Patent Description:
At present, three wastes (i.e., exhaust gas, waste water and industrial slag) have caused serious environmental pollution in the organic chemical industry and the medical and chemical industry, and in particular in the recovery of organic solvents where the employment of vacuum leads to a high volatility of the solvents, and hence the volatilization of organic solvents inevitably results in environmental pollution. Many engineers are committed to solving this problem. The currently frequently used methods include: method A, absorption of tail gas with activated carbon and activated fiber; method B, treatment by means of cryogenic process or multi-stage cooling; and method C, neutralization of the tail gas before discharge thereof into a wastewater treatment system to be treated. With regard to method A, high-temperature desorption is required, operation steps are complicated, and the investment is high; the multi-stage cooling of method B has a limited effect, while the cryogenic process requires a large amount of liquid nitrogen, and hence it is not convenient for industrial production; method C is very limited in that the method cannot be used for tail gas that is insoluble in water, while once the tail gas is dissolved in water, wastewater is generated, requiring a supporting biochemical treatment system. At present, the recovery rate of organic solvents is between <NUM>-<NUM>%. The lower the boiling point, the greater the volatility, and the lower the recovery rate. For example, the recovery rate of chloroform and ethyl acetate is generally about <NUM>%, which means that <NUM>% of the solvent is discharged into the atmosphere as unorganized exhaust gas and cannot be recovered, which is not only a waste of resources but pollutes the environment. According to statistics, the annual emission of organic exhaust gas is of an order of magnitude of about <NUM> million tons. Therefore, there is an urgent need of a simple and feasible method that can improve the recovery rate of organic solvents, thus reducing the pollution of organic exhaust gas to the environment and realizing a green recovery of organic liquids.

The <CIT> discloses a macromolecule reduced pressure distillation device. The macromolecule reduced pressure distillation device comprises a reduced pressure distillation kettle, a heat exchanger, a single body receiving kettle, a gas-liquid separator, a vacuum buffering tank and a vacuum pump. A discharging port of the reduced pressure distillation kettle is connected with a feeding port of the heat exchanger through a pipeline, and a discharging port of the heat exchanger is connected with a feeding port of the single body receiving kettle through a pipeline. An exhaust port of the heat exchanger is connected with a feeding port of the gas-liquid separator through a pipeline, a discharging port of the gas-liquid separator is connected with the vacuum buffering tank through a pipeline, and the vacuum buffering tank is connected with the single body receiving kettle. The vacuum pump is connected with the vacuum buffering tank through a pipeline. The <CIT> discloses a (4R cis, ) <NUM> the cyanogen methyl <NUM>, <NUM> the dimethyl <NUM>, <NUM> the dioxolanes tert butyl acetate high vacuum distillation device, including stills, condensers, distillation gas-phase pipe, first receipt cauldron, the cauldron is received to the second, real empty can and high-vacuum pump unit, stills is connected through distillation gas-phase pipe with the condenser, the other end of condenser is connected with the air inlet of first receipt cauldron and the air inlet of second receipt cauldron simultaneously, the gas outlet of first receipt cauldron and the gas outlet of second receipt cauldron are connected with real empty can's air inlet, real empty can's gas outlet is connected with the air inlet of high-vacuum pump unit, the high vacuum unit adopts more than <NUM> grades lobe pump and vertical nothing oil reciprocating pump. The <CIT> discloses an underpressure distillation system, including controller and distillation reactor cauldron, the distillation reactor cauldron is connected with the aspiration pump, and the series connection has the vacuum buffer tank between aspiration pump and the distillation reactor cauldron, and the aspiration pump is connected to the top of vacuum buffer tank, the output of aspiration pump is connected with exhaust gas discharging pipe, the aspiration pump includes first vacuum pump and second vacuum pump, first vacuum pump and second vacuum pump series connection or parallel connection, and first vacuum pump is roots vacuum pump, and the second vacuum pump is the reciprocating vacuum pump, being equipped with pressure sensor on the distillation reactor cauldron, being provided with the automatic valve of bleeding on the connecting tube of bleeding between distillation reactor cauldron and the vacuum buffer tank, the pressure sensor electricity is connected to the signal input part of controller, the automatic valve electricity of bleeding is connected to the signal output part of controller. The <CIT> discloses a decompression vapor-liquid balancing system with an automatic pressure control function. The decompression vapor-liquid balancing system comprises a vapor phase sampler, a liquid phase sampler, a vapor-liquid balancing kettle, a pressure stabilizing tank, a vacuum tank, a set of temperature control device and two sets of pressure control devices. The decompression vapor-liquid balancing system is used for measuring decompression vapor-liquid balancing data, has the characteristics of high pressure control precision, low labor intensity and accurate data and is beneficial to the further realizing automatic and digital improvement. The <CIT> discloses a rectification buffer tank capable of controlling vacuum degrees and a rectification tower. The rectification buffer tank comprises a liquid discharge pipeline, a ball valve, atank body, a vacuum gauge, an exhaust pipeline, a pressure control pipeline and a needle valve. On the basis of a common rectification buffer tank, one pressure control pipeline is added, and by adjusting the needle valve of the pressure control pipeline, a trace amount of air is sucked into the rectification tower, so that the purpose of controlling the vacuum degree of the whole rectification tower can be achieved. The <CIT> discloses a vacuum intermittent formula rectifying column, the solenoid valve inlet of backward flow solenoid valve connects in a vacuum collection jar gas outlet of a vacuum collection jar and the 2nd vacuum collection jar gas outlet of the 2nd vacuum collection jar, the first gas outlet of solenoid valve of backward flow solenoid valve is connected in the filled tower backward flow air inlet of filled tower, the solenoid valve second gas outlet of backward flow solenoid valve is connected in the condenser backward flow air inlet of top condenser. The <CIT> discloses a solvent separation device of a phytoextraction mixture. The device comprises a gas inlet I, a tank body, a stirring assembly and the like; the phytoextraction mixture is heated up by introducing hot water into an interlayer of the tank body of the device; an inert gas or nitrogen is injected into the tank body, in the process of heating the tank body and stirring continuously, a vacuum pump extracts a gas, negative pressure is formed in the tank body, and a solvent is gasified, and nitrogen or the inert gas replaces the solvent gas, thereby separating the solvent.

