DE2637401C3 - Process for the separation of individual n-alkanes from crude oil - Google Patents

Description

The invention relates to a process for separating individual n-alkanes from crude oil, according to the preceding patent claim.

n-Alkanes (paraffin hydrocarbons) are widely used in various areas of petroleum chemistry. They are used in the production of synthetic fatty acids, higher fatty alcohols, tri-olefins, biodegradable surfactants (detergents), chlorinated paraffins, which are used in the production of lubricating oil additives, plasticizers, fireproof fabrics and paper. One of the most important uses of n-alkanes is microbiological synthesis, namely the production of synthetic protein for cattle and poultry fattening based on n-paraffins.

The n-alkanes, which are the raw material for all the production processes mentioned, are subject to ever higher requirements with regard to the content of actual n-alkanes and admixtures, especially aromatic hydrocarbons.

Particularly strict requirements are placed on the raw material for the production of higher fatty alcohols, artificial protein and biologically degradable sulfonates obtained by sulfonation. This raw material should not contain more than 0.01% aromatic hydrocarbons, at least 99.0% base material and, in the production of protein, no carcinogenic 3,4-benzopyrene.

The &eegr;-paraffins used in the known processes mostly have the hydrocarbon composition Ci _O -C ₂ 4. A particularly promising raw material for the production of detergents, emulsifiers and additives are only individual &eegr;-paraffins with a very high degree of purity.

There are a number of processes for the production and separation of n-alkanes for large-scale purposes.

One of the known processes is the Fischer-Tropsch synthesis. The process consists in

A mixture of hydrogen and carbon monoxide is passed over an iron-containing catalyst at a temperature of 160 to 420 ⁰ C or a cobalt-magnesium catalyst at a temperature of 160 to 200 ⁰ C and at a pressure of 7.8 to 9.8 bar. During the synthesis, a mixture of n-paraffin hydrocarbons is formed with a boiling range that depends on the conditions of the synthesis. The n-alkane obtained is fractionated by vacuum distillation into gasoline, kerosene, gas oil fraction distillates and the bubble residue.

To separate the individual n-alkanes, each of the fractions obtained is subjected to a sharp rectification to obtain narrow-boiling concentrate fractions which contain 70 to 90% by weight of one of the individual n-alkanes.

Each of the concentrates obtained is subjected to another sharp rectification, whereby n-alkanes with a base material content of 94 to 97 wt.% are obtained.

For the production of n-alkanes of the required degree of purity, an additional purification of the obtained n-alkanes with sulphuric acid followed by neutralisation with aqueous alkali solution, washing of the

Alkalis with water, drying and recrystallization under isothermal conditions required. \L

Another method for the separation of n-alkanes is the method for adsorption of n-alkanes from I/

Petroleum distillates on molecular sieves (zeolites). The process requires fractionation and purification '»*

of the adsorption products. f

One of the promising processes for separating n-alkanes from crude oil is a process using <*

use of carbamide (see for example JP-PS 15 376, FR-PS 14 08 798, and DE-AS 9 54 635). "*

In some of these processes, carbamide is used in its crystalline state, in others in the form of its _v

Solutions, for example aqueous solutions. The processes are carried out according to different technological t

Schemes were carried out, the reactors either with stirring of the reaction mass or with pumping through the *■

Starting Rchcrdcls inserted through cmc stationary layer of crystalline carbarnide on support. &mdash;

These processes make it possible to separate only the sum of the η-paraffins from the crude oil, without separating them into individual components at this stage. The purity of such n-alkanes without additional purification is 97 to 99%. To produce individual η-paraffins with a purity of 99.0 to 99.5% by weight of the base material, in addition to the stage of separating the sum of the η-paraffins from the crude hydrocarbons, the following stages of additional treatment are required:

a) Rectification, which requires as many columns as the number of individual hydrocarbons to be separated:

b) sulphuric acid and/or adsorption and/or hydro-purification of each individual η-paraffin; in the case of sulphuric acid purification, alkaline washing and rinsing with water of each individual n-paraffin is required until a neutral reaction is achieved;

c) Isothermal recrystallization of each individual n-paraffin.

Thus, all modern processes for producing a single n-alkane with a purity of 99.0 to 99.5% consist of at least 4 to 5 steps.

