Abstract:
The invention relates to a method and a system for on board production of hydrocarbon fuels. Electrochemistry is used to combine CO 2  produced by an internal combustion engine with hydrogen and optionally, water, to produce syngas and other fuels.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to methods and apparatus for using CO 2  produced via an internal combustion engine (ICE), preferably on a moving vehicle to product liquid or gaseous hydrocarbon fuel via electrochemistry, as well as an apparatus system for accomplishing this. Among the advantages provided by the invention are the ability to use energy in exhaust gas as the energy to convert the CO 2  to liquid or gaseous fuel. Storage of the converted fuel on board the vehicle is also possible 
       BACKGROUND AND PRIOR ART 
       [0002]    The transportation industry has experienced increasingly stringent regulations, especially in the area of CO 2  emissions from engines, such as e.g., gasoline and diesel engines. Hence, there is increased interest in how to lower the emission of CO 2  and other gases when moving vehicles using any form of internal combustion engine (ICE) are operated. 
         [0003]    The prior art shows much more effort in capturing CO 2  from combustion of fuels, when the source of the CO 2  is stationary. Applying the principles of CO 2  capture used for stationary sources, to mobile ones, is not always possible. The limited approaches to CO 2  capture “on board” mobile sources either use pure O 2  for combustion, and provide no means for re-use and regeneration of the agent used to capture the CO 2 , and/or do not use waste heat that is also recovered in the process. 
         [0004]    Solving the problem of capture and reuse of CO 2  on a moving vehicle for, e.g., generation of usable fuel onboard the vehicle has been viewed as difficult, or at least impractical, because of space limitations, energy and apparatus requirements, and the dynamic nature of a vehicle&#39;s operating cycle, e.g., intermittent periods of acceleration, followed by periods of deceleration. 
         [0005]    It is a goal of this invention to provide a process and apparatus system for on board use of CO 2  and waste heat, produced by ICEs, with transformation of the CO 2  into liquid or gaseous fuel, which can then be stored, on board, until a suitable facility is reached for removal. 
         [0006]    Further, the fuel produced on board can be used as a secondary fuel in dual (or “bi”) fuel vehicles. 
         [0007]    Dual fuel vehicles operate by using a primary, or main fuel, and a secondary, or pilot fuel. Among the materials suggested as fuels to improve engine performance, and to permit use of fuels involving fewer processing steps, are ethanol, syngas, hydrogen, and methane. These secondary fuels are injected into the cylinder with the main fuel as needed, but generally, to suppress “knock” at higher engine loads. 
         [0008]    Also, the secondary fuel can be used in so-called “splash blending,” in order to increase the octane level of the main fuel. In turn, the main fuel can be one subjected to less processing, or of a lower octane quality, thus making the engine fuel more cost effective, and allowing for control over NO x  and soot emissions, in compression ignition engines. 
         [0009]    Dual fuel engines have great value for various reasons. Via utilization of waste heat (produced via the ICE), to produce fuel on board, better energy efficiency is achieved. Also, via using the CO 2  produced by the ICE to make a secondary fuel and then using the fuel, storage and offloading systems are no longer needed. On a more “global” level, refineries produce less CO 2  because less primary fuel is needed, and fuel consumption costs are reduced, due to the interaction between the primary and secondary fuels. 
         [0010]    How this is accomplished will be seen in the disclosure which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIGS. 1 a -1 d    present block diagrams of the process of the invention, using high temperature chemical reactors. 
           [0012]      FIGS. 2 a -2 d    present block diagrams of the process of the invention using low temperature electrochemical reactors. 
           [0013]      FIG. 3  shows generally how a solid oxide electrolysis cell (“SOEC”), functions to carry out steam electrolysis. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    Referring now to  FIGS. 1 a -1 d   , an ICE “ 101 ” is shown, which is a source of exhaust gas, which is shown by  102 . In the embodiments shown in  FIGS. 1 a  and 1 b   , CO 2  is not separated from the exhaust gas, all of which moves to an electrochemical reactor  103 . Electrochemical reactors are known which require either high or low temperatures to function. In  FIGS. 1 a  and 1 b   , high temperature reactors are used, and hence, the hot exhaust gas moves directly to the reactor, to provide the required heat. “High temperature” as used herein refers to temperatures above 400° C. and up to about 900° C. A source of electrical current (not shown) provides current to both the electrochemical rector  103  and, in the case of  FIG. 1 a   , to a compressor  105 , discussed briefly infra. 