The technical problem to be solved by the present invention is to provide a method for purification and recovery of organic liquids with high recovery rate and less generation of exhaust gas.

To solve the above technical problem, the present invention discloses a method for purification and recovery of an organic liquid by using an apparatus, wherein the apparatus comprises:
a distillation kettle, a receiver tank connected to the distillation kettle by a distillation pipe, and a vacuum pump; a vacuum storage tank is arranged between the receiver tank and the vacuum pump; the vacuum storage tank and the receiver tank are connected by a vacuum regulating pipe; a first vacuum regulating valve being arranged on the vacuum regulating pipe; and the vacuum storage tank and the vacuum pump are connected by an evacuation pipe, a second vacuum regulating valve being arranged on the evacuation pipe; the method comprises:.

During the process, the liquid to be processed may be heated to a preset temperature after being fed into the distillation kettle in step <NUM>); and in step <NUM>), the temperature inside the distillation kettle is stabilized at a preset value first and then the vacuum storage tank is slowly opened to evacuate the receiver tank for distillation.

Further, the vacuum storage tank is provided with a condensing device.

Further, a temperature monitoring device, a pressure monitoring device, the first vacuum regulating valve, the second vacuum regulating valve and the vacuum pump are each connected to an intelligent controller through control circuit.

Further, a cooling device is arranged outside the distillation kettle, a cooling water pipe and a steam pipe of the cooling device being each provided with an automatic control valve which is connected to the intelligent controller through control circuit.

Further, the intelligent controller comprises a vacuum regulating controller and a safety controller; the first vacuum regulating valve, the second vacuum regulating valve, and the pressure monitoring device of the vacuum storage tank are connected to the vacuum regulating controller; and the temperature monitoring device and the pressure monitoring device of the distillation kettle, the pressure monitoring device of the receiver tank, and the automatic control valves of the cooling device are connected to the safety controller through control circuits.

Further, the process of purification and recovery is controlled by the intelligent controller, wherein the vacuum regulating controller of the intelligent controller monitors the pressure in the vacuum storage tank and controls the opening and closing of the first vacuum regulating valve and the second vacuum regulating valve and the on and off states of the vacuum pump; and the safety controller of the intelligent controller monitors the pressure in the receiver tank and the pressure and temperature in the distillation kettle, controls the on and off states of the cooling device and a stirring device of the distillation kettle, and sounds an alarm when necessary.

