Butane, delivered to your house.

[David Thomas]

As we head into winter, it’s time for a few creative, technical endeavors, perhaps better called “Stupid Engineer Tricks”.

The concept: extract butane from the natural gas piped to my house and refill backpacking canisters with that.

Continued in the next, editable post.

[David Thomas]

The problem:  I have to go to the store and buy 16-ounce / 450-gram butane canisters at a high price/BTU to refill my 4-ounce canisters.  At $8.99 a canister, that’s $42/100,000 BTU.

Lots of other fuels are cheaper per BTU.  Propane purchased in bulk at a few local filling stations, even 5 gallons at a time, is $2.89/gallon in my town or $3.18/100,000 BTU.

Natural Gas is $0.91/100,000 BTU delivered to my house.

But natural gas isn’t all methane.  2%-8% of it is ethane and about 1% is propane.  A few tenths of a percent (= a few parts per thousand) are butanes and heavier hydrocarbons.  I use 100 ccd = 100 therms = 10,000 cubic feet of natural gas a month which contains about 20 cubic feet or 3 pounds of butane.

If I run all that natural gas through granular activated carbon (GAC), the heavier hydrocarbons (butanes) will preferentially adsorb while the methane and ethane pass through.  Then I can put a vacuum pump on the (then isolated) GAC, warm it a bit to help de-sorb the butane, and pump it into a pressure canister.

That GAC vessel would be in line with my natural gas delivery line, or rather, my water heater since it uses 95% of the gas because it provides both domestic hot water and all space heating.

What could possibly go wrong?

[Jacob]

Did you consider zeolites? There may be one that absorbs/adsorbs butane more selectively based on molecular size.

https://www.google.com/search?client=firefox-b-1&ei=3fb1W6iFFqHB7gLxxZfADw&q=zeolites+butane&oq=zeolites+butane&gs_l=psy-ab.3…10273.10933..11327…0.0..0.237.584.2j1j1……0….1..gws-wiz.Uz2wzKZ05NE

https://www.deltaadsorbents.com/5a-molecular-sieve

CPS has a class1Div2 ‘sparkless’ recovery pump.

Also don’t forget proper evacuation and all that safety jazz. Your GAC should start at <100microns, then when full simply heat it based on a butane vapor pressure curve to get the pressure you want. That way you don’t have to pull on the saturated GAC with a vacuum pump, you should only do that with a rated recovery pump (butane/isobutane is R600/R600a)

If you use a fire protection check valve to prevent mistakes traveling upstream and do all this outside with ample space that will significantly limit the possibilities of what could go wrong.

Sounds fun!

[David Thomas]

Jacob:  I haven’t ever used zeolites.  I know the big buys (oil refineries, etc) do because there are so many different zeolites and one can select desired properties for a particular application. I’ve used GAC on over 100 of my projects.

Good point, if I just “boil” it off (desorption occurs under a vacuum or at roughly a compound’s boiling point), I can skip the vacuum pump, and just keep the receiving vessel cold to condense the vapors.

But propane will boil off first (it would vacuum-desorb first, too).  And I don’t want (much) propane, I want butane.  Butane will displace propane on GAC, being a longer hydrocarbon chain.  So if I wait for the GAC to saturate, it will be mostly butane (and higher weight stuff).

[Daryl and Daryl]

I’m too dumb to try these experiments but smart enough to know I shouldn’t try these experiments.

I’m sure I could quickly demonstrate “what could go wrong?”.

[Roger Caffin]

David – would having 5% propane matter at all? I would not have thought so.
For that matter, do we even know what % propane is found in canisters labeled ‘butane’? We do know (now) that many of these ‘butane’ canisters contain both n-butane and iso-butane. I seriously doubt that any of that gas has been purified to any extent.

For a quite safe extraction method, how about running your town gas through a refrigerated stage? Held at -5 C, the n-butane would condense out. Held at -15 C both n-butane and iso-butane should condense out. However, the cost of the refrigeration stage might cover the cost of new canisters for the rest of your life …

Cheers

[MJ H]

When you run the numbers of the cost-effectiveness of this, maybe include the cost for your time and something to account for the odds of blowing up the house.

[David Thomas]

Roger:  Some propane in the mix is final fine, but too much and it’s not a butane-propane, but essentially propane and (1) I can get that easily and cheaply already and do refill propane containers myself and (2) I shouldn’t put high-percentage propane into butane canisters.

Modest refrigeration is easy on cold days at my house – just pipe it outside.  I’m not sure what the “dew point” equivalent for natural gas is (that temperature at which some liquids start to condense) is called, but I suspect it is maintained by the gas utility to a lower temperature than it would be in milder climates.

