JPS644961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a continuous purification device for high-purity selenium, and in particular, it converts selenium powder with a purity of 99.9% into flaky or selenium with a purity of 99.999% or more by vacuum distillation. The present invention relates to an apparatus suitable for continuous conversion into granular high-purity selenium. The present invention is characterized in that, in order to effectively evaporate and condense molten selenium, a rectification column is equipped with a lower evaporation zone and an upper condensation zone containing a constant temperature body.

Background of the Invention Selenium has long been used as an additive in the glass and ceramic industries, as an alloy additive, and as a raw material for pigment production and as a sensitizer.
In addition, it is widely used as a selenium rectifier and a photoconductive element for electrophotographic photoreceptors. In particular, with the recent spread and progress of electrophotographic technology, demand in this field is increasing. When selenium is used in the field of photoreceptors for electrophotography, a high purity level of 99.99% is required, and selenium powder in powder form is easily scattered during vapor deposition, so selenium in granular or flake form is required. ing.

Conventional technology Generally, granular high-purity selenium is produced by baking anode slime obtained by electrolytic refining of copper to produce selenium oxide, then dissolving it in water to make a selenite solution, and then blowing SO ₂ gas. The resulting crude selenium is evaporated by heating under reduced pressure or normal pressure, the resulting vapor is cooled to around the melting point to form liquid selenium, and the liquid selenium is dropped into pure water. Ta. This yields granular selenium with a diameter of 2 to 3 mm. However, in this method, the granular selenium produced contains a large amount of water, and various selenium oxides (SeO, _SeO2, etc.) are mixed in due to the reaction with oxygen in the air. Once these impurities are mixed in, they are difficult to separate using normal methods. It has been recognized that if a selenium film is prepared by evaporating granular selenium in a state in which such impurities are still mixed, the photoelectric recording characteristics are significantly adversely affected due to the formation of traps and the like. For this reason, a method of adding specific impurities (Japanese Patent Publication No. 19740/1974) has been proposed, but quality control is difficult and the method is not satisfactory.

As another method, a method has been proposed in which liquid selenium obtained by vacuum distillation is poured into a sealed container under reduced pressure and solidified (Japanese Patent Publication No. 16927/1983).
This method requires the operation of pulverizing the plate-shaped selenium produced, which is time-consuming and has the disadvantage that impurities are likely to be mixed in during the pulverization. Moreover, the apparatus disclosed therein is not suitable for industrial production, although it may be suitable for laboratory scale.

Another problem with conventional vacuum distillation equipment is that
Due to quality control reasons for selenium, the batch method was sometimes assumed. For this reason, a certain amount of crude selenium is charged into the distillation chamber for each distillation operation.
The dissolution-evaporation-condensation operation must be repeated, and the temperature and pressure inside the distillation chamber must be controlled each time, resulting in poor production efficiency and complicated operations.

Under these circumstances, the applicant has developed a method for industrially and consistently producing selenium in the form of high-purity granules or flakes from crude selenium (Japanese Patent Application No. 32703/1983). See No. 3084)). In this method, crude selenium raw material is continuously supplied to a melting furnace, molten selenium is sucked in a fixed amount into a distiller under reduced pressure, the molten selenium is evaporated in the distiller, and the selenium vapor is transferred to a condenser. The process consisted of condensing liquid selenium in the process, dropping the condensed liquid selenium into the granulation chamber via a downcomer and solidifying it, and was significant in that it realized consistent continuous operation. Furthermore, a device as shown in FIG. 4 was also proposed as a device for realizing this method. In this selenium continuous vacuum purification equipment, the melting furnace 1'
The crude selenium dissolved in is sucked into the distiller 12' through the riser 10'. The inside of the distiller is maintained at around 350°C, and liquid selenium is continuously evaporated. Selenium vapor flows into the condenser 14' through the mist removal device 13'. Within the condenser 14' are a plurality of internally water-cooled buffle plates 16', on contact with which the selenium vapor is cooled to a liquid form and flows down to the bottom of the condenser where it collects. A vacuum outlet 15' is provided at the top of the condenser. Liquid selenium accumulated at the bottom of the condenser is continuously drawn out to a storage tank 21' via a downcomer pipe 20'. Liquid selenium droplets dripping from the storage tank 21' in the granulation chamber 26' solidify on the cooling rotating drum 27' and are scraped off by the scraper 28'.