Finally, it is known to carry out complex formation with solid carbamide in the presence of activators (DD-PS 26 356). Compared to this state of the art, the subject matter of the invention differs with regard to a very specific management of the feed product.

It is known that any n-alkane forms a complex with carbamide in a very wide temperature range, which is not limited by the lower temperature limit

The upper limit of complex formation is the maximum temperature at which complex formation of the individual n-alkane with the crystalline carbamide begins and quantitatively ends.

If the n-alkane and the carbamide are not sufficiently pure, the complex formation is carried out in the presence of an activator.

Examples of activators that can be used are acetone, methyl ethyl ketone, lower alcohols and other known activators.

The amount of activator depends on the chemical composition of the raw material and is proportional to the content of substances that inhibit complex formation (resinous substances or active, sulphur-containing compounds).

In order for the respective n-alkane to be separated from the multicomponent mixture with other hydrocarbons at the temperature at the upper limit of complex formation with the crystalline carbamide, it is necessary that this is an n-alkane with the highest molecular weight in this mixture (with maximum n) . If, for example, all n-alkanes with η = 10 to 24 are present in the mixture, only the n-alkane with η = 24 needs to be separated from it.

n-Alkanes with a number of carbon atoms in the molecule of π <24 cannot form a complex with carbamide at the temperature of the upper limit of complex formation of the n-alkane with η = 24, because the temperature of their upper limits of complex formation with carbamide is lower than the temperature of the upper limit of complex formation with carbamide of the n-alkane with η = 24.

After complete binding to the complex of the n-alkane with η = 24, the n-alkane with η = 23 and so on can be separated in the order of decreasing molecular weight until all individual n-alkanes contained in the raw material have been completely separated.

The temperature of the upper limit of complex formation of the respective n-A'kan with carbamide in the multicomponent mixture can be calculated using the following equation:

0 _rm = &Thetas; - c&trade;» ■ ± approx.

/-3

where Θ is the temperature of the upper limit of complex formation of the respective n-alkane with carbamide at ⁰ °C; Q _cm is the temperature of the upper limit of complex formation of the same n-alkane in the multicomponent mixture at ⁰ °C; δ is the gradient of the reduction in the temperature of the upper limit of complex formation per unit of increase in the mass concentration of the /'-th component of the multicomponent mixture in°C/mass%; c is the total mass concentration of all /-th components except the one to be separated, mass%; c is the mass concentration of the /-th component of the multicomponent mixture, mass%.

Her component means any component of the mixture other than the one to be separated.

A second obligatory condition for the possibility of separating a particular n-alkane from the multicomponent mixture is washing the complex of this n-alkane with urea with the same n-alkane contained in the complex. During such washing, all other components of the multicomponent mixture that have not entered the complex will be removed from the intercrystalline space of the complex. This space will be filled with the same n-alkane that is contained in the complex. The amount of washing agent increases in proportion to the mass of crystalline urea used to separate the particular n-alkane. After the decomposition of such a complex, only crystalline urea and a particular n-alkane will be present in the system, which will be removed from the system as a solid end product.

The temperature interval of the decomposition of the complex of the respective n-alkane with the carbamide is limited by the temperature at the upper limit where the quantitative complex formation of this alkane with the carbamide still takes place and the decomposition temperature of the carbamide itself.

By separating n-alkanes from multicomponent mixtures at temperatures of their upper limits of complex formation with carbamide, followed by washing the complexes with the same n-alkanes contained in the complex and decomposing the complexes, individual n-alkanes with a purity of not less than 99.99 mass%, which do not contain aromatic impurities, are obtained. The technology of the process has been significantly simplified compared to the known processes, because the n-alkanes obtained by the process according to the invention do not require additional purification.

The process is simple in technological execution and is carried out as follows.

The process can be carried out under mechanical stirring of the quasi-liquefaction and in the stationary layer of the crystalline carbamide.

A preferred variant of the process is the separation of the n-alkanes from the crude oil in the stationary layer of the crystalline urea. To carry out this process, a reactor block is required for each individual n-alkane, which consists of three reactors of identical design that operate in alternating cycle mode and are combined to form a column-type apparatus.
In each reactor, three stages of one and the same cycle take place one after the other: a) complex formation, b) washing of the complex, c) decomposition of the complex.

