DE1948951B2 - PROCESS FOR SEPARATION OF HYDROCARBONS - Google Patents

Description

The invention relates to a method for the separation of hydrocarbons for the recovery of Petrol and, under normal conditions, gaseous hydrocarbons from the gaseous-liquid effluent a hydrocarbon conversion plant. in which the gaseous-liquid outflow occurs in several (10 sequential separation stages linked to one another through the return of material flows is separated using fractionation, gas / liquid separation and absorption zones.

In the conversion of heavy hydrocarbon feedstocks, like crude oil residues from vacuum distillation of reduced crude oil. Vacuum tar. reduced crude oils, i.e. crude oils from which low-boiling components, such as kerosene and

Gasoline fractions that have been distilled off, topped crude oils, mixtures of such materials, etc., through a heat treatment, e.g. thermal cracking, the heated feedstock is converted into coke and lower molecular weight products. The coke is removed from the coking drum, the gaseous-liquid effluent is fed to hydrocarbon recovery facilities. Known working methods for separating the effluent from such a caking process generally use a fractionation column, an absorption column and a stabilization column. Usually coker gasoline, coker gas oil and under norm; <oil conditions contain gaseous hydrocarbons, ₅ th.

A process for working up the product effluent from the conversion of a hydrocarbon feedstock boiling above HH V is already known (French patent 1547 873). in which the outflow in a hot separator is separated into a first liquid flow and a first injection flow, the first steam flow is cooled and then in a cold separator at the same pressure as in the hot separator into a hydrogen-rich second steam flow and a /. wide liquid flow is separated, at least a portion of the first liquid stream is separated in a hot expansion evaporation zone at significantly reduced pressure into a third liquid stream and a third vapor stream, the third vapor stream is cooled and combined with the second liquid stream, and the resulting mixture in a cold expansion evaporation zone in a fourth Vapor flow and a fourth liquid flow is separated. The fourth liquid flow from the cold flash evaporation zone can partly be returned to the cold separator and partly, after mixing with the liquid flow from the hot flash evaporation zone, be subjected to fractionation in a fractionation column after heating.

In these known processes, gaseous constituents, consisting of C ₃ hydrocarbons and lighter components as well as hydrogen sulfide, flow from the cold flash evaporation zone and must, if the (^ hydrocarbons are to be obtained, be subjected to a further separation. The gasoline obtained as the overhead product of the fractionating column still contains at least (^ hydrocarbons and must also be subjected to a further separation if the (^ hydrocarbons and a stabilized gasoline are to be obtained separately.

The object of the invention is to create a method for separating the outflow of a coal = Hydrogen conversion zone into gaseous hydrocarbons under normal conditions and under Normal conditions liquid hydrocarbons, in particular a method for separating the gaseous liquid Outflow of a coking zone in gasoline and gaseous hydrocarbons under no. this leads to better separation and product recovery than previous procedures and is to be carried out safely.

This object is achieved by a method of the type mentioned at the beginning, which according to the invention is characterized in that one

(a) the effluent in an ercten fractionation zone into a light distillate fraction, the gasoline and Contains gaseous hydrocarbons under normal conditions, and at least one gas oil fraction separates,

(b) the light distillate fraction in a separation into a first gaseous stream and a first separates liquid stream,

(c) introducing at least a portion of the first gaseous stream into a first absorption zone and in this absorption zone at least part of the first liquid stream as absorbent initiates,

(d) from the first absorption zone a first rich oil stream loaded with absorbed constituents and withdraws a second gaseous stream,

(c) pass the second gaseous stream into a second absorption zone; end in this absorption zone at least part of the gas oil fraction from step (a) as an absorbent.

(f) from the second absorption zone a second rich oil stream laden with absorbed constituents and a first product stream, the CV hydrocarbons and lighter components includes, subtracts.

(g) the first rich oil stream to the separation zone of step (b) and the second rich oil stream to the Fractionation zone of stage (a) conducts, and

(h) introducing the remaining liquid stream of stage (b) into a second fractionation zone and separating therefrom a second product stream, which contains gaseous hydrocarbons under normal conditions, and a third product stream comprising gasoline ¹ .

According to a preferred embodiment, part of the third product stream is passed as an absorbent into the first absorption zone.

