https://patents.google.com/patent/US8530679B2/en?q=thc&q=butane&q=cannabis

In 2007, a patent was filed for delta-9 THC processing. It covered a range of organic solvents with boiling points preferably below 0C – ie “low boiling point solvents.” This fits the description of several hydrocarbons – the author preferred isobutylene, propane, butane, and cyclobutane.

This patent was validated with very pure THC – from 95-99% – nearly reagent grade. So while it validates the situation in under perfect laboratory conditions, it does not reflect the true extraction conditions that happen every day for medical and recreational extractions.

The important points of this patent are the temperatures. The desired solvent exists as a gas at room temperature, but can be in the liquid phase when put under pressure and temperature constraints. Controlled temperatures not only dictate the phase of the hydrocarbons (i.e. gas or liquid), but also prevent degradation of cannabinoids, preserve terpenes, and reduce solubility of plant lipids.

Some side notes on the choice of solvents were low toxicity, low environmental impact, and generally recognized as safe for use in pharmaceutical applications. These factors combined are some of the reason for using propane and butane as the industry standard for cannabis extractions.

That covers the theory behind the process. Below you’ll find a few points on the methods that make this a very good process.

Assuming one has an understanding of the standard closed loop extraction process, you can imagine how this process goes. You’ve passed your butane/propane through the extraction column and the extract is sitting in the collection vessel.

It does not specifically say in the patent, but there are two ways this could go. The first option is that the butane is boiled off (reclaimed) to a certain percentage, and then transferred to a secondary container. The second is that the butane is allowed to boil off without care for reclaiming. I find the second option less likely, but it is a possibility.

Assuming the first option, the partially purged extract is transferred to a second collection chamber while it is still of high enough viscosity. This process is called a cannula transfer. The second collection vessel is where there are inert conditions, and the butane/propane is evaporated off.

Solvent is evaporated by increasing the temperature of the second collection vessel and passing inert gas over the surface of the extract – in this case, I’m almost sure the author used a side-arm round bottom flask. I’ve covered the value of inert gasses in a few of my posts at Hemphacker, but it is definitely a standard operating procedure in a chemistry laboratory. In this case, they use argon gas to assist the removal of butane from the extract.

Using inert gas helps remove the solvent by changing the dynamics of partial pressures at the surface of the solution – this is a long topic and out of the scope of this article. However, the change in partial pressure increases the rate of evaporation for butane and allows one to to reduce the temperature to 4C, from what would normally be done at much higher purging temperatures. Now we’re in terpene preservation territory.

The low temperatures are beneficial because it reduces the degradation of the cannabinoids, and also keeps the terpenes in a low-volatility condition. In addition, the author claims that these temperatures make it easier to handle the extract.

As a result of evaporating off propane/butane at a lower temperature, the author claims that the invention induces a more crystalline form of the extract rather than the formation of a homogenous solid. I would hypothesize that the slow cool temperatures allow crystal formation, in what is a more gentle process that does not disrupt the nucleation of seed crystals. They claim to have shown this by x-ray diffraction, but no data is given to supplement the claim. Still, the extract is not 100% crystalline, as claimed by the author; as an analogy, think of how some parts of an extract will auto-butter before others.

One point to keep in mind is that this is a pure starting material, for the sake of explaining the invention of the process. By experience, a chemist performing extractions knows that the results vary by strain to strain, because of the different distribution of cannabinoids and terpenes.

This is a fundamental patent to understand the origins of live resin extractions. This author has several more patents on the subject, but I chose to write about this one because it was the “first mover.” The cannabis community owes much thanks to pioneers in science, who laid the way for us to preserve the ultimate essence of the plant.
I hope that you all find this interesting. Please share your thoughts and comments!

Four temperatures parameters.

Terpenes are a valuable product captured the extraction process. Not controlling temperatures through the extraction will cause you to lose terpenes. There are four temperature parameters that need to be controlled in live resin extractions – fresh plant materials, butane, column, and purging temperatures.

Freezing live plant materials under inert conditions.

Live resin requires low temperatures to extract cannabinoids and terpenes and leave behind water and plant waxes. Since dry ice and ethanol are required for almost every step, it makes sense to use it for flash freezing the plant material. This is done by filling vacuum bags with fresh plant material in a way that maximizes surface area. Once filled with plant material, the bags are filled with dried CO2 gas to purge out the humidity from the room. The bags are vacuum sealed, dipped into a dry ice bath until fully frozen, and are then made ready to fill into a prechilled column.

There are many ways to freeze plant material. Choose the one that works best for you. 

Cooling your butane with a condensing coil.

Control your butane temperature before it comes in contact with the plant material. If you don’t, your freshly frozen plant materials will thaw from the warm butane, and start to release plant lipids. Pass your butane through a condensing coil that is submerged in a dry ice/ethanol bath – on average, the dry ice bath will cool the butane down anywhere from -20C to -50C. The cooling capacity, or rate of cooling, is dependent on the size of the bath and the amount of dry ice added to it. Once cooled down, the liquid butane passes into your packed column and the extraction begins.

Temperature control at the column is key to long soak times.

A commonly missed point is that the column must be frozen in the freezer prior to extraction. Do this, and you’re one step ahead of the game.

A problem with long soak times is that the frozen plant material can be warmed up if the column temperature is not controlled. This causes the water that’s locked up in the solid phase (i.e. ice) from plant cells to release water, water-soluble phytochemicals, and plant lipids/waxes. 

