ALL IMPORTANT INDICATOR NUMBER IN PETROLEUM (TAN ,CETANE, OCTANE)

                                                              TAN NUMBER 

The total acid number (TAN) is a measurement of acidity that is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. It is an important quality measurement of crude oil.

• The TAN value indicates to the crude oil refinery the potential of corrosion problems.
•  It is usually the naphthenic acids in the crude oil that cause corrosion problems. This type of corrosion is referred to as naphthenic acid corrosion (NAC).

TAN values may also be useful in other industries where oils are used as lubricants to determine oxidation and the subsequent corrosion risk to machinery.

TAN value can be deduced by various methods, including

• Potentiometric titration: The sample is normally dissolved in toluene and propanol with a little water and titrated with alcoholic potassium hydroxide (if sample is acidic). A glass electrode and reference electrode is immersed in the sample and connected to a voltmeter/potentiometer. The meter reading (in millivolts) is plotted against the volume of titrant. The end point is taken at the distinct inflection of the resulting titration curve corresponding to the basic buffer solution.
• Color indicating titration: An appropriate pH color indicator e.g. phenolphthalein, is used. Titrant is added to the sample by means of a burette. The volume of titrant used to cause a permanent color change in the sample is recorded and used to calculate the TAN value.
• Spectroscopic methods: as with many chemical parameters, spectroscopy can be used to make fast, accurate measurements once calibrated by a reference method. Mid and near infrared spectroscopy are most commonly used for this purpose. Spectroscopic methods are valuable as they can also be used to simultaneously measure a number of other parameters and do away with the need for wet chemistry.

 

                                                            CETAN NUMEBR

• Cetane number (cetane rating) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. 
• It plays a similar role for diesel as octane rating does for gasoline.
•  The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel fuel's quality include (but are not limited to) energy content, density, lubricity, cold-flow properties and sulphur content.  

                                     OCTANE NUMBER 

• An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. 
• The higher the octane number, the more compression the fuel can withstand before detonating. 

NOTE:-  Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's capability against compression.

Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines, which may yield higher power for these engines. Such higher power comes from the fuel's higher compression by the engine design, and not directly from the gasoline

In contrast, fuels with lower octane (but higher cetane numbers) are ideal for diesel engines because diesel engines (also called compression-ignition engines) do not compress the fuel, but rather compress only air and then inject fuel into the air that was heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, which is ignited near the end of the compression stroke by electric spark plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Using gasoline with lower octane may cause engine knocking (pre-ignition)