         [0015]    At  103 , water can be added but, in the case of most exhaust gases, is already present. At the electrochemical generator, the majority of the reaction products are CO and H 2 , in the mixture known as “syngas.” As is shown in  FIGS. 1 a  and 1 b   , these, and other gases, are channeled back to the ICE to serve as fuel. If operation of the system disclosed herein does not yield enough syngas, one may channel additional electricity from, e.g., the battery or alternator. 
         [0016]    Both of  FIGS. 1 a  and 1 b    show that the waste heat, i.e., the heat energy from the exhaust gas, can be used to generate electricity at a thermoelectric generator  104 . To elaborate, a heat transfer surface is integrated into thereto electric materials, to reduce resistance to heat transfer and to increase conversion efficiency. The electricity produced here can be used to power the electrochemical reactor  103 , or in other optional embodiments discussed herein. 
         [0017]    As noted, supra,  FIG. 1 a    includes a compressor, which can be used when further reactions are desired. If, e.g., a Fischer Tropsch reactor  106  is used and H 2  and CO are channeled thereto, the compressor is used because pressure conditions for the Fischer Tropsch reactions to take place may vary. The temperature necessary for the reaction is well known to range from 150-300° C. This requires removal of heat from the exhaust gas, as is discussed herein, and at the heat transfer surface, referred to supra. 
         [0018]    The compressor is an optional apparatus, to be used when one wishes to operate the Fischer Tropsch reactor at pressures above atmospheric pressure. While increased pressures increase the conversion rate, i.e., the production of hydrocarbons, long chain alkanes result, and these solids are undesirable. Gas moves to the compressor from  104  via transport means  110 . it should be noted that this gas has lost heat which has been converted to electricity. As noted, supra, a compressor is needed at higher pressures. Thus, the system of  FIG. 1 a    can be so used, while that of  FIG. 1 b    requires the use of a compressor inserted between Fischer Tropsch reactor  106  and separation unit  107 . As this is optional, it is not shown. 
         [0019]    As is shown in  FIGS. 1 a  and 1 b   , following reaction, the hydrocarbon products can be directed back to the ICE, or stored on board. 
         [0020]    It is to be noted that the Fischer Tropsch reaction discussed herein is optional, and neither compressor  105  nor reactor  106  are required by the invention. 
         [0021]      FIG. 1 b    differs from  FIG. 1 a    in showing a further, optional separation step, by which gases other than CO and H 2  (e.g., N 2 , H 2 O, and CO 2 ) are removed, using known processes, leaving only CO and H 2  to move to the Fischer Tropsch reactor. Such separation facilitates the reactions at the Fischer Tropsch reactor. 
         [0022]      FIGS. 1 c  and 1 d    depict additional embodiments of the invention embodied in  FIGS. 1 a  and 1 b   . As with  FIGS. 1 a  and 1 b   , these figures show the use of high temperature chemical reactions, where heat energy from exhaust gas passes through a heat exchange  108 , and is used to heat the electrochemical reactor. Additional heat is converted to electricity, as in  FIGS. 1 a  and 1 b   , and the resulting electricity is used to power the reactor. 
         [0023]      FIGS. 1 c  and 1 d    both differ from  FIGS. 1 a  and 1 b    in effecting partial separation of the components of the exhaust gas at  109  and transporting some of CO 2  and H 2 O to the electrochemical reactor, transporting some of these components to the Fischer Tropsch reactor if it is used, and removing the N 2 . Via selection of, e.g., particular separation membranes, the degree of separation of CO 2  and H 2 O from other materials can be controlled by the skilled artisan. Membranes, liquid solvents, and solid adsorbents, can all be used. 
         [0024]      FIG. 1 d    shows an additional optional embodiment, a means for a water gas shift  110 , where H 2 O is added to the CO and H 2 , resulting in production of more H 2 , and conversion of toxic CO to less noxious CO 2 . Adding more H 2  increases the octane number of the resulting product. 
         [0025]      FIGS. 2 a -2 d    parallel  FIGS. 1 a -1 d   , except that they employ a low temperature electrochemical reactor. “Low temperature” as used herein refers to reactors which operate at temperatures from room temperature to 400° C. While heat, as from, e.g., the exhaust gas is not essential to the operation of the electrochemical reactor, high temperatures are not so the order of items “ 104 ” and “ 103 ” is reversed in the process. 
         [0026]    The reactions which take place in the reactor, discussed infra, lead to the production of one or more of liquid hydrocarbon fuel, syngas, hydrocarbon gas, or a liquid oxygenate, which is stored on board the vehicle, and which may then be offloaded at, e.g., a gas station or other appropriate depot. As noted supra, these products may also be used on the moving vehicles. 
         [0027]      FIG. 3  depicts, generally, what occurs in the electro-chemical reactor. A solid oxide electrolysis cell (“SOEC”)  201  is depicted, showing a mixture of CO 2  and H 2 O. 
         [0028]    The SOEC displays a cathode  202  and an anode  203 , where a series of “preliminary” reactions occur, followed by reactions which yield hydrocarbon fuels. 
         [0029]    Within the electrode, water reacts with the anode, such that H 30   and O 2−  species are formed. At the anode, the reaction: 
         [0000]      2O 2− →O 2 +4 e   − 
 
