Inexpensive Method for Dewatering Gels and Viscous Liquids

Background

In industrial sectors like pulp manufacturing, biorefining, and food processing, the effective dewatering of viscous liquids, gels, and semi-solids is a critical operational requirement. Materials such as black liquor, wet lignin, superabsorbent polymers, and sugar solutions must be concentrated to recover valuable byproducts and minimize waste volumes. Removing water from these complex mixtures is essential for producing biofuels, carbon fibers, and chemical precursors. Consequently, there is a fundamental need for efficient dewatering processes capable of handling highly viscous streams while preserving the integrity of the extracted solids.

Conventional dewatering technologies, including multi-effect evaporators, thermal dryers, and mechanical presses, suffer from significant limitations. Thermal evaporation is highly energy-intensive because it relies on vaporizing water, requiring massive inputs of latent heat. Furthermore, operating at high temperatures frequently causes severe thermal degradation in heat-sensitive materials, leading to issues like the caramelization of industrial sugars. Traditional drying methods also physically alter substrates; thermal drying often destroys the natural porous microstructure of materials, resulting in a fused morphology that degrades downstream rheological properties. Additionally, alternative chemical extraction methods frequently rely on hazardous organic solvents, creating severe environmental and safety concerns.

Technology

This dewatering solution utilizes pressurized subcritical or supercritical carbon dioxide (CO2) to extract water from viscous materials like black liquor, polymer gels, and sugar solutions. Operating between 31°C and 200°C at pressures up to 4,000 psi, the process treats feedstocks with viscosities up to 30,000 cP. The pressurized CO2 rapidly lowers the system’s pH, precipitating dissolved solids to establish a porous matrix. Instead of relying solely on thermodynamic solubility, the CO2 physically displaces free water from this matrix through viscous fingering. Upon depressurization, the expressed water is easily separated from the concentrated product.

This technology is highly differentiated by providing an energy-efficient, non-evaporative alternative to conventional thermal dryers. By physically displacing water rather than vaporizing it, the system bypasses the high latent heat of vaporization, drastically reducing energy consumption. Its moderate operating temperatures prevent thermal degradation, making it ideal for heat-sensitive materials. The solution uniquely preserves the highly porous microstructure of the dewatered solids, avoiding the fused morphology caused by traditional drying methods. Furthermore, it streamlines industrial operations by combining acidification, precipitation, and dewatering into a single step. By utilizing recyclable CO2, the process entirely eliminates the need for hazardous organic solvents.

Benefits

• Significant Energy Savings: Bypasses the high latent heat of vaporization required by traditional thermal evaporators by physically displacing water rather than vaporizing it.
• Preserves Heat-Sensitive Materials: Operates at moderate temperatures, preventing thermal degradation, discoloration, or caramelization in biological materials, polymers, and sugars.
• Maintains Porous Microstructures: Retains sharp, well-defined, and highly porous microstructural edges in the dewatered solids, improving downstream rheological properties and processing.
• Streamlined Process Integration: Combines acidification, precipitation (such as lignin recovery), and dewatering into a single, highly efficient unit operation for biorefineries and pulp mills.
• High Solids Retention: Delivers exceptional dewatering efficiency with extremely low solids loss (as low as 0.005%) in the expressed water.
• Environmentally Sustainable and Cost-Effective: Eliminates the need for hazardous organic solvents and utilizes easily recyclable CO2, minimizing both operating costs and greenhouse gas emissions.
• Broad Application Versatility: Effectively treats a wide range of industrially significant viscous liquids, gels, and semi-solids with viscosities from 2 to 30,000 cP and solids contents up to 95%.

Applications

• Black liquor concentration
• Lignin recovery and dewatering
• Dewatering superabsorbent polymer gels
• Concentrating industrial sugar solutions
• Dewatering harvested algal beds

Additional info

This non-evaporative method dewaters viscous materials (2–30,000 cP) using subcritical or supercritical carbon dioxide at 31°C–200°C and 1,080–4,000 psi. The pressurized gas lowers pH to precipitate solids into a porous matrix, physically displacing water via viscous fingering and dissolving it beyond solubility limits. Releasing pressure separates the water, preserving a porous microstructure in the remaining solids without thermal degradation.