JPH0639414B2 - Process for producing olefins from natural gas - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an olefin from natural gas.

PRIOR ART AND PROBLEMS TO BE SOLVED Natural gas is a rich fossil feedstock consisting essentially of methane. The reserves currently confirmed are around 10 ¹⁴ m ³ , which is about 50 years of global consumption. Gas veins often contain large amounts of ethane, propane, other higher alkanes, and other components such as H ₂ O,
Containing _{CO 2, N 2, H 2} S and He. Most of the propane and other higher alkanes associated with natural gas are liquefied and are called LPG (liquefied petroleum gas). In helium-rich veins (generally greater than 0.3% by volume), helium is separated due to its high commercial value. Similarly, due to its corrosive nature, hydrogen sulfide is separated because water forms hydrates that are detrimental to the transport of natural gas. The resulting natural gas is then called non-condensed gas,
It contains mainly (for example 55 to 99% by volume) methane, and ethane, generally propane, and optionally small amounts of nitrogen and / or carbon dioxide.

Most of the natural gas is used for industrial individual heating. However, there are several methods for converting natural gas into higher hydrocarbons.

Direct conversion of natural gas to ethylene is also a very desirable goal. This is because ethylene can be used as a raw material used for the synthesis of many important substances.

Both thermal and catalytic pyrolysis of methane are methods that can achieve this end. However, it involves very endothermic processes that require very large amounts of energy. Moreover, these two methods produce undesirably high amounts of coke.

The thermal decomposition of ethane is also a very endothermic and therefore very energy-consuming known method. However, the thermal decomposition of ethane is carried out at a lower temperature than the thermal decomposition of methane, so that these two compounds cannot be converted simultaneously. Thus, when operating at ethane conversion temperatures, the methane present in the feedstock containing ethane exits the reactor essentially unchanged.

Oxidative coupling of methane in sequential or simultaneous processes has been proposed to produce ethylene and other hydrocarbons.

The oxidative coupling reaction in the sequential method consists of separately carrying out the oxidation of methane by a reducing substance (agent reductible) and then the reoxidation of this reducing substance by the oxygen of the air. In many US patents (eg 4,499,
323, 4,523,049, 4,547,611, 4,567,307), metals, especially Mn, Ce, Pr, Sn, In, Ge, Pb,
The use of many oxides of Sb, Bi, Tb as reducing substances for this reaction is described.

The oxidative coupling reaction (scavenging of a mixture of methane and oxygen on a contact substance) in a simultaneous manner is qualitative (qualitat).
can be described as follows: CH ₄ + O ₂ → C ₂ H ₆ + C ₂ H ₄ + other hydrocarbons + CO + CO ₂ + H ₂ + H ₂ O Many patents (eg European patent EP 210 383 A2) , EP 189 0
79 A1, EP 206 044 A1 and WO 86 07351), in a simultaneous process, the oxidative coupling of methane of rare earth oxides, alkali and alkaline earth oxides, titanium, zirconium, hafnium and zinc oxides. A single or mixed use as a reaction catalyst is described.

About 65% of the above studies on oxidative coupling of methane
It should be noted that for the above C ₂ ⁺ product selectivities, a small ratio of ethylene to ethane was produced, generally about 0.8-1.2. Such small ethylene to ethane ratios require the separation of ethane from ethylene and the costly pyrolysis of ethane to ethylene. It should also be noted that the above work on the oxidative coupling of methane did not take into account the other major constituents of natural gas, such as ethane, propane and other saturated hydrocarbons. The oxidative coupling process of methane described above is hardly suitable for the selective conversion of natural gas to olefins because of the presence of significant amounts of light hydrocarbons (eg ethane and propane) in natural gas. The relative oxidation rate of light alkanes under the oxidative coupling condition of methane is about 15 to 100 times faster than that of methane. That is, light hydrocarbons are converted to ethylene and carbon oxides before methane starts the reaction. Therefore, the method cannot be effectively applied to natural gas.

[Means for Solving the Problems] The presence of propane and, in some cases, other higher alkanes in natural gas may lead to the occurrence of light hydrocarbons coming from another device, for example, located near the oxypyrolysis unit for natural gas. Taking into account its presence, it is very advantageous to make effective use of propane and possibly other higher alkanes in addition to methane and ethane.

Similarly, one of the objects of the present invention is to provide a process for the production of olefins, in particular ethylene and propene, from natural gas in high yields.