         [0000]    takes place. Meanwhile, at the cathode the H +  species becomes H 2 , while CO 2  is reduced to CO, permitting the reaction: 
         [0000]      (2 n+ 1)H 2   +n CO→C n H (2n+2)   +n H 2 O
 
         [0000]    to take place. Most of the product will be the mix of H 2  and CO referred to as syngas, and this can be stored on board the moving vehicle until such time as it is combined with primary fuel, or off loaded. C n H (2n+2)  is the formula for various hydrocarbon fuels. Further reactions can also take place, resulting in, e.g., methanol, dimethylether, both of which have roles as synthetic fuels. Other, larger molecules can result if, e.g., a Fischer Tropsch or other suitable reactor is employed. 
         [0030]    Exemplary reactions which take place within the reactor are: 
         [0000]      CO 2 +2H + +2 e   − →CO+H 2 O
 
         [0000]      CO 2 +8H + +8 e   − →CH 4 +2H 2 O
 
         [0000]      2CO 2 +12H + +12 e   − →C 2 H 4 +4H 2 O
 
         [0000]      2CO 2 +6H + +6 e   − →CH 3 OH+H 2 O
 
         [0000]      CO 2 +2H + +2 e   −e →HCOOH
 
         [0000]    see, e.g., Beck et al., Electrochemical Conversion of Carbon Dioxide to Hydrocarbon Fuels, EME580 (Spring, 2010), incorporated by reference. 
         [0031]    In general, the following reaction is a “guide”: 
         [0000]      CO 2 +2H 2 O→Fuel+2O 2  
 
         [0032]    Specific features of the invention, which are relevant, include the use of energy recovered from the exhaust gases, and the absence of any source for an external air stream. 
         [0033]    Referring back to  FIGS. 1 and 2 , it will be seen that the electrochemical reactor is supplied with electrical energy from, e.g., a thermoelectric generator. 
         [0034]    Hydrocarbon fuels produced in the reactor are immiscible with water, and are separated therefrom easily, as liquid fuel. This liquid fuel is moved to a storage container means, until such point as the moving vehicle reaches a site, such as a gas station, where it can be off loaded. 
         [0035]    Specific features of the invention which are relevant include the use of energy recovered from the exhaust gases, and the absence of any source for an external air stream. 
         [0036]    Other features of the invention will be clear to the skilled artisan and need not be reiterated here. 
         [0037]    The terms and expression which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expression of excluding any equivalents of the features shown and described or portions thereof, it being recognized that various modifications are possible within the scope of the invention.