WO2018047032A2

WO2018047032A2 - Process for selective conversion of hydrocarbons to c2 fraction and syngas composition

Info

Publication number: WO2018047032A2
Application number: PCT/IB2017/055120
Authority: WO
Inventors: Krishnan Sankaranarayanan; Pankaj S. GAUTAM; Aghaddin Mamedov; Sreekanth Pannala; Balamurali Nair; Istvan Lengyel; David West
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-09-08
Filing date: 2017-08-24
Publication date: 2018-03-15
Also published as: WO2018047032A3

Abstract

Embodiments of the invention include processes for the production of C₂ hydrocarbons (C₂H₂ and/or C₂H₄) in an energy and carbon efficient process.

Description

PROCESS FOR SELECTIVE CONVERSION OF HYDROCARBONS TO C2 FRACTION AND SYNGAS COMPOSITION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/384,903 filed September 8, 2016, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002] Conversion of natural gas or low value hydrocarbons such as heavy residue to high molecular hydrocarbons has been investigated over time. One aspect of natural gas conversion is the thermal conversion of methane to acetylene and hydrogenation of acetylene to ethylene. Methane is available in great quantities in natural gas. Methane is primarily used as a fuel, but processes are known for converting it to higher molecular weight products. For example, methane can be first converted to a methyl halide and then catalytically condensed to hydrocarbons having two or more carbon atoms. Other processes for methane conversion include converting methane to ethylene, acetylene, hydrogen and high surface area carbon by high temperature pyrolysis. Carbon produced by the process, although economically valuable, presents costly and sometimes difficult handling and disposal problems. In yet another example, U.S. Patent No. 8080697 to Lin et al. describes a thermal process for producing ethylene from methane through an acetylene intermediate. [0003] There remains a need for additional processes for more energy and carbon efficient methane and low value hydrocarbon conversion process.

SUMMARY

[0004] A discovery has been made that addresses some of the problems associated with the production of higher hydrocarbons from methane. The discovery is premised on conversion of low value hydrocarbons {e.g., heavy residue or petroleum coke) to C2 hydrocarbons while simultaneously producing other building block chemicals such as syngas.

[0005] Embodiments of the invention include processes for the production of C2 hydrocarbons (C2H2 and/or C2H4) in an energy and carbon efficient process. Certain embodiments are directed to an energy and carbon efficient process for conversion of hydrocarbon source to C2 hydrocarbons can include: (a) combusting in a first reaction zone a hydrocarbon source containing natural gas in the presence of oxygen to produce combustion products; (b) mixing the combustion products with a second hydrocarbon source in a second reaction zone in which pyrolysis occurs forming pyrolysis products that include C2H2, C2H4, and CO2, the second reaction zone being heated by the combustion in the first reaction zone; (c) quenching the pyrolysis reaction product; (d) subjecting the C2H2 to hydrogenation forming C2H4; and (e) subjecting the CO2 to hydrogenation forming a syngas. The hydrocarbon source can be a mixture of natural gas and heavy hydrocarbons. In certain aspects, the hydrocarbon source can be a mixture of natural gas and petcoke. In a further aspect, the hydrocarbon source can be a mixture of natural gas and heavy residue. In still a further aspect, the hydrocarbon source can be a mixture of natural gas and heavy oil. In certain aspects, the hydrocarbon source can be a mixture of natural gas and naphtha. The second hydrocarbon source can be ethane, propane, naphtha, or combinations thereof. In certain aspects, pyrolysis can result in an acetylene (C2H2) yield of at least 20, 25, 30, 35% or more. The C2H2 can be separated from the pyrolysis products and then subjected to hydrogenation. In certain aspects the C2H2 can be separated by selective solvation in a N- methyl-2-pyrrolidone ( MP) solvent. In a further aspect, unreacted H2 in the hydrogenation reaction can be recycled to the combustion zone. The process can further include separating CO2 from the pyrolysis product by amine absorption. The process can also include converting separated CO2 to methanol or olefins. In certain aspects, the unreacted H2 from acetylene hydrogenation can be used for CO2 hydrogenation. The process can further include reacting the CO2 hydrogenation product and the pyrolysis product to form methanol.

[0006] The term "natural gas" refers to a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but can include varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.

[0007] The term "heavy residue" refers to polyalkylbenzenes such as polyethylbenzenes (PEB's) and multi-ring compounds.