According to one embodiment, the procedure is as follows: that he

(a) the effluent from a hydrocarbon conversion plant having a coking zone; in the first fractionation zone into a light distillate fraction, the hydrogen, under normal conditions includes gaseous hydrocarbons and gasoline, a middle distillate fraction, which includes light gas oil, and a bottom fraction which includes heavy gas oil! embraces, separates,

(b) the light distillate fraction in a first separation zone at a comparatively low pressure in a first gaseous stream and a first separates liquid stream,

(b ₂ ) compresses the first gaseous stream and mixes the compressed stream with the first rich oil stream,

(bj) the _{mixture formed in step (b 2} ) in a second separation zone at a higher pressure than that of the first separation zone into a second gaseous stream and a second liquid. Electricity disconnects. (c) passes the second gaseous stream into the first absorption zone and there washes hydrocarbons with three or more carbon atoms therefrom by means of the absorbent, which consists at least in part of the first liquid stream of stage (b).

(d) from the first absorption zone a first lower portion of the fraction ionizing zone 13 through a Rich oil stream and a third gaseous line 16 is withdrawn to separate. Depending on the Electricity subtracts, properties and composition of the through

(e) the third gas-carrying line 12 entering the outflow in step (d) can lead more or less stream into the second absorption zone and the C ₃ and C ₄ carbon zones remaining therein 13 can be deducted.

lenwasserstoffe by means of the absorbent, the light distillate fraction, which in the gasoline range at least partially consists of a portion of the boiling components and gas oil fraction of stage (a), which is gas-light under normal conditions, contains shaped hydrocarbons, e.g. B. C ₂ -, C ₃ -washes, 10 and Q-hydrocarbons mixed with others (O from the second absorption zone the first gases, e.g. hydrogen, is through line 14 product stream, the hydrogen, methane and into a first separation zone 17 introduced which comprises ₂ hydrocarbons at ver-C, in the (g) withdrawing, proportionate low pressure is maintained. the first Reich oil flow for mixing the separation zone 17, appropriate separation conditions in step (b ₂₎ the compressed gaseous stream 15 for separation the light distillate fraction in and the second rich oil stream to which a first gaseous stream, which passes through a Lei fractionation zone of stage (a), device 18 is removed, and a first liquid (h) the second liquid stream from stage (b ₃ ) in the stream withdrawn through a line 19, the second fractionation zone with the withdrawal of a two- maintained.

th product stream, which consists essentially of C ₃ - 20 The material flowing off through line 18

and C ₄ hydrocarbons, and that comprises a mixture of under normal conditions

third product stream consisting of gasoline, gaseous hydrocarbons, including water

separates, serstotf and possibly acidic gases, and stands

(i) Part of the third product stream as a further under “aem relatively low pressure. To

Proportion of the absorbent to the first 25 of the preferred embodiment of the invention

sorption zone. this first gaseous stream of the line 18 one

Compression device 20 for increasing the pressure

Due to the suitable working method, a comparatively high value is supplied. The excellent yield of valuable gaseous, compressed gaseous stream is achieved from the compression hydrocarbons in the liquid gas range, ie C ₃ - 30 processing device 20 through a line 18a and ^ hydrocarbons. These coals, with a hydrogen, which will be explained in more detail below, are of high purity and thus mixed with a flowing stream from a line 21, of the quality shown above. Furthermore, a very stable gasoline separation zone is obtained through a line 22 into a relatively high pressure which is maintained at high quality standards and which is sufficient for this purpose. In a preferred embodiment 35 23 is inserted. In the separation zone 23, two gas oil fractions are still obtained, the remaining operating conditions being maintained which can be drawn off directly as products already from the first fraction that the mixture can be withdrawn into a second gaseous stream. which is withdrawn through a line 24, and a second liquid stream, which is guaranteed in the method of operation according to the invention and which is removed through a line 25 using materials 40 inherent in the process, is separated,
The second gaseous stream is introduced into a first absorption zone 26 by the quiet, very simple mode of operation, without a feed device 24, of non-process absorbents from the outside, preferably at its lower end. The absorber requirements. In the case of the preferred accumulation zone 26, the formation is maintained under absorption conditions not only with two absorption zones 45. It contains at least a larger proportion but also worked with two different absorption fluids withdrawn from the separation zone 17, which are fed into the first absorption zone as at least part of the stream therein. This makes an excellent turned absorbent. The yield of C ₃ - and Q-hydrocarbons from the separation zone. 17 incoming material is introduced into the absorption zone 26 through a line IS The method according to the invention and the various 50. As will be explained in more detail after the working stages of the understanding used in this context, a further bundle can be further explained below in connection with the absorbent content through a line 35 in the drawing. The drawing shows see- absorption zone 26 to be introduced. The rest of the flow chart of a preferred embodiment operating conditions in the absorption zone 26 who form the process. 55 the selected such that substantially the Gesamtmengi Through a line 10 is a high-boiling C ₃ - and C ₄ hydrocarbons and a Tei feedstock in a Kohlenwassersioffumwand- the CVKohlenwasserstoffe from the absorption zone lung passed 11, which is for itself. B. to be added to a medium. The resulting ersii conventional coking plant can act. The rich absorption oil is withdrawn from the absorption zone gaseous-liquid effluent of the conversion zone 60 26 through line 21 and with the ver is withdrawn through line 12 and introduced into a sealed gaseous material in line 181 fractionation zone 13. Mixed in the fractionation, as has already been mentioned,
zone 13 such fractionation conditions are ascending A third gaseous stream of C ₂ - and facilitated right obtained, comprising around the gas-liquid outflow tere gaseous components verunreinig first into a light distillate fraction obtained by 65 C ₃ - and C ₄ hydrocarbons A line 14 is withdrawn from de, a side cut absorption zone 26 abgenorr gas oil fraction through line 27, which is withdrawn through line 15 and fed into a second absorption zone 28, and a heavy gas oil fraction which leads from. When in the absorption zone 28 weer

