This study is on the use and operation of freezing drying equipment. In this first chapter the rule of the sublimation procedure and applications of freezing drying equipement will be given.
1.1 Freeze driers
Freeze driers are portion of the group of solid-solid dividing operations, this peculiar instance of solid-solid separating operation makes usage of the sublimation procedure. This sort of equipmentis used to divide a solid from another solid. Examples of other solid-solid separation methods include sorting- , screening- , hydrocyclones- , classifiers- , jigs- , tables- , centrifuges- , heavy media- , flotation- , magnetic- and electrostatic separation [ 1 ] .
1.2 Applications of freezing drying
1.2.1 Pharmaceutical and biotechnology
Pharmaceutical companies frequently use freeze-drying to increase the shelf life of merchandises, such as vaccinums and other injectables. By taking the H2O from the stuff and sealing the stuff in a phial, the stuff can be easy stored, shipped, and subsequently reconstituted to its original signifier for injection.
1.2.2 Food industry
Freeze-drying is used to continue nutrient and do it really lightweight. The procedure has been popularized in the signifiers of lyophilized ice pick, an illustration of astronaut nutrient. It is besides popular and convenient for tramps because the decreased weight allows them to transport more nutrient and restructure it with available H2O. Instantaneous java is sometimes lyophilized, despite high costs of freeze-dryers. The java is frequently dried by vaporisation in a hot air flow, or by projection on hot metallic home bases. Lyophilized fruit is used in some breakfast cereal. Culinary herbs are besides lyophilized, although air-dried herbs are far more common and less expensive. However, the freeze-drying procedure is used more normally in the pharmaceutical industry.
1.2.3 Technological industry
In chemical synthesis, merchandises are frequently lyophilized to do them more stable, or easier to fade out in H2O for subsequent usage. In bioseparations, lyophilization can be used besides as a late-stage purification process, because it can efficaciously take dissolvers. Furthermore, it is capable of concentrating substances with low molecular weights that are excessively little to be removed by a filtration membrane.
Freeze-drying is a comparatively expensive procedure. The equipment is about three times every bit expensive as the equipment used for other separation procedures, and the high energy demands lead to high energy costs. Furthermore, lyophilization besides has a long procedure clip, because the add-on of excessively much heat to the stuff can do thaw or structural distortions. Therefore, lyophilization is frequently reserved for stuffs that are heat-sensitive, such as proteins, enzymes, micro-organisms, and blood plasma. The low operating temperature of the procedure leads to minimum harm of these heat-sensitive merchandises.
1.2.4 Other utilizations
Organizations such as the Document Conservation Laboratory at the United States National Archives and Records Administration ( NARA ) have done surveies on lyophilization as a recovery method of water-damaged books and paperss. While recovery is possible, Restoration quality depends on the stuff of the paperss. If a papers is made of a assortment of stuffs, which have different soaking up belongingss, enlargement will happen at a non-uniform rate, which could take to distortions. Water can besides do cast to turn or do inks shed blood. In these instances, lyophilization may non be an effectual Restoration method. In bacteriology lyophilization is used to conserve particular strain.
In high-level environments, the low temperatures and force per unit areas can sometimes bring forth natural mas by a procedure of lyophilization. Advanced ceramics processes sometimes use freeze-drying to make a formable pulverization from a sprayed slurry mist. Freeze-drying creates softer atoms with a more homogenous chemical composing than traditional hot spray drying, but it is besides more expensive.
Recently, some animal stuffers have begun utilizing lyophilization to continue animate beings, such as pets.
Freeze drying is besides used for flowered saving. Marrying corsage saving has become really popular with brides who want to continue their nuptials twenty-four hours flowers.
1.3 Freeze drying equipment
There are basically three classs of freeze-dryers: rotary evaporators, manifold freeze-dryers, and tray freeze-dryers.
