After Treatment Of Polycyclic Aromatic Hydrocarbons

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AFTER-TREATMENT OF PAH IN AUTOMOTIVE
1. Summary
2. Motivation
2.1. Environmental issues
2.2. Health issues
2.3. Laws and regulations
3. Objectives
3.1. Control techniques
3.2. Economics 4. Introduction
Polycyclic Aromatic Hydrocarbons (PAHs) consist of two or more benzene-ringed compounds made of only carbon and hydrogen. Compounds which are made of two rings are known as di- aromatics whereas those made of three benzene rings are known as tri- aromatics and so forth. As the number of rings increase, molecular weights of these compounds also increase and the compounds tend towards higher thermodynamic stability. Most common examples of PAHs are naphthalene, phenanthrene, pyrene etc.
Further, as these compounds become heavier, the particle’s size increases and hence these compounds are also known to be pre-cursors of soot formation. In this report we will only be studying PAH in the vapour phase whose particle sizes will be restricted to less than 1.5 nm. Following diagram shows the formation of PAH resulting in soot, in a premixed flame. Figure 1: Formation of PAH followed by soot. (Howard originally in Bockhorn) In a study carried out by Y. Lev et al, it is seen that the concentration of total PAH is around 0.25 ng to 1 ng per µg of total particulate matter depending on the number of rings, which is a very small quantity of the total hydrocarbon emission from automotive. Figure 2: Ratio of total PAH to PM depending on the size of the compound [Y.Lev]
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