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Short-Path Distillation

2018-09-04 16:39:00


Many materials, including petroleum,heavy residue, chemical medicine, medicine and natural food, health care products, fatty acid and so on, are generally heat sensitive and viscous. Moreover, they also possess high boiling points. Separating these materials from their components and maintaining the quality of such products are only able to distillate at low boiling points or even lower than the boiling temperature. Besides, it is also capable of reducing the thermal decomposition or polymerization to the minimum in a short period, so as to eliminate the damage to products.

When the operating vacuum is about 500 Pa, it is capable of conducting in the scratch film evaporator or falling film evaporator. However, if the distillation is operate under the high vacuum status( for instance, the pressure ranges from 0.001 to 100Pa), problems are bound to cause. Therefore, it is necessary to choose the evaporator which the vapor pressure id no less than pressure difference caused by heating and cooling surface, and the evaporator quipped with outside condenser is excluded from the distillation process under the high vacuum range.

In contrast, the short-path evaporator is quietly adaptable to this occasion, and the condenser should be placed within evaporator and opposite to heat distillation. Therefore, as a relatively new equipment which is not widely applied in industrial production, the short-path distillation is able to solve many tough issues that normal distillation technical cannot conquered.

Short-path distillation

Short-path distillation

Working principle

The pressure difference between the boiling film and condensing surface is the driven force of stem flow, and the minimum pressure will cause the flowing of steam. Under the 1mbar, the operation requires the boiling surface and condensing surface have the shortest distance. The evaporator manufactured based on the principle is called short-path distillation. The short-path distillation (molecular distillation) is equipped with a inside condenser which is opposite to the heating surface, and make the operation pressure reduce to under 0.001mbar. Its relative low boiling temperature is very suitable to the material with heat sensitive and high boiling point.

Basic constitution: the column cylinder equipped with outside heating mantle, rotor and inside condenser. The fixing frame of rotor is precisely equipped with scratch film and anti-splash device. The inside condenser is placed in the center of evaporator, and the rotor should rotor between column cylinder and condenser.

Distillation process: The material should add from the top of evaporator and continuously spread to the heating surface through the material covered on rotor. Then, the scratch film is capable of scratching the material into a thin and flowing liquid film. During this process, the light molecular exceeded the heating surface form the condense liquid on inside condenser without any collision. Then, the molecular flows along the condenser tube, and discharge through the discharge tube on the bottom of evaporator. The residue liquid (heavy molecule)is collected on the circular channel under the heating zone, and flows through the discharge tube on one side.

The molecular distillation serves as a special distillation process which is conducted under the high vacuum status within the range of 1Pa-0.01Pa. The molecular flows directly from heating surface to condensing surface. As the picture illustrated, the molecular distillation can be concluded as the following four steps.

Short-path distillation

Short-path distillation

1.Molecular spreads from liquid body to evaporation surface:

Generally speaking, the spread speed of liquid is the main factor in controlling the speed of molecular distillation, so it is adoptable to reduce the liquid thickness as much as possible to strength the flowing of liquid.

2.Molecular is capable of free evaporating on the liquid surface:

The evaporation speed lifts with the increase of temperature, but the separation factors sometimes reduce with the increase of temperature. Therefore, it is wise to choose the economical evaporation temperature with the premise of heat stability of manufactured materials.

1. Molecular spreads from evaporation surface to condensation surface:

During the process of spreading from evaporation surface to condensation surface, they are capable of conducting collision with each other, or with the air molecular between two surfaces. Due to the evaporation surface is far weight than air molecular, and both two of them have the same operating direction

4.The condensation of molecular on condensing surface

As long as to keep the heating and cooling surface have abundant temperature difference( in general 70-100℃), and the adoptable and smooth condensing surface guarantee the condensing steps can be completed in a moment. Therefore, it is of great importance to choose the suitable condenser.

From the above mentioned text, we can concluded the conditions of molecular distillation as following:

1. The partial pressure of residual gas must be very low, making the average length of residual gas is a multiple of distance between distiller and condenser surface.

