Fischer-Tropsch is one process for doing it. But it's generally not terribly practical as an energy investment. The main source of energy in a hydrocarbon is the hydrogen. Where are you getting the hydrogen from? If your answer is oil: Bzzt! You're greenwashing for the fossil fuel industry, no thanks!

If your answer is electrolysis or thermolysis of water: Great choice! But it takes a lot of energy to do this. Where are you getting the energy? If your answer is the power grid: Bzzt! You're greenwashing for the fossil fuel industry, no thanks! If your answer is renewable energy: Great choice! But now you've got a lot of renewable energy that you could just use directly instead of using it for hydrogen. If you're still intent on turning it into hydrogen, okay, that's a valid choice. Let's continue.

Now you've got hydrogen, and you've used renewable energy to make it, great! What's your next step? Well, you could just burn the hydrogen or use it in fuel cells. This is about the most efficient thing you can do with hydrogen. But hydrogen is really difficult to store safely in large quantities, it's not energy-dense, and it can be dangerous since it's highly volatile and explosive. We have little to no infrastructure for it and quite a few high profile disasters that give it a bit of a bad reputation.

Here's where the interest in hydrocarbons starts. You can slam 4 of those troublesome hydrogen atoms (2 hydrogen molecules) onto a single carbon atom and now you've got methane. It's somewhat more energy dense, much easier to transport and store, and safer to work with. We are very familiar with this product, we already use a slightly impure fossil fuel form of it called natural gas everywhere and we have all the infrastructure and experience we need to take great advantage of it.

But first, we have another question to answer. Where are you getting the carbon? If your answer is atmospheric carbon dioxide: Great choice! This is not as easy as it seems though and takes more (renewable) energy, which is now compounding your investment into making fuel rather than making energy. If your answer is plants: Okay choice! But now you have to grow the plants, and they're taking up farmland and sunlight and water that could be used for food, drinking, or solar panels. If your answer is oil: Bzzt! You're greenwashing for the fossil fuel industry, no thanks!

We can continue like this down the hydrocarbon chain, but the questions and problems and energy investment continue to compound massively as you move to increasingly denser, more convenient fuels. Methane can become Propane, and propane is a lot denser and more manageable than natural gas is, so that's nice, but is it worth it? Propane can then become Butane, Butane can become Octane, which starts to resemble Gasoline, and the chains get longer and get mixed in more complex ways, you start to get all the benefits of those heavier fuels we are used to, but it comes at a significant cost (financial and energy and opportunity costs all apply here) and increasing complexity and infrastructure needed to produce it and is it really worth it?

Where should we draw the line? Nobody has decided yet, but realistically it's probably going to be pretty low down the hydrocarbon chain if we end up using hydrocarbons at all. The familiarity of heavy hydrocarbons are simply not worth the effort to synthesize them at large scales when we can usually find easier and more efficient alternatives lower down the energy and cost investment levels.