Process for producing syngas

Abstract

A process for converting carbon dioxide to syngas comprising the steps of introducing a feed gas comprising carbon dioxide, a carbon source, and a catalyst into a reactor, operating said reactor at a temperature of up to 900°C and at a pressure of up to 500 kPa to convert the feed gas and carbon source into a product comprising carbon monoxide and hydrogen, wherein the reactor is heated using a microwave source.

Description

[0001] PROCESS FOR PRODUCING SYNGAS

[0002] Field of Invention

[0003] The invention relates to a process for producing syngas using the reverse Boudouard reaction.

[0004] Background

[0005] The Reverse Boudouard reaction is a process that converts carbon dioxide into carbon monoxide by gasifying carbon-based materials with carbon dioxide as shown in Equation 1 :

[0006] CO2 + C -> 2CO (Equation 1)

[0007] The efficient conversion of carbon dioxide to carbon monoxide is highly dependent on the reactivity of the carbon-based materials and the carbon dioxide feed gas utilised. In order to produce commercially valuable syngas, carbon monoxide obtained from the reaction in equation 1 is mixed with hydrogen typically supplemented from an external source. It would be desirable to reduce or eliminate the need for hydrogen supplementation to reduce overall production costs.

[0008] An aim of the invention therefore is to provide an improved process for converting carbon dioxide to syngas to overcome the above issue.

[0009] Summary of Invention

[0010] In an aspect of the invention there is provided a process for producing syngas comprising the steps of: introducing a feed gas, a carbon source such as carbon black and / or plastic waste, and an alkali metal salt catalyst into a reactor, said feed gas comprising carbon dioxide, optionally with methane and / or steam; operating said reactor at a temperature of up to 900°C and at a pressure of up to 500 kPa to convert the feed gas and carbon source into a product comprising carbon monoxide and hydrogen; characterised in that the gasification of carbon black and / or plastic waste produces a higher ratio of hydrogen to carbon monoxide gas within the reactor.

[0011] In one embodiment the feed gas comprises methane and / or steam. Advantageously the resulting product comprises hydrogen which reduces / eliminates the need for additional hydrogen gas supplementation to produce syngas.

[0012] Advantageously the coupling of carbon black with plastic waste in the gasification process enables higher amounts of in-situ hydrogen production which further reduces / eliminates the need for additional hydrogen gas supplementation to produce syngas.

[0013] Advantageously for hydrogen to carbon monoxide ratio of up to 2:1 , the need for external hydrogen gas supplementation can be eliminated. For hydrogen to carbon monoxide ratio of more than 2:1 , the need for external hydrogen gas supplementation can be reduced.

[0014] Advantageously silica carbide as the reactor bed material enables better absorption of microwave radiation, conversion of microwave radiation into heat and heat retention. Additionally, silica carbide ball can be utilised to reduce the pressure drop across the reactor.

[0015] In one embodiment the microwave source typically powered at 1 to 5 kW irradiates the carbon black and / or plastic waste with a radiation frequency of approximately 2450MHz. In addition to the operating temperature of 900°C, a high pressure is not required, as the reactor can be operated at 500 kPa or less. Advantageously the low power, temperature and pressure requirement leads to significant energy savings and a lower carbon footprint.

[0016] Typically the microwave source is solid state and / or a magnetron.

[0017] A further advantage is that the process utilises readily available carbon dioxide obtained from carbon dioxide emitting industries such as natural gas and petrochemical plants as well as carbon black from methane pyrolysis plants.

[0018] Brief Description of Drawings

[0019] It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

[0020] Figure 1 is a schematic diagram of a reactor for gasifying carbonaceous material in accordance with an embodiment of the invention.

[0021] Detailed Description

[0022] The present invention discloses a catalytic carbon dioxide gasification process using carbon black derived from methane pyrolysis and / or plastic waste as feedstock. The coupling of carbon black with plastic waste in the gasification process enables in-situ hydrogen production thus allowing syngas production in a single step thereby reducing / eliminating the need for additional hydrogen gas top up depending on downstream requirements.