Complex formation

The initial raw material and ethyl alcohol (activator) are mixed in a three-way mixing device. The resulting mixture is heated in a heat exchanger to the temperature of the upper limit of complex formation of n-alkane with η carbon atoms in the molecule (0 _fm ) and fed to the bottom of the first of the three reactors charged with crystalline carbamide. The layer of crystalline carbamide in this reactor is previously heated to the same temperature.

is According to the migration of the raw material mixture through the stationary layer of the crystalline carbamide, it enters into the complex formation reaction with the n-alkane, which contains η carbon atoms in the molecule.

The complex formation stage is considered to be completed when the calculated amount of raw material has passed through the reactor from bottom to top. Working with the n-alkane to be separated "under breakthrough" is not permitted, because traces of n-alkane with η carbon atoms in the molecule reduce the purity of the n-alkane with η - 1 carbon atoms that is separated in the next block. The product emerging from the upper part of the first reactor of the first block, which does not contain traces of n-alkane with η carbon atoms in the molecule, is fed to the first reactor of the second identical block to separate the n-alkane with η - 1 carbon atoms.

After the complex formation in the first reactor of the first block is completed, the stream of the starting crude oil is fed into the second reactor of the first block, where the stage of separating the n-alkane with η carbon atoms in the molecule begins, while in the first reactor of the first block the stage of washing the complex begins.

Washing the complex

The n-alkane with n carbon atoms in the molecule is fed through the steam heater to the bottom of the first reactor of the first block. This n-alkane washes away the crude hydrocarbons that did not react with the carbamide from the surface of the crystals of the complex formed.
From the top of the first reactor of the first block comes the washing agent (n-alkane with η hydrocarbon atoms in the molecule) contaminated with the washed-off raw material components. The first 10-12 mass % of this washing agent is particularly contaminated and is sent as reflux for mixing with the starting crude oil. The remaining 88-90 mass % of the washing agent is used as washing agent in the next cycle for separating n-alkane with η carbon atoms in the molecule in the same reactor.

Washing is carried out at a temperature above the temperature of the upper limit of complex formation of the n-alkane having η carbon atoms in the molecule with the carbamide and below the decomposition temperature of the complex formed.

The washing stage is considered to be completed when the quality of the detergent at the outlet from the reactor is identical to its quality at the inlet into this reactor.

From this point on, the stage of complex formation begins in the third reactor of the first block, the stage of washing in the second and the stage of decomposition of the complex in the first.

Decomposition of the complex

The decomposition of the complex occurs by heating it to a temperature that is 2 to 5 ^° C above the decomposition temperature of the complex. The individual n-alkane separates out and is derived from the first block as a finished product of high purity.

Thus, the first block, consisting of three reactors, operates continuously as a whole, although each of the reactors is operated in an alternating cycle mode.

In an analogous manner, in the next, second technological block, the n-alkane with η - 1 carbon atoms in the molecule is separated , then in the third block the n-alkane with η - 2 carbon atoms in the molecule, and so on, until all n-alkanes contained in the starting raw material are completely separated.

The process of the invention is illustrated by the following examples.

example 1

The raw material, a straight run fraction with a boiling range of 150 to 240 ^° C, taken in a technical rectification column with 10 plates at a reflux ratio of 1.5:1, has the following chromatographically determined component composition: n-tetradecane 6.24 wt.%; n-tridecane 9.72 wt.%; n-dodecane 24.4 wt.%; n-undecane 20.14 wt.%; n-decane 5.74 wt.%; n-nonane 1.32 wt.%; components that do not form a complex with the carbamide, 32.00 wt.%; total 100.00 wt.%.

Separation of n-tetradecane According to the equation

e _cm = &Thetas; - c° · ⁶⁰ ' · &Sgr; c,a,

The separation of n-tetradecane from the raw material mentioned is carried out at a temperature:

0 _fm = 86.0 - 93.76 ^{0 609} (9.72 0.037 + 24.84 0.0076

+ 20.14 0.0116 + 5.74 0.0156

+ 1.32 0.0196 + 32.0 ■ 0.0360) = 58.6°C

in a stationary layer of crystalline carbamide, which is charged in an amount of 10 kg. The process is carried out at a weight ratio of carbamide/n-tetradecane of 3.5:1. With the mentioned charging, 10/3.5 = 2.857 kg of n-tetradecane can be separated from this raw material. To do this, the pump is used to press through the stationary carbamide layer from bottom to top

