CONSTRUCTION OF THE DEVICEThe device is made to separate pollutants Essay

CONSTRUCTION OF THE DEVICE:

The device is made to separate pollutants by chemical scrubbing. It consists of:

A main body–

It is the cuboidal shell of the device where the cleaning process takes place. In the prototype it is 20in tall, 6in long and 6in wide. The body is made up of stainless steel for its property to resist corrosion and having high melting point. This is the part where various assembly of the device is fixed and also various chemical reaction will take place.

These reactions are all exothermic in nature and will produce lot of heat. Thus, device is made up of a conducting material. There is 6 inches pipe with the cross-section of 2 inches diameter welded on it as main protrusion to connect the connection tube and used as inlet of exhaust gases.

Connection tube –

Connection tubes are responsible for transfer of exhaust gases to inlet of the main body. These gases have a very high temperature of about 100? to 150? and also have a high pressure.

Thus tubes are chosen so they can endure high temperature and pressure. For this experiment, vulcanised rubber is chosen.

Saw-dust cleaner –

It is actually a filter device, used to separate shoot particles, especially unburnt carbon. It is made up of cylindrical vessel, truncated at both ends and filled with saw dust. The saw dust act as fine particles which collides with the shoot particles and adsorp them. The device is made up of a thick material, which will have ability to withstand pressure created due to semi-plugging the exhaust gas.

Chemical chamber –

The system uses a chemical wet scrubbing process to clean the pollutant particles. For this purpose, a chamber is made in the main box. It has upper and lower edge sealed by the metal sieve which as small holes. This make the chamber gas permeable and also have capacity to hold the packing material. Packing material used is bitumen coal.

Distribution System –

This system is responsible for the uniform distribution of the scrubbing material over the chamber. It is made up of a bucket to be used as overhead tank which can be replaced by a normal bucket with a suitable motor. There is rubber pipe sealed at one end. The other end of the pipe is connected to the tap attached to the bucket. This pipe is pierced with number of holes. When scrubbing material flows in the pipe, it spills out of these holes. The pipe is arranged such that it will reach most of the places and thus chemical is distributed.

?

DESCRIPTION:

The exhaust gases is made to pass through a saw dust cleaner with the help of connection tubes before they go into the setup device. In the device, an exhaust fan is present just below the entry point. Its purpose is to create forced draught in the device so that all the gases move upwards. In the middle section of the device, there present bituminous coal which acts as absorber to absorb various pollutants particles. A continuous shower of aq. NaOH solution is poured on the bituminous coal. Thus, various reactions happens converting the oxides of carbon, nitrogen, sulphur into their respective salts and water. Most of the water gets vaporised due to the large heat produced during the reaction, rest of the water containing all these salts flow from the bottom of the device where it is collected in order to perform confirmatory tests on it in chemistry lab to check presence of these salts. The sample thus collected after using 2 L of NaOH was about 150 mL-200 mL.

?

POLLUTANTS AND THEIR REACTIONS:

Carbon Dioxide (CO2):

The balanced equation:

CO2 (g) + 2NaOH(aq) ? Na2CO3(aq) + H2O(l)

1 mol of CO2 will react with 2 molNaOH to produce 1 mol Na2CO3.

?rH?= -171.3 kj/mol

Nitrogen Dioxide (NO2):

The balanced equation:

2NO2(g) + 2NaOH(aq) ? NaNO2(aq) + NaNO3(aq) + H2O(l)

2 mol of NO2 will react with 2 mol of NaOH to produce 1 mol each of NaNO2 and NaNO3 .

?rH?= -328kj/mol

Sulfur Oxides (SOX):

The balanced equation:

SO2 (g)+ 2NaOH(aq) ? Na2SO3(aq) + H2O(l)

Sulfur dioxide reacts with sodium hydroxide to produce sodium sulfite and water.

?rH?= -679.75kj/mol

Particulate Matter (PM):

Exhaust particulates mainly consists of small solid primary soot particles of diameters 40nm and their agglomerates of diameters up to 1 µm as well as nucleation mode particles almost entirely of condensed liquid.

A part of it can be filtered using saw dust collector put in between the device and the engine. Some of it gets absorbed in the wet charcoal used as absorbent in device.