After the cooling coil, butane temperature needs to be controlled at the column. Keeping the column at a temperature less than -20C (optimally -30C to -40C) ensures water and waxes do not contaminate the extract. The column temperature can be controlled by a dry ice/ethanol bath; it can be connected to a cryogenic pump or just be an open sleeve/cylinder filled dry ice and ethanol. If dry ice isn’t available, an ice bath will improve your extractions.

Transferring to thin film and purging.

You’ve finally got your live resin extract in the collection chamber of your extractor. Live resin extracts are low viscosity – the additional terpenes decrease the internal friction of the liquid. Pour the extract onto silicon mats, then scrape out the collection chamber with a silicon spatula and transfer it onto a second mat. You’re now ready to purge.

Live resin purging – temperature and time.

Two important components in any chemical reaction are temperature and time. Higher temperatures cause loss of terpenes, but decrease the purging times to boil off all the butane. Keep your purging conditions below room temperature and not much below 5C. This preserves terpenes, but is still above the boiling point of butane. To make up for the lower temperature, increase the amount of time spent purging to 5 days. This is the simplest process to preserve your terpenes, and make your live resin runs worth while.

General purging tips.

A favored way of purging is to heat the extract up to it’s purging temperature for 30 minutes without pulling a vacuum. Once the oil is up to your desired purging temperature, you can pull a full vacuum. Purging times vary from strain to strain, but you can follow the bubbles to see when your extract is purged. The purging has nearly completed when the major bubbles of butane stop forming – those bubbles are typically large and burst when they reach their maximum size. You’re looking for the point when the bubbling slows down and only small bubbles form. At this point, you can dial in your process with residual solvent testing at your local laboratory to confirm when your extract is fully purged.

Conclusion.

Properly controlling temperatures of fresh plant materials, butane, column, and purging will improve your process. There are multiple benefits at each step, that when combined create perfect conditions for preserving the essence of the fresh plant – the terpenes. Not all starting materials are worthy of making live resin. When you do have good starting materials, you will be rewarded with knockout flavor and taste that would have otherwise been lost to the atmosphere. Follow these steps and enjoy the experience.

 

As always, if you have any questions please post them in the comments section. Your questions and time are valuable and we will make every attempt to help you through your process.

Minimum standards for making live resin hash oil extracts

So what is a bare bones method to making live resin? Well, just about any extractor can be made to meet the minimum standards of a terpene rich extract. Whether you’re trying to go with fresh frozen material, or material that is just about ready to start curing, you can do your best to preserve terpenes and minimize the amount of plant waxes that are extracted. I’ll keep this post short, since most of this information is covered in other posts.

Step 1: dehydrate your butane.

This is a simple step that few extraction artists I’ve spoken to take advantage of. If there’s one thing that helps the extraction process, it’s this. If you don’t dehydrate your butane, you increase the chances of there being blockages in the column or even your braided stainless steel hoses caused by freezing water. In addition, it improves the extraction efficiency because water will change up the solubility properties of the butane.

Hands down, putting 3A molecular sieves in-line on the low pressure side of your recovery pump will improve your extraction efficiency. It’s not hard to do, and it will improve your process and end product.

Step 2: freeze your plant materials.

Whether you’ve chosen to run fresh frozen, dry your buds to the point before curing, or cure your buds, you’re going to benefit from freezing them before extracting. This equilibrates the temperature of the buds to the temperature of the butane, and reduces the amount of plant waxes pulled during an extraction. In step 3, you’re going to freeze your butane. Now imagine this mass of buds packed into your column, and both the buds and the column are at room temperature. Now imagine that -50C butane rifling into the column and hitting buds and stainless steel that are at a warm 20C…

You can surely see where this is going – the butane will be warmed up and the buds will be cooled down. When that happens, you’re defeating the purpose of chilling your butane in the first place – you’re now extracting the very plant waxes that you were trying to avoid extracting in the first place! The point is, try to make everything as cold as possible to get the best results. Terpene rich extracts are higher quality and have more medicinal potential – don’t skimp out on this simple step that anyone can accomplish.

Step 3: freeze your butane.

This is perhaps the simplest step to take to improve your extractions. If you’re going to take any steps towards making live resin, freeze your plant materials, column, and butane. You don’t necessarily have to dehydrate your butane, but if you take steps 2 and 3 into account, you’ll certainly improve your product.

While you may not have dry ice on hand, you do likely have ice on hand just for the sake of recovering your butane. Take the time to submerge your recovery cylinder in an ice bath. That ice bath can be dry ice with denatured alcohol, or it can just be ice, salt, and water. Either way, this step will reduce the amount of waxes that are butane soluble by reducing temperature.

Step 4: cold purge.

While you may not have the capacity to purge your extract with an inert gas (e.g. dried CO2 gas), you do have the ability to extract at room temperature and pull a full vacuum, assuming you have a vacuum chamber. The boiling point of butane is -0.5C at standard atmospheric pressure (1 bar/1 atm/14.5 PSI). When you pull a vacuum, you reduce the boiling point, and a major factor becomes time. Give an extract enough time at room temperature while under vacuum, and you’ll be able to pull off all the butane while preserving terpenes.

While it’ll be different for every situation (elevation, room temperature, quality of vacuum), 5 days at room temperature with a full vacuum will purge out your butane and leave you with a terpene rich extract. For smokable forms, I always suggest having a residual solvents test run by your local testing facility to make sure that you’re below the threshold for butane.

Conclusion.

These four steps will take you well on your way to higher quality extracts that preserve terpenes. If you can start working in this direction you’ll be using the trade secrets that some of the best extraction artists use day in and day out. Best of luck and enjoy those terpenes!

 

As always, if you have any questions please post them in the comments section. Your questions and time are valuable and we will make every attempt to help you through your process.