Another object of the invention is to provide a process for the dehydrogenation of alkanes leaving a methane oxidation reactor without the need for a separate pyrolysis reactor.

These objects can be achieved by the process according to the invention of the oxypyrolysis of natural gas, which comprises the following steps: (1) a step of separating the natural gas into two fractions: the methane-rich first gas fraction. (Which is preferably substantially free of ethane, propane and other hydrocarbons associated with natural gas),
Second gas fraction enriched with hydrocarbons higher than methane (especially ethane and propane, with or without non-hydrocarbon gases); (2) molecular in the presence of contact substances A step of selectively oxidizing a first gas fraction containing methane with oxygen to form an effluent containing C ₂ hydrocarbons and water as main products: (3) enriched with hydrocarbons higher than methane The separated second gas fraction into two new fractions: a propane-rich first gas fraction and an ethane-rich second gas fraction; (4) introduced in step (2) Where the at least about 80% by volume (preferably at least about 95%) of molecular oxygen has been consumed, the ethane-rich second gas fraction coming from step (3) is Or the presence of gas became Etanritchi not than derived from natural gas, step
Adding to the effluent of the selective oxidation reaction of methane of (2); (5) pyrolyzing a mixture of the effluent and the ethane-rich second gas fraction from step (3); (6) Where the pyrolysis effluent of step (5) has an olefin / C ₂ ⁺ alkane molar ratio of at least 0.5, with the propane-rich first gas fraction coming from step (3), alone or in natural gas. Adding to the pyrolysis effluent of step (5) in the presence of a propane-rich gas that is not derived; and (7) pyrolyzing the mixture resulting from step (6) to become olefin-rich. Producing a mixed gas mixture.

The oxypyrolysis method of natural gas according to the present invention has the following main features: (a) The heat generated during the selective oxidation reaction of methane (about 250 KJ per mol of reacted methane) is the effluent. Immediately used for the thermal decomposition of alkanes and other alkanes added; (b) sequential additions of ethane and then propane can be used to derive better benefits from this generated heat; (c) of olefins / alkanes Appropriate ratio of pyrolysis process (5)
And (7) by controlling the residence time and the temperature of the gas effluent immediately resulting from the selective oxidation of methane; (d) the effluent of the selective oxidation reaction of methane is The reaction can be introduced and used as a dehydrogenating diluent for the thermal cracking reaction of ethane and other saturated hydrocarbons; (e) ethane to ethylene by conventional thermal cracking methods,
There is no need to convert propane to propene; (f) this method allows the treatment of the entire natural gas, not just the methane contained in the natural gas. The C ₃ ⁺ alkanes can be better utilized, in particular by adding propane, and optionally other higher alkanes, after the addition of ethane.

In particular for processes in which the addition of ethane and propane to the oxidation reaction effluent of methane is simultaneous, the process according to the invention makes it possible to avoid substantial conversion of propane to propene. After such conversion, propene decay occurs before a high conversion of ethane to ethylene is obtained.

As regards the contact material for the selective oxidation reaction of methane to higher hydrocarbons (step (2) of the process of the invention), any contact material known for this use can be used,
The following contact materials are preferred; (a) normal oxidative coupling conditions, eg temperature about 650 to about.
Operable at 1,200 ° C, preferably about 650 to about 950 ° C, (b) at least about 65% for a conversion of about 15% methane.
C2 ⁺ products with a selectivity of, and (c) those that maintain their activity and selectivity during prolonged operation.

Contact materials which meet the above conditions and are therefore preferably used are generally alkali metals (eg lithium, sodium, potassium, rubidium and cesium), alkaline earth metals (eg beryllium, magnesium, calcium, strontium and barium) and rare earths. Oxides and / or carbonates of metals (eg yttrium, lanthanum, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, europium and lutetium) alone (of rare earths and alkaline earths). As in the case) or in admixture (in the case of alkaline earth metal with added alkali metal, and in the case of alkali metal and / or rare earth metal with added alkaline earth metal) ) It is intended to include. Other contact substances which meet the above conditions are oxides and / or carbonates of titanium, zirconium, hafnium, manganese, cerium, tin, indium, germanium, lead, antimony, zinc and bismuth, preferably alkali metals, alkalis. Included with one or more oxides and / or carbonates of earth metals, rare earths and silica. The above-mentioned contact substance is effective either by itself or by adding a halide or oxide of phosphorus or sulfur.

