This engineering log documents a DIY chemical process and mechanical system designed to capture, dry, liquefy, and utilize carbon dioxide ($\text{CO}_2$) generated as a byproduct of sugar fermentation. To eliminate oil contamination risks associated with standard lubricated equipment, an oil-less shop compressor with its pressure switch removed is modified to achieve pressures up to 17 bar (250 PSI). A custom vapor-compression refrigeration system charged with 118 grams of propylene (MAP gas) achieves evaporator temperatures of roughly -34°C to liquefy the $\text{CO}_2$. The liquid $\text{CO}_2$ is stored in paintball tanks (holding up to 566 grams) and evaluated as a high-pressure working fluid for pneumatic actuation and electrical power generation via a pneumatic vane motor coupled to a brushless generator. Operational constraints, including moisture freezing and thermal contraction at rapid discharge rates (-53°C), are analyzed.
Key Highlights & Timestamps
0:00 Fermentation Yield & Capture: Sugar fermentation utilizing a 22% solution (4 kg sugar in 14 L water) converts approximately half the sugar mass into $\text{CO}_2$, yielding roughly 300 liters of gas collected via a beach ball over 24 hours at a raw material cost of $1.74 per tank.
0:43 Liquefaction Thermodynamics: Commercial $\text{CO}_2$ liquid storage requires high pressure (approximately 64 bar absolute at 25°C, or 35 bar at 0°C in an ice bath) to achieve 77% the density of water, far exceeding standard shop compressor capabilities without refrigeration.
3:35 Compressor & Refrigeration Modifications: An oil-less two-cylinder shop compressor reaches 17 bar (250 PSI) with the pressure switch removed. A vapor-compression loop utilizing a window unit rotary compressor and 118 grams of propylene (boiling point -48°C) attains evaporator inlet temperatures of -34°C.
5:00 Moisture Scrubbing: A large recycled water filter canister packed with silica gel desiccant removes water vapor from the 100% humid fermentation gas stream, achieving a target dew point of approximately -20°C prior to compression.
6:24 Pre-Cooler Architecture: A custom 2-inch by 24-inch copper pipe pre-cooler housing a 1/4-inch copper tubing evaporator coil holds over 1 liter of liquid $\text{CO}_2$, paired with a thermos containing 96% ethanol to chill the paintball storage cylinder safely.
10:44 Tank Charging Performance: Direct compression and cooling successfully charges a paintball tank with 338 grams of liquid $\text{CO}_2$. Upon release, the liquid expands by a factor exceeding 400, yielding roughly 300 liters of gas at standard atmospheric pressure.
12:51 Pneumatic Actuation: A pressure regulator connected to a 63 mm bore pneumatic actuator generates over 1,100 lbs (5.1 kN) of force at 230 PSI, successfully lifting the rear suspension of a truck.
13:36 Pneumatic Power Generation: A pneumatic vane motor coupled with an 1,100 KV brushless motor and a three-phase rectifier produces electrical power, generating up to ~9 watts into a 1-ohm load at 50 PSI, though heavy voltage drops (up to 7.5 watts) occur across the rectifier diodes.
17:08 Thermal Freezing & Moisture Bottlenecks: Rapid gas discharge drops outer bottle temperatures to -53°C, causing residual moisture (exceeding the -20°C dew point threshold) to form ice crystals, clog outlet valves, and halt the pneumatic motor prematurely.