I'm approaching purple science and noticed that caustic solution is useful now. I am assuming that brine water electrolysis produces as much NaOH as Chlorine, so I'm thinking that I have to keep making PVC to get rid of the Chlorine.

Maybe I could get a bit of caustic via the caustic from pure water recipe, which seems to yield slightly more than the saline recipe, but at a great energy cost.

Have I missed some alternative solution? Right now the other plastic recipe seems nice but unusable because of this issue.

Check the FAQ tab for an in-depth discussion of how to deal with chlorine byproduct.

At your tech level, the main method that you're missing is mineral dust plus hydrochloric acid -> sludge -> wastewater -> outfall. You will get lots of gravel for mineral dust from normal smelting, however if you need more you can make as much mineral dust as you want from crushed limestone or iron ore, and then the stone you get from crushing it can be used to make even more mineral dust.

In the next tech tier you'll get a more efficient option for getting rid of chlorine, calcium chloride solution, and then several more options in later tiers.

Ah yes, I was already making sludge but I didn't realize how much chlorine that takes and that you might make dust on purpose. Thanks!