CONFIRMATORY TESTS DONE IN LABORATORY TO CHECK EXISTENCE OF DIFFERENT SALTS :

Confirmatory tests for anions are performed by using water extract when salt is soluble in water and by using sodium carbonate extract when salt is insoluble in water .We have salts soluble in water, so only ,water extract will be used.

8.1 TEST FOR CARBONATE IONS (CO32-):

Take salt in a test tube, adddilute sulphuric acid to it.

CO2 gas is evolved with brisk effervescence which turns lime water milky.

On passing the gas for some more time, milkiness disappears.

REACTIONS INVOLVED:

If there is effervescence with the evolution of a colourless and odourless gas on adding dil.H2SO4 to the salt, this indicates the presence of carbonate ion.The gas turns lime water milky due to the formation of CaCO3.

Na2CO3 + H2SO4? Na2SO4 + H2O + CO2

Ca(OH)2 + CO2 ? CaCO3 + H2O

If CO2 gas is passed in excess through lime water, the milkiness produced disappears due to the formation of calcium hydrogen carbonate which is soluble in water.

CaCO3 + CO2 + H2O?Ca(HCO3)2

Result of test = Positive

8.2 TEST FOR SULPHITE ION (SO32-):

On treating sulphite with warm dil. H2SO4, SO2 gas is evolved which is suffocating with the smell of sulphur.

Na2SO3 + H2SO4?Na2SO4 + H2O + SO2

The gas turns potassium dichromate paper acidified with dil. H2SO4 green

K2Cr2O7 + H2SO4 + 3 SO2?K2SO4 + Cr2(SO4)3 + H2O

An aqueous solution or sodium carbonate extract of the salt produces a white precipitate of barium sulphite on addition of barium chloride solution.

Na2SO3 + BaCl2 ? 2NaCl + BaSO4

This precipitate gives following tests.

This precipitate on treatment with dil. HCl dissolves due to decomposition of sulphite by dil.HCl. Evolved SO2 gas can be tested.

BaSO3 + 2HCl ? BaCl2 + H2O + SO2

Precipitate of sulphite decolourises acidified potassium permanganate solution.

BaSO3 + H2SO4 ? BaSO4 + H2O + SO2

2KMnO4 + 3H2SO4 ? K2SO4 + 2MnSO4 + 3H2O + 5O

SO2 + H2O + O ? H2SO4

Result of test = Positive

8.3 TEST FOR NITRITE ION (NO2-):

On treating a solid nitrite with dil. H2SO4 and warming, reddish brown fumes of NO2 gas are evolved.

Addition of potassium iodide solution to the salt solution followed by freshly prepared starch solution and acidification with acetic acid produces blue colour.

2NaNO2 + H2SO4? Na2SO4 + 2HNO2

3HNO2? HNO3 + 2NO + H20

2NO + O2? 2NO2

Result of test = Positive

?

CALCULATIONS:

Total heat emitted = sum of heat of all reactions occurred in the setup

=171.3kJ/mol + 328kJ/mol + 679.75kJ/mol

=1179.05kJ/mol

The temperature of water we pour in the setup is assumed to be 25?C.

Heat required by water to reach 100?C = mC?T

=1kg x 4.2kJkg-1?C-1×75?C

=315kJ

m denotes mass of water in kg

C denotes heat capacity of water in kJkg-1?C-1

and?T denotes change in temperature.

Heat of vaporisation of water = 2257.2kJ/kg

Total heat required for vaporisation of water if its initial temp. is 25?C

=315kJ + 2257.2kJ

=2572.2kJ

Thus, 2572.2kJ of heat will be required for 1 litre of water to vaporise.

Total Moles of NaOH used in these reactions = 2

Moles of NaOH required to produce 2572.5kJ of heat= (2?1179.05)/2572.2

= 5.5

Thus we would need 5.5 moles of NaOH for vaporising 1L of water.

Thus Molarity of Solution required,

= (Moles of NaOH)/(Volume of solution)

= 5.5/1

=5.5 M

Thus Molarity of solution is 5.5M.

Thus mass of NaOH pellets to be dissolved in 1L of water is =5.5?40

=220g