1.3.1 Rotary evaporators
Rotary freeze-dryers are normally used with liquid merchandises, such as pharmaceutical solutions and tissue infusions. Droping trays of lyophilized stuff from a little cabinet-type freeze-dryer
1.3.2 Manifold freezing driers
Manifold freeze-dryers are normally used when drying a big sum of little containers and the merchandise will be used in a short period of clip. A multiplex drier will dry the merchandise to less than 5wt % wet content. Without heat, merely primary drying ( remotion of the unbound H2O ) can be achieved. A warmer must be added for secondary drying, which will take the edge H2O and will bring forth a lower wet content.
1.3.3 Tray freezing driers
Tray freeze-dryers are more sophisticated and are used to dry a assortment of stuffs. A tray freeze-dryer is used to bring forth the driest merchandise for long-run storage. A tray freeze-dryer allows the merchandise to be frozen in topographic point and performs both primary ( unbound H2O remotion ) and secondary ( bound H2O remotion ) lyophilization, therefore bring forthing the driest possible end-product. Tray freeze-dryers can dry merchandises in majority or in phials. When drying in phials, the freeze-dryer is supplied with a stoppling mechanism that allows a stopper to be pressed into topographic point, sealing the phial before it is exposed to the ambiance. This is used for long-run storage, such as vaccinums. Improved freezing drying techniques are being developed to widen the scope of merchandises that can be freeze dried, to better the quality of the merchandise, and to bring forth the merchandise faster with less labour. Ever since the 1930s, industrial freezing drying is depended on a individual type of equipment: the tray
freezing drier. In 2005 a quicker and less-labor intensive freezing drying method is developed for majority stuffs. This freezing drying procedure can bring forth free fluxing pulverization from one individual vas. Known as [ Active Freeze Drying ] AFD engineering. The new proces uses uninterrupted gesture to better mass transportation and therefore cutting processing clip, while besides extinguishing the demand to reassign to and from drying trays and downstream size decrease devices.
1.4 Sublimation procedure
In this study the sublimation separation procedure will be used as solid-solid separation and farther analyzed ( in peculiar ice – ascorbic acerb separation with usage of sublimation ) . The sublimation procedure makes usage of the physical belongingss of the constituent to be separated. The rule of sublimation is based on the fact that under certain fortunes the regular order of stages ( solid – & gt ; liquid – & gt ; vapour ) can be adjusted. Figure 4 displays the fortunes under which the stages of H2O exist.
General Working rule
Freeze-drying ( besides known as freeze-drying or cryodesiccation ) is a desiccation procedure typically used to continue a perishable stuff or do the stuff more convenient for conveyance. Freeze-drying plants by stop deading the stuff and so cut downing the surrounding force per unit area and adding plenty heat to let the frozen H2O in the stuff to sublimate straight from the solid stage to the gas stage ( see figure 2 ) .
2.1 The freeze-drying procedure
There are three phases in the complete drying procedure: freeze, primary drying, and secondary drying.
In a lab, this is frequently done by puting the stuff in a freeze-drying flask and revolving the flask in a bath, called a shell deep-freeze, which is cooled by mechanical infrigidation, dry ice and methyl alcohol, or liquid N. On a larger-scale, freeze is normally done utilizing a freeze-drying machine. In this measure, it is of import to chill the stuff below its ternary point, the lowest temperature at which the solid and liquid stages of the stuff can coexist. This ensures that sublimation instead than runing will happen in the undermentioned stairss. Larger crystals are easier to freeze-dry. To bring forth larger crystals, the merchandise should be frozen easy or can be cycled up and down in temperature. This cycling procedure is called tempering. However, in the instance of nutrient, or objects with formerly-living cells, big ice crystals will interrupt the cell walls ( discovered by Clarence Birdseye ) , ensuing in cell devastation, and, in the instance of rehydrated nutrients, a hapless texture. In this instance, freeze is done quickly, in order to take down the stuff to below its eutectic point rapidly, therefore avoiding the formation of ice crystals. Normally, the freeze temperatures are between ?50 °C and ?80 °C. The freezing stage is the most critical in the whole freeze-drying procedure, because the merchandise can be spoiled if severely done. Amorphous stuffs do non hold a eutectic point, but do hold a critical point, below which the merchandise must be maintained to forestall melt-back or prostration during primary and secondary drying. Large objects take a few months to freeze-dry.
