EP1463789A2

EP1463789A2 - Steam-cracking of modified naphtha

Info

Publication number: EP1463789A2
Application number: EP03712222A
Authority: EP
Inventors: François BOUVART; Robert Duchesnes; Claude Gutle
Original assignee: Atofina SA; TotalFinaElf France SA
Current assignee: Total Petrochemicals Research Feluy SA; Total Marketing Services SA
Priority date: 2002-01-10
Filing date: 2003-01-09
Publication date: 2004-10-06
Anticipated expiration: 2023-01-09
Also published as: EP1463789B1; ATE329984T1; FR2834515B1; CN1615353A; US20060089518A1; FR2834515A1; KR20040086264A; WO2003057802A2; DE60306105D1; CA2471491C; KR101062768B1; DE60306105T2; CA2471491A1; EP1463789B9; PT1463789E; CN1306011C; US7838712B2; DK1463789T3; ES2266792T3; AU2003216795A1

Abstract

Disclosed is a method for steam-cracking naphtha, according to which a charge of hydrocarbons containing a portion of paraffinic naphtha, which is modified by adding a combination of a first component containing a portion of gasoline and a second component containing a portion of at least one hydrocarbonated refinery gas, and a paraffin-rich change containing at least one paraffin selected among propane, butane, or a mixture thereof are fed through a steam cracker in the presence of vapor. Also disclosed is a hydrocarbon composition suitable for steam cracking, containing a portion of a paraffinic naphtha, which is modified by adding a combination of a first component containing a portion of gasoline and a second component containing a portion of at least one hydrocarbonated refinery gas and a paraffin-rich charge containing at least one paraffin selected among propane, butane, or a mixture thereof.

Description

Modified Naphtha Steam

The present invention relates to a process for the steam cracking of naphtha, a hydrocarbon composition suitable for steam cracking, a process for controlling a steam cracker, an apparatus for controlling a steam cracker and a process for treating a charge of sulfur gasoline.

The petrochemical industry requires monomers (in English, "Building Blocks") consisting, for example, of olefins, diolefins and aromatics. In Europe, olefins are mainly obtained by steam cracking of charges obtained from refineries. The fillers available are mainly naphtha fillers including paraffins, isoparaffins and aromatics. A charge of naphtha usable in steam cracking is known in the art as comprising a petroleum cut, the lightest constituents of which contain five carbon atoms and which has a final boiling point of approximately 200 ° C., the naphtha comprising high carbon constituents with a boiling point of at least 200 ° C. Steam cracking of naphtha gives light olefins such as ethylene and propylene, and diolefins such as butadiene, as well as gasolines containing aromatics.

When a typical naphtha is subjected to steam cracking, the cracked product typically has the following composition (in% by weight) at the outlet of the oven:

% in weight

(approximate)

Hydrogen 1

Methane 16

Acetylene 0.2

Ethylene 22

Ethane 5

methylacetylene,

Propadiene 0.3

Propylene 14

Propane 0.5

Butadiene 4 C4 5

C5 4

Benzene 9

Toluene 5

Non-aromatic essence 2

Aromatic essence 6

Fuel oil 6

Total 100

The most interesting cuts in the cracked product are the light olefins, namely ethylene and propylene. Their yield is directly linked to the presence of paraffins in the charge. When straight chain paraffins are present, the formation of ethylene is favored. When isoparaffins are present, the formation of propylene is favored. The relative propylene yield is expressed as the weight ratio of propylene relative to ethylene and is typically between 0.5 and 0.75. Recently, due to the growth in olefin requirements, the supply of feedstock for paraffinic naphtha to a petrochemical plant supplied from a refinery has tended to be somewhat limited.

DE-A-3708332 describes a thermal cracking process for ethylene in a steam cracker, where the ethylene is mixed with naphtha so as to prepare a feedstock consisting essentially of naphtha and from 10 to 80% by weight of ethylene, optionally containing , in addition to naphtha, fractions up to diesel (boiling point up to 350 ° C) and / or recycled by-products from a petrochemical plant which can range up to 50% of naphtha. This process has the disadvantage that it requires relatively large quantities of ethylene (at least 10%) in the raw materials and that the yields of ethylene (relative to the ethylene introduced in the feed) and of propylene do not are not particularly high. US-A-3786110 describes a process for the production of unsaturated hydrocarbons obtained by pyrolysis, where the undesirable fractions are reduced by the addition to the pyrolysis products of a polymerization inhibitor containing asphaltic hydrocarbons.

