petroleum test methods

petroleum test methods

Petroleum is classified according to several criteria and tests, starting from crude oil to the final products. These tests determine the classification of petroleum from light to heavy and know the percentage of containing types of hydrocarbons (paraffin - naphthene’s - aromatics), impurities, and minerals, which affect The reactions and material used, and for this reason, these tests are very important to know the quality of oil and to determine the variables of the process and determine the final products that can come out of it, and its price in the market.

We can classify these tests as follow:

1.    APPEARANCE:   (Visual, Color, Particulate Contamination)

2.    COMPOSITION:  (Acidity, Aromatics, Olefins, Sulfur)

3.    VOLATILITY: (Density, Distillation, Vapor Pressure, Flash Point /Fire Point)

4.    COMBUSTION:(Antiknock Quality (Ron / Mon), Ignition Quality (Cetane No), Burning Quality (Calorific Value))

5.    FLUIDITY: (Viscosity, Viscosity Index, Penetration)

6.    STABILITY:(Induction Period, Gum Content)

7.    CHANGE OF STATE:(Freezing Point, Pour Point, Cloud Point, Drop Point for Grease, Softening Point)

8.    CORROSIVITY: (Total Sulphur, Doctor Test, Acidity / Alkalinity, Copper / Silver Corrosion)

9.    OTHERS:(Ash / Sediments/ Carbon Residue, Asphaltenes, water Tolerance Metal Content, Benzene/Aromatics, Olefins/PAH)

A most important test of crude oil:

     In this paragraph we going to talk about the most important tests of crude oil that determined the quality and the price:

API GRAVITY:

API is a gravity measuring parameter for all petroleum oil. This is related as:

API = 141.5/s − 131.5 

where “s” is the specific gravity of oil at 15.5°C (60°F) with respect to water at the same temperature. The greater the specific gravity, the lower the API gravity. For water, API gravity becomes 10 and for oil, it is greater than 10. Crude oil having an API gravity as low as 9 has been found, which is heavier than water but most commonly it is always greater than 10. Thus, high API gravity crude oil is rich with lighter fractions and thus costlier. The price of oil is fixed depending on the API gravity as it is an easily measured entity and is directly related to the presence of lighter hydrocarbons.

 

CHARACTERISATION FACTOR

The next entity is the characterization factor (CF), which is most commonly used with API gravity to judge the quality and many physical properties of crude oil and its products. This is defined as the ratio of cubic root of the mole average boiling point (Tb, in Rankine) of oil to its specific gravity (s) at 15.5°C. Thus, it is expressed as:

CF = (Tb)1/3/s.

 
BOTTOM SEDIMENT AND WATER

Bottom sediment and water (BSW) is a measure of the quantity of residual sediment mostly settleable from the crude oil (if sufficient time is allowed for settling) and water. This may contain both heavy asphaltic hydrocarbon oil and non-hydrocarbon, such as inorganic salts. An amount of BSW is routinely tested for every batch of crude oil received in a refinery. Water, salt, and sediment are removed from the storage tanks, followed by electrical desalting. Throughout the world, petroleum products are tested according to the methods and equipment specified by the American Standard for Testing Materials (ASTM).

Initial Boiling Point (IBP):

          heating and vaporizing the crude oil by a gradual increase in temperature followed by collection after condensation. When crude oil is heated in a distilling flask, vapors start emanating

         as the temperature rises and these vapors are collected after condensation using ice-cold water. The temperature of vapor giving the first drop of condensate is reported as the initial boiling point (IBP), which may be above or below 0°C depending on the presence of the lowest boiling hydrocarbon in crude. This vaporizing phenomenon is so fast at the beginning that temperature measurement is quite uncertain as the vapor of the first drop is immediately followed by the mixture of vapors with increasing boiling points hence this must be noted in the shortest possible period (within 5–10 min) after the charge is heated.

True Boiling Point (TBP):

       Usually, the composition of crude oil varies from well to well and it is essential to have a separate TBP analysis for each batch of oil purchased before refining. Hence, the yields of light to heavy fractions will vary from crude to crude. A small variation in TBP analysis may have a wide variation in the chemical constituents of the boiling fractions. This analysis indicates the maximum possible yields of raw cuts of products that could be obtained by distillation. In a refinery, a distillation column is used to separate these cuts at large rates continuously, where the yields of the raw cuts are slightly different from the TBP analysis. In fact, a distillation column is designed based on the TBP analysis of crude oil. Crude oils having wide differences in TBP analysis cannot be distilled in the same column without sacrificing the yields and quality of the products. It is, therefore, inevitable that the design of a distillation column of a refinery must be done judiciously, depending on the availability of the crude oils, which may have little difference in TBP analysis.

The experience is heating 100 ml and vaporizing the crude oil by a gradual increase in temperature followed by collection after condensation. When crude oil is heated in a distilling flask, vapors start emanating as the temperature rises, and these vapors are collected after condensation using ice-cold water as heating is continued, more and more hydrocarbon vapors with increasing boiling temperature are separated from crude and collected as condensates. This process is continued with gradual heating until no further vaporization takes place. The vapor temperature and the volume of liquid condensates (fraction boiling point FBP) collected are measured and reported as the distillation analysis of crude oil.