[0008] The term "petcoke" or petroleum coke refers to a carbonaceous solid delivered from oil refinery coker units or other cracking processes.

[0009] The term "heavy hydrocarbons" refers to hydrocarbons which are solid or extremely viscous at standard processing conditions. Non-limiting examples of heavy hydrocarbons include materials asphaltenes, tars, paraffin waxes, coke, refining residuum, and other similar residual hydrocarbon materials. For the purposes of the present invention, heavy hydrocarbons include any material that comprises a majority of hydrocarbon materials with a molecular weight range of about 700 to 2,000,000.

[0010] The term "heavy oil" refers to heavy crude, oil sands bitumen, bottom of the barrel and residue left over from refinery processes (e.g., visbreaker bottoms), and any other lower quality material that contains a substantial quantity of high boiling hydrocarbon fractions (e.g., that boil at or above 343 °C, more particularly at or above about 524 °C. Non-limiting examples of heavy oil feedstocks include Lloydminster heavy oil, Cold Lake bitumen, Athabasca bitumen, atmospheric tower bottoms, vacuum tower bottoms, residuum (or "resid"), resid pitch, vacuum residue, and nonvolatile liquid fractions that remain after subjecting crude oil, bitumen from tar sands, liquefied coal, oil shale, or coal tar feedstocks to distillation, hot separation, and the like and that contain higher boiling fractions and/or asphaltenes.

[0011] The term "naphtha" refers to flammable liquid hydrocarbon mixtures.

[0012] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having" in the claims, or the specification, may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0013] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0014] The terms "wt.%", "vol.%", or "mol.%" refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0015] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0016] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result. [0017] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0018] As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0019] The methods of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non- limiting aspect, a basic and novel characteristic of the methods of the present invention are their abilities to convert low value hydrocarbons into C2 hydrocarbons and carbon oxides.

[0020] Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF THE DRAWINGS [0021] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of the specification embodiments presented herein.

[0022] FIG. 1 shows a schematic of one embodiment of the combustion/pyrolysis process in combination with an amine separation system.

[0023] FIG. 2 shows a schematic of one embodiment of the syngas production process.

DESCRIPTION

[0024] Aspects of the invention relate to a process for the conversion of natural gas and/or any hydrocarbon feed such as heavy residue or petcoke to useful products, such as C2 hydrocarbons (acetylene and/or ethylene). The process can include the simultaneous production of syngas compositions making the overall process a high carbon efficient process. Aspects of the current invention are directed to methods that result in a more carbon efficient process. The current invention can be used to convert a wide range of hydrocarbon feedstock, such as heavy residue or petcoke, which are low value hydrocarbons, to more useful products such as C2 hydrocarbons while simultaneously producing other useful products such as syngas.

[0025] Conversion of methane to acetylene by thermal combustion is well known process (US patents 5,824,834 and 5,789,644) described as Hoechst technology. This process may include different options: combustion of methane in the first step and injection of methane in the second step to the combustion zone. In another option of the process, methane at very high temperature in one-step can be converted to mixture of acetylene and syngas + CO2.

[0026] Oxidative pyrolysis of methane is accompanied by selective oxidation reactions that generate high amounts of heat:

2CH4 + 1.5 O2 = C2H2 + 3H₂0 ΔΗ= -41 kcal/mol (1)

CH4+ 1.5 O2 = CO+ 2H₂0 ΔΗ= - 103 kcal/mol (2) CH4+ 2 O2 = CO2+ 2H₂0 ΔΗ= -174 kcal/mol (3)

[0027] The oxidative pyrolysis process conditions can depend from the CH4/O2 ratio and can require a critical ratio for elimination of coke and soot formation. The ratio of acetylene to syngas ratio can also depend from the process conditions and the CH4/O2 ratio.

[0028] One embodiment described herein includes two main reaction zones and one quenching zone. The first reaction zone, where preheated methane can be combusted, serves to supply the necessary heat for the second reaction zone, where a fresh feed of methane can be injected for pyrolysis and mixed with the combustion products of the first zone {See, FIG. 1). In the quenching zone, water or heavy oil can be used as a coolant.

