How much would it cost to put a tank into your car that trapped the CO2 gas given off by combustion, converted it into liquid form, then kept it there in the tank you could dispose of it? Has anyone worked on this idea?
Carbon dioxide does not liquify at any reasonable pressure.
Damn. I figured you just needed -78C temperatures.
Wanna bet?
It depends on what you call reasonable. At 0 degrees C the vapor pressure is just over 500psi, rising to around 800psi at 20 degrees. Those are high but scarcely exotic pressures.
This page has a phase diagram for CO2. It shows that you can’t have liquid CO2 at any temperature unless the pressure is above 1 atmosphere. At -78.5C, CO2 is a solid (dry ice) at 1 atmosphere.
But the OP presumably would be satisfied with trapping CO2 as a solid rather than a liquid. The trouble with this idea is likely to be the energy required - it’s hard to produce those kind of low temps without expending lots of joules.
I wouldn’t even call them particularly high. Scuba tanks are routinely filled to between 3000 and 4500 PSI. Liquid CO[sub]2[/sub] is used extensively in food service for beverage carbonation systems due to the large amount that can be stored in a relatively small space as compared to compressed gas.
The flaw in the plan is that it would take a significant amount of energy and equipment to trap exhaust gasses, cool them and compress them to liquid.
How would you ‘dispose’ of CO2?
I assume you are trying to reduce the amount of CO2 in the atmosphere, so even if possiable you will have to come up w/ a infrastructure where the CO2 doesn’t’ get back into the air.
Also many people are pissed that they are forced to carry some of the oxygen along with fuel needed for combustion (oxygenaged gas), which reduced the total power per gallon in that gas, or increases weight for the same energy - all which reduces MPG’s and usually increases the cost per gal. Now you want people to also carry their exhaust also?
Don’t liquefy it. Bubble it through a solution of calcium hydroxide. Dump off the calcium carbonate to landfill, it’s only chalk in another form. Simple.
Also, you can manufacture more calcium hydroxide simply by roasting chalk and dissolving the residue in water.
/feels momentary concerned that there may be a hole in his bucket.
Doesn’t this release CO[sub]2[/sub]?
Ahahaha. Chemistry is a cycle.
Exactly. So what do we do with the CO[sub]2[/sub] created by heating chalk?
D’ja notice this bit? 
I did, but couldn’t make heads or tails out of it. Elucidate.
If you’re truly worried about the CO2 that you generate in driving a car, then plant a few trees. Your proposed solution makes very little sense in that it requires considerable extra machinery in the car and doesn’t provide a mechanism for actually disposing of the waste gases.
This would be wacky hard.
Step One: Your exhaust is not pure CO[sub]2[/sub]. How do you handle the CO, water and any unburned fuel?
Why would you want to do this? At best, you’d just be relocating your exhaust by an environmentally meaningless distance. The impact of moving that tank of liquid CO[sub]2[/sub] for the sake of moving it would be much greater than simply letting it out as it’s produced. And I certainly wouldn’t want to use it in my soft drinks!
I was thinking about this, why not use some kind of electronegative atom and change the carbon dioxide to something else.
Wouldn’t sodium chloride also work to convert CO2 into CO2Cl though. I don’t know if CO2Cl is liquid or solid at room temperature though. If it is just a gas that really isn’t an improvement.
I don’t know if adding a strong acid to CO2 then adding water would also create carbonate. But that could work too if we don’t have any hydroxide.
In some sense, neither do the trees. While they are alive, they are taking CO2 out of the atmosphere, storing carbon and releasing oxygen. When they die, the process is reversed as they decay.
But if you can increase net biomass (say, by planting trees that will be allowed to regenerate indefinitely) then you are increasing the total amount of bound carbon.
Well, yeah. But if nothing else, you bind the carbon for a hundred years+. I’m sure by then that will have reached Peak Oil and will be using some less CO2 intensive forms of transport (or fewer more intensive forms such as horses).
If you want to get rid of it longer than that, plant peat moss 
And I imagine that at least some of the biomass gets absorbed into soil as organic compounds.
Bubbling exhaust through a concentrated solution of calcium or sodium hydroxide could work, but rougly 84% of the mass of gasoline is carbon. For every gallon of gas you burn, you’d get something like 4 kg of calcium carbonate; 80 pounds per 10 gallon tank. You’d need a huge, energy gobbling infrastructure to make that much hydroxide. There’s probably some carbon dioxide absorbing zeolite that could be made to work reversibly, but the capacity needed to deal with burning gasoline is still huge.