Question

Explain the meaning of the pour point, flash point for crude oil

Answer 1

Actually the Pour point and flash point are mainly related to the petroleum products i.e. after refining this crude oil but the knowledge of flash point and pour point is equally important for crude oil as well.

I will start in this way: When the crude oil transportation needs to take place the most important thing which is focussed on is the frictional effects in the pipe and how the multiphase flow will occur.This is because the crude oil is a mixture of parffins,aromatics,asphaltenes and other lower and heavy molecular weight compounds.So during the transport of crude oil the crude oil gets heated due to viscous dissipation and may form vapour which if brought in contact with little spark may catch fire but again it depends on the ignition temeprature of mixture.Now coming to the main point:

Flash point : This is defined as the temperature at which the crude oil vapours formed at particular temperature may ignite or spark for a second and beyond which any increase in temperature may catch fire.Actually this might look a hazy definition but it is actually so.You can understand its significance in this way:the diesel engine which are installed in automobiles are made of materials which can sufficiently resist high temperature and can exchange heat easily because due to rapid compression of diesel in the engine increases the temperature of diesel because of dissipative effects like friction and hence form the vapour mixture and if this vapour mixture comes into contact with fire,it may get a spark and then further fire.This is true for other petroleum products like petrol,kerosene also.

Testing Method for flash Point: In lab we put the mixture for which flash point needs to be tested in a container and place the entire sample in a hood.Now a source for ignition is brought into the contact with the vapour of mixture just above it for a fraction of seconds to check whether the mixture is ignitable at not.The temperature corresponding to which we get a spark ,we usully report a temperature below that for flash point.If we increase temperature above this then this mixture can catch fire also for any ignition with fraction of second itself.This test is usually done for lower boiling point products like kerosene,diesel,petrol because they can form ignitable mixture at lower temperature.

Pour Point : The crude oil when fractionated in adistillation column,petroleum products like kerosene,ATF,diesel,etc. are drawn from the column.So when they are cooled down it is possible at that at certain point they ceases to flow depending on the average molecular weight of the mixture.Now what happens when a crude oil mixture is cooled down at certain temperature it gets waxy apperance,which is called as cloud point.upon further reduction of this temperature the flow property of the mixture ceases and we call that temperature as Pour point.This pour point is also a relative indication of whether our crude contains higher paraffinic amount or aromatic compounds,lower the pour point lower the paraffinic content,as paraffins are heavy molecular weight compound for same number of carbon as compared to aromatics and thus lower pour point and vice-versa.This is usually important from the purpose of storage and transportation of petroleum products also.