Starting raw material. The process is carried out in the presence of ethyl alcohol as an activator, which is taken in an amount of 3% by weight, based on the charged carbamide. The activator can be added to the raw material simultaneously or with a metering pump throughout the process in portions or continuously. After complex formation is complete, the product emerging from the reactor with the stationary layer of crystalline carbamide and not containing n-tetradecane is fed to the identical reactor of the second block for separation of n-tridecane, while the complex formed is washed with n-tetradecane in an amount of 3:1, based on the weight of carbamide, to remove from the intercrystalline space of the complex the remaining unreacted components. Washing of the complex is carried out at temperatures of 58.6 to 86.0 ⁰ C. The first 10 to 12% by weight of the particularly heavily contaminated washing agent (n-tetradecane) that comes out of the reactor is used as reflux in the next cycle of separating the n-tetradecane and the remaining 88 to 90% by weight is used as washing agent in the next cycle. The washed complex is decomposed at a temperature of 120°C and the separated liquid n-tetradecane is discharged from the reactor. In the first cycle, the separated n-tetradecane has a purity of 99.8 to 99.9% by weight and, starting from the second and at most from the third cycle, a purity of at least 99.99% by weight with a complete absence of aromatic hydrocarbons.

The process can also be carried out under conditions of mechanical stirring or quasi-liquefaction while maintaining the specified temperature control and the specified proportions of the raw material and the reagents.

Separation of n-tridecane

The raw material is the product emerging from the first reactor of the first block, which does not contain n-tetradecane and has the following component composition: n-tridecane 10.37 wt.%; n-dodecane 26.49 wt.%; n-undecane 21.48 wt.%; n-decane 6.12 wt.%; n-nonane 1.41 wt.%; components that do not form a complex with the carbamide, 34.13 wt.%; total 100.00 wt.%. The separation of the n-tridecane is carried out at the following temperature:

Q _cm = 82.6 - 89.63 ^{0 609} ■ (26.49 0.004

+ 21.48 0.0083 + 6.12 0.0127
+ 1.41 0.017 + 34.13 0.035) = 57.9°C.

The raw material mentioned contains n-tridecane in an amount of (45.800 - 2.857) · 0.1037 = 4.453 kg.

15.6 kg of crystalline carbamide is introduced into the reactor. To activate the complex formation, 15.6 - 0.03 = 0.468 g of ethyl alcohol must be added to the reaction zone. From the reactor, where the n-tetradecane is separated, approximately ¹ h of the alcohol used to activate the separation of the n-tetradecane, ie

= 0.1 kg.

Therefore, approximately 0.37 kg of ethyl alcohol must be fed to the reactor to separate n-tridecane. After complex formation is complete, the product leaving the reactor, which does not contain n-tridecane, is fed to the next identical reactor of the next block to separate the n-dodecane, while the formed complex is washed with n-tridecane in an amount of 3:1, based on the amount of carbamide.

Washing is carried out at a temperature of 57.9 to 82.6 ⁰ C. The complex is then decomposed at 115 to 120 ⁰ C and the separated end product is discharged from the reactor. The first 10 to 12 wt.% of the particularly heavily contaminated washing agent (the n-tridecane) leaving the reactor is used as reflux in the next cycle of separating the n-tridecane, while the remaining 88 to 90 wt.% is used as washing agent in the next cycle.

Starting from the second or third cycle, n-tridecane is obtained with a purity of at least 99.99 wt.% and the complete absence of aromatic hydrocarbons.

Separation of n-dodecane

The separation of n-dodecane is carried out in an analogous manner. The complex formation is carried out at a temperature

of Q _cm = 55.2°C. The complex of n-dodecane is washed with carbamide at a temperature of 55.2 to 78.5°C, the washed complex is decomposed at a temperature of 115 to 120 ⁰ C and the final product separated out, which has a purity of at least 99.99% by weight (after the second or third cycle) and no longer contains aromatic hydrocarbons, is discharged from the reactor.

Separation of n-undecane

The separation of n-undecane is carried out in an analogous manner. The complex formation is carried out at a temperature of 0 _cm = 52.5°C. The complex of n-undecane is washed with carbamide at a temperature of 52.5 to 73.9°C, the washed complex is decomposed at a temperature of 110 to 115°C and the separated end product, which has a purity of at least 99.99% by weight (after the second or third cycle) and no longer contains any aromatic hydrocarbons, is discharged from the reactor.

