Petroleum refining

API gravity : measure of density of the petroleum fractions.ºAPI = 141.5/specific gravity – 131.5 ,specific gravity is measured at 60 ºF. Higher values of API gravity indicate lower specific gravity.

Flash point : temperature above which the product flashes forming a mixture capable of inducing ignition with air.

Fire point: temperature well above the flash point where the product could catch fire.

Cloud point : When a petroleum product is cooled, first a cloudy appearance of the product occurs at a certain temperature. This temperature is termed as the cloud point.

Pour point : Upon further cooling above cloud point, the product will ceases to flow at a temperature. This temperature is termed as the pour point.

Aniline Point : The lowest temperature at which an equal volume mixture of the petroleum oil and aniline are miscible is the aniline point.If the oil has more paraffin, it will require a higher temperature and thus higher aniline point in order to be miscible in aniline (for diesel fuels).

Smoke Point : The smoke point is a test measures the burning qualities of kerosene and jet fuel. It is defined as the maximum height in mm, of a smokeless flame of fuel.

Octane number : Iso-octane is given an octane number of 100, n-heptane is given a scale of 0. Therefore, the octane number of a fuel is equivalent to a mixture of a iso-octane and n-heptane that provides the same compression ratio in a fuel engine.Thus an octane number of 80 indicates that the fuel is equivalent to the performance characteristics in a fuel engine fed with 80 vol % of isooctane and 20 % of n-heptane

Cetane Number : The cetane number measures the ability for auto ignition and is essentially the opposite of the octane number. The cetane number is the percentage of pure cetane (n-hexadecane) in a blend of cetane and alpha methyl naphthalene which matches the ignition quality of a diesel fuel sample.

Crude chemistry : 84 – 87 wt % carbon, 11 – 14 % hydrogen, 0 – 3 wt % sulphur, 0 – 2 wt % oxygen, 0 – 0.6 wt % nitrogen and metals ranging from 0 – 100 ppm.

Crude Distillation : Crude oils are first desalted and then introduced with steam to an atmospheric distillation column. The atmospheric residue is then introduced to a vacuum distillation tower.

Atmospheric distillation unit (ADU) : It separates various ‘cuts’ of hydrocarbons namely, fuel gases, LPG, naptha, kerosene, diesel and fuel oil at close to atmospheric pressure. The heavy hydrocarbon residue left at the bottom of the atmospheric distillation column is sent to vacuum distillation column for further separation of hydrocarbons under reduced pressure.

Vacuum distillation unit (VDU) : heavy hydrocarbon residues from atmospheric distillation unit are sent to a Vacuum Distillation Column for further separation of hydrocarbons under reduced pressure.

Hydrotreater : removal of sulfur as H2S using Hydrogen.

Fluidized catalytic cracker : the unit is useful to transform desulfurized HVGO to lighter products such as unsaturated light ends, light cracked naphtha, heavy cracked naphtha, cycle oil and slurry is performed by FCC ( generate more lighter products from a heavier lower value intermediate product stream).

Naphtha splitter : It consists of a series of distillation columns which separates light naphtha and heavy naphtha.

Solvent Extraction : lube oil stock is treated by a solvent, such as N-methyl pyrrolidone (NMP), which can dissolve the aromatic components in one phase (extract) and the rest of the oil in another phase (raffinate). The solvent is removed from both phases and the raffinate is dewaxed.

Solvent Dewaxing :The raffinate is dissolved in a solvent (methyl ethyl ketone, MEK) and the solution is gradually chilled, during which high molecular weight paraffin(wax) is crystallized, and the remaining solution is filtered. The extracted and dewaxed resulting oil is called ‘‘lube oil’’.

Catalytic Reforming : In this process a special catalyst (platinum metal supported on silica or silica base alumina) is used to restructure naphtha fraction (C6–C10) into aromatics and isoparaffins. The produced naphtha reformate has a much higher octane number than the feed. This reformate is used in gasoline formulation and as a feedstock for aromatic production (benzene–toluene–xylene, BTX).

Hydrotreating : This is one of the major processes for the cleaning of petroleum fractions from impurities such as sulphur, nitrogen, oxy-compounds, chlorocompounds, aromatics, waxes and metals using hydrogen. The catalyst is selected to suit the degree of hydrotreating and type of impurity. Catalysts, such as cobalt and molybdenum oxides on alumina matrix, are commonly used.

Catalytic Hydrocracking : For higher molecular weight fractions such as atmospheric residues (AR) and vacuum gas oils (VGOs), cracking in the presence of hydrogen is required to get light products. In this case a dual function catalyst is used.It is composed of a zeolite catalyst for the cracking function and rare earth metals supported on alumina for the hydrogenation function. The main products are kerosene, jet fuel, diesel and fuel oil.

Catalytic Cracking : Fluid catalytic cracking (FCC) is the main player for the production of gasoline. The catalyst in this case is a zeolite base for the cracking function.The main feed to FCC is VGO and the product is gasoline, but some gas oil and refinery gases are also produced.

Alkylation : Alkylation is the process in which isobutane reacts with olefins such as butylene to produce a gasoline range alkylate. The catalyst in this case is either sulphuric acid or hydrofluoric acid. The hydrocarbons and acid react in liquid phase. Isobutane and olefins are collected mainly from FCC and delayed coker.

Isomerization : Isomerization of light naphtha is the process in which low octane number hydrocarbons (C4, C5, C6) are transformed to a branched product with the same carbon number. This process produces high octane number products.One main advantage of this process is to separate hexane (C6) before it enters the reformer, thus preventing the formation of benzene which produces carcinogenic products on combustion with gasoline. The main catalyst in this case is a Pt-zeolite base.

Delayed Coking : This process is based on the thermal cracking of vacuum residue by carbon rejection forming coke and lighter products such as gases, gasoline and gas oils. Three types of coke can be produced: sponge, shot and needle. The vacuum residue is heated in a furnace and flashed into large drums where coke is deposited on the walls of these drums, and the rest of the products are separated by distillation.

Flexicoking : In this thermal process, most of the coke is gasified into fuel gas using steam and air.The burning of coke by air will provide the heat required for thermal cracking. The products are gases, gasoline and gas oils with very little coke.

Visbreaking : In this mild thermal cracking process used to break the high viscosity and pour points of vacuum residue to the level which can be used in further downstream processes. In this case, the residue is either broken in the furnace coil (coil visbreaking) or soaked in a reactor for a few minutes (soaker visbreaker). The products are gases, gasoline, gas oil and the unconverted residue.