Problems to be Solved by the Invention The above device is of a type in which a distiller and a condenser are placed side by side, and 1) the upper part of the equipment is large; 2) generated steam is transferred from the distiller to the condenser. The condensation effect is poor because the selenium must flow sideways and rise to contact the baffle plate; 3. The mist that accompanies the selenium vapor easily mixes into the condensed selenium liquid; 4. It flows down in the condenser. The drawbacks such as interference between liquid selenium and ascending selenium vapor and unstable recovery of high-purity selenium have come to be recognized once again.

The object of the present invention is to provide an apparatus for carrying out a method for industrially and consistently producing selenium in the form of high purity granules or flakes from crude selenium, avoiding the drawbacks of the above-mentioned apparatus, and producing high-purity selenium in the form of high purity. The objective of the present invention is to develop a high-purity selenium production equipment that makes it possible to stably produce selenium with high reliability.

Structure of the Invention As a result of studies aimed at the above object, the present inventors attempted to use a vertical rectification column having a lower evaporation zone and an upper condensation zone, and obtained good results. A constant temperature body is installed in the upper condensation zone to condense selenium vapor, and a receiver is provided near the constant temperature body to receive liquid selenium. A selenium vapor contactor having a large number of selenium vapor passage holes is interposed between the lower evaporation zone and the upper condensation zone. A configuration is adopted in which the lower evaporation zone communicates with a riser pipe leading to the melting furnace, and a downcomer pipe leading to the storage tank is connected to the receiver.

Thus, the present invention provides: (a) a melting furnace for melting crude selenium;
a melting furnace equipped with a hopper for supplying crude selenium raw material; (b) a rectification column installed above the melting furnace,
a lower evaporation zone having a heater at the bottom for evaporating molten selenium; a constant temperature body provided above the evaporation zone for condensing selenium vapor; and a constant temperature body provided near the constant temperature body for receiving condensed liquid selenium. A selenium vapor contacting body having a large number of selenium vapor passage holes is interposed between the lower evaporation zone and the upper condensation zone, and an exhaust system is provided at the top. (c) a riser pipe connecting the melting furnace and the bottom of the rectification tower; (d) a downcomer pipe for leading out the liquid selenium received at the receiver of the rectification tower; e) a storage tank for receiving and storing liquid selenium from the downcomer pipe; and (f) a rotating cooling drum for cooling and solidifying the liquid selenium dripping from the storage tank, and for scraping off the solidified selenium from the drum. A high-purity selenium processing apparatus including a granulation chamber containing a scraper is provided.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, a melting furnace 1 is, for example, an electrically heated, closed structure furnace for melting crude selenium. The raw material is continuously fed through the hopper 3. The hopper is equipped with an appropriate mechanism such as a double valve to seal the inside of the furnace. The crude selenium used as a raw material is, for example, about 99.9% and contains impurities such as sulfur, silver, lead, oxygen, iron, tellurium, copper, cadmium, thallium, and bismuth. In a preferred embodiment, a conduit for introducing and discharging an inert gas is provided on the furnace to fill the space above the liquid level with an inert gas such as nitrogen or argon during melting. The input crude selenium is melted at a temperature of 300°C and is sucked up through the riser pipe as described below. In order to eliminate the influence of raw material input, a partition plate 5 is interposed between the immersion part of the riser pipe and the raw material input part. The bottom of the melting furnace 1 is sloped, and an extraction port 7 is provided at the lower end of the slope for periodically extracting deposited impurities.

The liquid selenium melted in the melting furnace 1 is sucked into the rectification column 20 through the riser 10 as described above. The interior of the rectification column is under negative pressure of 1 Torr or less, and liquid selenium is continuously sucked up from the melting furnace to the rectification column due to the pressure difference. An electric heating coil and a heat insulating material are arranged around the riser pipe 10 to provide heat retention. The length and inner diameter of the riser pipe 10 are determined to maintain the melting furnace atmospheric pressure and the internal negative pressure of the rectification tower so that liquid selenium is continuously drawn up from the melting furnace and an appropriate liquid level is maintained at the bottom of the rectification tower. With this in mind, the riser pipe is designed to provide a suitable hydrostatic head.