A process for the steam cracking of naphtha capable of providing a commercially acceptable yield of olefins, in particular light olefins like ethylene and propylene, while reducing the amount of paraffinic naphtha starting material required, is therefore necessary in the technical.

Refineries produce a wide range of products. Some of them may, depending on the technical requirements of local markets and other commercial considerations, have low commercial value and are therefore considered to be "surplus". Currently, products such as gasoline and certain gaseous hydrocarbons are considered to be obtained in too large quantities. If products of this type can be used in certain petrochemical processes, they are not commonly used in steam cracking operations, since, for liquid products, they do not have the required amount of paraffins.

Ethane and propane are used as feedstocks for steam cracking, particularly in the United States, where the natural gas from which they are extracted is abundant. These paraffins generate a large amount of ethylene (greater than 50%), when they are steam cracked, which leads to treating these fillers in units specifically dimensioned for this type of fillers. Some refinery hydrocarbon gases, such as FCC gases, contain substantial amounts of paraffins (ethane and propane) and olefins (ethylene, propylene). However, when they are steam cracked as such, they tend to generate cracked gaseous effluents having a composition which is different from that of steam cracking effluents of normal naphtha. This poses a problem, as it generates an imbalance in the section, downstream (in particular, the distillation columns) of a naphtha-cracking steam cracker.

Butane and propane are also used, either alone or in admixture with naphtha, as feedstocks for steam crackers. When trying to use them exclusively, the problem of imbalance in the downstream section of a naphtha steam cracker also arises.

Depending on the availability of the refinery or the market, these liquefied gases may be in excess and it is therefore advantageous to use them as a filler for a steam cracker.

DE-A-3708332, already cited, does not address the technical problem which consists in producing an effluent whose composition corresponds to that produced by the steam cracking of a naphtha. In the examples of

DE-A-3708332, when ethylene is added (alone) to naphtha, the composition of the effluent, particularly with regard to ethylene and propylene, is substantially altered compared to the cracking of naphtha alone in the same conditions, which can lead to a significant reduction in the capacity of the steam cracking unit.

A petrochemical process which brings greater economic value to "surplus" refined products, such as gasoline and gaseous hydrocarbons, is also required in the art. The invention aims to at least partially satisfy these needs.

To this end, the invention provides a process for the steam cracking of naphtha, this process comprising the passage through a steam cracker, in the presence of steam, of a hydrocarbon feed, which comprises part of a paraffinic naphtha modified by l addition of the combination of a first component, comprising a part of gasoline, and of a second component, comprising a part of at least one hydrocarbon refinery gas, and of a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of both. The invention also provides a hydrocarbon composition suitable for steam cracking, comprising a part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a part of gasoline, and a second component, comprising a part of at least one hydrocarbon refinery gas, and of a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of the two.

The invention further provides a method for controlling a steam cracker, this process comprising providing a steam cracker and a hydrocarbon feed comprising part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a part of gasoline, and a second component, comprising a part of at least one hydrocarbon refinery gas and of a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of the two, and continuously monitoring the contributions of paraffinic naphtha, of the second component and of gasoline in the feed, in order to give the effluent a desired target composition.

The invention further provides an apparatus for controlling a steam cracker, this apparatus comprising means for supplying a steam cracker with a hydrocarbon charge comprising part of a paraffinic naphtha, modified by the addition of the combination of a part d '' a petrol and a part of at least one hydrocarbon refinery gas and / or a part of butane or propane or a mixture of the two, and means for continuously controlling the parts of paraffinic naphtha, refinery gas and / or butane or propane or a mixture of the two, and gasoline in the feed, in order to give the effluent a desired target composition.

The invention also provides a method for treating a charge of sulfur gasoline, this method comprising the following phases: combining a charge of sulfur gasoline with a charge of naphtha to provide a composite charge; passing the composite charge through a steam cracker, in the presence of steam, to produce an effluent, the effluent containing at least light olefins, the light olefins comprising at least one of the C2 to C4 olefins, and C5 + hydrocarbons; and separating from the effluent a first fraction which is practically free of sulfur and comprises light olefins, and a second fraction which contains sulfur and comprises C5 + hydrocarbons.

