NL9300168A - Catalytic conversion of methane - Google Patents

Abstract

Method and apparatus for the catalytic conversion of methane to hydrocarbons having at least two carbon atoms, wherein a first feed gas containing methane and oxygen is delivered to a catalyst-containing first reaction chamber, said reaction chamber is kept under such temperature and pressure conditions that an exothermal conversion reaction takes place, and a product gas is discharged from the reaction chamber, which gas is relatively rich in hydrocarbons having at least two carbon atoms and water vapour, a second reaction chamber which is in heat-exchange contact with the first reaction chamber being simultaneously supplied with a second feed gas which contains hydrocarbons with or without steam or carbon dioxide, said second reaction chamber is kept under temperature conditions such as to cause an endothermal reaction to take place therein, and a product gas having the desired composition being discharged from the second reaction chamber, the process being managed in such a way that heat transfer from the first and second reaction chamber allows the temperature in both chambers to be controlled.

Description

CATALYTIC CONVERTING OF METHANE

The invention relates to a process for the catalytic conversion of methane to hydrocarbons with at least two carbon atoms, in which a first feed gas containing methane and oxygen is fed to a catalyst-containing first reaction space, this reaction space is maintained under such conditions of temperature and pressure that an exothermic conversion reaction takes place and discharges from the reaction space a product gas which is relatively rich in hydrocarbons with at least two carbon atoms and water vapor.

Catalytic oxidative conversion of natural gas (methane) to hydrocarbons with at least two carbon atoms, with higher added value, for example ethane and ethylene, is important for providing raw materials for useful chemicals.

Catalytic conversion of methane to hydrocarbons with at least two carbon atoms, especially ethane and ethylene, is a known reaction commonly referred to as methane coupling. Methan coupling in the presence of oxygen is an exothermic reaction, which releases large amounts of heat. The heat released can be used in known manner for the production of steam and, subsequently, for the generation of electricity. In practice, the exothermic nature of the catalytic conversion of methane requires measures to dissipate and convert the generated heat, which inherently leads to conversion losses. The required measures and the inherent conversion losses are the reason why the catalytic conversion of methane cannot be economically used on a large scale for the production of hydrocarbons with at least two carbon atoms.

The object of the invention is to provide a process for the catalytic conversion of methane to which the aforementioned economic disadvantage is not associated.

This object is achieved in accordance with the invention by a process in which a second feed gas containing hydrocarbons with or without steam or carbon dioxide is maintained at such conditions of temperature simultaneously to a second reaction space which is in heat exchange contact with the first reaction space. that an endothermic reaction takes place therein and a product gas of the desired composition is discharged from the second reaction space, such that the temperature in both spaces can be controlled by heat transfer from the first to the second reaction space.

Conducting the exothermic methane coupling reaction in addition to an endothermic reaction of the above type, in which heat exchange contact takes place, offers the important advantage that the methane coupling reaction can be better controlled by removing an excess of heat. For example, a less controlled reaction leads to production of CO2 instead of the desired hydrocarbons with at least two carbon atoms and to an increased production of undesired heat. The heat of reaction in the process of the invention is used to conduct an endothermic reaction. An additional advantage is that the reaction heat is used in situ, so that losses due to transport are avoided and the energy gain is maximized. Further advantages of the selective oxidation of methane according to the invention are limitations of CO2 emissions and limitation of raw material consumption.

Advantageously, the temperature in the second reaction space is kept substantially equal to the temperature in the first reaction space.

In an exemplary embodiment, the temperature in the first reaction space is kept at a value between about 600 ° C and about 1000 ° C, preferably at a value between about 700 ° C and about 900 ° C.

The pressure in the first reaction space is advantageously set to a value of approximately 1 atm.

In an exemplary embodiment, the endothermic reaction is a thermal cracking reaction, the second feed gas contains ethane, propane, LPG, butane, naphtha, gas oil or other hydrocarbons, and the product gas is rich in olefins.

In another exemplary embodiment, the endothermic reaction is a steam cracking reaction, the second feed gas contains ethane, propane, LPG, butane, naphtha, gas oil or other hydrocarbons, and the product gas is rich in olefins.

In a further exemplary embodiment, the endothermic reaction is a catalytic or non-catalytic reforming reaction for making synthesis gas, wherein the second feed gas contains methane, natural gas, LPG or other hydrocarbons in addition to steam, and the product gas is rich in carbon monoxide and hydrogen.

In yet another exemplary embodiment, the endothermic reaction is a catalytic or non-catalytic reforming reaction for making synthesis gas, wherein the second feed gas contains methane, natural gas, LPG or other hydrocarbons in addition to carbon dioxide and the product gas is rich in carbon monoxide and hydrogen.

