extraction of natural compounds using supercritical co2

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Extraction of natural compounds using supercritical CO2: Going

from the laboratory to the industrial application

Jose M. del ValleU.C. de Chile

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Contents

Introduction Previous work Predictive Modelling: Extraction of vegetable oil Estimation of production costs Study case Conclusions

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Introduction scCO2 extraction processes have well established commercial

applications: Bitter flavor from hops Decaffeinated coffee beans High value compounds of herbs, species, vegetables etc.

Wrong misconception that scCO2 extraction processes is not fully competitive

There is lack of a predictive model for simulating this processes Accurate cost estimates would reduce risk on investing in commercial

applications

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Previous Work

Author

Extraction

VesselsVolume [L]

Mass Flow Rate CO2

[kg/h]

Operating

Pressure [bar]

Substrate Conclusions/contribution

Körner 3 300 2000 300Spices(Aroma

and Oleoresin)

• Production cost comparable to that of a conventional plant

• Equivalent fractionation process in a single process

Novak and

Robey2 974 4550 300

Herbs and Spices (Aroma

and Flavor Compound

s)

• Estimated cost of larger SFE plants using equipment-specific scaling factors

• Increasing the SFE plant size by a factor of four decreased production cost from USD 1,1/kg to USD 0,50/kg

Fiori 3 800 2000 550Grape Seeds

(Oil extraction)

• Development of a mathematical model that predicted the extraction process in simulated countercurrent mode.

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Previous WorkAuthor Conclusions

Bravi • Proposal of a three-stage CO2 recovery system that dramatically reduces the energy requirement for the CO2 recompression

Rosa and Meireles

• Development of a simple method to determine the Cost of Production (CoM)

• CoM can be compared to the actual price of the extract in the market.

Del Valle• Experimental determination of the cumulative extraction curve• The cumulative extraction curve is a key parameter for the

determination of CoM and cost optimization.

Clavier • Optimization of extraction time by computer simulation rather than experimentally

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Extraction time critically affects SFE costs

Process conditions (d, T, P, U) may be optimized in the laboratory

Relationship between extraction yield and process time depends on scale-specific variables

Predictive modeling: Extraction of vegetable oils

Cumulative Extraction Curve

OBJECTIVE: To develop a predictive model which provides the relationship between oil yield and extraction time

optimize time by computer simulation using a mass transfer model

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Prepressed oilseed: network of interconnected open pores filled with oil Shrinking Core (SC) mass transfer model based on effective diffusivity


• Csat: solubility of oil in scCO2 (solute partition between the soulte core and intraparticle scCO2)

• De: effective diffusivity of the solute in the soild

• kf: external mass transfer coefficient

• DL: axial dispersion coefficient (transport in the scCO2 phase)

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Physical properties of solvent are estimated as function of T and P Funazukuri equation for Infinite dilution binary diffusion coefficient

(D12)

Solubility of oil in scCO2 Csat

Axial dispersion DL


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Film mass transfer coefficient kf in a packed bed operating with SCF

Effective diffusivity of oil in the prepressed substrate (De)


Fm: pre-treatment dependent microestructural factor

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Unitary production cost per year investment + operational costs Include extraction vessels, cascade depressurization, system for

vessel reconditioning and auxiliaries

Estimation of production cost

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Solvent cycleExtraccion vessels with on-off valves

Vessel reconditioning

cycle

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Investment cost: function of mass flow rate of CO2 (Q), volume and number of extraction vessels. Expressed as annuity (CI).

Annual cost of labor Unitary energy cost of the solvent cycle


Ir: reference cost; β:cost corresponding to solvent; f(H/D) correction factor for each vessel

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Solvent cycle in a supercritical fluid extraction plant


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Total unitary production cost Annual cost of investment Labor Energy expend in the solvent cycle, depressurization and repressurization Prepressed oilseeds CO2 vented from extraction vessels or lost with the recovered oil

Estimate the unitary production cost as a function of extraction computer simulation!


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Study Case: Minimization of production cost

25°C6,43 MPa

60°C8 MPa 40°C

30 MpaV=1 m3

Q= 12 t/h of CO2

Extraction of oil from prepressed oilseed particles using a simulated countercurrent process.

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Study Case: Minimization of production costCumulative Extraction Yield and Plant Productivity

Increasing Oil Yield decreases Oil Production After the constant extraction-rate period

limitations in mass transfer occurs which preclude scCO2 leaving the vessel without reaching saturation.

The initial extraction rate is controlled by the solubility of the oil in scCO2.

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Study Case: Minimization of production costProduction Cost as a Function of Extraction Time

The minimum extraction cost is just after the constant extraction-rate period finishes As the Oil Yield increases the contribution of substrate and CO2 (Variable Cost) decreases As the Oil Yield increases the contribution of fixed cost increases

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Study Case: Minimization of production costEffect of particle diameter on the production of cost

As the particle diameter increases the internal mass transfer is more difficult

As the particle size decreases the mass transfer is controlled externally

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Study Case: Minimization of production costEffect of particle diameter and superficial velocity

It advantageous to use smaller particle sizes and higher superficial velocities

The limit is the fluidization velocity Fluidization of the bed is undesirable because

it can clog the screen of the extraction baskets and induce channeling phenomena

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Study Case: Minimization of production costEffect on the number of extraction vessels

As the number of vessels increases the extraction time increases due to the decrease of extraction in the initial stages

Increasing the number of vessels improves the solvent power of scCO2 that is because the CO2 is closer to saturation

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ConclusionsPerspectives and Future Directions

For decreasing the production costs it is desirable to: Decrease particle size Increase CO2 mass flow rate Increase of extraction pressure (Increase of oil solubility) Increasing the plant size

Reconditioning time may be large when: Extraction pressure is high Free volume of the vessel is high When H/D ratio is small due to limitation in heat transfer

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ConclusionsPerspectives and Future Directions Pretreatments:

Are useful to: Release solutes from the cells Ease solvent flow through the packed bed Increase extraction vessel load

Size-reduction Breaks superficial cells Increases the specific surface of the substrate Small particles are inconvenient due to: agglomeration, low packing density and

channeling High-Shear-Stress proceses

Examples: Pressing, Pelletization Destroys cell walls and barriers without reducing particle size Increases the vessel load capacity

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Thank you for your attention!

extraction of natural compounds using supercritical co2

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