The invention is based on the surprising discovery by the Applicant that by selecting certain quantities and qualities of these gasolines and of these gaseous hydrocarbons and by using them as fillers in combination with naphtha, it is possible to steam crack the composite charge to thereby produce a composition for the cracked product (called in the art "product palette") which strongly resembles a product palette resulting from a steam cracking, under similar conditions, of a charge of paraffinic naphtha only. The composition of the effluent produced according to the invention is within a range of ± 20% by weight and, from preferably ± 10% by weight, for each component, relative to that of the effluent, when the latter is an unmodified paraffinic naphtha.

In reality, therefore, part of the charge of paraffinic naphtha is, according to the invention, replaced by a combination of a charge of petrol and a charge of hydrocarbon refinery gas and / or a charge of butane or propane or a mixture of both.

This has the combined advantages (a) of reducing the amount of paraffinic naphtha feedstock required for the steam cracking process and (b) of using "excess" gaseous and petroleum products in the steam cracking process to produce economically beneficial and useful products, namely light olefins, with only a few minor modifications to the steam cracking unit, since the overall material balance is only slightly modified.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 shows schematically a unit for the steam cracking of charges containing naphtha according to an embodiment of the invention.

According to the invention, a process for the steam cracking of naphtha uses a charge of a hydrocarbon composition, which comprises a part of a paraffinic naphtha, modified by a part of a gasoline in combination with a part of a gas. hydrocarbon refinery and / or part of butane or propane or a mixture of the two

The paraffinic naphtha to be used in the process of the invention comprises from 10 to 60% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 35% by weight of naphthenes, from 0 to 1 % by weight of olefins and from 0 to 20% by weight of aromatics. A typical paraffinic naphtha for use in the process of the invention comprises about 31% by weight of n-paraffins, 35% by weight of isoparaffins (giving a total paraffinic content of 66% by weight), 26% by weight of naphthenes , 0% by weight of olefins (typically 0.05% by weight of olefins) and 8% by weight of aromatics. According to the invention, this charge of starting paraffinic naphtha is modified by adding thereto a gasoline and a hydrocarbon refinery gas and / or butane or propane or a mixture of the two. is preferably a cut from a unit of

FCC ("fluidized-bed catalytic cracking") of an oil refinery (here called FCC gasoline), which, advantageously, has not been subjected to a hydrogenation treatment (designated in the technique "hydrorefining"), which increases the paraffin content of gasoline by hydrogenating the unsaturated functions (such as those present in olefins and diolefins) of gasoline. The advantage of using a non-hydrorefined FCC gasoline is that by avoiding a hydrogenation process, production costs are reduced, eliminating or reducing the use of hydrogen and avoiding the need for capacity. additional hydrorefining.

The essence of FCC is a cut or mixture of cuts from the FCC unit typically having a distillation range between 30 and 160 ° C, preferably a cut or mixture of cuts boiling in the range between 30 and 65 ° C, 65 to 105 ° C and 105 to 145 ° C. The choice of particular FCC gasoline or mixture thereof to be used can be determined based on the requirements at any time for the various cuts produced by the refinery. For example, some gasoline cuts have an octane deficit and could be better valued in a steam cracker rather than having to increase the octane number in the refinery. In addition, the FCC gasoline to be used may have a sulfur content which would be too high for gasolines to be used in the automotive sector and which would require a hydrogen desulfurization treatment, which is expensive because it consumes l hydrogen and requires the corresponding capacity on a desulfurization unit.

It is preferred to use non-hydrorefined FCC gasoline because, in the refinery, where there is a need for hydrorefined gasoline for other uses, this can cause bottlenecks in the unit treatment. hydroprocessing. By reducing the amount of non-hydrorefined gasoline present in the refinery, namely by consuming the non-hydrorefined gasoline in the steam cracking process of the invention, this can drain the apparatus and the hydrorefining units, thereby improving flow management in the refinery, and also reducing the need for hydrogen.

Typically, the essence of non-hydrorefined FCC comprises from 0 to 30% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 80% by weight of naphthenes, from 5 to 80% by weight olefins and from 0 to 60% by weight of aromatics. More typically, the non-water-refined FCC gasoline comprises approximately 3.2% by weight of n-paraffins, 19.2% by weight of isoparaffins (giving a total paraffin content of 22.4% by weight), 18% by weight of naphthenes, 30% by weight of olefins and 29.7% by weight of aromatics.