[0029] In one embodiment of the invention the gas after cooling can be fed to an acetylene absorbing unit where liquid phase acetylene is hydrogenated to ethylene in the presence of hydrogenation catalyst {See, for example FIG. 1). For example, n-methyl-2-pyrrolidone ( MP), dimethylformamide (DMF), acetone, tetrahydrofuran (TUF), dimethylsulfoxide (DMSO), monomethylamine (MMA) and chloroform can be used to preferentially absorb acetylene from a gas stream. The solvent containing absorbed acetylene can then be subjected to hydrogenation in the liquid phase. A number of hydrogenation catalysts are known in the art such as nickel or nickel/molybdenum dispersed on a high surface area support. Other hydrogenation catalyst include a noble metal catalytic element dispersed on a high surface area support. Non-limiting examples of noble metals include Pt and/or Pd dispersed on gamma-alumina. Hydrogenation conditions can include a temperature of about 200 °C to about 300 °C, or greater than, equal to, or between any two of 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C and 300 °C. Other operating conditions such as space velocity and pressure for the hydrogenation zone are known in the art. In certain aspects, a portion of syngas, after separation of acetylene, can be fed to the combustion zone for generating heat together with the combustion of methane. In another embodiment of the invention, a carbon monoxide (CO) and hydrogen (H₂) mixture can be used as a source of hydrogen for the hydrogenation of acetylene to ethylene. In one embodiment of the invention, acetylene hydrogenation can be carried out in liquid phase.

[0030] In a preferred embodiment of the invention, the final products of the process are C2H4 and CO2. The molar ratio of C2H4 and CO2 in weight basis can be within 1.3 - 1.45. The total process can be described as follows:

3 CH₄ + 3 O2→ C2H4+ CO2 + 4H₂0 (4) [0031] Formation of side products, such as CO2 can lead to a decrease in selectivity of acetylene production and effectivity of the process. CO2 with hydrogen can be used for syngas conversion reactions such as syngas to methanol or syngas to olefins, which requires only a limited amount of CO2. The present invention utilizes the CO2 by-product of methane to acetylene process for generation of syngas composition for further processing, which increases the economics of the process significantly.

[0032] Separation of the products from the methane to acetylene reactor can involve separation of CO2 from the product stream and then separation of the C2 hydrocarbons. Separation of CO2 can be conducted by any known method, for example, by amine adsorption. Separation of C2 hydrocarbons from the product stream can include cold box separation or pressure swing adsorption (PSA). In one aspect, after separation of C₂ hydrocarbons, CO2 can be mixed with H₂ in the necessary ratio to produce a syngas composition having an appropriate H2/CO2/CO ratio for methanol or olefins synthesis (See, for example, FIG. 2).

[0033] In one embodiment, a portion of the syngas composition can be used for hydrogenation of acetylene. The gas composition produced during the hydrogenation of acetylene can contain more CO and less hydrogen, and can be mixed with the CO2 hydrogenation gas mixture. The adjusted syngas composition can be used for methanol or olefins synthesis depending on the composition of syngas generated from CO2 hydrogenation reaction. In certain aspects, the CO2 byproduct can be converted to syngas using hydrogenating agent, e.g., hydrogen or any suitable compound that can provide hydrogen for hydrogenation reaction. Hydrogenation of CO2 to syngas composition can be described by the following reactions:

[0034] Reaction (5) is an equilibrium controlled reaction and depends on the H2/CO2 ratio, for example:

3H₂ + CO2→ CO + 2H₂ + H2O (6) or

4H₂ + CO2→ CO + 3H₂ + H2O (7)

[0035] Catalysts for CO2 hydrogenation to syngas can include mixed oxides of redox metals, for example, chromium (Cr), iron (Fe), manganese (Mn), or copper (Cu) based oxides. In some embodiments, a Cr based industrial Catofin® (CB&I, U.S.A.) catalyst can be used, Such a catalyst can produce a desired syngas mixture for methanol production. The composition of syngas can depend on the molar H2/CO2 ratio and from the reaction temperature. With variation of the process conditions, it is possible to direct the process for different purposes.

[0036] The process can be applied for converting of wide range hydrocarbons, such as heavy residue and also low value carbon resources such as petcoke. The hydrocarbon feed can be a mixture of different hydrocarbons, such as mixture of natural gas with heavy residue, mixture of natural gas with ethane, propane, or mixture of methane with naphtha, or mixture of methane with petcoke.

