Patent Application
20090317669
This invention relates to improvements of carbon efficiencies, and reduction of carbon dioxide emissions in hydrocarbons produced by a Fischer-Tropsch process.
The Fischer-Tropsch process is used primarily to convert carbon monoxide and hydrogen, also known as “syngas”, into liquid hydrocarbons for use as fuel.
A typical process flow diagram where a Fisher-Tropsch process is used to synthesize hydrocarbons is as follows:
In the above process gasifier feedstocks are usually coal or methane gas. In this diagram Q1 represents the energy input into the gasification (in the case of a coal feedstock) or reforming section (in the case of a methane gas) and Q2 represents the energy output from the Fischer-Tropsch synthesis process.
Where coal is used as the feedstock it is, initially, converted to carbon monoxide (CO) and hydrogen gas (H2) by the following gasification process:
C+H2O→CO+H2
The carbon monoxide is then partially converted to carbon dioxide (CO2) and hydrogen (H2) by the following water gas shift process:
CO+H2O→CO2+H2
The water gas shift process is controlled so as to provide the required CO:H2 molar ratio for the Fischer-Tropsch process. Typically the CO:H2 molar gas ratio is 1:2. The CO2 produced in this way is emitted by the process and leads to carbon inefficiencies.
Where methane (CH4) is used as the feed the reforming process is used:
CH4+H2O→CO+3H2
As in the case of the coal fed process the water gas shift process partially converts the carbon monoxide to carbon dioxide so as to provide the required CO:H2 molar ratio of 1:2 for the Fischer-Tropsch process. The carbon dioxide created in this way is emitted by the process.
As indicated above, the CO and H2 gas combination is termed “syngas” and it can be used in the Fischer-Tropsch process to produce a wide range of carbon based chemicals perhaps the most important of which is fuel for internal combustion engines.
Syngas production processes are endothermic and, consequently, require considerable quantities of energy. This, also results in the emission of significant quantities of carbon dioxide which, because it is a so-called “greenhouse gas”, militates against the above-described synthetic fuel plants. On the other hand, dwindling and increasingly expensive crude oil stocks, coupled with significantly large resources of natural gas and low grade coal, militate for the erection and operation of such plants.
It should be noted that the following terms, when used in this specification, have the following meanings:
It is an object of this invention to provide an improvement of carbon efficiencies in hydrocarbon production with a consequent reduction of carbon dioxide emission.
In accordance with this invention there is provided a process for producing hydrocarbons from a CO2-rich syngas produced from a suitable feedstock comprising reacting the CO2-rich syngas in a Fischer Tropsch process to produce hydrocarbons according to the overall process mass balance:
CO2+3H2—CH2—+2H2O.
There is also provided for a water gas shift process to be used, where necessary, to modify the CO2 rich syngas and achieve a desired CO2 concentration.
There is also provided for CO in the CO2-rich syngas to be used to produce hydrocarbons according to the process:
CO+2H2—CH2—+H2O.
There is further provided for syngas to be produced by combination gasifier and reforming processes where more than one feedstock, preferably coal and natural gas or methane is used, alternatively gasifier processes only where a solid feedstock, preferably coal is used, further alternatively reforming processes only where a natural gas, preferably methane is used, in a gasifier/reformer.
There is further provided for the methane to be sourced from a natural gas reservoir or alternatively for the methane to be produced by microbial degradation of waste products.
There is also provided for energy input to the gasifier/reformer stage to be adjusted to move the chemical reactions in favour of CO2 production, and for the CO2 to be used in combination with hydrogen to form hydrocarbon compounds in the Fischer Tropsch process.
There is further provided for unreacted carbon dioxide, carbon monoxide and hydrogen to be recirculated, used to produce electricity and/or to generate steam.
The invention extends to the use of unconsumed, alternatively waste CO2 and H2 to be used in fuel cells, preferably molten carbonate fuel cells, to provide electrical energy.
The invention will be described below by way of example only and with reference to the drawings in which:
Referring to
Where coal is used as a feedstock it is processed to produce carbon monoxide and hydrogen. This gasification process is as follows:
C+H2O→CO+H2.
Where methane from a natural gas source is used as the feedstock it is converted into carbon monoxide and hydrogen by a reforming process which is as follows:
CH4+H2O→CO+3H2.
The carbon monoxide from either process is then partially converted to carbon dioxide and hydrogen by the following water gas shift process:
CO+H2O→CO2+H2.
All of the above reactions occur in the gasifier/reforming process (3) and the concentration of carbon dioxide can be altered to suit particular requirements by altering the operating conditions of the gasification/reforming process.
The syngas produced in the gasifier/reforming process (3) is piped to a Fischer Tropsch synthesis section (5) where it is, at least partially converted into a hydrocarbon which, depending on the kinetics of the reaction, can be suitable for use as a fuel for internal combustion engines, as a lubricating oil or as a floor polish to name but a few products. The Fischer Tropsch process using, primarily carbon dioxide and hydrogen, is as follows:
CO2+3H2→—CH2—+2H2O.
Carbon monoxide in the CO2 rich syngas can be reacted with hydrogen to produce hydrocarbons as follows:
CO+2H2→—CH2—+H2O.
Unreacted carbon dioxide, carbon monoxide and hydrogen may be recirculated from the Fischer Tropsch synthesis section (5) into the gasifier/reforming process stage (3) via a conduit (7) or back to the Fischer Tropsch synthesis section.
The energy requirements for the gasification/reforming process (8) are considerably reduced by producing a CO2 rich syngas rather than a CO rich syngas as in the conventional process.
In addition to the above and unreacted carbon dioxide, carbon monoxide and hydrogen can be used to generate electricity and/or steam in for example and IGCC process.
In addition to the above and referring to
As carbonate ions from the electrolyte are used up in the reactions it is necessary to inject carbon dioxide into the cell to compensate for this consumption.
It is envisaged that the above alternative to the conventional Fischer Tropsch process for producing synthetic carbon products from CO2-rich syngas and conventional processes for producing syngas produce significantly less carbon dioxide which is emitted into the atmosphere and are thus more environmentally friendly.
The following table provides data on the required feed as well as the products produced in both a conventional Fischer Tropsch process based on CO-rich syngas as well as the process considered in this patent based on CO2-rich syngas. The feed considered was coal. The carbon dioxide emissions and carbon efficiencies of the two processes are also provided.
Production of 1 Ton of Hydrocarbons from a Coal Feedstock
These calculations are based on idealized targets for the process and it is envisaged that a person skilled in the art will be able to adapt the processes to suit particular conditions and desired outputs. In addition it should be appreciated that alternative feeds can be used instead of or in conjunction with coal. Examples of such alternative feeds include methane-rich natural gas derived from natural gas deposits or generated by fermentation of natural waste dumps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006/03239 | Apr 2006 | ZA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2007/001057 | 4/24/2007 | WO | 00 | 7/28/2009 |