If, however, a hydrorefined FCC gasoline was used, a substantial amount of hydrogen would be required to hydrogenate it and the hydrorefined composition would resemble a typical naphtha used for steam cracking. With respect to the refinery gas which is added, in combination with FCC gasoline and / or butane or propane or a mixture of the two, to paraffinic naphtha, to produce a composite charge for steam cracking, this gas hydrocarbon is rich in C ₂ and C ₃ hydrocarbons, in particular in paraffins (ethane and propane) and in olefins (ethylene and propylene). Preferably, the refinery gas has the following composition ranges: 0 to 5% by weight of hydrogen, 0 to 40% by weight of methane, 0 to 50% by weight of ethylene, 0 to 80% by weight of ethane, 0 to 50% by weight of propylene, 0 to 80% by weight of propane and 0 to 30% by weight of butane. A typical composition of such a refinery gas is approximately 1% by weight of hydrogen, 2% by weight of nitrogen, 0.5% by weight of carbon monoxide, 0% by weight of dioxide of carbon, 10% by weight of methane, 15% by weight of ethylene, 32% by weight of ethane, 13% by weight of propylene, 14% by weight of propane, 2% by weight of isobutane, 4% by weight weight of n-butane, 3% by weight of butene, 2% by weight of n-pentane, and 1.5% by weight of n-hexane.

With regard to butane and / or propane or the mixture of the two which is added to paraffinic naphtha, in combination with FCC gasoline and optionally refinery gas, to produce a composite charge for steam cracking, this butane and / or this propane or the mixture of two may contain compounds olefins such as butenes and / or propylene, or saturated compounds such as butanes (normal and / or iso) and / or propane. Preferably, the butane and / or propane or the mixture of the two contains more than 50% by weight of saturated compounds to maximize the production of light olefins such as ethylene and propylene. Butane and propane are preferably n-butane and n-propane.

According to the process of the invention, the parts of naphtha, refinery gas, butane or propane or a mixture of the two, and gasoline are combined to form a composite charge, which is then subjected to steam cracking. Preferably, the composite charge comprises from 5 to 95% by weight of naphtha, from 5 to 95% by weight of a mixture of refinery gas, butane or propane or a mixture of the two, and of gasoline. Typically, the mixture of refinery gas, butane or propane or a mixture of the two, and gasoline which is added to naphtha comprises up to 60% by weight of refinery gas and / or butane or propane or a mixture of the two, and at least 40% by weight of gasoline, more typically up to 50% by weight of refinery gas and / or butane or propane or a mixture of the two, and up to 50% by weight of gasoline. More preferably, the composite naphtha comprises 80% by weight of naphtha, 7% by weight of refinery gas and / or butane or propane or a mixture of the two, and 13% by weight of non-hydrorefined FCC gasoline .

The composite charge of naphtha, gasoline, refinery gas and / or butane or propane or a mixture of the two, is typically subjected to steam cracking under conditions similar to those known in the art, namely a temperature comprised between 780 and 880 ° C, preferably between 800 and 850 ° C. The amount of vapor can also fall within ranges known in the art, typically between 25 and 60% by weight based on the weight of the hydrocarbon feed.

With reference to Figure 1 of the accompanying drawing, the hot section of a steam cracking unit to be used in the process of the invention is shown schematically. The steam cracking unit, generally indicated by 2, comprises a heating assembly consisting of ovens 4, which is provided with coils 6 having a first inlet 8 for the load of hydrocarbons to be cracked and a second inlet 10 for the steam. An outlet pipe 12 from the assembly of heating is connected to a primary fractionation column 14. The primary fractionation column 14 includes a reflux of gasoline at the head 15 and outlets for the various fractionated products, including an upper outlet 16 for light hydrocarbons and a lower outlet 18 for heavy hydrocarbons, which can be returned at 19 after cooling in line 12 to control the temperature or withdrawn at 17 in the form of heavy products called pyrolysis oil.

In this simplified description and in the presentation of the examples which follow, only the fillers coming from outside the steam cracker, commonly called fresh fillers, are considered, and not any recycles of products originating from the steam cracker itself, such as ethane often recreated until extinction.

If desired, the entire composite charge of naphtha, refinery gas, and / or butane or propane or the mixture of the two and gasoline can be supplied from the common hydrocarbon inlet 8 or, alternatively, the four components of naphtha, FCC gasoline, refinery gas and / or butane or propane or a mixture of the two can be cracked separately in specific tubular coils. In a particular embodiment, naphtha and FCC gasoline, on the one hand, butane and / or propane or a mixture of the two, and refinery gas, on the other hand, are cracked separately. The reason is that naphtha and FCC gasoline are typically cracked at temperatures which are close to each other, typically in the range of 750 to 850 ° C, while butane, propane and refineries that contain ethane and propane must be cracked at higher temperatures, typically in the range of 800 to 900 ° C. The two effluents can be combined at the outlet of the heating assembly before the primary fractionation column.