The process of the method for purification and recovery of organic liquids using the aforementioned apparatus herein may also be as follows:.

Further, the distillation kettle is preheated to a preset value before step <NUM>); and the liquid to be processed is preheated to a preset value before being fed into the distillation kettle in step <NUM>).

Further, the process of purification and recovery is controlled by the intelligent controller, wherein the vacuum regulating controller of the intelligent controller monitors the pressure in the vacuum storage tank and controls the opening and closing of the first vacuum regulating valve and the second vacuum regulating valve and the on and off states of the vacuum pump; and the safety controller of the intelligent controller monitors the pressure in the receiver tank and the pressure and temperature in the distillation kettle, controls the on and off states of the cooling device and the stirring device of the distillation kettle, and sounds an alarm when necessary.

A vacuum storage tank is arranged between the receiver tank and the vacuum pump herein, such that the vacuum degree of the receiver tank is regulated by the vacuum storage tank to realize the recovery of organic liquids (organic solvents) under a reduced pressure and in an environment that is isolated from the vacuum pump. The vacuum pump is turned on intermittently instead of working continuously so as to avoid a direct and continuous evacuation of the system by the vacuum pump, thereby preventing the organic liquids from being sucked out during a continuous evacuation, which will result in a waste of the organic liquids and environmental pollution. An intelligent controller is arranged herein for an intelligent control of the vacuum and safety of the entire system, thereby greatly improving the accuracy of the vacuum degree, keeping the entire process in a stable, safe and controllable range, and further improving the recovery rate of the organic liquids (solvents) in a simple process that is easy to achieve. A recovery rate of organic liquids (solvents) of <NUM>-<NUM>% is generally reached with the apparatus herein for purification and recovery thereof, with almost no loss. It is estimated that <NUM> million tons of organic solvents can be prevented from being discharged into the atmosphere annually if the apparatus herein is fully promoted, which will not only save resources while generating no pollution, but save energy. It is a green apparatus of the present invention for reduction of exhaust-gas emission during the recovery of organic solvents. The invention is suitable for both batch feeding and continuous feeding, wherein batch feeding is generally adopted by small-scale production, and continuous feeding by large-scale production.

The single Figure is a schematic diagram of connections according to the present invention.

In the accompanying drawings: <NUM> denotes a distillation kettle; <NUM> denotes a vacuum pressure gauge; <NUM> denotes a thermometer; <NUM> denotes a stirring motor; <NUM> denotes a motor control switch; <NUM> denotes a distillation pipe; <NUM> denotes a receiver tank; <NUM> denotes a receiver-tank vacuum gauge; <NUM> denotes a vacuum regulating pipe; <NUM> denotes a storage tank; <NUM> denotes a storage-tank vacuum gauge; <NUM> denotes an evacuation pipe; <NUM> denotes a vacuum pump; <NUM> denotes an intelligent controller; <NUM> denotes a first vacuum regulating valve; <NUM> denotes a second vacuum regulating valve; <NUM> denotes a vacuum regulating controller; and <NUM> denotes a safety controller.

The content of the utility model is described hereinafter in more details in combination with the embodiments. The implementation of the present invention is not limited to the embodiments hereinafter but limited to the appended claims.