2. Under the saturation pressure, the average free length of steam molecular should have the same number with the distance between evaporator and condensing surface.

Under the ideal condition, the evaporation is capable of conducting from residual gas without any obstruction. If all vapor molecular do not encounter any other molecular, they will reach to the condenser surface during process of returning to liquid. Under the certain temperature, the evaporation speed is bound to reach the maximum. Due to the distillation speed is proportional to vacuum degree, so the The amount of distillate during molecular distillation is relatively small.

During the SPE short-path distillation, the distance between condenser and heating surface is about 20-60mm. When the pressure of residual gas is about 10-3mba, the average free length of residual gas molecular is double than its original length. Therefore, the short-path evaporator could meet all necessary requirements of molecular distillation.

Short-path distillation

Short-path distillation

Device characteristics

▲Material with high boiling point

Using the specialized metal components is capable of treating the material whose boiling points reaches 450℃ under the vacuum condition of 0.001mbar.

▲Viscous solid material

Scratch immersing into the liquid film produce the strong shear force, which is greatly reducing the material with the viscosity of 50Pas.

▲ Solid content surplus

Scratch immersing into the liquid film produce a strong stirring force, and it is also capable of preventing the solid scale on the heating surface.

▲Color sensitive material

During the SPE type short-path distillation, HEC have designed an equipment which is used for preventing the metal damage.

▲High distillation ratio

Using the scratch with precise manufacture means the liquid film is capable of smearing on the heating surface and making it heated and damped, so as to satisfy the requirement of high distillation ratio. Thus, more than 90% products are capable of being distillated, remaining a certain amount of residual.

▲Low maintaining cost

The suitable structure design and unique rotor avoid the damage of scratch and metal surface.

Short-path distillation

Short-path distillation

Structure characteristics

1. Precise rotor

The section of rotor is in the shape of squirrel cage, and the HEC has the two rotors to produce the liquid film. They are deeply immersed into scratch of film liquid, so as to produce the strong Swirl, thus leading products on the heating plate conduct better heat transfer than other rotors( for instance: PTFE tube on metal rod). The following examples are cyanate purified from prepolymer, and the final ontent is less than 0.1%.( ChartⅡ)

From the above mentioned examples, we can concluded that different scratches with the same heating area produced different results, and the SPE is capable of increasing 20% distillation amount.

2. Precise condenser

The condenser is generally adopt coil, U-tube or bundle, which are fixed at the bottom of distiller. The shape of condenser and its distance with heating surface are directly connected with the separate purification, yield ratio and vacuum degree of distiller. Therefore, HEC has designed various inside condenser in accordance with different technical materials from the experience accumulated in distillation and evaporation.

The inside condenser in the right picture is in tube bundle type, which is located in the center of distiller. Moreover, it also boasts such advantages as smooth surface, average temperature and large space of gas transfer. It is also set the distance between heating surface and condensing surface appropriately, so as to guarantee the SPE short-path distillation conduct under the high vacuum condition.

3.Mist separator

Mist separator is necessary to some products, and it is capable of setting between the rotor and scratch as well as behind the scratch. These splash prevention equipment is capable of discarding any liquid added by steam stream.

As a complete component, the splash prevention equipment is easy to stretch. According to the technical characteristics, it can be divided into blind shape, herringbone shape and groove shape.

Short-path distillation

Short-path distillation

Equipment type

Under the high vacuum condition, the short-path distillation has a specific requirements to scratch and inside condenser. In order to reduce the displacement of strengthen liquid and the thickness of liquid film, HEC can divided its products into the following two types according to the scratch type:

▲SPE-A type short-path distiller

The type of scratch is radial sliding type, which is evolved from WFE-VA scratch evaporator. The scratch is kept in the U guide groove of the rotor, and the U guide groove spread around the rotor. The rotor is in the shape of squirrel cage, and the dynamic vapor-liquid separation device is set between guide slot so as to prevent the spread of liquid.