The process of the invention can operate continuously and has the advantage of eliminating excess gasoline from the refinery, and also reducing the need in the refinery for a desulfurization process. Petrol contains sulfur and, following the steam cracking process, in which petrol provides part of the composite charge, the most interesting light olefins in the effluent are free of sulfur, while sulfur remains concentrated in the game C5 + of the effluent current. Therefore, the use of gasoline as part of a steam cracked feedstock to produce lighter olefins results in partial desulfurization of the gasoline portion of the feedstock, since the sulfur is concentrated in the carbon number fraction higher and commercially less attractive effluent, namely the C5 + stream.

Correspondingly, in another aspect, the invention provides a method for treating a charge of sulfur gasoline, the method comprising the following steps: combining a charge of sulfur gasoline with a charge of naphtha to provide a composite charge; passing the composite charge through a steam cracker, in the presence of steam, to produce an effluent, the effluent containing at least light olefins, the light olefins comprising at least one of the C2 to C4 olefins, and C5 + hydrocarbons; and separating from the effluent a first fraction which is practically free of sulfur and comprises light olefins, and a second fraction which contains sulfur and comprises C5 + hydrocarbons. In this way, the sulfur is redistributed in the higher carbon number fraction, producing a lower sulfur-free olefinic fraction, which is an effective way to partially desulfurize the gasoline charge.

In addition, the method offers the advantage that the steam cracking treatment dehydrates at least partially the ethane present in the refinery gases, the dehydrogenation being carried out at a temperature high enough to efficiently produce ethylene.

The invention also offers the advantage that by adding to the charge of naphtha, which does not contain or only a small amount of olefins, a non-water-refined essence, which contains a relatively high amount of olefins, typically from 5 to 80% by weight of olefins, the composite charge for steam cracking has a higher overall content of olefins, compared with the naphtha alone, and this translates into a lower energy expenditure for the production of light olefins (i.e. ie ethylene and propylene) from this charge, by comparison with the steam cracking of paraffins or paraffinic charges into light olefins of this type. According to another aspect of the invention, software, using linear or non-linear programming, is used continuously to control the steam cracking conditions, in particular to control the parts of paraffinic naphtha, refinery gas, butane and / or propane or a mixture of both and FCC gasoline in the feed, so that the effluent has the desired target composition. For example, the target composition can have substantially the same effluent composition for the important constituents, that is to say ± 20% by weight, preferably ± 10% by weight relative to that of the unmodified filler. The software can also control the shipment of refinery gas and / or control the quantities of FCC gasoline and / or butane or propane or a mixture of the two, taken from the refinery, by shipping, for example, excess quantities to storage tanks. The invention will now be described in more detail with reference to the following two examples.

EXAMPLE 1 In this example, a composite charge comprising 80% by weight of naphtha and 20% of a mixture of refinery gas and non-hydrorefined FCC gasoline, according to a weight ratio of one third of gas and two thirds of gasoline, has been subjected to steam cracking.

Naphtha has the following approximate starting composition:

- 31% by weight of n-paraffins,

- 35% by weight of isoparaffins (giving a total paraffinic content of 66% by weight),

- 26% by weight of naphthenes, -0.05% by weight of olefins,

- 0% by weight of diolefins,

- 8% by weight of aromatics. The refinery gas has the following approximate starting composition:

- 1% by weight of hydrogen,

- 2% by weight of nitrogen,

- 0.5% by weight of carbon monoxide, - 0% by weight of carbon dioxide,

- 10% by weight of methane,

- 15% by weight of ethylene, - 32% by weight of ethane,

- 13% by weight of propylene,

- 14% by weight of propane,

- 2% by weight of isobutane, - 4% by weight of n-butane,

- 3% by weight of butene,

- 2% by weight of n-pentane,

- and 1.5% by weight of n-hexane.

The non-hydrorefined FCC gasoline has the following approximate starting composition:

- 3% by weight of n-paraffins,

- 19% by weight of isoparaffins (giving a total paraffinic content of 22% by weight),

- 18% by weight of naphthenes, - 30% by weight of olefins,

- 30% by weight of aromatics.

After steam cracking, the overall effluent from all of the outgoing furnaces 12 without any recycling of ethane produced by the steam cracker to the composition indicated in Table 1.

