If you're looking for Refined Carbon in Abiotic Factor, that's probably because you've finally made it to Cascade Laboratories. Cascade is one of the meanest, most dangerous, and downright fascinating wings of GATE.
It's also a location you'll be returning to often, as it's host to an infinite supply of Refined Carbon (one of the most important mid-game crafting materials in the game) if you've got the right stuff to exchange. It's a little tough to come by at first, but farming Refined Carbon becomes a breeze once you know where to look.
How to get Refined Carbon
When you arrive in Cascade Laboratories, you'll likely first find Refined Carbon (it looks like grey spheroids) by cracking open Carbon Analysis Machines throughout the Adjustment Wing on the third floor.
After you exhaust that limited resource, you can get more by finding the Refined Carbon Exchanger. There are a handful of trade stations in the Adjustment Wing (reached by taking the huge circular lift to the third floor) used to farm key materials. The Refined Carbon trade station can be found by going upstairs from the main Adjustment Wing lobby (the room full of irradiated Exors, sorry) and taking a right.
The Exchanger will spit out one Refined Carbon for every Silver Scrap you feed it. So how do you get Silver Scrap? That's where a specific portal world comes in.
Get Silver Scrap from The Train
All the silver scrap you'll ever need can be farmed from The Train, one of the portal worlds in Manufacturing West. You'll find it in the northwest tram station in Manufacturing, guarded by a pair of soldiers.
Once you've reached The Train, you're looking for Pocket Watches and silverware. Check every cabin and under every table, and you should find a handful of each. Silverware is picked up as Silver Scrap, and Pocket Watches can be broken down into Exquisite Chains, which can then be salvaged for Silver Scrap.
Unlike the main GATE facility, portal worlds completely reset every few in-game days at midnight, so you can make a run through The Train regularly to stock up on silver and turn it all into Refined Carbon. Just be aware that Exquisite Chains are also needed to make trinkets, so maybe don't scrap all of them.
