Keeping ratio of butane/propane blend after recovery

[BuckUp]

Howdy everyone,

This is my first post on here and just wanted to thank everyone for all of the information on here!

I've been running a closed loop system for some years now and have just switched to running a 70% n-butane/30% propane blend. What I'm wondering is how do you keep the ratio of butane to propane around the same after recovery?

I'm pumping about 18lbs of gas into the system and losing about 2lbs of gas in the system before it hits the collection pot. Goes through a material column and then sits in the dewax column for at least an hour. Then another lb or two of gas left in the collection pot so I can pour and not scrape. So afterwards I need to add more gas to my injection tank but not sure how much propane vs butane to add to keep the ratio correct.

Thanks in advance for any insight!

 

[KLITE]

I prlly been doing it wrong but if say i lost 1ld, i add 50% butane and 50% propane. Tried that ratio after @Fadedawg reccomended it. makes recovery quicker and picks upa little bit less waxes.

On another issue, have you tried letting gas pulp up longer than 1hr? What filters do you use?

 

[BuckUp]

When you say pulp up do you mean in the dewax column?

I always do at least an hour usually minimum 1.5 hours at -40 but often I let it sit there overnight. I've got the dewax column on a -40 chiller which I leave running when I'm rolling the system consecutive dates. If I leave overnight I don't usually need to run dry ice in it. Otherwise I need to add dry ice in order to get the temp down to -40 quickly after it gets filled with warmer gas.

My dewaxing column is packed with stainless scrubbers. Then I filter through 25 micron filter paper which I cut to fit my 6" filter stacks, 2 in a row. 2 just in case one of the papers breaks or isn't put in quite right.

 

[Fadedawg]

Once mixed, propane and butane are not readily separated, so if you are replenishing three pounds every run, on an 18 pound system, just continue to replace with what ever mix you are using.

The mixture is also not magic at exactly 50/50, it was just a convenient place to drive a process stake, to maintain a controlled process. 70/30 works but begins to get sluggish before 50/50% does, so you can operate at lower temperatures with 50/50%. At -30C, 70/30 still works well in our systems, but not as good as 50/50% below -50C. My guess is that that it would take sensitive instruments to measure the difference in viscosity between 48/52% and 52/48% and there are more variables in chilling systems and subzero temperature measurement.

 

[Fadedawg]

My dewaxing column is packed with stainless scrubbers. Then I filter through 25 micron filter paper which I cut to fit my 6" filter stacks, 2 in a row. 2 just in case one of the papers breaks or isn't put in quite right.

Have ya'll considered cutting to the chase with a 4" X 8" polyester felt 1 micron sock filter, such as used to filter biodiesel?? Because they have so much filter area, you can filter to a finer micron level without clogging, and finish faster.

 

[BuckUp]

You know I read about using the filter socks and I ended up ordering a kit from Duda diesel but the housing I got had the drain port partway up the side. Ended up returning it because I figured the gas wouldn't fully drain unless the port was on the bottom. From the looks of your system I saw on another thread it seems like you have different housing then what I had.

A lot of times I'm only trying to do a run per day anyway so the loss of time doesn't matter. I've got plenty of other stuff that keeps me busy in between. I haven't seen a whole lot of difference when using 10 micron filter paper on the bottom filter stack (not much of anything on the paper). I figured the scrubbies are grabbing most of the waxes and such.

Do you find that a lower micron produces a higher quality product or just speeds up the process? Does a lot of oil get stuck on the filter sock? They seemed kind of thick to me but they were bigger ones (can't remember the size now).

 

[BuckUp]

Thanks for the replies on the mix ratios. I read somewhere that a mix of propane and butane will gas off unevenly because of the different boiling points of the gases. I'll probably just stick to adding more gas at a 50/50 ratio.

So far I haven't seen a whole lot of difference in the final shatter between just running butane and the propane/butane mix. Seems a bit more terpy but the main reason I added the propane was to try and lighten up the end product. I'm running trim
from last fall so it's coming out darker now.