Table 1

Composition of the effluent of Example 1

° λ D by weight

(approximate)

H ₂ 0.9

Methane 16.0

Acetylene 0.2

Ethylene 22.0

Ethane 5.3

methylacetylene

Propadiene 0.3

Propane 0.6

Propylene 12.5

Butadiene 3.4

C4 4.4 C5 3.8

Benzene 8.9

Toluene 6.3

Non-aromatic essence 2.0

Aromatic essence 6.9

Fuel oil 6.5

In contrast, when 100% of the same naphtha was subjected to steam cracking under the same conditions, the effluent obtained had the composition indicated in Table 2.

Table 2

Naphtha Refinery gas FCC gasoline, non-refined

Hydrogen 0.8 2.6 0.6

Methane 15.2 27.4 13.6

Acetylene 0.2 0.2 0.1

Ethylene 21.8 43.5 12.5

Ethane 5.0 12.5 3, 1

MAPD 0.4 0, 1 0.3

Propylene 14.2 2.7 7.5

Propane 0.6 0.5 0.3

Butadiene 3.7 1.7 2.2

C4 5, 1 0.4 2.5

C5 4.3 0.6 2.2

Benzene 9, 1 3.8 10.0

Toluene 5.4 0.5 14.9

Non-aromatic essence 2.4 0, 1 1, 1

Aromatic essence 5.8 1.4 16.8

Fuel oil 6.0 2.0 12.3

It can be seen that the effluent resulting from the steam cracking of the combination of the three charges of paraffinic naphtha, refinery gas and non-hydrorefined FCC gasoline, very closely resembles the effluent resulting from the steam cracking of a single corresponding paraffinic naphtha. Thus, the composition of the effluent of the composite charge of Example 1 is similar (± 10% by weight for each constituent) to that of the naphtha alone, but part of the naphtha has been replaced by the addition of FCC refinery and gasoline for the reasons and with the benefits stated above. It can be seen that high yields of ethylene and propylene are obtained according to the process of the invention, similar to those which can be obtained simply by steam cracking of paraffinic naphtha. Table 2 also shows, by contrast, the compositions of the effluents obtained by steam cracking of the only refinery gas and, separately, of the only FCC gasoline. It can be seen that the steam cracking of non-hydrorefined FCC gasoline produces a low yield of ethylene and propylene and that the steam cracking of refinery gas produces a high yield of ethylene, but a low yield of propylene. However, when the three charges of naphtha, refinery gas and non-hydrorefined FCC gasoline, are combined, the composition of the effluent is very similar to that of normal naphtha.

EXAMPLE 2

In this example, a composite charge comprising 60% by weight of naphtha and 40% by weight of a mixture of butane and non-hydrorefined FCC gasoline, according to a weight ratio of half gas and half gasoline, has been subjected to steam cracking.

Naphtha has the same starting composition as in the previous example.

In this example, butane is normal pure butane, as it can be produced at the outlet of an alkylation unit in a refinery.

The non-hydrorefined FCC gasoline has the same starting composition as in the previous example.

After steam cracking, the overall effluent from all of the outgoing furnaces 12 without any recycling of the ethane produced by the steam cracker to the composition indicated in Table 3.

Table 3 Composition of the effluent of Example 2

% in weight

(approximate)

H ₂ 0.8

Methane 15.4

Acetylene 0.2 Ethylene 21.9

Ethane 4.8

methylacetylene

Propadiene 0.4

Propylene 14, 1

Propane 0.5

Butadiene 3.2

C4 5.9

C5 3.7

Benzene 7.7

Toluene 6.3

Non-aromatic essence 2, 1

Aromatic essence 6.9

Fuel oil 6, 1

In contrast, when 100% of the same naphtha was subjected to steam cracking under the same conditions, the effluent obtained had the composition indicated in Table 2 and recalled in Table 4.

Table 4

Naphtha Butane Essence of FCC not hydrorefined

Hydrogen 0.8 0.9 0.6

Methane 15.2 18.8 13.6

Acetylene 0.2 0.4 0.1

Ethylene 21.8 32.7 12.5

Ethane 5.0 5.9 3, 1

MAPD 0.4 0.3 0.3

Propylene 14.2 19.7 7.5

Propane 0.6 0.4 0.3

Butadiene 3.7 2.8 2.2

C4 5, 1 11.2 2.5

C5 4.3 2.2 2.2

Benzene 9, 1 2.2 10.0

Toluene 5.4 0.6 14.9

Non-aromatic essence 2.4 0.8 1.1

Aromatic essence 5.8 0.5 16.8

Fuel oil 6.0 0.6 12.3

It can be seen that the effluent resulting from the steam cracking of the combination of the three charges of paraffinic naphtha, butane and non-hydrorefined FCC gasoline very closely resembles the effluent resulting from the steam cracking of the only corresponding paraffinic naphtha.