7 ^w 8

(The last absorbent is a component of the lighter gas oil stream, which is gaseous under normal conditions, and which results from the fractionation, which is then removed in the fractionation zone 32 through the line 15. Furthermore, the preferred discharge is This discharge form consisting of lighter gas oil is characterized in that not only is sorbent introduced through a line 29 in FIG A first product stream which, when operated in this way, will _{produce C 2} and lighter components with the inclusion of an excellent recovery of C ₃ and C ₄ coils - Hydrogen and optionally acidic gas includes.

Suitable operating conditions for bringing about 30 are withdrawn from the absorption zone 28 through a line and preferably fed into the heating gas of the various according to the above explanatory system. The second rich separation processes formed can be drawn off from the absorption zone 28 by the average person skilled in the art within the scope of his normal line 31 and returned to the fractionating activity according to the individual case, preferably selected as reflux. The fractionation, absorption and fractionation zones with feed at a separation stage are conventional work measures with regard to the individual stage point above the discharge point of the lighter gas oil, which according to the invention result in a novel way out of the separation zone 23, the second liquid 20 special composite has been combined, with current being passed through line 25 into a second fractionation zone 32 which is achieved by this composite, and which are fractionated when appropriate. The separation conditions required in individual cases to generate a gaseous stream are operated to a considerable extent by the preferably C ₂ hydrocarbon properties of the flowing through line 12 and substances contaminated with C ₃ and C ₄ hydrocarbons to be separated gaseous-liquid mixture of substances, encompassed and withdrawn through a line 33 influences.

will. It is particularly preferred to use the In the example below is an advantageous one

Obtaining C ₃ - and C ₄ -hydrocarbons so operating mode for carrying out the preferred

To make as large as possible, illustrated by line 33 ÄUMÜhrungäfarrn of the invention

flowing material through conduit 37 into 30 R ^- I

Separation zone 23 to be carried out in a mixture with the previous example

The first rich absorption oil mentioned above, which became a coking plant of technical size

flows through line 21. However, it can be operated in a conventional manner. The gaseous

if desired, a further product stream which became this liquid effluent after the coke had been separated off

includes light hydrocarbons, passed through the line 35 into a system which essentially corresponds to the

device 33 can be withdrawn from the system. A second flow diagram corresponded to the drawing.

Product stream, the C ₃ - and Q-hydrocarbons when feeding the coking plant

comprises, is from the fractionation zone 32 through a (line 10) it was a vacuum-reduced

Leitune36 decreased, while a third per- cented crude oil with the following properties:

_{duct flow of the specific gravity} formed by the conversion 40 ^ ₂₀ ° c 0.940

Gasoline comprises 0.16 weight percent through line 34 from the plant

is carried out. It is preferred, such as _pre-C onradson coking,

starting from already mentioned, part of the r.pwirhunrrwpnt inQ

third product weight percent flowing through line 34 10.9

Flow through line 35 into the first absorption 45. After preheating, the feed was in

