Extraction Equipment

Subcritical Water Extraction (SWE) Plant

Subcritical Water Extraction (SWE), also known as pressurized hot water extraction, uses liquid water heated above its normal boiling point but held below its critical point, with sufficient pressure applied to keep it in the liquid state. In this range the dielectric constant of water falls sharply, so the medium behaves progressively like a mid-polarity organic solvent and dissolves a wide spectrum of phenolics, flavonoids, polysaccharides and aroma compounds from botanicals. Because water is the only solvent, the process is clean, non-flammable and free of residual solvent concerns. Mechotech engineers turnkey SWE systems tailored to each feedstock and target compound.

Subcritical Water Extraction works by tuning temperature (typically in the sub-critical band up to around 374 degrees C) and pressure so that ordinary water gains organic-like solvating power without vaporising. Raising temperature lowers water polarity, viscosity and surface tension while improving mass transfer, which delivers strong yields and adjustable selectivity by simply changing the operating temperature rather than switching solvents. The result is a green, low-cost process with an excellent thermal profile for heat-sensitive natural products and no organic-solvent recovery burden. Mechotech fabricates the extraction vessels, heat exchangers and high-pressure circuit in SS 304 and product-contact SS 316L to hygienic, GMP-oriented standards, with PLC/SCADA control of temperature, pressure and flow. Capacity is configured from pilot to commercial scale to suit each process requirement.

Technical Specifications

Technology	Subcritical Water Extraction (SWE) / Pressurized Hot Water Extraction
Working Principle	Pressurized liquid water heated below its critical point; falling dielectric constant makes water act as a tunable organic-like solvent
Operating Temperature	Configurable within the subcritical range up to approx. 374 degrees C
Operating Pressure	Configurable, set to keep water liquid at the chosen temperature
Solvent	Water (deionised / process water); no organic solvents required
Operating Modes	Static soak and dynamic flow-through (configurable)
Product-contact Material	SS 304 / SS 316L
Automation	PLC/SCADA (configurable) with recipe management and batch data logging
Capacity	Configured to process requirement - pilot to commercial
Utilities	Steam / thermic fluid or electric heating, cooling water, chilled water, power, compressed air
Compliance	GMP / cGMP hygienic design
Final Output	Aqueous extract; optional concentrate or dried powder via downstream evaporation and drying

Manufacturing Process

Feed preparation & loading

Milled or sized botanical material is loaded into the extraction vessel and the system is sealed. Correct particle size improves contact area and mass transfer during extraction.

Filling & pressurisation

Deionised or process water fills the vessel and a high-pressure pump raises system pressure. Pressure is set high enough to keep water liquid at the chosen operating temperature.

Heating to subcritical range

The water is heated through a heat exchanger or jacket into the subcritical band. As temperature rises the dielectric constant drops, turning water into a tunable, organic-like solvent.

Static or dynamic extraction

The hot pressurised water contacts the matrix in static soak or continuous flow-through mode. Target compounds dissolve into the water phase as mass transfer proceeds.

Cooling & pressure let-down

The loaded extract stream is cooled through a heat exchanger and the pressure is reduced in a controlled manner. Rapid, controlled cooling helps protect thermally sensitive actives.

Separation & collection

The aqueous extract is separated from spent solids and routed to collection. Fines are removed by filtration to yield a clean liquid extract.

Concentration & drying

The clarified extract can be concentrated by evaporation and converted to powder by spray or freeze drying downstream. This delivers a shelf-stable finished extract.

Cleaning & batch turnaround

Water flushing and CIP prepare the system for the next batch. Because only water is used, changeover and cleaning are simplified.

Applications

Nutraceutical and dietary-supplement actives
Phytochemicals such as polyphenols, flavonoids and antioxidants
Essential oils, oleoresins and natural aroma compounds
Pharmaceutical botanical actives and standardised extracts
Food, beverage and natural flavour ingredients
Pectin, polysaccharides and functional carbohydrates
Cosmetic and personal-care botanical extracts
R&D, pilot studies and process scale-up

Key Features

Green, solvent-free process
Water is the only solvent, eliminating flammable organic solvents, residual-solvent testing and solvent-recovery costs for a cleaner, safer plant.
Tunable selectivity by temperature
Lowering the dielectric constant of water with temperature lets a single medium target different compound classes, so selectivity is adjusted without changing solvents.
High yield and fast mass transfer
Reduced viscosity and surface tension of subcritical water improve penetration into the matrix, giving strong yields in shorter extraction times.
Controlled thermal profile
Integrated heat exchangers and rapid, regulated cooling help protect heat-sensitive natural products while still exploiting elevated-temperature kinetics.
Hygienic, GMP-oriented build
Product-contact parts in SS 316L with smooth finishes and CIP-friendly design support pharmaceutical, nutraceutical and food-grade production.
Full automation & data logging
PLC/SCADA control of temperature, pressure and flow with recipe management and batch records ensures repeatable, traceable operation.

Frequently Asked Questions

What is Subcritical Water Extraction (SWE)?

Subcritical Water Extraction, also called pressurized hot water extraction, is a green extraction method that uses liquid water heated above its normal boiling point but kept below its critical point. Enough pressure is applied to keep the water liquid, and in this state it can dissolve a broad range of botanical compounds using water alone as the solvent.

How does subcritical water extraction work?

As water is heated toward the subcritical region, its dielectric constant, viscosity and surface tension drop while its solvating power rises. The heated, pressurised water therefore behaves more like a mid-polarity organic solvent, penetrating the plant matrix and dissolving target compounds. Adjusting the temperature changes which compound classes are extracted, then the loaded stream is cooled, depressurised and collected.

What are the advantages of SWE compared with conventional solvent extraction?

SWE uses only water, so it removes flammable organic solvents, residual-solvent testing and costly solvent recovery, making it cleaner and safer. Selectivity can be tuned simply by changing temperature, mass transfer is fast for good yields, and the process suits heat-sensitive natural products when cooling is well controlled. It is widely regarded as an environmentally friendly, low-cost extraction route.

What can a subcritical water extraction plant process?

It is well suited to phenolics, flavonoids and antioxidants, polysaccharides such as pectin, essential oils and aroma compounds, and standardised botanical actives for nutraceutical, pharmaceutical, food, beverage and cosmetic use. It is also valuable for R&D and pilot studies where a solvent-free, tunable method is preferred.

What capacity is available?

Mechotech configures capacity to the process requirement, from pilot and R&D systems through to commercial-scale plants. The extraction volume, heating and cooling duty, pressure rating and cycle time are all sized around the target feedstock, throughput and finished-product specification, and we recommend validating parameters on a pilot system before scaling.

What material of construction and compliance does Mechotech use?

Product-contact parts are built in SS 316L with SS 304 used for structural and non-contact areas, finished to smooth, CIP-friendly, hygienic standards. Systems are engineered following GMP and cGMP hygienic design principles so they suit pharmaceutical, nutraceutical and food-grade production, with documentation to support qualification.

Does Mechotech provide turnkey design, manufacture, installation and commissioning?

Yes. Mechotech designs, engineers and fabricates the complete subcritical water extraction system, including the pressure vessels, heat exchangers, high-pressure circuit and PLC/SCADA automation, and then installs and commissions it as a single, performance-verified turnkey plant. We support the project through scale-up, training and process validation.

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Subcritical Water Extraction (SWE) Plant