Similarly, the contact material for the selective oxidation of methane is also advantageously: (a) very short, generally effective for contact times of about 300 milliseconds or less; (b) ) During a very short contact time, at least about 80% by volume of molecular oxygen in the feed (preferably at least about 95%).
%) That can be consumed.

Particularly preferred contact materials are the following: (a) substantially corresponds to the following formula, alkaline earth and contact material comprising a rare earth _{compound: T a Ln 2 O b-} c (CO 3) c ( wherein T Represents one or more alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium, and Ln represents one or more rare earth metals such as yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium. , Gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, a = 0.001 to 1,000, b = 3 + a,
c = 0.1 to b. Preferred rare earth metals are lanthanum, neodymium and samarium, alone or mixed. The preferred rare earth metal is lanthanum. ).

(b) substantially corresponds to the following formula, an alkali earth contact material containing rare earth, and a Group IVA _{compound: T a M d Ln 2 O} e-f (CO 3) f ( wherein T is 1 Tsumata Represents multiple alkaline earth metals,
M is one or more Group IVA metals such as titanium,
Represents zirconium and hafnium, Ln represents one or more rare earth metals, a = 0.001 to 1,000,
d = 0.001 to 2, e = 3 + a + 2d-z, f = 0.1 to e,
z = 0 to 0.5d. In this formula, z is 0 to 0.5d. Thus z is 0 when the oxidation state of all Group IVA metals is +4, 0.5d when the oxidation state of these metals is +3, and the oxidation states of these metals +3 and +4. 0-0.5d when a mixture of is present.
Preferred rare earth metals are lanthanum, neodymium and samarium, and more particularly lanthanum).

However, the contact substances (a) and (b) are not limited to the above formula. In fact, the beneficial effects of rare earth metals, alkaline earth metals and, in some cases, Group IVA metals, appear in whatever form they are present. However, the form of oxide and / or carbonate is preferred.

(c) approximately corresponding to the following formula, the contact material comprises two or more alkaline earth _{metals: T g T '2-g} O h (CO 3) 2-h ( wherein T is, T' and the Represents different one or more alkaline earth metals such as beryllium, magnesium, calcium, strontium and barium, and T'is
Represents alkaline earth metals known to form stable carbonates at high temperatures, such as calcium, trontium and barium, g = 0.1-1.8, h = 0-2. Preferred alkaline earth metals T'are strontium and barium).

However, the contact substance (c) is not limited to the above formula.
In fact, the beneficial effect of the presence of at least two alkaline earth metals, of which at least one constituent is, for example, calcium, strontium or barium, is present no matter which form these metals are present. However, the form of carbonate or oxide and carbonate is preferred.

The glass fraction subjected to oxidation (step ((2)) of the method according to the invention) can be used without diluent or diluted with an inert gas such as nitrogen, carbon dioxide or steam. In order to avoid too large a temperature rise, which would impair the selectivity of the operation,
The oxygen content in methane should generally not exceed 40 mol%. Therefore, this content may be about 0.1 to 40 mol%, preferably about 5 to 25 mol%.

Temperature of oxypyrolysis reaction (step (2) of the method according to the present invention
(5) and (7)) are generally about 650 to about 1200 ° C, preferably about 650 to about 950 ° C.

The total pressure (steps (2) (5) and (7)) may be for example about 1 to about 100 bar, especially about 1 to about 20 bar. The contact time for the oxidative coupling of methane (ie the time required to carry out the consumption of at least about 80% of the molecular oxygen in the feed) is usually 10 ⁻⁶ to 1 second, preferably 10
^{It is -6} to 10 ^-1 second. The total residence time in the two pyrolysis zones (steps (5) and (7) of the process according to the invention) is preferably about 10 ⁻⁵ to 10 seconds, in particular about 10 ⁻³ to 2 seconds.

The selective oxidation of the gas fraction containing methane (step (2) of the process according to the invention) can be carried out in any type of reactor, especially in fixed bed, boiling bed, flow bed or fluidized bed reactors, preferably fixed bed reactors. It may be implemented.

Examples The following non-limiting examples illustrate embodiments that can be used to demonstrate the oxypyrolysis of natural gas according to the present invention. These methods include C after the selective oxidation step of methane.
_With stepwise addition of ₂ ⁺ saturated hydrocarbons. These first
Shown in Figures and FIG.