EXAMPLES [0037] The following examples as well as the figures are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples or figures represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. EXAMPLE 1

(Combustion of Methane and Its Pyroiysis at High Temperature to Acetylene and

Ethylene Mixture)

[0038] Combustion of methane and its pyrolysis was performed in pilot scale reactor. The gas composition from the reactor is shown in Table 1. The combustion chamber bulk gas temperature was approximately 2400 °C with maximum temperature of about 2900 °C. The pyrolysis inlet temperature was about 1750 °C at the inlet and decreased to 1400 °C in the reactor due to endothermicity of the pyrolysis reactions.

Table 1

(Oxidative Cracking of C₂ and C3 Hydrocarbons and Naphtha)

[0039] A mixture of C2 and C3 hydrocarbons and naphtha were oxidatively cracked in place of natural gas using the same reactor and process conditions as Example 1. The only difference of the process for natural gas and other hydrocarbons was in product distribution where C2H2/C2H4 ratio changed. The invention in this case also includes the steps of natural gas conversion. Table 2 lists the conditions, compositions, and performance metrics of the process. Table 2

EXAMPLE 3

( Hydrogenation of Acetylene in Gas or Liquid Phase)

[0040] Hydrogenation of Acetylene in the Gas Phase. Gas phase hydrogenation of acetylene was performed in a quartz reactor in the presence of a 0.5 wt.% Pd/Ti02 catalyst. The inlet gas composition was 10% C2H4 + 60% H2 + 30% CH₄. The catalyst loading 20 mg, total flow rate 150 cc/min. Hydrogenation temperature was 40 °C. Hydrogenation results were: (i) C2H2 conversion - 96.0 % mol, (ii) C2H4 selectivity - 86.0 %mol, (iii) C2H5 selectivity - 10.2 %mol, and (iv) CH₄ selectivity - 3.8% mol.

[0041] Gas phase hydrogenation of acetylene was performed in a 4 mm metallic reactor coated with Pd-Ti02 catalyst. The metallic tube first was washed with T1O2 suspension, dried at 120 °C then washed with Pd(N0₃)2. After washing, the reactor was dried at 120 °C for 2 hours then used for gas phase hydrogenation of acetylene. The inlet gas composition was 10 % C2H4 + 60% H₂ + 20% CH₄ + 10% CO2. The total flow rate was 150 cc/min. The reaction temperature was 200 °C. The Hydrogenation results were: (i) C2H2 conversion - 96.3 % mol, (ii) C2H4 selectivity - 91.5 % mol, (iii) C2H6 selectivity - 3.1 % mol, and (iv) CH4 selectivity - 5.4% mol.

[0042] Hydrogenation of acetylene to ethylene in liquid phase. This example included methods where acetylene was separated from the gas phase using NMP (N-methyl pyrrolidine) solvent (See, for example, U.S. Patent Publication No. 2005/0049445 to Johnson et al., Synfuels International). Acetylene dissolved in NMP was separated from the gas phase containing C2H2 + CO + H2 + CH4 + CO2 and hydrogenated in the liquid phase in the presence of 0.3 wt.% Pd-Zn/AhCb catalyst by portion of the gas separated from acetylene. Conversion of acetylene was about 100% with the ethylene selectivity close to 98%. The green oil (e.g., a mixture of C₄ to C20 olefins and paraffins), which was produced as a byproduct, was separated from the liquid phase and recycled back to the combustion zone. The portion of the gas not used for hydrogenation step after separation of CO2 was recycled back to the combustion zone for generation of heat.

EXAMPLE 4

(Production of Synthesis Gas By Hydrogenated of CO2 From Methane Pyrolysis)

[0043] A syngas composition produced from the pyrolysis step was mixed with the syngas composition produced from CO2 hydrogenation step and used for methanol synthesis or olefins production. In another scheme, the syngas composition produced from pyrolysis step was used for heat generation and as a CO2 hydrogenation syngas to be used for methanol synthesis.

[0044] Hydrogenation of CO2 was carried out at isothermal conditions in a metal reactor with a catalyst loading of an industrial Catofin® catalyst (80 ml) at 564 °C and flow rates of H2 - 426.4 cc/min and CO2 - 106.6 cc/min. The results are shown in Table 3.