[0023] Carbon dioxide feed gas with (a) methane, (b) steam, (c) methane and steam or (d) just carbon dioxide only allows the following reactions to occur: (Equation 2) (Equation 3) (Equation 4)

[0024] As per the equations above, hydrogen production increases which reduces / eliminates the need for external hydrogen to be supplied for syngas production. This also allows the current process to be a single-step process for the production of syngas. For hydrogen to carbon monoxide ratio of up to 2:1 , the need for external hydrogen gas supplementation can be eliminated. For hydrogen to carbon monoxide ratio of more than 2:1 , the need for external hydrogen gas supplementation can be reduced. Catalytic microwave co-gasification of carbonaceous material with plastic waste produces syngas with a higher hydrogen to carbon monoxide ratio (>1) as the process increases in-situ hydrogen production.

[0025] Figure 1 illustrates a reactor comprising a carbon source inlet for receiving carbon black and / or plastic waste from a feed hopper, a feed gas inlet for receiving carbon dioxide, with or without methane impurity and a steam inlet. A catalyst can be introduced into the reactor to improve the reactivity of the carbon source. Preferably the catalyst is an alkali metal or transition metal such as potassium carbonate.

[0026] The reactor is a fixed bed reactor equipped with a microwave source so that it can be heated to a temperature of up to 900°C and beyond if required. This allows the carbon black and / or plastic waste and carbon dioxide to be gasified via microwave radiation to form carbon monoxide and hydrogen which is then channelled to a particulate separator, a cooler and finally an amine scrubber to yield syngas. Ashes from the gasification process can be removed via an ash bin.

[0027] The reactor is equipped with silica carbide as bed material which enables better absorption of microwave radiation, conversion of microwave radiation into heat and heat retention. Advantageously, silica carbide ball can be utilised to reduce the pressure drop across the reactor.

[0028] The microwave source typically powered at 1 to 5 kW irradiates the carbon black and / or plastic waste with a radiation frequency of approximately 2450MHz. Typically the microwave source is solid state and / or a magnetron. In addition to the operating temperature of 900°C, a high pressure is not required, as the reactor can be operated at 500 kPa or less. The low power, temperature and pressure requirement leads to significant energy savings and a lower carbon footprint.

[0029] Advantageously as the microwave gasification process allows for volumetric heating where microwave radiation is absorbed by the materials in the reactor and is converted into heat, the microwave gasification process is instantaneous when compared to a conventional gasifier where a longer duration is required during operation, especially during start up and shut down, due to the nature of thermal heating (convection and conduction of heat).

[0030] Microwave volumetric heating results in consistent and even temperature distribution across the materials in the reactor as compared to thermal heating which is based on conduction and convection causing uneven temperature distribution across the materials in the reactor. This is due to the utilisation of silica carbide in the microwave reactor which improves heat and mass transfer between feed gas and carbon black and / or plastic waste.

[0031] Also, carbon black derived from methane pyrolysis has a high carbon content thus it is a good microwave absorbing material and is able to convert microwave radiation into heat at a higher rate when compared to thermal heating employed in a conventional gasification process.

[0032] Advantageously the invention allows waste from existing processes to be converted into useful materials, while also improving on the conventional methods of doing so.

[0033] It will be appreciated by persons skilled in the art that the present invention may also include further additional modifications made to the process which does not affect the overall functioning of the process.

Claims

CLAIM1 . A process for producing syngas comprising the steps of: introducing a feed gas, a carbon source such as carbon black and / or plastic waste, and an alkali metal salt catalyst into a reactor, said feed gas comprising carbon dioxide, optionally with methane and / or steam; and operating said reactor at a temperature of up to 900°C and at a pressure of up to 500 kPa to convert the feed gas and carbon source into a product comprising carbon monoxide and hydrogen; characterised in that the gasification of carbon black and / or plastic waste produces a higher ratio of hydrogen to carbon monoxide gas within the reactor.

2. A process according to claim 1 wherein a microwave source provided to heat the reactor and is solid state and / or a magnetron.

3. A process according to claim 2 wherein the microwave source is powered at 1 to 5 kW.

4. A process according to claim 2 wherein the microwave source irradiates the carbon black and / or plastic waste at a frequency of 2450MHz.

5. A process according to claim 1 wherein the feed gas comprises methane and / or steam.

6. A process according to claim 1 wherein the reactor is equipped with silica carbide as bed material.

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