Spent botanical marc after extraction often retains residual organic solvents, which brings multiple production problems.
Environmentally, outdoor stacking of marc allows residual solvents to volatilize and pollute the air. In terms of safety, flammable solvents such as hexane and ethanol in stacked marc pose constant fire and explosion hazards. Economically, unremoved residual solvents mean recoverable production resources are wasted.
Traditional water washing desolventising has obvious drawbacks: high water consumption, large wastewater discharge, and material deterioration. Many botanical materials turn into sticky pastes after water soaking, increasing subsequent processing difficulty. One client once tried water washing on Tripterygium wilfordii marc, which resulted in a viscous mess that could not be processed normally.
We recommend low-pressure steam purging as an alternative optimal solution.
The working principle is simple: low-pressure steam is injected from the bottom of the extractor to heat the marc, vaporize internal residual solvents, and carry solvent vapors out from the top for condensation and recovery. Steam penetrates deep into the porous structure of botanical materials to remove trapped residual solvents that are difficult to eliminate via conventional methods.
The core of efficient desolventising lies in the precise coordination of pressure and time, rather than blind high-pressure operation.
Many operators mistakenly believe that increasing steam pressure accelerates desolventising and adopt a steam pressure of 0.5 MPa or higher. However, high-pressure steam forms preferential flow channels inside the marc bed, creating penetrating "rat holes". Steam only passes through these channels, leaving most internal marc unpurge. The material surface appears dry, but obvious solvent odor remains inside the bulk material.
Verified by field experience, the optimal process is sustained low-pressure steam purging at 0.3 MPa combined with intermittent burst venting.
Low-pressure steam penetrates the marc bed slowly and evenly, heating the entire material uniformly. Open the vent valve fully for rapid pressure relief and vapor discharge every 10–15 minutes to expel accumulated solvent vapors thoroughly. Repeat this cycle several times to achieve comprehensive desolventising from the surface to the core of the marc.
Specific process parameters can be adjusted according to material characteristics. Our universal standard process for clients is: steam pressure of 0.25–0.3 MPa, total purge time of 40–60 minutes, and 3–4 intermittent burst venting operations. The purge process is complete when the solvent concentration in condensed recovered liquid drops below 5%.
After standardized steam purging, the marc forms dry granular material with no residual solvent odor and can be directly disposed of. This process avoids the problems of water washing, eliminates wastewater treatment costs, and recycles usable solvents for redistillation and reuse, achieving environmental, safety and economic benefits simultaneously.