Still playing with injection temperature. I've been playing with getting the gas colder by running it through a coil in an alcohol/dry ice bath before it hits the material column. Haven't seen a difference from doing that but I'm thinking I may need to find a way to get the material itself cold. Don't have a way to measure the temperature of the gas going in either so I don't know what temp it's being injected. It's definitely cooling it quite a bit but not to -30 or -50.

I do like the extra pressure that propane adds as I'm not adding nitrogen now for injection pressure or pushing the substance through the filters.

 

[Fadedawg]

You know I read about using the filter socks and I ended up ordering a kit from Duda diesel but the housing I got had the drain port partway up the side. Ended up returning it because I figured the gas wouldn't fully drain unless the port was on the bottom. From the looks of your system I saw on another thread it seems like you have different housing then what I had.

A lot of times I'm only trying to do a run per day anyway so the loss of time doesn't matter. I've got plenty of other stuff that keeps me busy in between. I haven't seen a whole lot of difference when using 10 micron filter paper on the bottom filter stack (not much of anything on the paper). I figured the scrubbies are grabbing most of the waxes and such.

Do you find that a lower micron produces a higher quality product or just speeds up the process? Does a lot of oil get stuck on the filter sock? They seemed kind of thick to me but they were bigger ones (can't remember the size now).

Sweetleaf has an inline stainless filter housing with triclamp fittings on each end.

There are face filters which are membranes with pores, and there are body filters, which entrap the particles in a matrix, as well as cross flow, which is more or less pumping the concentrate through a blotter paper straw that weeps and further concentrates the solution. They are called cross flow because the flow rushing past the permeable walls keeps the particles from plugging the pores as fast.

The 4" X 8" polyester felt sock filters that I suggest, are body filters and offer some advantages. The first is that because of their large overall surface area relative to the volume, and their matrix body filtering that offers even more area, they will process a large volume fast.

A second is that filtering to 1 micron filtration removes more fines than can act as points of nucleation for waxing. 1 micron lab filters with filter plates, would blind in a heart beat from plant wax.

You can wash and recycle sock filters a few times, though at their cheap price, most folks probably don't.

Concentrates filtered to 1 micron have greater clarity than concentrates filtered to 15/25 microns.

 

[Fadedawg]

Thanks for the replies on the mix ratios. I read somewhere that a mix of propane and butane will gas off unevenly because of the different boiling points of the gases. I'll probably just stick to adding more gas at a 50/50 ratio.

So far I haven't seen a whole lot of difference in the final shatter between just running butane and the propane/butane mix. Seems a bit more terpy but the main reason I added the propane was to try and lighten up the end product. I'm running trim
from last fall so it's coming out darker now.

Still playing with injection temperature. I've been playing with getting the gas colder by running it through a coil in an alcohol/dry ice bath before it hits the material column. Haven't seen a difference from doing that but I'm thinking I may need to find a way to get the material itself cold. Don't have a way to measure the temperature of the gas going in either so I don't know what temp it's being injected. It's definitely cooling it quite a bit but not to -30 or -50.

I do like the extra pressure that propane adds as I'm not adding nitrogen now for injection pressure or pushing the substance through the filters.

You can separate the two through fractionally distillation, but the towers that refineries use to do so are tall and at your high replenishment rates, it has limited opportunity to dramatically change the ratio. We lose a small fraction of that replenishment rate, because we don't pour off at the end and we bake out the columns, yet still don't suffer separation issues.

Both the propane and butane mixture is above its boiling points under the conditions in a collection pot under vacuum. If you wanted to fractionally distill them, you would control the temperature and vacuum to be below the boiling point of the butane, but above that of propane.

They are both simple alkanes (C3H8 & C4H10), so when we boil their mixture, they ostensibly boil at the temperature of the azeotrope, not that of propane or butane. That vapor is ostensibly enriched in propane, but all of the vapor passing through the pump goes back into the collection tank, where it turns to a liquid.

Once back in a liquid, there is no segregation, so you are starting over again fresh.