2.1.2 Primary drying
During the primary drying stage, the force per unit area is lowered ( to the scope of a few millibars ) , and plenty heat is supplied to the stuff for the H2O to sublimate. The sum of heat necessary can be calculated utilizing the sublimating molecules’ latent heat of sublimation. In this initial drying stage, approximately 95wt % of the H2O in the stuff is sublimated. This stage may be slow ( can be several yearss in the industry ) , because, if excessively much heat is added, the stuff ‘s construction could be altered. In this stage, force per unit area is controlled through the application of partial vacuity. The vacuity speeds sublimation, doing it utile as a deliberate drying procedure. Furthermore, a cold capacitor chamber and/or capacitor home bases provide a surface ( s ) for the H2O vapor to re-solidify on. This capacitor plays no function in maintaining the stuff frozen ; instead, it prevents H2O vapour from making the vacuity pump, which could degrade the pump ‘s public presentation. Condenser temperatures are typically below ?50°C ( ?60 °F ) . It is of import to observe that, in this scope of force per unit area, the heat is brought chiefly by conductivity or radiation ; the convection consequence is considered to be inefficient.
2.1.2 Secondary drying
The secondary drying stage aims to take unfrozen H2O molecules, since the ice was removed in the primary drying stage. This portion of the freeze-drying procedure is governed by the stuff ‘s surface assimilation isotherms. In this stage, the temperature is raised higher than in the primary drying stage, and can even be above 0 °C, to interrupt any physico-chemical interactions that have formed between the H2O molecules and the frozen stuff. Normally the force per unit area is besides lowered in this phase to promote desorption ( typically in the scope of baryes, or fractions of a pascal ) . However, there are merchandises that benefit from increased force per unit area every bit good. After the freeze-drying procedure is complete, the vacuity is normally broken with an inert gas, such as N, before the stuff is sealed. At the terminal of the operation, the concluding residuary H2O content in the merchandise is highly low, from 0,5wt % to 4wt % .
2.1.3 Semi-continuous and non-stop
The moved freezing drier ( figure 5 ) is highly suited as a research tool for applications in aboratory-environment. This new technique can besides be used for larger graduated table applications in the industrial field. For semi-continuous or even non-stop operation the filter is put following to the drier. During the drying procedure already sufficiently dried atoms end up in the filter. The advantage is double. In the first topographic point, it is possible to acquire all dried stuff out of the filter for farther processing, whilst the moved freezing drying procedure continues. Second, stuff, already sufficiently dried, is non unnecessarily exposed to farther motions and, accordingly, hazard of harm.
The CONRAD™ works is to the full automatic and requires minimum staff for the uninterrupted operation. Every motion and procedure parametric quantity is carefully controlled, monitored and tagged through the most modern PLC/PC system. The CONRAD™ works consist of four chief subdivisions:
The cabinet, which is a long cylindrical chamber desgined to run under vacuity. At the front-end – inside the cabinet – there is an lift forstacking the trays with the frozen merchandise. Each tray is come ining the cabinet through an uniquely designed air lock system that allows the trays to enterwithout breakingthe vacuity, which would otherwise hold a negative impact on the sublimationprocess. When the lift has made a full stack, the full stack is pushed frontward into the first drying zone, where the temperature on the warming home bases is adjusted to the existent merchandise type, composing and H2O content. More tonss are filled and they are pushed in bend through the assorted and subsequent drying zones in the cabinet. The conditions in each zone is adjusted to supply the optimum drying features. When the trays on the stack arrives at the drier issue, an lift will drop the trays and dispatch them once more through an air lock. The dried merchandise is emptied from the trays and conveyed to the wadding room.
