Different gasses bond to the material in different ways. Propane, for example grabs less of the plant’s matter compared to butane when extracting in a closed-loop extractor. Butane will pull more plant matter and produce a higher yield, but may produce a darker colored product. Since propane grabs less of plant matter, it typically produces a blonde, light end product.
Blended gas mixtures have become very popular to use in closed-loop BHO extraction systems in the recent years because of the product it can yield. By using a blended mixture of gas while extracting essential oils, you get the best of both worlds. The butane part of the mix will keep the pressure inside the extraction machine very low and pull out a large percentage of the plant’s oils, while the propane will increase the pressure slightly, but it will grab slightly less chloroplast from the material (which causes dark color). This will cause your end product to be significantly more blonde and clear.
The vapor pressure of propane and butane differ greatly. Propane at the 40°F has a vapor pressure of approximately 65psi, while butane’s vapor pressure is barely above 3psi. When dealing with a blended gas mixture, it is important to know the vapor pressure curve of that blend. For instance, in a 70-30 butane/propane mix, the vapor pressure at 40°F is 20psi. This curve is in between the vapor curves of propane and butane. Butane will remain at a relatively low vapor pressure regardless of it’s temperature. It is imperative that you monitor the vapor pressure inside BHO closed loop extraction systems to ensure a safe and efficient operation.