Preferably, the catalyst in the first reaction space is particulate and is kept in a fluidized state by means of the feed gas. For example, Ca0 / Sm2O3 or α-201203 is introduced as catalyst in the first reactor.

Methan coupling in the presence of oxygen generates a lot of heat. When the selectivity of the methane coupling is sufficiently high, the CO2 production is significantly less than with a non-selective methane conversion. The selectivity of the methane linkage is defined as the percentage ratio of the number of carbon atoms in the C2 hydrocarbons formed to the number of carbon atoms from methane converted. For example, the CO2 emissions per unit of heat produced are halved compared to normal combustion when the selectivity of the methane coupling is about 85%. Thus, by cooling the exothermic methane coupling by means of an endothermic reaction, for example, cracking of ethane or other hydrocarbons, and carrying out both reactions in the same vessel but in separate compartments, both CO2 emissions and consumption of raw materials are limited.

The invention further relates to an apparatus for carrying out the above-described method, comprising a reactor in which a first reaction compartment with a catalyst for carrying out the exothermic reaction is located.

According to the invention, a second reaction compartment for carrying out the endothermic reaction is also present, which second reaction compartment is in heat-exchanging contact with the first reaction compartment.

In such a device, the endothermic reaction proceeds in a reaction space separated from the reaction space of the methane coupling. In case the endothermic reaction is, for example, the thermal cracking of ethane, this offers the following advantages. Any oxygen that has not reacted with methane cannot react with ethane or its cracking products. This prevents the yield of useful olefins from being reduced, which would be the case if any oxygen could react with ethane because the reactivity of ethane with oxygen is much higher than that of methane with oxygen. Another advantage is that the separation of olefins and unreacted starting materials is more efficient when the concentration of the former is as high as possible. In a separate reaction space, the reaction product from the second reaction compartment is prevented from being mixed with the waste gases from the first reaction compartment.

In an exemplary embodiment of an apparatus according to the invention, the reactor is tubular and consists of two concentric tubes, the compartments within these tubes each being connected to a feed gas inlet and a product gas outlet.

In another exemplary embodiment, the reactor has an upright cylindrical reaction vessel, comprising a feed gas inlet and a product gas outlet, within which the first reaction compartment is located, and the second reaction compartment is formed by a wound tube with its own inlet and outlet, which tube the first reaction compartment is running.

The wound tube consists of, for example, stainless steel or another metal. However, since the selectivity of the methane coupling reaction decreases when the methane-oxygen mixture is in direct contact with a metal at a temperature of about 750 ° C or higher, the wound tube preferably consists of or is coated with a ceramic material.

The ceramic material is selected, for example, from SiO 2, Al 2 O 3, SiN, SiC, ZrO 2, CaO, BaO, and ZnO or another basic oxide.

According to the invention, heat exchangers are preferably present in the device for heat exchange between feed gases and product gases.

The presence of heat exchangers further increases the energy efficiency of the device.

The heat exchangers are included, for example, in the supply and discharge pipes to the inlets or from the outlets of the reaction compartments, but can also be included in the reactor.

The invention will be explained in more detail below with reference to the drawing.

In the drawing: figure 1 shows a schematic representation of a methane coupling reactor in which an ethane cracking reactor is integrated; and Figure 2 is a schematic representation of a methane coupling reactor in which an ethane cracking reactor and a heat exchanger are integrated.

Figure 1 shows a reactor with a first reaction compartment 1 in which a wound tube 2 is incorporated as a second reaction compartment in a bed of catalyst material 14 (fluidized in an operating reactor). The operation of the reactor is as follows. Methane and oxygen are passed through supply lines 3 and 4 through the catalyst bed 14, which becomes fluidized. The first product gases resulting from the catalytic oxidation of the methane are discharged via a discharge pipe 5 and cooled in heat exchangers 6 with the feed gases methane and oxygen in the supply pipes 3 and 4. Steam can be generated from the excess heat in a heat exchanger 7 which is discharged via a pipe 8. The second reaction compartment 2 is fed with ethane via a supply line 9; the second product gases are discharged through discharge line 10, in heat-exchanging contact with the ethane supply line 9 in heat exchangers 11. An excess of heat is used in heat exchanger 12 to produce steam which is discharged via line 13. The temperature in the first reaction compartment is, for example, 1100 K. In addition, figure 1 shows the mass flows, expressed in molar as calculated from a reaction entropy balance. For these calculations, it is assumed that 70% of the heat is transferred from the reaction product streams and the remaining 30% is converted into steam at high pressure, from which, for example, the energy required for oxygen separation can be recovered. Cracking in the tubes proceeds with a conversion rate of 50% ethane; 95% of this (based on carbon) is converted into ethylene, the remainder is recovered as methane. The results of a thermodynamic analysis of the integrated crack are shown in Table 1.

