It’s important to find out the bodily and chemical characterizations of crude oil via a crude oil assay, since they’re used in different areas in the petroleum refining industry. The most typical purposes of petroleum assays are:

To provide extensive detailed experimental data for refiners to ascertain the compatibility of a crude oil for a particular petroleum refinery

To anticipate if the crude oil will fulfill the required product yield, high quality, and production

To find out if during refining the crude oil will meet environmental and different requirements

To assist refiners to make choices about modifications in plant operation, growth of product schedules, and examination of future processing ventures

To provide engineering corporations with detailed crude oil analyses for their process design of petroleum refining plants

To facilitate companiescrude oil pricing and to negotiate possible penalties because of impurities and other nondesired properties

A crude oil assay is a compilation of laboratory (bodily and chemical properties) and pilot-plant (distillation and product fractionation) data that characterize a specific crude oil. Assay analyses of entire crude oils are carried out by combining atmospheric and vacuum distillation units, which when combined will provide a true boiling-level (TBP) distillation. These batch distillation methods, though taking between 3 and 5 days, allow the collection of a sufficient amount of distillation fractions for use in additional testing. The values of the distillation ranges of the distilled fractions are usually defined on the basis of their refinery product classifications. The commonest distillation ranges used in international assays of crude oils are reported in Table 1.5.

Desk 1.5. Typical Distillation Range of Fractions in Petroleum Assays

TBP Distillation

Range (°C)

Distillate

IBP-71

Gentle straight-run naphtha

71-177

Medium straight-run naphtha

177-204

Heavy straight-run naphtha

204-274

274-316

Kerosene

316-343

Straight-run gasoil

343-454

Gentle vacuum gasoil

454-538

Heavy vacuum gasoil

R 538°C+

Vacuum residue

There are various types of assays, which range considerably in the quantity of experimental data determined. Some embody yields and properties of the streams used as feed for catalytic reforming (naphtha) and catalytic cracking (gas oils). Others give further particulars for the potential manufacturing of lubricant oil and/or asphalt. At a minimum, the assay ought to include a distillation curve (typically, TBP distillation) for the crude oil and a selected gravity curve.

Essentially the most full assay contains experimental characterization of your entire crude oil fraction and numerous boiling-range fractions. Curves of TBP, particular gravity, and sulfur content are normal information contained in a well-produced assay. As an example, assays of varied Mexican crude oils are offered in Table 1.6. The API gravity of these crude oils ranges from 10 to 33°API. Kinetic Energy Petroleum Refinery API gravity is a measure of the relative density of a petroleum liquid and the density of water (i.e., how heavy or mild a petroleum liquid is in comparison with water). Though, mathematically, API gravity has no units, it’s all the time referred to as being in “levels.” The correlation between specific gravity (sg) and degrees API is as follows (the specific gravity and the API gravity are both at 60°F):

Viscosity should be offered at a minimum of three temperatures so that one can calculate the pattern viscosity at different 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 those temperatures, the sample must be heated and higher temperatures are used, equivalent to in the case of the 10 and 13°API crude oils reported in Table 1.6. As soon as viscosities at three temperatures are available, a plot of a double logarithm (log10) of viscosity in opposition to the temperature can be constructed, and viscosities at other temperatures can be obtained easily, as shown in Determine 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 Ok issue just isn’t decided experimentally; fairly, it’s calculated using the next equation (for petroleum fractions):

the place MeABP (in levels Rankine) is the mean common boiling level of the sample calculated with distillation curve information.

Typically, if Ok > 12.5, the pattern is predominantly paraffinic in nature, whereas Ok < 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.

Desk 1.6. Assay of assorted Mexican Crude Oils

ASTM Method

Crude Oil

10 ° API

13 ° API

Maya

Isthmus

Olmeca

Particular gravity, 60°F/60°F

D-1298

1.0008

0.9801

zero.9260

0.8584

0.8315

API gravity

D – 287

9.89

12.87

21.31

33.34

38.67

Kinematic viscosity (cSt)

D-445

At 15.5°C

299.2

16.0

5.Four

At 21.1°C

221.6

12.5

four.6

At 25.0°C

19,646

181.4

10.Three

At 37.8°C

5,102

At fifty four.4°C

7,081

1,235

At 60.0°C

4,426

At 70.0°C

2,068

Characterization issue, ,KUOP

UOP-375

11.50

11.60

eleven.71

11.Ninety five

12.00

Pour level ( ° C)

D – 97

+ 12

zero

-33

-39

Ramsbottom carbon (wt%)

D-524

20.67

16.06

10.87

4.02

2.10

Conradson carbon (wt%)

D – 189

20.42

17.94

11.42

four.Eighty five

2.76

Water and sediments (vol%)

D – 4007

1.40

0.10

<0.05

< 0.05

Whole sulfur (wt%)

D – 4294

5.72

5.35

three.57

1.Forty six

0.Ninety nine

Salt content (PTB)

D – 3230

744.0

17.7

15.Zero

four.1

3.9

Hydrogen sulfide (mg/kg)

forty four

fifty nine

Mercaptans (mg/kg)

uOP – 163

/p>

sixty five

75

Whole acid quantity (mg KOH/g)

D-664

0.48

0.34

zero.30

zero.Sixty one

zero.46

Complete nitrogen (wppm)

D4629

5650

4761

3200

1467

737

Basic nitrogen (wppm)

uOP – 313

1275

1779

748

389

one hundred fifty

nC7 insolubles (wt%)

D-3279

25.06

18.03

eleven.32

1.65

zero.Sixty eight

Toluene insolubles (wt%)

D – 4055

0.Forty one

0.20

0.09

zero.Eleven

Metals (wppm)

Atomic absorption

Nickel

94.2

83.4

fifty three.Four

8.9

1.6

Vanadium

494.0

445.0

298.1

37.1

8.0

Total

588.2

528.4

351.5

46.0

9.6

Chloride content material (wppm)

D – 808

86

four

10

9

Determine 1.1. Kinematic viscosities of several Mexican crude oils.

Desk 1.7. Relationship of Sort of Hydrocarbon to the Characterization Factor

Ok Issue

Sort of Hydrocarbon

12.15 – 12.Ninety

Paraffinic

eleven.50-12.10

Naphthenic-p araffinic

eleven.00-11.45

Naphthenic

10.50-10.Ninety

Aromatic-naphthenic

10.00-10.Forty five

Aromatic

Figure 1.2. True boiling-point curve of various Mexican crude oils.

Asphaltenes, that are generally reported as n- heptane insolubles, are, strictly talking, defined as the burden percentage of n- heptane insolubles (HIs) minus the load share of toluene insolubles (TIs) in the pattern (wt% of asphaltenes = wt% of Hi – wt% of TI). For the crude oils given in Desk 1.6 , their asphaltene contents are 24.Sixty five, 17.83, eleven.21, 1.Fifty six, and 0.57 wt% for the ten) API, 13°API, Maya, Isthmus, and Olmeca crude oils, respectively.

Figure 1.Three. API gravity of distillates versus average volume proportion.

Figure 1.4. Sulfur content material of distillates versus average quantity proportion.

TBP distillations for Mexican crude oils are introduced in Figure 1.2 . It is evident that mild crude oils which have excessive API gravity values current additionally the very best quantities of distillates [e.g., Olmeca crude oil (38.67°API) has 88.1 vol% distillates, whereas the 10° API has only 46vol% distillates]. Figures 1.3 and 1.4 illustrate plots of API gravity and the sulfur content material of distillates against the typical volume percentage of distillates of the various crude oils. Distillates of heavier crude oils have lower API gravity and a better sulfur content than those obtained from light crude oils.