The rectification column 20 includes a lower evaporation zone 22 and an upper condensation zone 30. At the top of the tower, there is 1 inside the tower.
An exhaust line leading to a vacuum pump is connected to port 35 for evacuation to below Torr. rising pipe 10
The liquid selenium 21 sucked up through the lower evaporation zone 22 is heated by a heater 23 and evaporated. Although the heater 23 is shown here as being provided at the bottom of the furnace, it may also be provided on the peripheral wall of the furnace. Preferably, a stirring device such as a magnetic stirrer 25 is provided to stir the liquid selenium 21 held at the bottom of the rectification column. Other possible stirring devices include the use of stirring blades, floating alumina-coated metal spheres on the liquid surface, and radial arrangement of riser pipe outlets. Stirring is difficult because selenium has poor thermal conductivity, and if it is not stirred, the temperature tends to become non-uniform, resulting in localized low temperatures, making it impossible to maintain a uniform evaporation effect, and local high temperatures causing bumping. This is done because this is likely to occur. Further, in order to expand the heating area, it is preferable to form the bottom wide as shown as 56 in FIG. It is also desirable to provide a withdrawal tube 27 to prevent the accumulation of impurities in the liquid selenium in the lower evaporation zone. By extracting liquid selenium in fixed amounts through the extraction pipe 27, the purity of liquid selenium can be maintained on the order of 99.9%.

The selenium vapor evaporated in the lower evaporation zone 22 passes through a selenium vapor contact body 29 having a number of curved passage holes and rises. The contact body 29 is shown here as a stack of two or three plates each having a large number of diagonal passages perforated to form a zigzag passage, but other plates such as a perforated plate, a mesh plate, a plate with slots, etc. may also be used. You can also use When the selenium vapor comes into contact with the contact body 29, mist and high boiling point components entrained in the vapor are removed. Thereafter, the selenium vapor flows into an upper condensation zone 30 comprising a constant temperature body 31 maintained at a constant temperature of, for example, 270°C.

The constant temperature body 31 is, for example, an oil bath that stores oil in a circulating state and is maintained at a predetermined temperature. The selenium vapor condenses upon contact with the constant temperature body.
The condensed liquid selenium is received by a receiver 32 disposed near, ie, below and around the constant temperature body. Since the rectifier is evacuated at the top,
A suitable baffle plate 33 is installed above the constant temperature body to prevent selenium vapor from escaping.

As shown in FIG. 1, the shape of the thermostatic body is preferably convex at the upper and lower parts when liquid selenium is collected at the center. Alternatively, the lower part of the constant temperature body may be formed into a recessed structure as shown by 57 in FIG. 2, and the body may be received by a receiver 58 attached to the wall surface.

In addition, as for the above-mentioned receiver, as shown in FIG. 2, by providing the upper receiver 59 above the constant temperature body, even higher purity selenium can be recovered there.
On the other hand, selenium of lower purity than the above can be recovered by the lower receiver 58, and thereby two types of selenium can be recovered separately. for example,
If the quality of the charged selenium is 99.9%, the selenium recovered in the upper receiver 59 will be 99.9999%.
On the other hand, the selenium collected in the lower receiver 58 is 99.999
%become.

The liquid selenium received in receiver 32 is removed from the rectification column via downcomer 40. downcomer pipe 40
Like the riser, it is also equipped with suitable heat retention means.
The lower end of the downcomer leads into the reservoir 42 . The dimensions of the downcomer are selected to allow continuous withdrawal of liquid selenium under negative pressure inside the rectifier and under pressure in the reservoir.

Liquid selenium flowing down from the downcomer is temporarily stored in the storage tank 42. The storage tank is provided with a conduit system for sealing inert gas in the upper space and heating and insulation equipment for preventing the temperature of liquid selenium from decreasing. Although liquid selenium is discharged from the storage tank 42 through a feed pipe 44, it is preferable to provide a partition plate to avoid interference with the selenium flow falling from the downcomer pipe. Further, if a separate supply tank is provided to the granulation chamber 50, the above problem is further alleviated.