Separation of n-decane

The separation of &eegr;-decane is carried out in an analogous manner. The complex formation is carried out at a temperature of

@ _cm - 44.7 ⁰ C. The complex of η-decane is washed with carbamide at a temperature of 44.7 to 68.0 ⁰ C, the washed complex is decomposed at a temperature of 110 ⁰ C and the precipitated final product is discharged from the reactor, which has a purity of at least 99.99 wt.% (after the second or third cycle) and no longer contains aromatic hydrocarbons.

After separating the n-alkanes from n-tetradecane to η-decane inclusive, the residue contains 15.2 kg of hydrocarbon mixture, which has a crystallization temperature of 62.8°C and contains 3.9% by weight of n-nonane and 6.3% by weight of aromatic hydrocarbons. This residue can be used as a component of jet fuels in civil aviation.

Example 2

In analogy to Example 1, from the petroleum fraction with a boiling range of 60 to 180 ^° C, obtained on a technical atmospheric plant and having an octane number of 42.6, n-undecane, η-decane, n-nonane, n-octane, n-heptane and η-hexane are separated in succession with 100% removal from the potential after each component with a purity of at least 99.99% by weight (after the third cycle) in the absolute absence of aromatic hydrocarbons.

The crystalline carbamide, the raw material and the activator (ethyl alcohol) are used in a ratio of 3.5:1:0.105.

Table 1 concentration Temperature, ^0C Decomposition of the Quantity ratio 1 - 50 To be separated the compo Complex Washing the Complex Laundry detergent/ 1 component nent in
raw material education Complex Carbamide 1 % by weight 105-110 1 55 1.22 29.4 29.4- 73.9 100-105 3.0 1 n-Undecan 3.46 17.1 17.1- 68.0 95-100 3.0 1 n-Dean 7.64 15.9 15.9- 58.0 90-95 2.8 n-Nonan 8.18 12.1 12.1- 48.0 85-90 2.5 60 n-octane 4.71 3.7 3.7- 38.0 80-85 2.3 n-Heptane 1.09 -11.4 -ll,4-+28,0 — 2.0 n-hexane 73.70 — — Components that 65 Carbamide no Form complex 100.00 In total

After separation of all mentioned n-alkanes, the octane number of the residue of the petroleum fraction with boiling range 60 to 180 ^° C increased by 31 and amounted to 73.6.

Example 3

In analogy to examples 1 and 2, n-tetracosane, n-tricosane, n-dokosane, n-heneicosane and n-eicosane are separated successively from the oil fraction with a boiling range of 350 to 395 ⁰ C, which has a pour point of 32.4 ° C, with 100% removal of the potential after each component with a purity of at least 99.99 wt. % (after the third cycle) and with the absolute absence of aromatic hydrocarbons. The process parameters are shown in Table 2. The crystalline carbamide, the raw material and the activator (ethyl alcohol) are taken in a weight ratio of 3.5:1:0.105.

Table 2

To be separated
component

concentration
the component
in the
raw material

% by weight

Temperature, ⁰ C

Complex- Washing of the formation complex

Decomposition of the
Complex

Quantity ratio

Laundry detergent/

Carbamide

n-Tetrakosan 2.56 93.9 93.9-99.7 128-130 3:1

n-Trikosan 3.63 89.7 89.7-99.2 125-130 3:1

n-Dokosan 5.14 84.2 84.2-98.7 122-125 3:1

n-Heneikosan 2.12 79.8 79.8-98.2 120-125 3:1

n-Eikosan 0.78 64.3 64.3-97.2 120-125 3:1

Components containing 85,77 - - - Carbamide no
Form complex

After separation of all mentioned n-alkanes, the pour point of the petroleum fraction drops to 2.0 ⁰ C. The temperatures of the upper limit of complex formation of the individual n-alkanes are given in Table 3, the temperature gradients of the calculation equation σ, in Table 4.