In general ,the scratch material consist of PTFE, graphite and so on.

SPE-B type short-path distiller

The SPE-B scratch is similar to WFE-VC( the right picture), and the scratch close to heating surface bu relying on the centrifugal force. In terms of

Such type has a wide application, and it is capable of adjusting centrifugal force to adapt various viscosity by changing the frequency and quality of scratch.

The shape size of standard equipment is illustrated as the Charter Ⅲ.

The contact surface between distiller and product is made of stainless steel,。 according to clients’ requirements, it is also adoptable to use the carbon steel, composition board and other special materials, for instance: hastelloy, nickel, titanium, Monel, etc.

Short-path distillation

Short-path distillation

Specialized application

The Chart IV is the application of some typical materials:

a) Single distillation unit of short-path distiller

The materials which completes pre-heating and gas escaping is capable of entering into short-path distiller, and the lighter unit is evaporated and condensed in the inside condenser. Moreover, the lighter unit and recombination unit are discharged through different paths( flowchart 1).

b)Recombination distillation unit of scratch evaporator and short-path distiller.

A great amount of materials with low boiling points are removed within the scratch evaporator, and the distillation of products are produced in the rear stage short distance distiller(flowchart 2).

Experiment before production

We hope you can receive the best results as much as possible. For this, HEC company has the short-path distillation equipment which is used in operation testing, so as to identify the liquid quality and the short-path distillation efficiency.

Similarly, we also build complete short-path distillation equipment during the distillation process of laboratory and experiment station, which could accelerate the development and optimize manufacture process of products.

We are capable of providing a complete set of laboratory equipment, short-path distiller and necessary auxiliary equipment, for instance: pipe fittings, pipelines, wells and pump valves.

Short-path distillation

Short-path distillation

Complete distillation equipment

Henan Lanphan not only dedicate to design and manufacture the single equipment, but also design, manufacture and develop the complete set of equipment.

Design is base on the experience accumulated for several years and the technical data provided form you.

A complete set of equipment is needed foe completing the distillation and evaporation of products. If we need to separate multiple distillation form the mixed liquid, multiple sets of equipment are generally required.

According to our needs, the short path distillation is capable of overall supply with auxiliary equipment( such as: cold wells, material pumps, condensation pumps, vacuum pumps). Moreover, the single unit of short path distillation is also optional.

In order to achieve the short path distillation, apart form short path distiller, we also need other equipment, including the degassing, product treatment, heating, vacuum system and etc..

Henan Lanphan has dedicated to the selection of the most effective set and equipment unit for several years. We are always making the best synthesis between your benefit and our experience.

▲Degassing equipment

The material to be treated usually contains dissolved gases and a small amount of materials with low boiling points. Under the medium and high vacuum conditions, it is not easily for us to be condensed by the condensing water with normal temperature, so as to affect the vacuum degree. Before entering into the short-path distiller, the load of vacuum pump should be maintained as lower as possible. Therefore, it is suggest to add a degassing equipment in front of the short-path distiller, and remove the materials with low boiling point in advance.

It is proved that the this film evaporator is a quiet good degassing equipment. At the same time, it is also capable of conducting preheating.

▲Products treatment

The degassing equipment and short-path distiller can achieve connection by the displacement, and the materials is capable of entering into the short-path distiller from degassing equipment under the gravity. If the two equipment stay in the same height, it is necessary to transfer the materials from degassing equipment to short-path distiller by pumps. The feeding of materials must be continuous, and the discharging of it can be continuous or intermittent.

▲ Vacuum equipment

The short-path distiller must conduct the vacuum operation at certain degree, so it is important to choose the suitable vacuum equipment. In general, we adopt the combination between mechanical pump and steam ejecting pump. If the absolute pressure is maintained at the range of 0.1-1Pa, the diffusion pump is also necessary.

In addition, in order to keep the partial pressure maintain as lower as possible, we should set a cold well between the distiller and vacuum pump, and the cold well uses low temperature water and cooling liquid as the cold medium.

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