Table 1. Integrated squats in fluidized bed C yield 93.8% CH4 consumption 0.355 t / t C2H4 C2H6 consumption 0.813 t / t C2H4

Steam generated 1.01 t / t C2H4 = 1.173 GWs electricity 02 consumption 0.637 t / t C2H4 = 1.127 GWs electricity

Steam exports 0.04 t / t C2H4 CO2 production 219 kg / t C2H4

Exergy loss 2.96 GWS / t C2H4

The integrated crack provides a great improvement over a non-integrated thermal crack. The main improvements are shown in Table 2 below.

Table 2.

Integrated thermal crack crack C yield,% 93.8 64.2 C2Hó consumption, t / t C2H4 0.813 1.141 CH4 consumption, t / t C2H4 0.355 0.562 CO2 production, kg / t C2H4 219 1746

Export steam, t / t C2H4 0.04 9.15

Loss of exergy, GWS / t C2H4 3.0 18.1

The improvements mean great savings in raw material consumption; this directly affects product costs (ethylene costs) and reduces CO2 emissions by almost one order of magnitude. An additional advantage of this method is the absence of flue gases; CO2 is not released uncontrolled into the atmosphere; N0X formation is in principle not possible. On the contrary, the integrated crack provides nitrogen (from the air separation plant) and CO2 as valuable by-products.

Figure 2 shows a schematic representation of a methane coupling reactor in which a hydrocarbon cracking reactor 2 and two heat exchangers are integrated. This device is particularly intended for integrated steam cracking reactions. In reaction compartment 1, another wound tube 2 is incorporated as a second reaction compartment in a bed of catalyst material 14. The operation of the reactor is as follows. A methane-oxygen mixture is supplied via supply line 15 to the first reaction compartment 1, in which it is preheated in a heat exchanger 16 before it is led via a distribution line 17 and vertical pipes 18 into the bottom of the catalyst bed 14. The first product gases formed during the catalytic oxidation of the methane are again discharged via a discharge pipe 5, the reaction heat being released to a wound tube 2 in the catalyst bed 14, a heat exchanger 19 in which water supplied via line 20 is converted into high-pressure steam, respectively. which is discharged via line 21 and to heat exchanger 16 in which the methane-oxygen mixture supplied via line 15 is preheated. The second reaction compartment 2 is fed via a supply line 22 with a hydrocarbon and water-containing reaction mixture which is preheated in heat exchanger 11 with the gases that are the product of the cracking reaction in the second reaction compartment 2 and which are removed via line 10. In this installation the excess heat generated in the first reaction compartment 1, i.e. the heat not used in the cracking reaction in the second reaction compartment 2, is transferred particularly efficiently via the heat exchangers 19 and 16 incorporated in the first reaction compartment 1.

It should be noted that the invention is not limited by embodiments. For example, it is possible to modify a device shown in Figure 1 such that the first reaction compartment is fed with ethane, which is cracked therein, and the methane-oxygen mixture is fed to the second reaction compartment 2, in which the methane coupling then takes place. The second reaction compartment 2 then contains a solid catalyst, while the fluidized bed 14 may contain, for example, sand, Al2O3 or corundum.

Examples

Tests were conducted in a tubular quartz reactor with two separate concentric compartments. The reaction therefore took place in separate gas flows. Cracking was performed in the inner tube and the methane coupling in the outer tube. The reaction was performed under adiabatic conditions. This was accomplished through the use of a power source that supplied a predetermined amount of power to the oven independent of the oven temperature. With this arrangement, temperature fluctuations in the inner ethane cracker tube could be attributed to the heat generated by the methane coupling reaction. All tests were performed in this configuration.

The catalyst used during the experiments under Example 1 is CaO / Sm 2 O 3 (30/70 mol / mol). The choice of this catalyst is based on tests demonstrating that this combination produces a good yield and exhibits good stability. The amount of catalyst used was 3 g and provided a sufficient methane conversion at 825 ° C (25 mol%).

The flow rate of the reaction mixture CH4 + 02 + He was adjusted from the start to 158 ml / min, with the volume ratio He: 02: CH4 = 44:19:37. The flow rate of C2H6 + He in the inner tube was adjusted to 110 ml / min with the volume ratio C2H6: He = 26:74.

To demonstrate the heat exchange between a combination of exothermic and endothermic reactions, the following series of tests was performed.