Table 3

Number of carbon atoms
in the molecule

Temperature of the upper limit of complex formation of the individual n-alkane and the carbamide

6
7
8th
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

28.0 38.0 48.0 58.0 68.0 73.9 78.5 82.6 86.0 88.7 91.0 93.1 94.7 95.9 97.2 98.2 98, 7 99.2 99.7

Table

Summary table of constant gradients of the main calculation equation of the upper complex formation

Components Basic component of the n-Undecan &igr; n-Dodecane Mixture n-Tetra n-Penta- n-Hexa- n-Dean n-Tridecane dean dean <, dean _ _ n-Trilosane _ - - _ - - - n-Docosane - - - - - - - n-Heneicosane - - - - - - n-Eicosan - - - - - - - n-Nonadecane - - - - - - - n-octadecane - - - - - - - n-Heptadecane - - - - - - - n-Hexadecane - - - - - - 0.00300 n-pentadecane - - - - - 0.00335 0.00640 n-Tetradecane - - - - 0.00370 0.00695 0.00980 n-Tridecane - - - - 0.00760 0.01065 0.01320 n-Dodecane - - 0.00435 0.00400 0.01160 0.01435 0.01670 n-Undecan - 0.00470 0.00905 0.00830 0.01560 0.01805 0.02010 n-Dean - 0.01000 0.01385 0.01270 0.01960 0.02165 0.02350 n-Nonan 0.00500 0.01530 0.01855 0.01700 0.02360 0.02535 0.02700 n-octane 0.01100 0.02060 0.02335 0.02130 0.02760 0.02905 0.03040 n-Heptane 0.01700 0.02590 0.02815 0.02560 0.03160 0.03275 0.03380 n-hexane 0.02300 0.03200 0.03365 0.03000 0.03610 0.03695 0.03770 Hydrocarbons that 0.03000 0.03500 do not form a complex

Table 4 (continued)

Components Basic component to be separated n-Octa n-Nona of the Gern ic n-Doko n-Triko- n-Tetra- n-Hepta dean dean n-Eiko n-Henei san san kosan dean _ _ san kosan _ 0.00035 n-Trilosane _ - - - 0.00070 0.00260 n-Docosane - - - - - 0.00100 0.00300 0.00485 n-Heneicosane - - - - - 0.00345 0.00535 0.00710 n-Eicosan - - - - 0.00135 0.00590 0.00770 0.00935 n-Nonadecane - - 0.00200 0.00170 0.00395 0.00835 0.01005 0.01160 n-octadecane - 0.00235 0.00480 0.00440 0.00645 0.01080 0.01240 0.01385 n-Heptadecane - 0.00535 0.00770 0.00710 0.00905 0.01325 0.01475 0.01610 n-Hexadecane 0.00270 0.00835 0.01050 0.00980 0.01165 0.01570 0.01710 0.01835 n-pentadecane 0.00590 0.01135 0.01340 0.01250 0.01415 0.01815 0.01945 0.02060 n-Tetradecane 0.00910 0.01435 0.01620 0.01520 0.01675 0.02060 0.02180 0.02285 n-Tridecane 0.01230 0.01735 0.01910 0.01790 0.01935 0.02305 0.02415 0.02510 n-Dodecane 0.01550 0.02035 0.02190 0.02060 0.02185 0.02550 0.02650 0.02735 n-Undecan 0.01870 0.02335 0.02470 0.02330 0.02445 0.02795 0.02885 0.02960 n-Dean 0.02190 0.02635 0.02760 0.02600 0.02705 0.03040 0.03120 0.03185 n-Nonan 0.02510 0.02935 0.03050 0.02870 0.02965 0.03285 0.03355 0.03410 n-octane 0.02830 0.03235 0.03330 0.03141 0.03215 0.03530 0.03590 0.03635 n-Heptane 0.03150 0.03535 0.03620 0.03410 0.03475 0.03775 0.03825 0.03860 n-hexane 0.03470 0.03895 0.03950 0.03680 0.03735 0.04070 0.04100 0.04125 Hydrocarbons that 0.03840 0.03990 0.04035 do not form a complex

Claims (1)

Patent claim: Process for separating individual n-alkanes from crude oil by complex formation with crystalline carbamide in the presence of an activator and subsequent thermal decomposition of the complex, characterized in that S a) the complex formation is carried out at the temperature of the upper limit where the quantitative complex formation of the n-alkane to be separated with the highest molecular weight still takes place, b) washing the complex thus formed with the underlying n-alkane at a temperature which is above the temperature of the upper limit of complex formation and below the decomposition temperature of the complex formed, c) the complex is then heated to a temperature 2 to 5°C higher than its decomposition temperature, and the n-alkane thus separated is recovered, and d) the individual n-alkanes are separated and recovered from the remaining crude oil in the order of decreasing molecular weights.