In order to use energy to the freezing drying procedure a figure of heating home bases made of anodized aluminium are placed inside the cabinet. Hot H2O is circulated through the system to procure an efficient heat transportation by radiation to the merchandise to be freeze dried. The H2O temperature can be regulated during the freezing drying procedure to accomplish the optimum vaporization laps and avoid overheating of the merchandises. By right lading into the cabinet the merchandise trays are placed between the warming home bases for optimum heat transportation. Direct contact between the merchandise trays and heating home bases must be avoided as heat harm of the merchandise will be the consequence.
To distill the sublimed H2O vapour, the cabinet is equipped with a figure of vapor capacitors for Continuous De-Icing ( CDI ) . When one of the vapour capacitors has to be de-iced ( typically after one hr operations the subdivision is sealed off while the other takes over the condensation map. To run the accrued ice, H2O vapour ( vacuum steam ) at 25 ? C is led into the room. The H2O vapour will now distill on the cold icy surface of the capacitor and therefore melt the ice. In order to reconstruct the de-iced capacitor to runing conditions any staying vapour in the capacitor chamber must be condensed by chilling it down until operating temperature and vacuity is reached. A direct switch over when the following de-icing rhythm is needed can now be done without loss of operating vacuity.
Via an external combined lift and convey system the empty trays are conveyred back to the coldstore for replenishing with frozen merchandise.
The CONRAD™ benefits:
- Continuous production
- Economic operation
- 98 % or more efficiency
- Low care costs
Infusions with 25wt % dry affair
Capacity input kg/h
Capacity end product kg/h
The internal vapour capacitor with constitutional de-icing system, is the alone characteristic of all Atlas freezing driers. The benefits: it saves infinite, it is more dependable, it does non do the loss of merchandise and it uses less power compared with traditional external systems.
The particular vapour capacitors are optimized and built into the side of the drying chamber.
The capacitor system does non trust on big external vacuity valves with force per unit area beads that are hard to procure. Using the internal system, de-icing is performed under vacuity avoiding the demand to seal the chamber against big force per unit area derived functions.
Low merchandise loss
Nor merchandise scratch and low vapour speeds within the drier warrant every bit small as 0.1 wt % loss during the procedure.
Low power ingestion.
Defrosting under vacuity instead than at atmospheric force per unit area, eliminates the demand to re-establish vaccum. This, combined with optimum vapours flow conditions, reduces power ingestion by up to 40 wt % compared with ordinary freezing drying engineering.
2.2 Properties of freezing dried merchandises
If a lyophilized substance is sealed to forestall the resorption of wet, the substance may be stored at room temperature without infrigidation, and be protected against spoilage for many old ages. Preservation is possible because the greatly decreased H2O content inhibits the action of micro-organisms and enzymes that would usually botch or degrade the substance.
Freeze-drying besides causes less harm to the substance than other desiccation methods utilizing higher temperatures. Freeze-drying does non normally cause shrinking or toughening of the stuff being dried. In add-on, spirits, odors and nutritionary content by and large remain unchanged, doing the procedure popular for continuing nutrient. However, H2O is non the lone chemical capable of sublimation, and the loss of other volatile compounds such as acetic acid ( acetum ) and intoxicants can give unwanted consequences. Lyophilized merchandises can be rehydrated ( reconstituted ) much more rapidly and easy because the procedure leaves microscopic pores. The pores are created by the ice crystals that sublimate, go forthing spreads or pores in their topographic point. This is particularly of import when it comes to pharmaceutical utilizations. Freeze-drying can besides be used to increase the shelf life of some pharmaceuticals for many old ages.
