Analytical Techniques and Instrumentation

Combustion & Detection Techniques:

Combustion in simple words is burning or making a chemical change that produces heat & light (energy).

Combustion requires a compound and an oxidant. We see this process every day when natural gas burns in our stoves. Natural gas is the compound that burns with air (oxidant) and we see heat being produced, used for cooking. During welding, mixture of acetylene (fuel) and air (oxidant) produces lot of heat needed to melt and fuse metals. Therefore, essentially, combustion can be best understood when some fuel burns with oxygen.

Any material that can undergo combustion is called combustible material. All fuels are combustible.

Sulfur, chlorides and nitrogen are present in fuels (crude oil, diesel, gasoline, jet, bunkers, naphtha, blend stocks & other streams) as undesired impurities and can be detected and quantified by combustion methods as well, especially when needed to detect very low levels.

ASTM D 5453 detects sulfur to 1 ppm level by burning a known quantity of fuel with oxygen at very high temperature when sulfur is burned to sulfur dioxide (so2). This so2 is then exposed to a UV light and then measured by a photomultiplier tube detection system. The quantity of sulfur is measured by comparing the sulfur signal curve to a previously established calibration curve.

ASTM D4629 is a similar method for measuring nitrogen in fuels by combustion method down to 1 ppm level. The fuel undergoes combustion in the presence of oxygen at high temperature when nitrogen in the fuel is changed to oxides of nitrogen. Nitrogen is then measured by the chemiluminescence produced and detected the signal by photomultiplier tube detection system.

ASTM D 4929B is another method based on combustion followed by coluometric titration for organic chlorides in crude oil and other streams. Crude oil is first distilled to receive a naphtha cut. This naphtha is then washed and a small volume of naphtha is introduced into the combustion chamber along with a stream of 80% oxygen and 20% inert gas (like argon). The chlorides are converted to oxychlorides and then the resultant combustion gases dissolved and titrated using coulometric titration.