1. Initially, the methane coupling reaction was conducted in the outer reactor and ethane cracking was simultaneously conducted in the inner tube (both co-and countercurrent configurations). Both reactions were allowed to proceed until steady state and conversion were measured.

2. The methane coupling reaction mixture in the outer tube was then replaced with helium (helium is inert and does not produce heat). After stationary levels were reached, the conversion of ethane in the inner tube and the temperature were measured.

The He in the outer tube was then replaced with reaction mixture and after reaching the stationary state, the ethane conversion in the inner tube was measured.

3. This cycle was then repeated.

The change in the degree of reaction in the inner tube at the transition from step 1 to step 2 is a measure of the use of the heat produced by the methane coupling reaction in the outer tube.

Example 1

A first series of tests was performed with both reaction mixtures flowing in the same direction.

At 825 ° C, the coupling produced 29.08% C2 products and 70.9% CO2 / CO2 for 27.4% methane conversion and 99.9% oxygen conversion. Under these conditions, the temperature of the ethane cracking compartment was 827 ° C, and the ethane conversion was 64.8%. When replacing the outer tube methane coupling mixture with helium, the temperature in the inner tube dropped to 787 ° C and the ethane conversion dropped correspondingly to 52.1%. These results clearly demonstrate that the heat produced during the methane coupling reaction causes the ethane conversion to increase (52.1 - * 64.8%). These results could be reproduced cyclically.

Example 2

A second series of tests was performed with α-Α1203 instead of Ca0 / Sm203. The volume α-Α1203 was the same as the volume of the catalyst used in the previous runs to keep the conditions in the reaction the same. At 850 ° C, the composition of the gases from the methane coupling compartment after the reaction became 83.6% CO2 / CO2 and only 16.4% C2 products. The conversions were: 99.2% for 02 and 14.8% for CH4. This amount of reaction also had an effect on the cracking reaction in the inner tube. The temperature rose from 787 ° C to 802 ° C and the ethane conversion rose from 47.92% to 62.45% when helium in the outer tube was replaced with natural gas, oxygen and helium.

The most striking aspect of these tests is that in both cases (α-Al 2 O 3 and CaO / Sm 2 O 3), in the absence of the methane coupling reaction in the outer tube (He flow only), the same ethane conversion was observed in the inner tube. This means that any other heat transfer effect need not be considered.

Example 3

A third series of tests was run under the same conditions as the first, but with the reaction mixtures flowing in opposite directions. The effect on cracking was clearly no greater with this type of flow. The temperature rose from 795 ° C to 828 ° C and the ethane conversion rose from 49.9% to 67.3% when the outer tube situation was changed from no reaction (He only) to methane oxidation producing heat.

Determination of the generated / used heat during the reactions.

In the methane coupling reaction compartment, an excess of heat is generated as a result of the reaction between oxygen and methane when the gas flow is changed from inert (He) to methane and oxygen. This causes an increase in the conversion of ethane in the inner compartment and the additional heat that this incremental conversion would produce has been calculated. This would correspond to determining the difference in concentrations at temperatures 787 and 827 ° C (this temperature difference is caused by introducing the methane coupling reaction mixture into the outdoor reactor in place of He). These two values of heat (the amount of heat generated by the methane coupling reaction in the outer tube and the heat required to convert ethane to ethylene in the inner reactor) were used to compare. The results of this comparison are summarized in Tables 3 and 4 below.

Table 3.

Concentrations of different products at the exit of the methane coupling reactor and the corresponding generated heat (minus sign indicates that the heat has been released (exothermic reaction)) during the reaction. (Catalyst Ca / Sm203) (Feed concentration CH4 = 33.56.10'4 and 02 = 17.23.10'4 mol / min)

Total heat generated by the above reactions is -0.605 kJ / min.

Table 4.

* situation if the methane oxidation takes place in the outer reactor

** no reaction in the outer tube; only helium flows *** value in this column corresponds to the difference in the heat used for the reaction 827 C and 787 ° C

Concentrations of different products at the ethane cracking reactor outlet and the corresponding heat generated / used (minus sign indicates heat released (exothermicity) and plus sign indicates absorbed heat (endothermicity) during the reaction.

Total heat used for the additional amount of reaction is 0.046 kJ / min.

Metane coupling under the reaction conditions of the above examples produces 0.605 kJ / min reaction heat in the outer reactor. This is the actual difference in heat produced when the flow in the outer reactor is changed from helium to the methane coupling reaction mixture because this outer reactor is supplied with a constant (fixed) heat flux from the external furnace.