Liquid selenium taken out in fixed amounts from the feed pipe 44 is dripped into the granulation chamber 50 through the nozzle 46. The granulation chamber 50 is composed of a casing 51, and the inside thereof is also sealed with an inert gas.
Inside the room, a rotary cooling drum 52 is installed directly below the selenium drip flow. The drum 52 is cooled by circulating water, and the selenium droplets that collide with the drum circumferential surface are cooled and solidified there. Also,
Cooling gas may be used instead of circulating water. The solidified selenium is scraped off by a scraper 53. The solid selenium scraped off has a flake-like or granular form. The scraped selenium grains 54 are accumulated on the bottom of the chamber and are collected from the outlet 55 as appropriate. In addition, when using the method shown in FIG. 2 described above, it is preferable that the downcomer pipes 40 are provided independently and separately, and that the system up to the granulation chamber is provided in a separate system.

In the granulation chamber, as shown in FIG. 3, granular selenium of a certain shape is obtained by receiving it in a supply pot 60 and dropping it onto an internally cooled rotating drum 62 through a small hole 61 at the bottom of the tip of the supply pot. .

In the illustrated equipment, the equipment walls or parts that come into contact with liquid selenium are preferably aluminum-plated or made of aluminum. Since aluminum does not form a solid solution with selenium, contamination of selenium is prevented.

Effects of the Invention 1 The present invention realizes an apparatus for consistently producing high-purity selenium in the form of granules or flakes from crude selenium on an industrial scale.

2 A configuration in which a single rectification column is installed above the melting furnace and its interior is divided into a lower evaporation zone and an upper condensation zone makes the equipment more compact than a configuration in which a distiller and a condenser are placed side by side, and the generated steam Since the steam is directly guided in the vertical direction, the steam flow is stable and the condensation effect is excellent.

3. By installing a constant temperature body in the upper condensation zone for selenium vapor condensation and using a receiver to receive liquid selenium, interference between the vapor flow and the liquid flow is reduced, and highly reliable and high-purity selenium can be stably obtained. It will be done.

4. Selenium of different purity can be recovered by using multiple receivers of different heights and downcomers connected to each one.

5 The selenium vapor rising vertically comes into contact with the selenium vapor contacting body which has a large number of selenium vapor passage holes interposed between the lower evaporation zone and the upper condensation zone, so that accompanying mist and high boiling point components are removed. This contributes to the production of highly reliable, high-purity selenium.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an outline of selenium rectification equipment according to the present invention, FIG. 2 is a schematic diagram of another specific example of a rectification column used in the present invention, and FIG. FIG. 4 is an explanatory diagram showing an outline of selenium rectification equipment proposed in the prior art. 1: Melting, 3: Hoppa, 10: Rising tube, 2
0: rectification column, 22: lower evaporation zone, 30: upper condensation zone, 23: heater, 25: stirrer, 27: extraction tube, 29: contact body, 31: constant temperature body, 32: receiver, 35: exhaust Port, 40: Down pipe, 42: Storage tank, 44: Feeding pipe, 46: Nozzle, 50: Granulation chamber, 52: Drum, 53: Scraper, 55: Output port.

Claims (1)

[Claims] 1. (a) A melting furnace for melting crude selenium, which is equipped with a hopper for supplying raw selenium raw material; (b) A melting furnace installed above the melting furnace. It is a rectification tower,
a lower evaporation zone having a heater for evaporating molten selenium at the bottom; a constant temperature body provided above the lower evaporation zone for condensing selenium vapor; and a constant temperature body disposed near the constant temperature body for receiving condensed liquid selenium. a selenium vapor contacting body having a large number of selenium vapor passage holes is interposed between the lower evaporation zone and the upper condensation zone, and an exhaust system is provided at the top. (c) a riser pipe connecting the melting furnace and the bottom of the rectification tower; (d) a downcomer pipe for leading out the liquid selenium received in the receiver of the rectification tower; (E) A storage tank for receiving and storing liquid selenium from the downcomer pipe; (F) A rotating cooling drum for cooling and solidifying the liquid selenium dripping from the storage tank, and for scraping off the solidified selenium from the drum. A high-purity selenium production device including a granulation chamber containing a scraper. 2. The high-purity selenium production apparatus according to claim 1, wherein the lower evaporation zone of the rectification column is equipped with a stirring device for stirring the molten selenium in the lower evaporation zone. 3. The high-purity selenium manufacturing apparatus according to claims 1 and 2, wherein the lower evaporation zone of the rectification column is equipped with an extraction pipe for extracting a fixed amount of molten selenium in the lower evaporation zone.