Thus, the composition of the effluent of the composite charge of Example 2 is similar (± 10% by weight for each constituent) to that of naphtha alone, but part of the naphtha has been replaced by the addition of butane and of FCC essence for the reasons and with the benefits set out above. It can be seen that high yields of ethylene and propylene are obtained according to the process of the invention, similar to those which can be obtained simply by steam cracking of paraffinic naphtha. Table 4 also shows, by contrast, the compositions of the effluents obtained by steam cracking of only butane and, separately, of only FCC gasoline. It can be seen that the steam cracking of non-hydrorefined FCC gasoline produces a low yield of ethylene and propylene and that the steam cracking of butane produces high yields of ethylene, propylene and C4 and low yields of heavy products. However, when the three charges of naphtha, butane and non-hydrorefined FCC gasoline are combined, the composition of the effluent very closely resembles that of a normal naphtha.

Claims

1. A method for steam cracking naphtha, this process comprising passing a steam cracker, in the presence of steam, a hydrocarbon charge which comprises part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a part of gasoline, and a second component, comprising a part of at least one hydrocarbon refinery gas and of a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of the two.

2. The method of claim 1, wherein the filler comprises from 5 to 95% by weight of naphtha and from 95 to 5% by weight of a mixture of the first and second components.

3. The method of claim 2, wherein the mixture of the first and second components which is added to the naphtha comprises up to 60% by weight of the second component and at least 40% by weight of gasoline.

4. The method of claim 3, wherein the mixture of the first and second components which is added to the naphtha comprises up to 50% by weight of the second component and at least 50% by weight of gasoline.

5. The method of claim 3 or 4, wherein the mixture of the first and second components which is added to the naphtha comprises approximately one third in% by weight of the second component and approximately two thirds in% by weight of gasoline.

6. A method according to any one of the preceding claims, wherein the filler comprises about 80% by weight of naphtha, about 7% by weight of the second component and about 13% by weight of gasoline.

7. Method according to any one of claims 1 to 6, in which the paraffinic naphtha comprises from 10 to 60% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 35% by weight naphthenes, from 0 to 1% by weight of olefins and from 0 to 20% by weight of aromatics.

8. A method according to any one of claims 1 to 7, wherein the gasoline is a section of a catalytic steam cracking unit in a fluidized bed (FCC).

9. The process according to claim 8, wherein the FCC gasoline is non-hydrogenated and therefore contains unsaturated hydrocarbons.

10. The method of claim 9, wherein the FCC essence is a cut or mixture of cuts of the FCC unit having a distillation range between 30 and 160 ° C.

11. The method of claim 10, wherein the FCC gasoline comprises from 0 to 30% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 80% by weight of naphthenes, 5 to 80% by weight of olefins and 0 to 60% by weight of aromatics.

12. Process according to any one of claims 1 to 11, in which the refinery gas comprises from 0 to 5% by weight of hydrogen, from 0 to 40% by weight of methane, from 0 to 50% by weight of ethylene, from 0 to 80% by weight of ethane, from 0 to 50% by weight of propylene, from 0 to 80% by weight of propane and from 0 to 30% by weight of butanes.

13. Method according to any one of claims 1 to 12 wherein the second component comprises a filler rich in paraffins containing at least 50% by weight of saturated hydrocarbons, said filler comprising at least propane or butane.

14. Method according to any one of claims 1 to 13 wherein the second component consists at least of propane and butane.

15. A method according to any one of claims 1 to 14, wherein the composite charge of naphtha, gasoline and and the second component is subjected to steam cracking under conditions comprising a temperature between 780 and 880 ° C.

16. The process according to any of claims 1 to 15, wherein the amount of steam is 25 to 60% by weight based on the weight of the hydrocarbon feed.

17. Hydrocarbon composition suitable for steam cracking, comprising a part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a gasoline part, and a second component, comprising a part of at least one hydrocarbon refinery gas and of a paraffin-rich feed comprising at least one paraffin selected from propane and butane or a mixture of the two.