As helium changes to the methane coupling reaction mixture in the outer reactor, the temperature in the inner reactor, where ethane cracking occurs, increases. Accordingly, the ethane conversion increases as this is an endothermic process and more heat is available. This increase in absorbed heat, 0.046 kJ / min, must come from the heat of reaction of the methane coupling compartment since, as already noted, the furnace heat flux is constant.

Tables 3 and 4 show that the amount of heat used in the inner ethane cracking compartment is less than that produced in the methane coupling compartment; this can be caused by heat losses arising from the geometry of the reactor. In experiments of the examples, the heat of an exothermic reaction has been used to continue an endothermic reaction that requires heat.

Claims (20)

A process for the catalytic conversion of methane to hydrocarbons with at least two carbon atoms, wherein a first feed gas containing methane and oxygen is fed to a catalyst-containing first reaction space, this reaction space is kept under such conditions of temperature and pressure that an exothermic conversion reaction takes place and discharging from the reaction space a product gas which is relatively rich in hydrocarbons having at least two carbon atoms and water vapor, characterized. to simultaneously supply a second feed gas containing hydrocarbons with or without steam or carbon dioxide to a second reaction space which is in heat exchange contact with the first reaction space, the second reaction space is maintained under such conditions of temperature that an endothermic reaction takes place therein and from the second reaction space discharges a product gas of the desired composition, such that the temperature in both spaces can be controlled by heat transfer from the first to the second reaction space. A method according to claim 1, characterized in that the temperature in the second reaction space is kept substantially equal to the temperature in the first reaction space. Method according to claim 2, characterized in that the temperature in the first reaction space is kept at a value between about 600 ° C and about 1000 ° C. Process according to claim 3, characterized in that the temperature in the first reaction space is kept at a value between about 700 ° C and about 900 ° C. A method according to any one of claims 1-4, characterized. that the pressure in the first reaction chamber is adjusted to a value of approximately 1 atm. Process according to claim 1 or 2, characterized in that the endothermic reaction is a thermal cracking reaction and the second feed gas contains ethane, propane, LPG, butane, naphtha, gas oil or other hydrocarbons and the product gas is rich in olefins. Process according to claim 1 or 2, characterized in that the endothermic reaction is a steam cracking reaction and the second feed gas contains ethane, propane, LPG, butane, naphtha, gas oil or other hydrocarbons and the product gas is rich in olefins. Process according to claim 1 or 2, characterized in that the endothermic reaction is a catalytic or non-catalytic reforming reaction for producing synthesis gas, the second feed gas containing methane, natural gas, LPG or other hydrocarbons in addition to steam and the product gas being rich of carbon monoxide and hydrogen. Process according to claim 1 or 2, characterized in that the endothermic reaction is a catalytic or non-catalytic reforming reaction for producing synthesis gas, wherein the second feed gas contains methane, natural gas, LPG or other hydrocarbons in addition to carbon dioxide and the product gas is rich of carbon monoxide and hydrogen. Process according to claims 1-9, characterized in that the catalyst in the first reaction space is particulate and is kept in a fluidized state by means of the feed gas. A method according to any one of claims 1-10, characterized. that Ca / Sm 2 O 3 is introduced as catalyst in the first reactor. A method according to any one of claims 1-10, characterized. that α-201203 is introduced as catalyst in the first reactor. Catalyst for converting methane to C 2 hydrocarbons according to claim 1, characterized in that it contains CaO / SmO 2. Device for carrying out the method of claim 1, comprising a reactor containing a first reaction compartment with catalyst for carrying out the exothermic reaction, characterized in that a second reaction compartment for carrying out the endothermic reaction is also present which second reaction compartment is in heat-exchanging contact with the first reaction compartment. Device according to claim 14, characterized in that the reactor is tubular and consists of two concentric tubes, the compartments within these tubes each being connected to a feed gas inlet and a product gas outlet. Device according to claim 14, characterized in that the reactor has an upright cylindrical reaction vessel, provided with a feed gas inlet and a product gas outlet, within which reaction vessel the first reaction compartment is located, and in which the second reaction compartment is formed by a wound tube with its own inlet and outlet, which tube passes through the first reaction compartment. Device according to claim 16, characterized in that the wound tube consists of or is coated with a ceramic material. Device according to claim 17, characterized in that the ceramic material is selected from SiO 2, Al 2 O 3, SiN, Sic, ZrO 2, CaO, BaO and ZnO or another basic oxide. 19. Device as claimed in claims 14-18, characterized in that heat exchangers are present for heat exchange between feed gases and product gases. Device according to claim 19, characterized in that at least one of the heat exchangers is included in the reactor.