2.3 Basic constituents freeze dry procedure
Illustrates a simplified freeze-dry system whose basic constituents, normally placed in series as in the diagram, a chamber, a capacitor, and a vacuity pump. The chamber can be of any cylindrical size every bit long as it can defy an exterior force per unit area of 1.033 kgs per square centimetre ( 14.7 lbs per square inch ) . It must be vacuum tight, refrigerated, and have an gap that provides easy handiness. The of import characteristic of a refrigerated capacitor is that it should be located in the direct way of traveling H2O vapour molecules where they can be trapped. When contact with the capacitor surface is made, the H2O bluess give up their heat energy, turn to frost crystals, and are removed from the system and prevented from going to the vacuity pump. Capacitors are chiefly of two types, internal or distant. The pick depends on the application desired. In the distant type the capacitor is housed in a vacuity chamber which is separate from the chamber that houses the frozen objects. This is shown in Figure 6 ( the chamber following to A ) . This type of capacitor can be isolated by a valve that will allow deicing. Smaller freeze-dryers can be defrosted with warm H2O or natural air. Some mid-size freeze-dryers have internal capacitors designed to organize an ice “ stopper ” that can be pulled out after utilizing hot gas to that it free. Apart from the proficient design characteristics required of a vacuity system, the pump should hold the capacity to cut down the chamber force per unit area to degrees below 4mm Hg. At force per unit areas above this degree the ice DO longer sublimes to H2O vapour but turns to liquid. A expression at Figure 1 will bear this observation out. There are two infrigidation compressors in the simplified freeze-dry system shown in One serves the frozen object ; it should hold the capacity of bring forthing controlled temperatures that go below -5 °C ( 23 °F ) . The other serves the refrigerated capacitor and should hold the capacity to bring forth temperatures of -40 °C ( -40 °F ) or less. Keep in head that the force that drives the H2O vapour from an ice surface is the difference in vapor force per unit area produced by the difference in the temperature between the frozen object and the capacitor. As already pointed out, heat energy is required for the sublimation procedure. Where it appears that conducted or radiated heat will non do for the measure of stuffs to be lyophilized, heating devices can be installed. In certain types of proprietary vacuity Chamberss warming devices are incorporated with the design.
2.3.1 Freeze drying chamber
A condensation chamber for freezing drying setup is designed such that wet incorporating air evacuated from a drying chamber base on ballss well uniformly over the cooled interior surfaces of the condensation chamber thereby maximising the available surface for wet condensation and freeze. This desirable consequence is achieved by a tubing which is connected to a vacuity pump and positioned through an terminal wall of the condensation chamber along the cardinal axis of the chamber. One unfastened terminal of the tubing is positioned next one terminal wall of the chamber and gaps are provided through the wall of the tubing adjacent the other terminal wall so that wet incorporating air come ining the chamber intermediate of the gaps in the tubing travel in both waies along the cooled interior surfaces of the chamber toward both gaps in the tubing.
2.3.2 Refrigerated condensor
The condensor is a pipe spiral system or in smaller versions of freezing driers, a cold trap, fitted in a vacuity tight container, which is connected to the drying chamber. In the smaller versions ( research lab ) the condensor is cooled by agencies of a C dioxide or liquid N and in larger workss by infrigidation units. Because of the importance of the infrigidation system, a freezing drier must be equipped with a capacitor designed and constructed with the ability to:
- ondense all bluess from the merchandise.
- Supply a vapor path of minimal distance to avoid impeding vapor flow.
- Permit easy defrosting after the tally.
- Prevent bluess from polluting the oil in the vacuity pump./
- Supply a simple cleansing operation.
- Supply the necessary BTU end product under burden to distill vapour at a maximal rate without upseting the merchandise ‘s selected primary sublimation temperature.
- Insure the necessary low temperature ( concentrated suction ) during the secondary drying to present the lower vacuity degrees needed for this stage.
- Supply a high grade of dependability.
2.3.3 Refrigeration unit
During the freezing drying procedure, the H2O contained in the stuff passes three phases. The merchandise should be cooled, frozen and so subjected to the sublimation phase. During this phase, heat must be applied to the stuff to counterbalance for the sublimation cold developed. This public presentation is regulated by the infrigidation unit. A failure in the infrigidation system leads to a concatenation reaction:
- A rise in capacitor temperature.