18. The hydrocarbon composition of claim 17, wherein the composition comprises from 5 to 95% by weight of naphtha and from 95 to 5% by weight of a mixture of the first and second components.

19. The hydrocarbon composition of claim 18, wherein the mixture of the first and second components which is added to the naphtha comprises up to 60% of the second component and at least 40% by weight of gasoline.

20. The hydrocarbon composition of claim 19, wherein the mixture of the first and second components which is added to the naphtha comprises up to 50% of the second component and at least 50% by weight of gasoline.

21. The hydrocarbon composition according to claim 19 or 20, wherein the mixture of the first and second components which is added to the naphtha comprises about one third in% by weight of the second component and about two thirds in% by weight of gasoline .

22. Hydrocarbon composition according to claim 21, wherein the charge comprises approximately 80% by weight of naphtha, approximately 7% by weight of the second component and approximately 13% by weight of gasoline.

23. Hydrocarbon composition according to any one of claims 17 to 22, in which the paraffinic naphtha comprises from 10 to 60% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 35 % by weight of naphthenes, from 0 to 1% by weight of olefins and from 0 to 20% by weight of aromatics.

24. Hydrocarbon composition according to any one of claims 17 to 23, in which the FCC gasoline comprises from 0 to 30% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 80% by weight of naphthenes, from 5 to 80% by weight of olefins and from 0 to 60% by weight of aromatics.

25. Hydrocarbon composition according to any one of claims 17 to 24, in which the refinery gas comprises from 0 to 5% by weight of hydrogen, from 0 to 40% by weight of methane, from 0 to 50% by weight of ethylene, from 0 to 80% by weight of ethane, from 0 to 50% by weight of propylene, from 0 to 80% by weight of propane and from 0 to 30% by weight of butanes.

26. Hydrocarbon composition according to any one of claims 17 to 25, in which the second component comprises a filler rich in paraffins containing at least 50% by weight of saturated hydrocarbons, said filler comprising at least propane or butane.

27. A hydrocarbon composition according to any of claims 17 to 26, wherein the second component consists of at least propane and butane.

28. A method for controlling a steam cracker, this process comprising providing a steam cracker and a hydrocarbon feed comprising a part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a part of gasoline, and of a second component, comprising a part of at least one hydrocarbon refinery gas and of a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of two, and the continuous control of the contributions of paraffinic naphtha, of the second component and of the gasoline in the feed, in order to give the effluent a desired target composition.

29. The method of claim 28, wherein the target composition is substantially the same effluent composition, namely ± 20% by weight for any given effluent component, as that obtained with unmodified paraffinic naphtha.

30. The method of claim 28 or 29, wherein the second component and the gasoline are both supplied directly by a refinery and further comprising controlling the dispatch of the second excess component to the flare and / or controlling the amount of gasoline in the refinery.

31. The method of any of claims 28 to 30, wherein the supply of the feed components to the steam cracker is software controlled.

32. Apparatus for controlling a steam cracker, this apparatus comprising means for supplying a steam cracker with steam and a hydrocarbon charge comprising part of a paraffinic naphtha, modified by the addition of the combination of a first component, comprising a part of gasoline, and a second component, comprising a part of at least one refinery gas hydrocarbon and a charge rich in paraffins comprising at least one paraffin selected from propane and butane or a mixture of the two, and control means for continuously monitoring the contributions of paraffinic naphtha, of the second component and of the gasoline in the feed, in order to give the effluent a desired target composition.

33. Apparatus according to claim 32, in which the control means are suitable for controlling the target composition in order to have substantially the same effluent composition, namely ± 20% by weight for any given effluent component, relative to that of unmodified paraffinic naphtha.

34. Apparatus according to claim 32 or 33, further comprising means for supplying both the second component and the gasoline directly from a refinery and further comprising means for controlling the dispatch of the second excess component to a fuel gas system and / or control the amount of gasoline in the refinery.

35. Apparatus according to any one of claims 32 to 34, in which the supply of the components of the charge to the steam cracker is controlled by software.

36. A method for treating a charge of sulfur gasoline, this method comprising the following stages: combining a charge of sulfur gasoline with a charge of naphtha to provide a composite charge; passing the composite charge through a steam cracker, in the presence of steam, to produce an effluent, the effluent containing at least light olefins, the light olefins comprising at least one of the C2 to C4 olefins, and C5 + hydrocarbons; and separating from the effluent a first fraction which is practically free from sulfur and comprises light olefins, and a second fraction which contains sulfur and comprises C5 + hydrocarbons.