Best ways to compress and store tons of CO2?
Poor carbon dioxide has been unnecessarily defamed as a greenhouse effect. This is not only gas in the atmosphere which is an infrared absorber. Guess what, water vapor is a major culprit as well along with methane (recall cows digestive system). Nature has a very delicate balance, carbon dioxide is plant's food as well.

I recall some people doing PhDs on carbon dioxide remediation in chemical engineering. One of options is to pump carbon dioxide into deep rocks with a hope that it will convert into carbonates, mainly calcium carbonate in deep layers. One can then study all types of phase diagram of carbon dioxide etc.

One green solution is a massive drive for the plantation of trees. This option is far better than more expensive options.