Table 3

Days C0₂, %mol CO, %mol H₂, %mol C0₂ con.%mol

46 10.36 11.8 74.6 53

48 10.4 12.2 76 53.6

49 10.4 11.9 75 53.4

50 10.5 12.2 76.3 53.7

EXAMPLE 5

(Hydrogenation of CO 2 at Isothermal Conditions)

[0045] Hydrogenation of CO2 at isothermal conditions was performed in a metal reactor at 560 °C in the presence of catalyst 5% Cu - 10% Mn / AI2O3 with a catalyst loading of 1.69 g.

The flow rates of gas components were as following: H2 - 112 cc/min and CO2 - 25 cc/min.

The results are shown in Table 4.

Table 4

Example 6

( Hydrogenation of CO2 at Isothermal Conditions)

[0046] Hydrogenation of CO2 was performed at isothermal conditions in a metal reactor at 730 °C in the presence of an industrial Catofin® catalyst with a catalyst loading of 7.2 g. The flow rates of gas components were as follows: H2 - 38.4 cc/min and CO2 - 9.6 cc/min. The results are shown in Table 5. Table 5

EXAMPLE 7

( Hydrogenatioii of C0₂ in the Presence of Industrial Catofin® Catalyst at Adiabatic

Reactor Conditions)

[0047] Hydrogenation of CO2 was performed in the presence of Industrial Catofin® catalyst at adiabatic reactor conditions where inlet temperature was 745 °C and outlet temperature was 586 °C. Catalyst loading was 464 mL. The flow rates of the gas components were CO2 at 628.7 cc/min and H2 at 2474 cc/min. The results are shown in Table 6.

Table 6

EXAMPLE 8

(Hydrogenation of CO2 in the Presence of Industrial Catofin® Catalyst at

Isothermal Reactor Conditions of 680 °C)

[0048] Hydrogenation of CO2 was performed in the presence of Industrial Catofin® catalyst at isothermal reactor conditions of 680 °C. Catalyst loading was 554.4 mL. The flow rates of gas components were CO2 at 1156 cc/min and H2 at 1734 cc/min. The results are listed Table 7.

Table 7

Claims

1. An energy and carbon efficient process for conversion of hydrocarbon source to C2 hydrocarbons, the process comprising:

(a) combusting in a first reaction zone a hydrocarbon source comprising natural gas in the presence of oxygen to produce combustion products;

(b) mixing the combustion products with a second hydrocarbon source in a second reaction zone under conditions sufficient to produce pyrolysis reaction products comprising acetylene (C2H2), ethylene (C2H4) and carbon dioxide (CO2), the second reaction zone being heated by the combustion in the first reaction zone;

(c) quenching the pyrolysis reaction products;

(d) subjecting the C2H2 to hydrogenation, forming additional C2H4; and

(e) subjecting the CO2 to hydrogenation, forming a synthesis gas product stream.

2. The process of claim 1, wherein the hydrocarbon source is a mixture of natural gas and heavy hydrocarbons

3. The process of claim 1, wherein the hydrocarbon source is a mixture of natural gas and petroleum coke (petcoke).

4. The process of claim 1, wherein the hydrocarbon source is a mixture of natural gas and heavy residue.

5. The process of claim 1, wherein the hydrocarbon source is a mixture of natural gas and heavy oil.

6. The process of claim 1, wherein the hydrocarbon source is a mixture of natural gas and naphtha.

7. The process of claim 1, wherein the second hydrocarbon source is ethane.

8. The process of claim 1, wherein the second hydrocarbon source is propane.

9. The process of claim 1, wherein the second hydrocarbon source is naphtha.

10. The process of claim 1, wherein pyrolysis results in an acetylene yield of at least 25%.

11. The process of claim 1, further comprising separating the C2H2 from the pyrolysis products and then subjected to hydrogenation.

12. The process of claim 11, wherein separation comprises contacting the C2H2 with N- methyl-2-pyrrolidone ( MP).

13. The process of claim 1, further comprising recycling unreacted H2 in the

hydrogenation reaction to the combustion zone.

14. The process of claim 1, further comprising separating CO2 from the pyrolysis product by amine absorption.

15. The process of claim 14, further comprising converting separated CO2 to methanol or olefins.

16. The process of claim 1, wherein unreacted H2 from acetylene hydrogenation is used for CO2 hydrogenation.

17. The process of claim 1, further comprising reacting the CO2 hydrogenation product and the pyrolysis product to form methanol.