«.One 26 to lead. If desired, however, an amount of 955 m ³ / operating day can be sold

also part of the flow zone through line 35 at a transition temperature of 482 "C

Material introduced through connections not shown and a coke chamber pressure of 5.3 atmospheres,

the fractionation zone 13 or the separation zone 17 or After separating the coke, the gaseous

the separation zone 23 are passed. After another 50 liquid outflow through line 12 into the fraction

In the preferred embodiment of the invention, zone 13 is introduced.

the material flowing through the line 35 into the The gaseous-liquid outflow from the coke chamber

Absorption zone 26 at a point above the einmer was in the lower section of the fractionation

Lead parts of the column 13 flowing in through line 19 at a temperature of 438 C below

first introduced liquid electricity. 55 initiated at a pressure of 5.3 atü. An overhead

It has been found that by the above stream, the Be gaseous under normal conditions

The operating mode described included extremely high and good components and gasoline, was replaced by di <

exploit (i.e. in terms of quantity and quality) of the line 14 at a temperature of 150 ° C

pulled gaseous coals under normal conditions; a side cut stream, the light gasö

substances, e.g. B. C ₃ - and ^ - hydrocarbons, reached 60 comprised, was through line 15 at a Tem

will. Furthermore, a stabilized gasoline temperature of 307 ° C is taken; a ground stream

proHukt and, in the preferred embodiment, comprised heavy gas oil, was approved by the Leituni

two gas oil fractions obtained as products. 16 discharged at a temperature of 399 ° C. Lower

Another feature of the preferred embodiment of these conditions became the following Pro

ring shape lies in the fact that the rich oil from the first 05 duct streams is separated from each other (the component!

Absorption zone in which a ratio is given in moles per hour); are below

Second separation zone maintained at high pressure passed the designations C ₂ ⁼ , Cj ", Q ¹ , etc. in the following

so that there is an enrichment of the liquid the corresponding unsaturated hydrocarbon

ίο

to be understood with a double bond, i.e. ethylene. Propylene, Butylenes etc.

component

H ₂ O

K ₂ S

H ₂

C ₁

CJ

C ₂

CJ

C ₃

Cl

iC ₄

nC ₄

C ₅ ⁼

• C ₅

nC ₅

C ₆ -170 ⁰ C

total

Head of M

114.00 0.58 24.86 99.14 13.55 54.86 31.55 55.44 39.17 9.43 30.50 39.41 18.69 37.90

229.48 The gaseous flowing through line 18 Stream was compressed in a circular compressor 20 from 4.3 atmospheres to 15.8 atmospheres and then in the above illustrated manner with a recycle stream of 399.5 mol / h from line 21 and 201.1 mol / h from line 37 mixed. The mixture was then in the separator 23 at a temperature of 38 C and a pressure of 15.1 atmospheres. Under these conditions it became gaseous Stream separated and withdrawn through line 24; the remaining liquid stream was through the line 25 removed. The compositions of these streams from the separator 23 would be like follows, given in mol / h.

■

798.56

Specific
Weight at

20 ⁰ C

m ³ / day

Weight percent S ..

0.830 285

0.1

Line _ .. [16

0.882 247

0.1

The material flowing off through line 14 was condensed by a condenser, e.g. B. a Air finned condenser, cooled to a temperature of 38 "C and fed into the separator 17, which was under a pressure of 4.3 atmospheres. A gaseous stream was passed through from the separator 17 line 18 and a liquid stream through line 19 withdrawn. These two streams had the following composition, given in moles / h.

component

total

management and 18a 19th 3.59 0.46 0.04 24.74 0.04 95.39 1.25 11.90 0.55 46.10 2.92 20.48 3.69 34.29 7.05 14.69 8.16 3.91 1.84 10.40 6.70 6.62 10.93 3.39 5.10 5.56 10.78 1.42 76.02 282.94 135.07

50

55

60 component

H ₂ O.
H ₂ S.