The apparatus of the present invention for purification and recovery of an organic liquid, as shown in Figure, comprises a distillation kettle <NUM>, a receiver tank <NUM>, a vacuum storage tank <NUM> and a vacuum pump <NUM>, wherein the distillation kettle <NUM> and the receiver tank <NUM> are connected by a distillation pipe <NUM> which extends from the top of the distillation kettle <NUM> and accesses the top of the receiver tank <NUM>; the receiver tank <NUM> and the vacuum storage tank <NUM> are connected by a vacuum regulating pipe <NUM> which extends from the top of the receiver tank <NUM> and accesses the vacuum storage tank <NUM>; the vacuum storage tank <NUM> and the vacuum pump <NUM> are connected by an evacuation pipe <NUM> which extends from the top of the vacuum storage tank <NUM> and accesses the vacuum pump <NUM>. A cooling device is arranged outside the distillation kettle <NUM>, a vacuum pressure gauge <NUM> and a thermometer <NUM> are arranged inside the distillation kettle <NUM>, and the distillation kettle <NUM> is further provided with a stirring device driven by a stirring motor <NUM>, the stirring motor <NUM> being provided with a motor control switch <NUM>. A first vacuum regulating valve <NUM> is arranged on the vacuum regulating pipe <NUM>; a second vacuum regulating valve <NUM> is arranged on the evacuation pipe <NUM>; and a receiver-tank vacuum gauge <NUM> and a storage-tank vacuum gauge <NUM> are respectively arranged on an upper side of the receiver tank <NUM> and an upper side of the vacuum storage tank <NUM>. The vacuum storage tank <NUM> is provided with a condensing device which uses internal condensation or external condensation, such as an internal circulation coil, or a jacket arranged outside the vacuum storage tank <NUM>.

The apparatus further includes an intelligent controller <NUM> which includes a safety controller <NUM> and a vacuum regulating controller <NUM>, wherein the safety controller <NUM> and the vacuum regulating controller <NUM> may be two functional modules or two separate control components. Intelligent safety control, which can greatly improve the control accuracy and safety, is extremely important in the chemical industry, especially in the process of high-risk chemical reactions.

The vacuum pressure gauge <NUM>, the thermometer <NUM>, the automatic control switch of the cooling device, and the motor control switch <NUM> are all connected to the safety controller <NUM> through control circuits; the first vacuum regulating valve <NUM>, the storage-tank pressure gauge <NUM>, the second vacuum regulating valve <NUM>, and the vacuum pump <NUM> are all connected to the vacuum regulating controller <NUM> through control circuits.

<NUM> of dichloromethane with a mass content of <NUM>% was fed into the distillation kettle <NUM> and heated to <NUM>. After closing the first vacuum regulating valve <NUM> and opening the second vacuum regulating valve <NUM>, the vacuum pump <NUM> was turned on to evacuate the vacuum storage tank <NUM> to -<NUM> MPa and then the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off. After the temperature of the distillation kettle <NUM> stabilized at <NUM>, the first vacuum regulating valve <NUM> was slowly opened until there was solvent being distilled off, which was collected in the receiver tank <NUM>, the openness of the first vacuum regulating valve <NUM> being regulated according to the flow rate. In an event of insufficient vacuum, the first vacuum regulating valve <NUM> was closed, the second vacuum regulating valve <NUM> was opened and the vacuum pump <NUM> was turned on to make up the vacuum. After a full complement of vacuum, the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off, and the first vacuum regulating valve <NUM> was opened for further distillation. In order to ensure a certain amount of the solvent distillate, a further complement of vacuum could be performed when there was an insufficient vacuum degree at a later stage during distillation, and moreover, the temperature inside the distillation kettle <NUM> could be adjusted appropriately as well during the same process. In the present embodiment, the temperature was up to <NUM> for distillation at a later stage until there was no more distillate flowing out. <NUM> of dichloromethane was recovered with a dichloromethane content of <NUM>%, the recovery rate being <NUM>%.

<NUM> of dichloromethane with a mass content of <NUM>% was subjected to vacuum distillation at room temperature with the existing vacuum distillation equipment and <NUM> of dichloromethane was obtained with a recovery rate of <NUM>% and a dichloromethane content of <NUM>%.

<NUM> of ethanol with a mass content of <NUM>% was fed into the distillation kettle <NUM>, and heated to <NUM>. After closing the first vacuum regulating valve <NUM> and opening the second vacuum regulating valve <NUM>, the vacuum pump <NUM> was turned on to evacuate the vacuum storage tank <NUM> to -<NUM> MPa and then the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off. When the temperature of the distillation kettle <NUM> stabilized at <NUM>, the first vacuum regulating valve <NUM> was slowly opened until there was solvent being distilled off, which was collected in the receiver tank <NUM>, the openness of the first vacuum regulating valve <NUM> being regulated according to the flow rate. In an event of insufficient vacuum, the first vacuum regulating valve <NUM> was closed, the second vacuum regulating valve <NUM> was opened and the vacuum pump <NUM> was turned on to make up the vacuum. After a full complement of vacuum, the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off, and the first vacuum regulating valve <NUM> was opened for further distillation. Same as in embodiment I, the distillation temperature was adjusted at a later stage to <NUM> until there was no more distillate flowing out. <NUM> of ethanol was recovered with an ethanol content of <NUM>%, the recovery rate being <NUM>%.