- A rise in chamber force per unit area.
- A rise in merchandise temperature.
- An irreversible eutectic thaw and the boiling of liquid fractions.
- Merchandise failure.
2.3.4 Vacuum pump
Freeze drier or lyophilizer applications have long been enfeebling to rotary vane vacuity pumps. The high concentrations of caustic bluess that are pulled into the pump rapidly condense and combine with the pump oil to organize a thick molasses type substance that kills most traditional rotary vane pumps. In order to maintain these pumps operational, the terminal user must alter the oil and clean the oil chamber on a really regular footing. The uninterrupted care and disposal of the risky waste oil is both expensive and inconvenient. Even with regular care, many rotary vane pumps still do n’t populate up to the terminal user ‘s outlooks.
The new Cole-Parmer Rotary Vacuum Pump addresses the jobs associated with hard freezing drier applications. These pumps combine the low base force per unit area and high pumping velocities of a rotary vane pump with the high chemical opposition of a PTFE stop pump. The diaphragm pump holds a vacuity on the head infinite of the rotary vane pump. As the caustic bluess are brought into the rotary vane pump, the stop pump pulls them on through before they can distill in the oil. A brace of capacitors on the mercantile establishment of the pump act to catch much of the dissolvers that have been evaporated, ensuing in cleansing agent, longer permanent oil in the rotary vane pump.
This combination pump has proven to be rather effectual in caustic freezing drier applications. ARUP Laboratories in Salt Lake City, Utah has been utilizing the 72226-70 Cole-Parmer Rotary Vacuum Pump on one of their existing freezing drier units for the past several months. This peculiar freezing drier is in usage about 24 hours a twenty-four hours, 7 yearss a hebdomad as they continuously process patient samples. As a consequence of the high use, ARUP ‘s Bioengineering Department had to alter the oil in their old pump on a monthly footing ; a four-to five-hour flushing and cleansing procedure that resulted in dearly-won downtime for the freezing drier. They have now been runing the new pump for over six months without necessitating a individual oil alteration. Expectations for oil care on the Cole-Parmer Combination Vacuum Pump in this application is one time per twelvemonth, greatly cut downing the care costs associated with the freezing drier.
If we assume some really sensible values for care costs, we can cipher the nest eggs ARUP has realized through the add-on of the Cole-Parmer Combination Vacuum Pump versus the standard rotary vane pump they antecedently used.
Standard Rotary Vane Pump:
Cole-Parmer Pump ( 72226-70 ) :
With a purchase monetary value of $ 5,031, the Cole-Parmer Rotary Vacuum Pump ( 72226-70 ) has a final payment of less than 6 months through the decrease in care costs. The increased life of the oil besides consequences in a longer permanent pump, which allows Cole-Parmer to safely offer a two year-warranty with the Cole-Parmer 72226-60, -65, -70, -75, -85 vacuity pumps.
The procedure in pattern
A procedure is restricted in general by a figure of demands related to the provender, merchandise and other issues. The latter are discussed under QESH ; quality safety and wellness.
3.2 Feed demands
The key variable in the provender demands is the content dry substance in the provender, this determines the drying continuance and energy ingestion. The solubility of ascorbic acid in H2O is 1gr/3ml ? 1gr/3 gr H2O. In order to bring forth 500 kg/h freezing dried ascorbic acid the provender ( ascorbic acid and H2O ) becomes 2000 kg/h. This consequences in a 75wt % H2O content in the provender.
Chemical technology unit operations consist of five categories:
- Fluid flow procedures, including fluids transit, filtration, solids fluidization
- Heat transportation procedures, including vaporization, condensation
- Mass transportation procedures, including gas soaking up, distillment, extraction, surface assimilation, drying
- Thermodynamic procedures, including gas liquefaction, infrigidation
- Mechanical procedures, including solids transit, oppressing and powder, testing and screening
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