Recycling IPA for 3d Printing

Safety First

The following post describes how i do modest recycling of IPA to get more life from my wash bath. It's important to be realistic about how much life you can get from IPA. I'm not an expert, but I do know that IPA can form hazardous peroxides and peroxide crystals that can be explosive and more flammable than IPA itself.I limit the number of times I recycle IPA and always store it in sealed containers to reduce the amount of interaction with air and moisture. I never use heat. I stop recycling when the IPA no longer looks clear or if it develops an odor. If in doubt, bring it to the disposal center. Of course do this in a well ventilated space and wear gloves and a mask. Always avoid treating a high volume of very spent IPA--that is where people end up with a gelatinous monster that ends up being a toxic soup.

My Recycling Basics

When I started 3D printing I found very little information on managing IPA beyond advice to dispose of it properly. In most cases that means bringing to a recycling center for hazardous materials. I wanted to reduce the number of trips to hazardous recycling, and stretch the life of the IPA. The solution I found has three components that I will describe in turn. 

1. Get most of the resin off the prints with a small amount of IPA using a low volume pre-wash. 

I do this with a sealed storage container that allows me to slosh the alcohol around and a squirt bottle to get into detail and deep grooves. That keeps my main wash bath cleaner longer. I then drain the part and put it into my agitated wash bath to get off stubborn resin. 

Low volume prewash diagram.

2  I expose used pre-wash IPA to UV light in low volumes, and then filter the IPA. 

Not treating too much at one time solves a common issue with recycling; the curing of resin suspended in IPA is limited by light penetration. If you do a low volume, you can get good penetration and cure a lot of the resin out. If you try to treat a high volume of dirty IPA you don't get very efficient curing and end up with a big mess. Cured and partially cured material will settle after 24 hours and can be filtered out with a coffee filter. A second UV exposure will pull out more resin. The partially cured resin in the filter at the end will harden. You can do this in a well ventilated space, or, better, put it in the sun in a place not accessible to children or animals. It becomes very hard.

I typically pre-wash with a pint of alcohol at most. For reference, that is a beer at the pub. I split this in two deli containers for treatment, and let it pre-settle before I expose it to UV--some resin will fall out on its own. You can buy deli containers in bulk, or do as I do, and take them from the recycling bin at work where people toss their takeout containers. Wash them well, you don't want mayonnaise in your IPA!

This photo shows used pre-wash IPA set up under the UV light panel. The cured resin then clings to the side of the container where the UV is strongest. 

The exposed resin clings to the side of the container.

Give it a shake, then let it settle, and it will look like this. This is a little more than 1/2 pint. 

This is my pour through filter set up.

It has a 3d Printed lid (there is a hole in the storage container for the drips to go through) The lid fits well enough to contain fumes. 

This is what you're left with, or more, depending on how much resin came out.

Another example.

I let the used filters harden by the exhaust fan in my printer enclosure. It usually takes a day or so with some periodic UV for them to stiffen. 

You can then either reuse the IPA, or, if it's not sufficiently clean, use it one more time at most and dispose it at the appropriate recycling venue.

3. I replenish my pre-wash supply with the used alcohol from my wash bath. 

I don't ever let the wash bath get very heavily soiled. I check it with a hydrometer. What you want to avoid is treating a high volume of very dirty IPA at one time. I treat as I go and make it part of my printing routine.

So is it worth it?

This might seem like a lot of work for a little reward, but it has allowed me to get more use out of my IPA. Your experience may vary. Whatever you do, please be mindful of your safety and the health of our environment. Please take care.