<NUM> of ethanol with a mass content of <NUM>% was subjected to vacuum distillation with the existing vacuum distillation equipment, and <NUM> of ethanol was obtained with a recovery rate of <NUM>%, and an ethanol content of <NUM>%.

<NUM> of dimethylbenzene of a mass content of <NUM>% was fed into the distillation kettle <NUM> and heated to <NUM>. After closing the first vacuum regulating valve <NUM> and opening the second vacuum regulating valve <NUM>, the vacuum pump <NUM> was turned on to evacuate the vacuum storage tank <NUM> to -<NUM> MPa and then the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off. When the temperature of the distillation kettle <NUM> stabilized at <NUM>, the first vacuum regulating valve <NUM> was slowly opened until there was solvent being distilled off, the openness of the first vacuum regulating valve <NUM> being regulated according to the flow rate. In an event of insufficient vacuum, the first vacuum regulating valve <NUM> was closed, the second vacuum regulating valve <NUM> was opened and the vacuum pump <NUM> was turned on to make up the vacuum. After a full complement of vacuum, the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off, and the first vacuum regulating valve <NUM> was opened for further distillation. Same as in embodiment I, the distillation temperature was adjusted at a later stage to <NUM> until there was no more distillate flowing out. <NUM> of dimethylbenzene was recovered with a dimethylbenzene content of <NUM>%, the recovery rate being <NUM>%.

<NUM> of dimethylbenzene with a mass content of <NUM>% was subjected to vacuum distillation with the existing vacuum distillation equipment, and <NUM> of ethanol was obtained with a recovery rate of <NUM>% and a dimethylbenzene content of <NUM>%.

<NUM> of ethyl acetate with a mass content of <NUM>% was preheated to <NUM> first by a heating kettle or other heating devices. The distillation kettle <NUM> was also preheated to <NUM>. The first vacuum regulating valve <NUM> and the second vacuum regulating valve <NUM> were opened and the vacuum pump <NUM> was turned on to evacuate the system to -<NUM> MPa, and then the second regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off. Ethyl acetate started to be fed continuously (The feed and the amount of solvent distillate remained substantially the same. ) into the distillation kettle <NUM>. In an event of insufficient vacuum, the first vacuum regulating valve <NUM> was closed, the second vacuum regulating valve <NUM> was opened, and the vacuum pump <NUM> was turned on to evacuate the vacuum storage tank <NUM> to -<NUM> MPa. Following a full complement of vacuum, the second regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off, and the first vacuum regulating valve <NUM> was opened for further distillation till there was no distillate. <NUM> of ethyl acetate was recovered with an ethyl acetate content of <NUM>%, the recovery rate being <NUM>%.

<NUM> of ethyl acetate with a mass content of <NUM>% was subjected to vacuum distillation with the existing vacuum distillation equipment and <NUM> of ethyl acetate was obtained with a recovery rate of <NUM>% and an ethyl acetate content of <NUM>%.

The first vacuum regulating valve <NUM> and the second vacuum regulating valve <NUM> were opened and the vacuum pump <NUM> was turned on to evacuate the distillation kettle system to -<NUM> MPa, and then the second vacuum regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off. <NUM><NUM> of exhaust gas of gasoline with a mass content of gasoline of <NUM>% started to be fed continuously and slowly into the distillation kettle <NUM>, and a small amount of gasoline was slowly distilled off. In an event of insufficient vacuum, the first vacuum regulating valve <NUM> was closed, the second vacuum regulating valve <NUM> was opened, and the vacuum pump <NUM> was turned on to evacuate the vacuum storage tank <NUM> to -<NUM> MPa. Following a full complement of vacuum, the second regulating valve <NUM> was closed and the vacuum pump <NUM> was turned off, and the first vacuum regulating valve <NUM> was opened for further distillation till there was no distillate. <NUM> of exhaust gas of gasoline was recovered with a gasoline content of <NUM>%, the recovery rate being <NUM>%.