The n-Butane wouldn’t condense at 0C – it’s normal boiling point, but only when butane’s mole fraction in that mixture of hydrocarbons is more than it’s vapor pressure at the its current temperature.  Say, n-butane is 1% of the mix, then at what temperature is n-butane’s vapor pressure 0.01 of an atmosphere = 7.6 mm Hg which looks to be about -81C (page 6 of https://www.gpo.gov/fdsys/pkg/GOVPUB-C13-53f578da43e73f0de68653a23dc01d5f/pdf/GOVPUB-C13-53f578da43e73f0de68653a23dc01d5f.pdf )

MJH: another perspective is that if this endeavor is less risky than other potential projects (I’m currently fabricated electrical heaters to lower down wells into the groundwater (what could go wrong?), it enhances my safety.  And if I factor my billing rate into DIY projects, I’d never do any of them unless I’ve got a billing number to bill a client’s project (like I have with those groundwater heaters).

[Roger Caffin]

Hi David

For some reason I had assumed that the n-butane fraction was much larger than that. Oh well.

Cheers

[Jerry Adams]

That sounds like a fun project.

Butane can be bought at the Korean Grocer for $5 for 4 cartridges of 8 ounces each, about 50% isobutane and 50% n-butane

Maybe there are no Korean grocers in Alaska

You in the cold land can use Propane which is cheaper

Do they have greenhouses in Alaska?  They sometimes use bulk butane to provide heat and butane releases more CO2 I believe which can be good for plants.  That would be cheap.

[David Thomas]

Jerry,

Fairly common up here are “high tunnels” constructed from 20-foot pipe (metal or PVC), bent into a semicircle, and covered with a clear polyethylene sheeting.  One end wall is framed in 2x4s and has a standard man-door for access.  USDA gives grants for them if you provide some data back to them.

Individuals use bulk propane to extend their season for earlier starts or a later harvest (makes for very expensive tomatoes).  They were a couple of commercial greenhouses in the area – at least one of them closed after the 2008-2009 recession – maybe they’ve sourced bulk butane.

There is an Asian grocery in Anchorage that has the horizontal canisters but not that cheap.  More like $2.50-3.00 each.  I have transferred from those into **clearly marked** backpacking canisters for use in the summer.

Yes, everyone, I know this would never pay for itself.  It’s just intriguing to me that in addition to water, power, telephone, internet, and (mostly) methane delivered to my house, I could potentially extract propane and butane as well.

In my role as President of our electric utility, I just accepted a budget for 2019 including $32,000,000 of natural gas.  And sometimes, the utility buys off-spec gas from a producer that is too rich in “liquids” for distribution as natural gas, while we like more BTUs for less money.  Some electrical co-operatives also sell propane to their members.  We could potentially extract propane from a feed stock we buy at a much lower price, but that’s definitely not a good setting for one of my DIY efforts and there’s already an oil refinery across the highway that is much more experienced at doing that sort of thing.

[Ben H.]

Do you know how much GAC you would need to store a pound of butane?  Would it store considerably less butane since your extracting it from a low concentration source?

[Ben H.]

hmmm…. to begin to answer my own question (David is still more of an expert on this than me):

https://www.sciencedirect.com/science/article/pii/S0017931007005042

It looks like you can expect 20-40% kg/kg of butane in GAC.  That sounds like you only need 5 lbs of GAC to store a pound of butane…. and the paper shows how sensitive the saturation is to a slight vacuum.  From a purely mass diffusion perspective you would have to divide that number (5 lbs) by the boundary condition driving butane into the GAC which would mean 100’s or 1000’s of pounds of GAC to store 1 pound of butane.  But…. I think the chemistry means the butane preferentially attaches to the GAC.

 

[Kevin Babione]

David – I’m an IT guy with an accounting background so the physics/chemistry/voodoo involved in extracting the butane from your inbound natural gas line is well beyond my comprehension, but I really do enjoy reading all of your posts.

It would not surprise me in the least if one day you post something like this:  “A friend of mine brought me back some cool rock samples from a dog sledding expedition up north and, after using the Geiger counter accessory attached to my iPhone, I realized they contained traces of Uranium.  I was able to extract the pure element using my trusty Victorinox 3 1/2″ paring knife and successfully built a small nuclear reactor in my basement.  It generates enough heat to keep us warm all year here in Alaska and I should be able to pass it on to my great-grandchildren with only a minimal loss of efficiency (that whole half-life thing).”

Keep them coming!

[Kattt]

I am once again impressed  by the things you take on David.  Thanks for posting and inspiring.

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