Pritam SharmaDepartment of ChemistryBahra university, Shimla Hills

Urea: As an effective cure to emission of NOx

How we all are walking towards the

Dead Silence?

Pollution is the introduction of contaminants into the natural environment that cause adverse changes in the environment.

Pollution can take the form of chemical substances, gases & wastes. Since the components of pollution can be either foreign substances/energies or naturally occurring contaminants.

Pollution are of following types:-1. Air pollution 2. Soil contamination

3. Light pollution4. Littering

5. Noise pollution 6. Radioactive contamination

7.Water pollution8. Plastic pollution.

Air pollution is the biggest problem in the modern life, as the number of motor vehicle and industries increases day by day.

POLLUTION

AIR POLLUTION

The release of chemicals and particulates matter into the atmosphere.

Common gaseous pollutant includes carbon monoxide, sulphur dioxide chlorofluorocarbon(CFCs) and oxides of nitrogen (NOX ) produced by industry

and motor vehicles.

Photochemical ozone and smog are created as oxides of nitrogen and HC react to sunlight.

Oxides of nitrogen are the major problem in today’s life because it is exhausted by both industries and motor vehicles and it is carcinogenic in nature. Which infects lungs of human as well as animal and also effecting activities of nature.

Oxides of Nitrogen Two of the most toxicology significant compound of nitrogen are nitric oxide (NO) and nitrogen dioxide (NO2).

NOx are produced during combustion, especially at high temperature.

The biggest contribution has nitric oxide (NO). Its content in flue gas is in the range of 100-1000 mg/m³.

The next contribution is nitrogen dioxide (NO2) in proportion 5-10% of NO. Its content in flue gases in the range of 10-100 mg/m³.

Now Question comes to mind that how urea used to be cure environment from oxides of Nitrogen ?

UREA is also named as carbamide in an organic chemistry with chemical formula CO(NH2)2. It is a colorless, odorless and have high solubility in water, and its non-toxic.

Urea is widely used as fertilizer as a source of nitrogen in field of agriculture and as well as it is also used for the reduction of emission of NOx.

Urea is used as a DEF (Diesel Exhausted Fluid). Diesel Exhaust Fluid is a non-hazardous solution which is 32.5% urea and 67.5% de-ionized water.

DEF is sprayed into the exhausted stream of diesel vehicles to break dangerous NOx emission into harmless nitrogen and water molecule.

Urea spraying is called Urea Decomposition/Hydrolysis Of Urea.

UREA CHEMISTRY

SCR is called Selective Catalytic Reduction in which we inject urea by decomposing into ammonia. This SCR system is totally depends on the working efficiency of catalyst. The catalyst are Vanadium oxide (also called Vanadium-SCR) or metal substituted zeolite have different operating temperature windows and must be carefully selected for SCR process.

SELECTIVE CATALYTIC REDUCTON

WHY UREA DECOMPOSITION ?Here urea used as reductant by decomposing it into ammonia, we don’t use aqueous or anhydrous ammonia as reductant directly to motor vehicles except industries, because of following reason:-

Pure anhydrous ammonia is extremely toxic and difficult to store but need no further conversion to operate with in SCR. It is typically favoured by large industrial SCR operator, because of its toxic nature we can’t use it.

Aqueous ammonia must be vaporised in order to use, but it is safer to store and transport than anhydrous ammonia. Ammonia –SCR has been used in industries process, in stationary diesel engines.

Urea is he safest to store but require conversion to ammonia immediately for exhausted gases (i.e. NOx) through thermal decomposition in order to be use as an effective reductant. It has been adapted for mobile diesel engines in both light and heavy duty applicants.

Ideally, injected urea decomposes to ammonia (NH3), according to chemical

reaction...

Since, this ammonia is then treated with exhausted gas i.e. Nitric oxide.

UREA DECOMPOSITION/HYDROLYSIS OF UREA

H2N-(CO)-NH2 + H2O + O2 (HEAT) → NH3 + HO-C≡N (ISOCYNIC ACID)HO-C≡N + H2O (HEAT) → NH3 + CO2 (min. Quantity)

TREATMENT OF NOx WITH AMMONIA

2NH3 + NO + NO2 ↔ 2N2 + 3H2O

THANK YOU