A natural gas stream (2), preferably purified (eg, subjected to conventional dehydration, desulfurization and carbon dioxide removal treatments),
Methane-rich gas fraction (3) in the separator (1)
And a gas fraction rich in hydrocarbons higher than methane
Sort into (4). The methane-rich gas stream (3) alone,
Alternatively, it is preheated in the presence of water vapor at a temperature generally not exceeding about 650 ° C. and then mixed with a gas rich in molecular oxygen (6) and then contacted with a fixed bed in the reactor (5). Contact materials (in fixed bed, powder, granules, extrudates, pellet form or on oxides and / or carbonates of alkaline earth metals and / or rare earth metals, zirconia, silica, alumina, quartz or monoliths such as cordierite, Mullite, which may be present in a supported form on alpha-alumina), is heated at a temperature generally from about 650 to about 1200 ° C due to the exothermic nature of the oxidation reaction.

The temperature of the contact material is a function of the initial temperature of the gas containing the mixture of methane and molecular oxygen, the effluent, and the amount and enthalpy of the mixture containing methane and oxygen, and the heat capacity of the effluent. In the case of a fluidized bed or fluidized bed reactor (5), a mixture of methane and molecular oxygen is added to the reactor.
Introduced at the bottom of (5). At that time, this raw material is used in the reactor.
Inhale hot contact material that is entrained to the top of (5). This contact material then generally descends through another passage to the bottom of the reactor (5) where it is either re-sucked or sent out of the reactor (5) for further processing. And then may be sucked again.

Then, at a location where at least about 80% (preferably at least about 95%) of the molecular oxygen is consumed, the reactor is
An ethane-rich gas stream (7) is added to the effluent of (5).

The ethane-rich added gas (7) may be introduced at ambient temperature or may be preheated at a temperature below the effluent temperature. In both cases, the additive gas
(7) serves to reduce the temperature of the effluent, producing a mixture at a temperature below that of the effluent. The temperature of this mixture can be controlled by adjusting the temperature of the feedstock of methane and the additive gas, and the initial proportion of molecular oxygen. The residence time of the mixture (effluent and said additive gas) in the pyrolysis reactor (8) is determined by the temperature of the mixture and the desired pyrolysis severity. The pyrolysis reaction may be carried out in the absence of a contact material or in the presence of one of the contact materials, such as those known for the selective oxidation of methane.

A propane-rich gas stream (9) is then added to the effluent of the reactor (8) where the effluent has an olefin / C ₂ ⁺ alkane molar ratio of at least 0.5. This added gas stream (9) may be introduced at ambient temperature or may be preheated at a temperature below the temperature of the effluent. In both cases, the addition stream (9) serves to reduce the temperature of the effluent, producing a mixture at a temperature below the temperature of the effluent. The mixture passes through a pyrolysis reactor (10).
The residence time here is determined by the temperature and the desired pyrolysis severity. The pyrolysis reaction may be carried out in the absence of a color-matching substance or in the presence of one of those known for the selective oxidation of catalytic substances, eg methane, or one of the known dehydrogenation of propane. Good.

The effluent gas of the reactor (10) is rapidly cooled (11) and discharged (12) if it is desired to use as it is. You may recycle this as well
(13). In that case, it is often advantageous to subject the gas to different fractions.

For example: -Purge. This allows gases such as H ₂ , He, N ₂
Or CO accumulation can be prevented; -amine wash. This makes it possible to remove the CO _2; - methanation. This gives CO and H ₂ to CH
₄ and H ₂ O.

These fractions are generally represented by device (14). The separated gas is removed via line (15).
The residual gas containing unconverted hydrocarbons, ethylene and propene is sent to the separator (1) via line (16).

The C ₂ ⁺ hydrocarbons coming from the separator (1) via the line (4) are subjected to the following various fractionations. For example: -C _2, C ₃ and C ₄ ⁺ fraction at low temperature that can separate under pressure, fractionation by condensation; - oligomerization of absorption in sulfuric acid, to the liquid fuel in the olefins (e.g., gasoline and / or gas oil) , Or a dimerization reaction capable of separating olefins from C ₂ , C ₃ and C ₄ ⁺ alkanes; and / or-allowing separation of olefins and C ₂ , C ₃ and C ₄ ⁺ alkanes from those skilled in the art. Any combination of known methods.