total

3.59

1.74

25.67

122.37
26.94

140.32
85.75

121.48
40.47
10.79
28.69
07/40
19.28
37.33

management

24

179.07
883.56

1.37

0.98

25.12

106.15

17.85

83.49

07/32

42.11

7.36

2 2 " ¹

4.64

2.98

1.62

2.49

0.55

331.00

25th

0.76

0.55
16.22

9.09
56.83
53.68
79.37
33.11

8.57
May 24th
37.09
17.66
34.84
178.52

550.34

The liquid stream draining through line 25 was introduced into fractionation zone 32 which was a fractionation zone divided into two separate distillation columns; the first column was formed by a gasoline stripping column for the removal of C 1 -C hydrocarbons and lighter fractions from the feed, the second column consisted of a debutanizing column for the recovery of C _{1 and C 4} hydrocarbons and gasoline as product streams. To simplify and improve clarity, the two fractionation zones are shown in the drawing in the form of a single column. When the fractionation zones were operated under conventional conditions of temperature and pressure, an overhead stream was withdrawn through line 33 which _{contaminated the C 2} and lighter components! with C, - and Q-hydrocarbons. included. In the preferred embodiment of the invention, 201.1 moles / hr of material flowing through line 33 was passed through lines 37 and 21 for mixing with the compressed vapors in line 18a, as discussed above. The gasoline stripping column was equipped with a; Temperature of 60 ^c C and a pressure of 17.0 ati operated. The Entbutanisierkolonne was run at a temperature of 204 C ^and a pressure of 13.7 ati. Under these conditions, a _{stream comprising C 3} and Ct hydrocarbons was generated

<r

from fractionation zone 32 through line 36 while gasoline product is withdrawn from the bottom the debutanizing column in the amount of 110 mol / h was discharged through the line 34 and returned in the amount of 142.8 mol / h through the line 35 into the absorption zone 26. To explain the in the separation achieved in the fractionation zone 32, the following compositions are given in mol / h.

component

H ₂ O

H ₂ S

H ₂

Q

C ₂ =

C ₂

C ₃ =

C ₃

C ₄ =

i-Q

nC ₄

C ₅ =

iC ₅

nC ₅

C— 17O ¹ C ...

total

0.50

0.12

0.48

13.34

6.26

12.78

76.54

110.02

Line 36

0.01

0.25

18.48

34.51

21.21

5.27

15.85

0.43

0.21

0.32

96.54

33 and 37

0.75

0.55

16.22

9.09

56.58

35.20

44.86

10.75

3.02

7.10

5.99

3.05

5.15

2.78

201.09

such operating conditions were maintained in the absorption zone 26 that the C ₂ and lighter fractions are effectively separated off in the absorption zone 26; s> e were removed from the absorption zone 26 through the line 27. The combined rich oil with the C ₃ and C ₄ hydrocarbons absorbed therein was withdrawn from the absorption zone 26 in an amount of 399.5 mol / h through the line 21, with 201.1 mol / h of material coming from the line 37 being mixed and then further mixed at 282.9 mol / h of the gases coming from the compressor 20 through the line 18 'for recirculation and liquid enrichment in the high-pressure separator 23. To illustrate the separation achieved in absorption zone 26, the following compositions are given in mol / h.

20th
component Flax
21 ln-j 27 H ₂ O 0.53 1.37
0.49 H ₂ S 0.38 24.78 ^{ί $} Η, 10.76 96.64 C, 5.95
1 * 7 f, A 12.45
/ 18 77 he 07/30
42.33
15.03
3.86
11.19 5.69
6.83
1.14
0.36
0 77 27.46
12.84
26.62
174.87 3.78
2.02
3.24
0.90 ³⁰ Cr ... 399.53 209.23 c C ₄ = i-Cj. ³⁵ nC, Cf .... i-C, n-C 40 Q, 170 C ... total

45

From the high pressure separator 23 the gaseous material flowing through the line 24 was passed into a first absorption zone 26 at a temperature of 38 "C and a pressure of 14.9 atmospheres. Operating conditions were maintained in the absorption zone 26 that essentially the total amount of C, - and C ^ hydrocarbons was dissolved in the poor oil, the latter consisting at least in part of the material flowing in through line 19, the composition of which was already given above In addition, a further portion of absorbent in the form of gasoline was introduced from line 34 through line 35 into absorption zone 26 (the composition of the material flowing through line 34 has already been indicated above) separated C ₂ - and lighter Ar'e ile. contaminated with C, + components, were introduced through line 27 into the second absorber 28 at a temperature of 47 ° C. and a pressure of 14.4 ati. The flowing through the line 27 Ga; was introduced into the lower section of the absorber TX and brought into contact in the absorber in countercurrent flow with poor oil introduced through the line 29 into the upper section of the absorption zone 28. As discussed above, the absorbent or absorbent for absorption zone 28 was a portion of the light gas oil product. which was withdrawn from fractionation column 1 through line 15 and the composition has already been indicated. The C ₂ and lighter fractions were finally removed through line 30 and added to the heating gas system. The rich oil from the second absorption zone 2 was withdrawn through line 31 and returned to the upper section of fractionation column 13 as additional reflux for this column. The compositions of the material streams obtained in the separation in d (absorption zone 28 are given below in mol / h.