Gasoline is not recoverable from exhaust gas of gasoline with a mass concentration of <NUM>% with the existing vacuum distillation equipment.

Batch feeding was adopted in the above embodiments I to III, while continuous feeding was adopted in embodiments IV to V. And during the distillation in embodiments I to V, the opening and closing of the first vacuum regulating valve <NUM> and the second vacuum regulating valve <NUM>, and the on and off states of the vacuum pump <NUM> can all be controlled by either manual operation or the intelligent controller <NUM>, the latter having a better control accuracy than the former.

The latter control is as follows:
the safety controller <NUM> monitors the vacuum degree in the distillation tank <NUM> and the receiver tank <NUM> at any time, and transmits signals to the vacuum regulating controller <NUM>, such that the vacuum regulating controller <NUM> regulates the openness of the first vacuum regulating valve <NUM> based on the required vacuum degree of the system, thereby regulating the vacuum degree in the receiver tank <NUM> and the distillation tank <NUM> to form vacuum distillation suitable for the corresponding solvent. When it is detected by the vacuum regulating controller <NUM> that the vacuum degree in the vacuum storage tank <NUM> is insufficient and hence a complement of vacuum is required, as controlled by the vacuum regulating controller <NUM>, the first vacuum regulating valve <NUM> will be closed, the second vacuum regulating valve <NUM> will be opened, and the vacuum pump <NUM> will be turned on to evacuate the vacuum storage tank <NUM>. When it is detected by the vacuum regulating controller <NUM> that the vacuum degree in the vacuum storage tank <NUM> has reached a preset value (-<NUM>-<NUM> MPa), as controlled by the vacuum regulating controller <NUM>, the second vacuum regulating valve <NUM> will be closed, the vacuum pump <NUM> will be turned off and then the second vacuum regulating valve <NUM> will be opened for further vacuum distillation.

The safety controller <NUM> can monitor the temperature and pressure in the distillation kettle <NUM> at any time. In a case of over-temperature and over-pressure in the system, the safety controller <NUM> will be started: in a case of over-temperature, the safety controller <NUM> will sound an alarm, close the heating valve of the distillation kettle <NUM> and start water cooling; and in a case of over-pressure, the safety controller <NUM> will also sound an alarm, and turn off the stirring in the distillation kettle <NUM>, start water cooling, and start vacuum relief.

Claim 1:
A method for purification and recovery of an organic liquid by using an apparatus, wherein the apparatus comprises:
a distillation kettle (<NUM>), a receiver tank (<NUM>) connected to the distillation kettle (<NUM>) by a distillation pipe (<NUM>), and a vacuum pump (<NUM>); a vacuum storage tank (<NUM>) is arranged between the receiver tank (<NUM>) and the vacuum pump (<NUM>); the vacuum storage tank (<NUM>) and the receiver tank (<NUM>) are connected by a vacuum regulating pipe (<NUM>); a first vacuum regulating valve (<NUM>) being arranged on the vacuum regulating pipe (<NUM>); and the vacuum storage tank (<NUM>) and the vacuum pump (<NUM>) are connected by an evacuation pipe (<NUM>), a second vacuum regulating valve (<NUM>) being arranged on the evacuation pipe (<NUM>);
characterized in that the method comprises:
<NUM>) feeding the organic liquid to be processed into the distillation kettle (<NUM>);
<NUM>) disabling communication between the vacuum storage tank (<NUM>) and the receiver tank (<NUM>), turning on the vacuum pump (<NUM>) to evacuate the vacuum storage tank (<NUM>) to a preset value and then turning off the vacuum pump (<NUM>), and disabling communication between the vacuum pump (<NUM>) and the vacuum storage tank (<NUM>);
<NUM>) enabling the communication between the vacuum storage tank (<NUM>) and the receiver tank (<NUM>), the organic liquid being distilled off and collected in the receiver tank (<NUM>);
<NUM>) repeating steps <NUM>) and <NUM>) in turn in an event of insufficient vacuum in the vacuum storage tank (<NUM>); and
<NUM>) repeating step <NUM>) for a plurality of times until there is no more liquid distillate being produced.