These fractions are generally represented by devices (17) and (20). The gas fraction enriched in C ₂ ⁺ hydrocarbons coming from the separator (1) is passed via line (4) to the separator (17)
Send to. Equipment for gas fractions rich in propane (17)
Is separated by and is sent to the thermal decomposition reactor (10) via the pipe (9). The unsaturated C ₃ and C ₄ ⁺ hydrocarbon-rich gas fraction is discharged from the device (17) via conduit (18). The gas fraction enriched in C ₂ hydrocarbons is fed to the device (17)
Separated by, and sent to the separator (20) via the pipe (19).
Here, the ethane-rich gas fraction is separated from the ethylene-rich gas fraction. The ethane-rich gas fraction is then passed through line (7) to the pyrolysis reactor (8).
Send to. Condense the ethylene-rich gas fraction through a conduit (21)
Through the device (20).

Samples can be taken from the lines (22) (23), in particular for measuring the conversion of molecular oxygen and the olefin / C ₂ ⁺ alkane molar ratio.

Whatever reactor type is used in the process according to the invention, separate reaction zones can be used for steps (2) (5) and (7) of said process (first
Alternatively, only a single zone containing three consecutive reaction zones may be used (Figure 2).

[Brief description of drawings]

1 and 2 are flow sheets showing an embodiment of the present invention.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C07C 11/06 9280-4H 11/08 9280-4H // C07B 61/00 300 (72) Inventor Alan Robin France Rueil Malmaison (92500) Ryu Massena 10 (72) Inventor Serge Bonode Parry France (75017) Rue du Schroy 4 (72) Inventor Patrick Chaumet France Bougival (France) 78380) · Cote de la Jonquer 34 (72) Inventor Guang Dan Veu Neuilly, France (92200) · Boulevard du General Leclerc 48 2

Claims (10)

[Claims] 1. A method for producing an olefin from natural gas containing methane, ethane and propane, wherein (1) natural gas is divided into two fractions, namely a methane-rich first gas fraction and carbonization higher than methane. Separation into a hydrogen-enriched second gas fraction, (2) In the presence of a contact substance, molecular oxygen selectively oxidizes the methane-enriched first gas fraction as the main product. Forming an effluent containing C ₂ hydrocarbons and water, (3) a second gas fraction enriched in hydrocarbons higher than methane with two new fractions, the first enriched in propane Separation into a gas fraction and an ethane-rich second gas fraction, (4) at least about 8 molecular oxygen.
When 0% by volume has already been consumed in step (2), mixing the ethane-rich second gas fraction coming from step (3) with the effluent of step (2) (5 ) Process
Pyrolyzing the mixture resulting from (4), (6) the propane-rich first coming from step (3) when the effluent of step (5) has an olefin / C ₂ ⁺ alkane molar ratio of at least 0.5. Mixing the gas fraction with the effluent of step (5), and (7) pyrolyzing the mixture resulting from step (6). 2. Prior to step (4), mixing the ethane-rich second gas fraction coming from step (3) with an ethane-rich gas not derived from natural gas,
The method according to claim 1. 3. Prior to step (6), the propane-rich first gas fraction coming from step (3) is mixed with a propane-rich gas not derived from natural gas. Or the method according to 2. 4. The process according to claim 1, wherein in step (2) oxygen is present in a proportion of about 0.001 to 0.4 mol per mol of methane. 5. The method according to claim 1, wherein the mixing in step (4) is carried out when at least 95% by volume of molecular oxygen has already been consumed in step (2). Method. 6. The steps (2), (5) and (7) are carried out at a temperature of about 650 to about 12.
A process carried out at 00 ° C. and a pressure of about 1 to about 100 bar.
~ A method according to one of 5-5. 7. The method according to claim 1, wherein the contact substance in step (2) is represented by the formula: T _a Ln _{2
O b-c (CO 3)} c ( wherein T represents at least one alkaline earth metal, Ln represents at least one rare earth metal, a = 0.001~1,000, b = 3 + a, c =
0.1-b). 8. The method according to one of claims 1 to 6, wherein the contact substance in step (2) is represented by the formula: T _a M _d L
_{n 2 O e-f (CO} 3) f ( wherein T represents at least one alkaline earth metal, Ln represents at least one rare earth metal, M is one or more Group IVA metal Representation, a = 0.001 to 1,000, d = 0.001 to 2, e
= 3 + a + 2d-z, f = 0.1 to e, z = 0 to 0.5d). 9. The effluent of step (7) is fractionated to remove carbon dioxide and then subjected to methanation to convert CO and H ₂ to CH ₄ and H ₂ O, Finally, the method according to one of claims 1 to 8, wherein the resulting gas effluent is sent again to step (1). 10. Process according to one of claims 1 to 9 for the production of ethylene and propane.