component

-ι

C ₁

C ₃

1.37

0.38

24.65

93.12

10.96

40.83

3.43

3.83

0.20

management

0.11 0.13

3.52 1.49 7.94 2.26 3.00 0.94

component

nC ₄

iC ₅

nC ₅

C ₆ -170'-C ..
170 to 343 ^J C

total

14th

management

0.09 0.10 0.04 0.03 0.02 0.00 0.01

179.06

0.27 0.67 3.74 1.99 3.22 0.90 81.93

112.11

1 sheet of drawings

Claims (3)

Patent claims: 1. Process for the separation of hydrocarbons for the extraction of gasoline and under Normal conditions gaseous hydrocarbons from the gaseous-liquid outflow of a Hydrocarbon conversion plant in which the gaseous-liquid outflow occurs in several successive ones and separation stages linked to one another through the return of material flows separated using fractionation, gas / liquid separation and absorption zones is characterized by that he (a) the effluent in a first fractionation zone into a 'c FRUITS distillate fraction. which contains gasoline and, under normal conditions, gaseous hydrocarbons, and separates at least one gas oil fraction, (b) the light distillate fraction in a separation zone in a first.i gasförr. separates its own stream and a first liquid stream, (c) introducing at least a portion of the first gaseous stream into a first absorption zone and in this absorption zone at least a portion of the first liquid stream as Introduces absorbent, (d) from the first Ahsorpti «.lszone one with absorbed constituents loaded first rich oil stream and a second gaseous one Draws electricity, (e) passing the second gaseous stream into a second absorption zone and into that absorption zone at least part of the gas oil fraction from step (a) as absorbent introduces, (f) from the second absorption zone a mi! absorbed constituents loaded second Rich oil stream and a first product stream, the Cj hydrocarbons and lighter ones Components includes, subtracts, Ig) the first rich oil stream into the separation zone of stage (b) and the second rich oil stream passes to the fractionation zone of stage (a), and (h) introducing the remaining liquid stream from step (b) into a second fractionation zone and there from it a second product stream, the hydrocarbons which are gaseous under normal conditions contains, and separates a third product stream comprising gasoline. 2. The method according to claim i, characterized in that that one part of the third product stream as an absorbent in the first absorption zone directs. 3. The method according to claim 1 or 2, characterized in that one (a) the effluent from a hydrocarbon conversion plant having a coking zone; in the first fractionation zone into a light distillate fraction, the hydrogen Normal conditions include gaseous hydrocarbons and gasoline, a medium one Distillate fraction comprising light gas oil and a bottoms fraction comprising heavy gas oil includes, separates. (b,) the light distillate fraction in a first separation zone at a comparatively low one Separates pressure into a first gaseous stream and a first liquid stream, (b ₂ ) compresses the first gaseous stream and mixes the compressed stream with the first rich oil stream. (b ₃ ) the mixture formed in step (b ₂ ) in '.:. cr separates the second separation zone into a second gaseous stream and a second liquid stream at a pressure higher than that of the first separation zone, (c) passes the second gaseous stream into the first absorption zone and wipes out hydrocarbons with 3 or more carbon atoms there by means of the absorbent, which consists at least in part of the first liquid stream of stage Ib ₁ ). (d) a first rich oil stream and a third gaseous stream from the first absorption zone Draws electricity, (e) the third gaseous form in the mare (d) Introduces current into the second absorption zone and there remaining C, - and (^ -hydrocarbons by means of the absorption medium, which at least partly consists of a portion of the light gas oil fraction of stage (a), washes out, (F) from the second absorption zone the first product stream, the hydrogen, methane and ('^ -Hydrocarbons includes, subtracts, (g) the first rich oil stream for mixing with the gaseous form compressed according to step (b) Stream feeds unc * the second rich oil stream to the fractionation zone of stage (a) directs, ("η) separates the second liquid stream from stage (b ₃ ) in the second fractionation zone with the deduction of a second product _{stream, which consists essentially of L 3} - and (^ -hydrocarbons, and the third product stream consisting of gasoline,
(i) a portion of the third product stream is returned to the first absorption zone as a further portion of the absorbent.