s the production of air fresheners or insecticides . The production was increased exponentially all around the world . The production methods were slightly improved, starting with simply aluminum in the following years another methods as the fusion of tin cans were used.

Not so far in the time , during the 70s, scientist discovered that the massive use of this sprays were damaging the ozone layer due to the CFC (Chlorofluorocarbon) . The industry as well as international organizations decided to put some order in that and forbid that components .

Nowadays , the industry is totally implicated with the environmental care with the maximum reduction of waste and recycling. The aerosol sprays are using recycled metal as well as other components substitutes of CFC.

In order to help the environment , 70 nations signed the Montreal Protocol . An agreement to drop off significantly the use of the CFCs in the next decade. Today the use of alternative propellants (we will explain later which ones) is totally common and helping to reduce the damage to the ozone layer.

How does an aerosol can work?

We can not fill the aerosol cans only with compressed gas, that would be totally ineffective ; because the gas should be at a potentially dangerous pressure and the can should be designed specially for a pressured recipient or , otherwise, the amount of gas in the can would be ridiculously low.

Normally , the gas is the vapor of a liquid with a slightly lower boil point than the environmental temperature . That means that inside the can, the vapor can be in equilibrium with its liquid ( with a higher pressure than the atmospherical one , but not so high ). As the propellant is in liquid state in the can , should be miscible with the useful element or dissolute in it.

Since the Montreal Protocol the most common substitutes are propane , n-butane and isobutane . Also dimethyl ether and methyl ethyl ether. The problem with those ones are that they are flammables . Nitrous oxide and carbon dioxide are also used as propellants for foodstuff . In the case of medicinal aerosol hydrofluoroalkane are the most used.

The modern aerosol can is composed by three main parts : the can , the valve and the “button” . The can use to be made by tin , and it could be made by two or three pieces of pressing metal putted together.

Aluminum cans are common as well but they are reserved for expensive products. The valve is crimped to the platform of the can, and the design of this component is important in determining the spray speed. The actuator is pressed by the user to open the valve.

We have different distribution system .For example for highly viscous products we use a piston barrier system ; in which we assure the separation between propellant and product. Also the spray speed is uniform and controlled.

Another one is with a “bag” in the system of the can. This system separes the product and the propellant with a multiple-layer bag hermetically sealed . Is a good system in order to extend the life cycle of the products. It is well known in the pharmaceutic industry and another products which require a complete separation between product and propellant.

Raw materials

Can

The cans are usually made by tin, aluminum or glass. Nowadays 75% of the cans are made by tin, 24% by aluminum and a small 1% by glass or plastic.

The extraction of this materiales is the same as in for another product that uses them so recycling them is a common and compatible practice with the waste management.

Tin is made by steel , with some pewter, passivated (sometimes with chromium) and a lacquer. Aluminum , which is even more resistant to corrosion, have also another lacquer.

Tin still more used mainly due to two reasons : price and resistance .

Propellant

As we said CFC were used until the late 80s when some scientist realized that the ozone layer was suffering a huge damage and 70 nations signed the Montreal Protocol in order to stop using CFC during the next decade.

CFCs come from saturated hydrocarbure. Are also used in refrigeration industry and , as we are analyzing right now, as a propellant of aerosol. The problem with this propellant is that they remain in the atmosphere between 50-100 years. There are not only one CFC , we have a lot of types :

-CFC12 : used at environmental temperature, used in car’s CC.

-CFC11: used to make holes in soft products.

-CFC113 : used to clean fat, glue and another wastes in electronic panels

Due to the scientific efforts of the last years a lot of alternatives to the CFC have been found the last years, the most popular ones are the hydrochlorifluoriccarb. (HCFC) and the hydrofluoricarbures (HFC) . Some of them are really useful because the components C-H are easily degraded by hydroxyl radicals from the troposphere. Also they have a low radioactivity and good protection against fir.

Anyway with the new technologies , specially in our case of the propellants , we can use different components (not HCFC or HFC) . As propellant we can use isobutane ,or dimethyl ether (mixed with water in order to drop off the flammability) .

Environmental impact

In the case of the can it depends on which material are we using for it , as the 99% are made by aluminum or tin we will focus o those two materials.

The good point with the tin cans is that they can be recycled ,theoretically, without limit using them again at the beginning of the process of the manufacturing of steel as a scrap metal. The only problem is the adding of pewter but is not a major problem nowadays. In the two main processes of production of steel , scrap metal is used as raw material. In the oxygen converter process we could use 25-35% of scrap metal and in the electric arc almost 100%.

Even though aluminum is the most common material in the earth , the extraction is not easy. Due to that recycling is an important point in environmental impact. An aluminum can takes 500 years to be fully degraded and if we throw two cans to the garbage we are wasting more energy more energy than one person uses in some poor countries. Aluminum recycling reduces a 95% the atmospherical contamination generated during its production and produce aluminum from recycled one uses a 90% less of the energy than in the primary process.

Anyway, for both : tin and aluminum, we can also sume up a few points concerning to the mineral extraction process :

-atmospherical dust from traffic , drilling , digging and clearing the place

-noise and emissions from the machines and vehicles

-alteration of the surface due to the paths

-alteration of the natural and historical resources.

Now we are going to talk about the environmental impact of the propellants, mainly the impact of CFCs.

Apparently the explanation about the “attack” of the CFC to the ozone layer is with a photochemical reaction . When the light hits on the molecule of CFC , an chlorine atom with a free electron is free, radical chlorine , really radioactive and really linkable with ozone what breaks its molecule.

The theories say that the reaction is catalytic reaction and a single chlorine atom would destroy 100000 ozone molecules. Even though some scientist say that the CFCs remain in the atmosphere more than 100 years, this is impossible if we analyze the weight of the CFC molecules, way more higher than the atmosphere density .

Later on , some studies proved that freons F11 and F12 reached maximum of 29-32 km and due to the required radiation to dissolve the molecule of CFC ; the radiation required to dissolve the CFC doesn’t reach the high of the first molecules because it is absorbed by the oxygen at over 45km.

Anyway, as we explained before, in 1987 , seventy different nations signed the Montreal Protocol to control the production and consumption of substances that destroy ozone . 1996 was established as the deadline to abandon the production and consumption of CFCs and the emergent countries had 10 years more to accomplish it.

Here we can see a NASA projection of stratospheric ozone, in Dobson units, if chlorofluorocarbons had not been banned.

As we see the ozone concentration or 2060 would have been close to zero with major damages in the life and cycle of the earth and environment.

Production processes

Can

First of all we will talk about the aluminum cans. As we said , aluminum is the most common material on earth. But the processes to get metallic aluminum from the minerals we can obtain directly are not enough chap yet.

The second most important process to extract aluminum is the electrolysis after the chlorine-alcali. Aluminum is mainly produced from the mineral bauxite what is converted afterwards in alumina and then it is used in another chemical reaction. Crushed bauxite is then dissolved under pressure and heated in digesters , mixing with lime and sodium we obtain

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