to the Aerogel project.
I hooked the system up Sunday. After freezing water in cleaned POWERADE ZERO bottles (They were on sale a while back, and so I had around 20-25 on hand), I then added the bottles to the water bath, and filled the container with water. In addition to destroying the need to buy Ice from grocery stores and gas stations every day, the Ice-Bottles are getting colder than 0° C. The Water bath is hanging out at -0.4 to -0.9° C, which reduces the pressure necessary to maintain CO2 as a liquid. The colder temp (Previously I was able to keep the Bath around 4°-9° C) also causes the CO2 to become denser, and helps force the Ethyl out of the ‘Gels faster.
The CO2 pressure is staying around 700-750, so this seems to be working quite well, and the CO2 should displace the Ethyl faster with the colder temps.
Oh, yeah… the Needle Valve. After getting the ‘Clave, CO2, Lines, Ice Bottles, & water bath set up, I let the whole shebang sit for an hour or so to allow the contraption to cool off prior to opening the CO2. I then cracked the CO2 Bottle open, opened the 2 new Ball Valves, and watched the pressure in the Autoclave rise to 675-700 PSI. I cracked the Exit Needle Valve, and watched the contraption for a bit. The Needle Valve froze over (like it always did) and I decided to implement the Warm-Needle Valve Bath Idea TJ & I came up with prior to his escape to Texas. So I stacked half of a 70mm Film can on a hot plate on a board on an MSC Direct “Big Book” Catalog, and poured H2O into the can. I turned the hot plate up to 7 (out of 12. Why 12? I dunno.) and watched the Ice melt. Then the needle valve spewed the frozen CO2/Ethyl plug into the Ethyl capture Jug, and started bleeding the normal CO2/Ethyl mix I have become accustomed to.
After an hour or two of bleeding off Ethyl, I turned off the Exhaust fan and the Hot Plate, and closed the needle valve. Then, after the collected Ethyl stopped moving, I marked the Bottle with a Sharpie at the level of ethyl collected. I had approximately 2.5 inches at the time.
The next day, After getting the boy to sleep, and after doing my house-chores, I returned to the Lab, and noted the amount of Ethyl in the container had doubled (just under 5″). I did not hear a hiss, and the Ethyl was still, so I proceeded with swapping the Ice-Bottles for freshly frozen Ice Bottles, waited a few minutes for the temperature to drop a few 1/10th’s of a degree, turned on the exhaust fan and hot plate, and proceeded to Bleed off more Ethyl. 2 hours later, I stopped the Ethyl/CO2 exhaust, turned off the Fan & Hot Plate, and marked the Ethyl collector bottle again. It was now around 6″ of Ethyl collected. I had marked the pressure on the CO2 Tank’s gauge with a Sharpie when I set it up, and I noted it had dropped in pressure (around 25-30 PSI). Not wanting another batch of useless dust, I swapped CO2 Tanks and left it for the night.
Day Three, There was 6.5″ in the collector on beginning the extraction. Same process repeated again (Swap Water bottles for Ice Bottles, put Water bottles back in the Chest freezer, turn on exhaust fan & hot plate, wait a few minutes, and bleed Ethyl for an hour or two, then shut off the bleed and turn off the fan & plate), and this time the level in the bottle hadn’t changed noticeably. I noted that on the collection bottle with the sharpie, and left the Lab.
Yesterday, when I checked on the system, I still had 750+ PSI in the CO2 Tank, The ‘Clave was sitting at 700+ PSI, and the Temperature was at 0.4° C. The collection bottle had reached 6.75″. I only bled the system for a few minutes, due to preparation for Norwescon, and closed up shop sooner than usual. I did not swap the Ice, nor did I turn on the Hot Plate (but the exhaust fan was turned on. The amount of CO2 released into the Lab Shouldn’t rise to hazardous levels in a few minutes, but I’m Crazy, not Stupid. Safety First! (Not just a Slogan, it’s also handy Firearms Advice)).
Tonight, I’ll check the level again. I do not expect significant changes to the setup since last night, so if there is a change to the system, I’ll note it in my next post.
If the Ethyl Level remains constant from last night, I will test the exhaust for Ethyl. If there is no trace, I’ll boil the CO2 off tomorrow (Supercritical CO2 = 1050 PSI (72.9 BAR) & 31.1° C. The Autoclave was built to withstand 3000 PSI (Two 3000 PSI Threaded 3.5″ caps (bottom welded on after leak discovered, top with two holes drilled & tapped to 1/4″ NPT), one foot section of 3.5″ Schedule 80 Stainless pipe, the 10,000 PSI Needle Valve, the 3000 PSI Check Valve, and the two (new) 600 PSI Ball Valves (to remain open when Bleeding, as the Check Valve Leaks when the pressure inside is over 490 PSI. That was discovered during the last batch, and I don’t want to damage either the Ball Valve on the Check Valve, or myself if it fails spectacularly))). I will typically allow it to reach 2000 PSI, & then Bleed the pressure down to 1200 PSI as the temperature keeps rising. So long as I keep the pressure up past 1050 PSI, as the system warms, the CO2 will remain a Liquid. Letting the pressure drop to below 1050 PSI allows the presence of Gaseous CO2, which kills the Aerogels, producing an expensive but unfortunately useless dust.
If I smell Ethyl on the coffee filters, I’ll let it sit over the weekend. If I do not smell Ethyl, Tomorrow is Supercritical Boil Off day. And the day of my first successful Aerogel Decanting will be a company holiday for my naescent Business.