SuperCritical Fluid Technology
Last discoveries in the field of supercritical fluids technology allowed to enlarge the range of configurations for plants working with supercritical CO2. In addition to the traditional extraction and fractionation systems, nowadays there are also continuous cycle pasteurization systems and multipurpose systems, containing all the functions listed below. In the following schemes plants having PLC control systems are described. The functioning of the manual plants is similar, but it presupposes the presence of the operator handling the valves according the necessities, and setting the temperatures on chiller and boiler. In this case pressure and temperature for every section will be recorded instruments flanking the plant.
Supercritical CO2 Extraction process (SFE=Supercritical Fluid Extraction)
Allplants realized by Separeco have in common the CO2 recirculation flow coming from the last separator. This configuration allows the recovery of the CO2 utilized during the process, in order not to loose it. Before being pumped again into the reactor, CO2 is condensed and collected in a proper tank. The plant is made of an autoclave E that can be equipped with a basket for the solid matrices treatment. The vases have a thermostatation coat which allows to set the process temperature between 20 and 85°C. On the top of the vases there is a rapid closure device, allowing a reduction in the un/loading time. The pump PCO2 sends the liquid CO2, at its maximum flow rate, into the extractor E. In the case of automatic plants, an inverter connected to a PLC pilots the pump varying the engine rounds, and so the flow rate, read by a flow meter with Coriolis effect. In this case pressure is automatically controlled by the PLC through the valve MV1. The PLC pilots the electric valves controlling the temperature in the vases, the membrane valves in control of the process pressure, the pumps flow rate, the chiller, the boiler, the temperature in every section, the alarms and every strategic component of the plant. The pressure is visualized on the plant as well, thanks to large manometers. The PLC is connected to a PC where a software named “Gerico” manages automatically the process and visualizes all the variables on the monitor, memorizing and printing graphs about each single control parameter. From the control panel the operator can change any of the process parameters. The manometers, the electronic pressure and temperature transducers give to the operator all the process data real time. The apparatus is equipped with at least two separation stages operating in series. The first one is a gravimetric separator (S1) Most of the extract is recovered in this stage. The second one is a cyclonic separator (S2). The most volatile part is recovered at this stage. The module K gathers all the safety systems.
Supercritical CO2 separation system (SFF – Supercritical Fluid Fractionation)
The countercurrent distillation tower constitutes the core of the fractionation plant. The tower contains filling bodies structured in order to increase the exchange surface, and it is designed for 250 bar operations. The fractionation tower T is connected to the pumps PCO2 and Pliquid. The operation temperature is controlled by the fluid circulating in the coat and it can vary between 20 and 85°C. The pump Pliquid sends the liquid to be fractionated to the tower. Both volumetric pumps are piloted by an inverter for the flow rate control. The refined product is accumulated at the base of the tower and it must be cyclically discharged. The temperature inside every single section of the tower is regulated separately, while the pressure in the cycle is controlled by the membrane valve MV1 which, in the case of automatic plants, is piloted by the PLC. In this case, differently from what is made in SFE plants, two high pressure dosing pumps are necessary. The apparatus is equipped wit hat least two separation stages operating in series. The first one is a gravimetric separator (S1) Most of the extract is recovered in this stage. The second one is a cyclonic separator (S2). The most volatile part is recovered at this stage. The module K gathers all the safety systems.
Supercritical CO2 pasteurization plant (SFP – Supercritical Fluid Pasteurization)
The pasteurization plant is designed for continuous 300 bar operations. The aim of this new stage is the realization of the pasteurization process of liquids at 30-35°C. The apparatus consists in a pasteurization reactor connected to the pump PCO2 and to the pump .Pliquid through a static mixer. The pasteurization reactor is thermostated with water at 30-35°C. The process pressure is controlled by the valve MV1, positioned downstream of the pasteurization reactor. The mixture liquid-CO2 is sent to a degassing recipient, which is connected to a compressor recovering the CO2 utilized in the process and resend it to the condenser for the sequent stocking in the recipient A1. The scheme of the plant described here refers to an industrial process. In the pilot plants or lab-scale plants, CO2 is extracted through a dispersed vacuum pump. The utilization of CO2 in this process is reduced to the minimum. Upon customers' request it is possible to add some sampling points inside the reactors of pasteurization, in order to determine most precisely the ideal retention time for the pasteurization process to be complete. As for the fractionation plant, here is necessary to have two high pressure dosing pumps too. The module K gathers all the safety systems.
SFE is an alternative compared to the classic separation systems like fractionated distillation, steam current distillation, solvent extraction or thermal desorption. SFE can be applied to systems on a different scale: from lab-scale, analytic (from few hundreds milligrams to few grams of sample) or preparative (few hundreds grams of sample), to the pilot scale (kilograms of matrix), up to the industrial scale treating tons of raw material (e.g. in the coffee decaffeinization process).SFE can substitute many traditional extraction processes from vegetable matrices for the obtainment of dry extracts or essential oils with specific characteristics. The extraction of substances from complex mixtures, in particular, can be made highly selective modifying properly the operational temperature and pressure conditions, in order to adapt them to the solubility of the different components of interest. An example is the terpenes removal from the essential oils from citruses and other officinal plants, through which a mixture of aromatic components stable to light and temperature is obtained (generally monoterpenes are not, and sometimes they contribute in no way to the smell).On the basis of such premises, SFE progressively imposed itself as one of the elective technologies for the treatment, with different goals, of several raw materials of alimentary, pharmaceutical and cosmetic interest (active principles extraction and officinal herbs components extraction). Although theoretically there are many supercritical fluids available for the purpose, CO2 is the fittest. In fact it is non toxic, inert, non flammable, cheap, recyclable and environmentally harmless. CO2 extraction is a modern extraction technology for hydrophobic vegetable components realized according to a clean procedures without release of any residue nor solvent substances. After the extraction the operation pressure is lowered and the CO2 loses its solvent power releasing the solute substances, which are available in a concentrated and pure form. For these reasons FDA marked this process as GRAS (Generally Recognized As Safe). Natural substances, moreover, usually are not very stable at high temperatures, and need to be kept at temperatures next to the environmental one: CO2's critical temperature is 31°C, making of it particularly fit as solvent for biologic substances. Proteins, carbohydrates, inorganic salts or metals are not co-extracted in any way. CO2 extracts are microbiologically stable and do not need particular storage conditions, because given their nature they are practically sterile. Unlike conventional procedures, the extraction selectivity is specific. The method does not involve thermal stress and does not need organic solvents.