It is vital to find out the bodily and chemical characterizations of crude oil by means of a crude oil assay, since they’re used in several areas within the petroleum refining business. The most common functions of petroleum assays are:
To offer extensive detailed experimental data for refiners to ascertain the compatibility of a crude oil for a specific petroleum refinery
To anticipate if the crude oil will fulfill the required product yield, quality, and production
To determine if throughout refining the crude oil will meet environmental and different requirements
To help refiners to make choices about changes in plant operation, development of product schedules, and examination of future processing ventures
To produce engineering firms with detailed crude oil analyses for their course of design of petroleum refining plants
To facilitate companiescrude oil pricing and to negotiate possible penalties resulting from impurities and other nondesired properties
A crude oil assay is a compilation of laboratory (physical and chemical properties) and pilot-plant (distillation and product fractionation) knowledge that characterize a specific crude oil. Assay analyses of whole crude oils are carried out by combining atmospheric and vacuum distillation items, which when mixed will present a true boiling-level (TBP) distillation. These batch distillation strategies, though taking between three and 5 days, allow the collection of a enough quantity of distillation fractions for use in additional testing. The values of the distillation ranges of the distilled fractions are often defined on the premise of their refinery product classifications. The commonest distillation ranges utilized in international assays of crude oils are reported in Desk 1.5.
Table 1.5. Typical Distillation Vary of Fractions in Petroleum Assays
Mild straight-run naphtha
Medium straight-run naphtha
Heavy straight-run naphtha
Gentle vacuum gasoil
Heavy vacuum gasoil
There are numerous forms of assays, which vary significantly in the amount of experimental info decided. Some include yields and properties of the streams used as feed for catalytic reforming (naphtha) and catalytic cracking (gas oils). Others give further details for the potential manufacturing of lubricant oil and/or asphalt. At a minimal, the assay ought to contain a distillation curve (sometimes, TBP distillation) for the crude oil and a selected gravity curve.
Essentially the most complete assay consists of experimental characterization of your complete crude oil fraction and various boiling-range fractions. Curves of TBP, particular gravity, and sulfur content are regular knowledge contained in a properly-produced assay. For example, assays of various Mexican crude oils are introduced in Desk 1.6. The API gravity of those crude oils ranges from 10 to 33°API. API gravity is a measure of the relative density of a petroleum liquid and the density of water (i.e., how heavy or gentle a petroleum liquid is compared to water). Though, mathematically, API gravity has no units, it is at all times known as being in “levels.” The correlation between specific gravity (sg) and degrees API is as follows (the precise gravity and the API gravity are each at 60°F):
Viscosity should be supplied at a minimal of three temperatures in order that one can calculate the sample viscosity at other temperatures. The most typical temperatures used to determine viscosity are 15.5, 21.1, and 25°C. If viscosities of the sample cannot be measured at these temperatures, the sample needs to be heated and higher temperatures are used, comparable to within the case of the ten and 13°API crude oils reported in Desk 1.6. As soon as viscosities at three temperatures can be found, a plot of a double logarithm (log10) of viscosity towards the temperature will be constructed, and viscosities at other temperatures might be obtained easily, as shown in Figure 1.1.
The characterization issue (KUOP or KWatson) of the Mexican crude oils reported in Desk 1.6 ranges from 11.5 to 12.0. The K issue will not be decided experimentally; fairly, it’s calculated using the following equation (for petroleum fractions):
the place MeABP (in degrees Rankine) is the mean common boiling point of the sample calculated with distillation curve data.
Normally, if Ok > 12.5, the sample is predominantly paraffinic in nature, while Okay < 10.0 is indicative of highly aromatic material. The characterization factor thus provides a means for roughly identifying the general origin and nature of petroleum solely on the basis of two observable physical parameters, sg and MeABP. More detailed relationships of the K factor to the nature of the sample are given in Table 1.7 . The characterization factor has also been related to other properties (e.g., viscosity, aniline point, molecular weight, critical temperature, percentage of hydrocarbons), so it can be estimated using a number of petroleum properties.
Table 1.6. Assay of various Mexican Crude Oils
10 ° API
13 ° API
Specific gravity, 60°F/60°F
D – 287
Kinematic viscosity (cSt)
At fifty four.4°C
Characterization factor, ,KUOP
Pour level ( ° C)
D – 97
Ramsbottom carbon (wt%)
Conradson carbon (wt%)
D – 189
Water and sediments (vol%)
D – 4007
Whole sulfur (wt%)
D – 4294
Salt content (PTB)
D – 3230
Hydrogen sulfide (mg/kg)
uOP – 163
Complete acid number (mg KOH/g)
Complete nitrogen (wppm)
Primary nitrogen (wppm)
uOP – 313
a hundred and fifty
nC7 insolubles (wt%)
Toluene insolubles (wt%)
D – 4055
Chloride content material (wppm)
D – 808
Determine 1.1. Kinematic viscosities of a number of Mexican crude oils.
Desk 1.7. Relationship of Kind of Hydrocarbon to the Characterization Factor
Type of Hydrocarbon
12.15 – 12.Ninety
Figure 1.2. True boiling-level curve of assorted Mexican crude oils.
Asphaltenes, which are generally reported as n- heptane insolubles, are, strictly talking, defined as the load share of n- heptane insolubles (HIs) minus the weight percentage of toluene insolubles (TIs) within the sample (wt% of asphaltenes = wt% of Hi – wt% of TI). For the crude oils given in Table 1.6 , their asphaltene contents are 24.Sixty five, 17.83, eleven.21, 1.Fifty six, and zero.57 wt% for the ten) API, 13°API, Maya, Isthmus, and Olmeca crude oils, respectively.
Figure 1.Three. API gravity of distillates versus average quantity proportion.
Figure 1.Four. Sulfur content of distillates versus average quantity share.
TBP distillations for Mexican crude oils are offered in Figure 1.2 . It is obvious that light crude oils which have excessive API gravity values present also the very best quantities of distillates [e.g., Olmeca crude oil (38.67°API) has 88.1 vol% distillates, whereas the 10° API has solely 46vol% distillates]. Figures 1.3 and 1.4 illustrate plots of API gravity and the sulfur content material of distillates against the average quantity percentage of distillates of the assorted crude Static And Dynamic Seals For Pyrolysis oils. Distillates of heavier crude oils have decrease API gravity and a higher sulfur content than these obtained from light crude oils.