Abstract:
A glycerol preparation method for preparation of medical grade glycerol from a by-product of a bio-diesel process includes a first stage phosphoric acid chemical reaction process and a posterior by-product centrifugal separation process to have the phosphoric acid chemical reaction by-product be separated into free fatty acid, potassium phosphoric acid, and a crude glycerol and methanol mixture. The crude glycerol and methanol mixture is further processed through a first step of thin film evaporation process where methanol is reclaimed, a second step of thin film evaporation process where the mixture is dehydrated, a third step of molecular distillation process where an industrial grade glycerol of purity over 95% is extracted, and a fourth step of molecular distillation process where a medical grade glycerol of purity in exceed of 99.75% that meets USP/BP standards is extracted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a glycerol (medical grade) preparation method and more particularly, to a glycerol preparation method using a by-product of a bio-diesel process. 
     2. Description of the Related Art 
     It is known that making bio-diesel by transesterification of vegetable oil produces vegetable gel, crude glycerol, free fatty acid, methanol (or ethanol), and a saponified by-products consisting of potassium hydroxide. 
     These saponified by-products have commercial value, however they are harmful to the environment if they are not refined. Regular medium and small-scale bio-diesel refinery plants usually sell these by-products to the market at a price ranging from 200 to 250 US dollars per metric tone (fourth season, 2007) just because they have no technique or equipment to process these by-products. 
     There are companies which would provide special techniques for refining crude glycerol into refined glycerol. However, this investment takes a big amount of capital, few people make this investment. When received these by-products, most downstream manufacturers use a part of the by-products to make soap and then put the wastes into fuel oil for use as fuel, or prepare the wastes for making feed. Some other downstream manufactures may add these by-products to heavy fuel oil for use as fuel oil. The end products according to these methods have low added value. That&#39;s too bad. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a glycerol (medical grade) preparation method using a by-product of a bio-diesel process, which is to let a by-product of a bio-diesel process be treated through an acid reaction process to form a crystallized potassium phosphoric acid mixture, and then to separate the crystallized potassium phosphoric acid mixture into free fatty acid, crushed crystalloid potassium phosphoric acid and a crude glycerol and methanol mixture, and to treat the crude glycerol and methanol mixture through a continuous four-step thin film evaporation and molecular distillation procedure for enabling methanol to be reclaimed for use by the bio-diesel oil plant and crude glycerol to be further refined into an industrial grade or medical grade glycerol. 
     To achieve this and other objects of the present invention, the invention provides an efficient and automatic glycerol manufacturing process, which comprises: 
     1. Phosphoric Reaction Process 
     
         
         
           
             During this process, a transesterification by-product obtained from a bio-diesel process is stored in an accommodation tank, and then add 85% phosphoric acid at the ratio over 30% to the transesterification by-product and at the same time add a small amount of water to the transesterification by-product to have the transesterification by-product be blended into a mixture and then homogenized with phosphoric acid in a homogenizer so that potassium in the by-product is crystallized with phosphoric acid into crystallized potassium phosphoric acid with the rest in the form of a crude glycerol and methanol mixture. The by-product is separated through a three-phase stack disc separator into free fatty acid for use as a fuel, crushed crystalloid potassium phosphoric acid for making potassium phosphoric acid fertilizer, and a mixture of crude glycerol and methanol for further refining.
 
2. Methanol (or Ethanol) Reclaiming and Dehydration Process
 
             The crude glycerol and methanol mixture is processed through a primary thin film evaporation process to extract methanol (or ethanol), and then a secondary thin film evaporation process to remove water from crude glycerol
 
3. Glycerol Refining Process
 
             Crude glycerol thus obtained is processed through a primary molecular distillation process so as to obtain an industrial glycerol of purity over 95%, and the industrial glycerol is then processed through a secondary molecular distillation process so as to obtain a medical grade glycerol of purity over 99.75%. 
           
         
       
    
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a glycerol preparation flow chart according to the present invention. 
         FIG. 2  is a schematic drawing showing the arrangement of the pre-treatment unit according to the present invention. 
         FIG. 3  is a schematic drawing showing the arrangement of the by-product separator unit according to the present invention. 
         FIG. 4  is a schematic drawing showing the arrangement of the thin film evaporator unit according to the present invention. 
         FIG. 5  is a schematic drawing showing the arrangement of the crude glycerol mixture dehydrator unit according to the present invention. 
         FIG. 6  is a schematic drawing showing the arrangement of the industrial grade glycerol molecular distillatory unit according to the present invention. 
         FIG. 7  is a schematic drawing showing the arrangement of the medical grade glycerol molecular distillatory unit according to the present invention. 
         FIG. 8  is a schematic drawing of a public facility constructed according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a glycerol preparation flow chart according to the present invention. A glycerol preparation method using a by-product of a bio-diesel fuel process requires a pre-treatment unit  100  for converting a transesterification by-product into a recyclable by-product, a by-product separator unit  200  for by-product separation, a thin film evaporator unit  300  for methanol recycling, a crude glycerol mixture dehydrator unit  400 , and an industrial grade glycerol molecular distillatory unit  500 , and a medical grade glycerol molecular distillatory unit  600 . The aforesaid by-product is waste crude glycerol or saponified glycerol of a commercial bio-diesel fuel process. 
       FIG. 2  illustrates an operation of the pre-treatment unit  100  in converting a transesterification by-product into a recyclable by-product. As illustrated, the pre-treatment unit  100  comprises a blending tank  101 , a phosphoric acid tank  102 , a clean water tank  103 , a homogenizer  104 , and delivery pumps  105 ˜ 108 . 
     During operation, put phosphoric acid purity 85% min. in the phosphoric acid tank  102  and guide clean water to the clean water tank  103 , and then deliver the transesterification by-product to the blending tank  101 , and then guide clean water from the clean water tank  103  to the blending tank  101  at a pre setting ratio and simultaneously guide phosphoric acid 85% from the phosphoric acid tank  102  to the homogenizer  104  at the ratio that the amount of phosphoric acid 85% is about 0.75˜1% by weight of the amount of the transesterification by-product, thereby lowering the viscosity of the transesterification by-product. After blended, operate the delivery pump  107  to deliver the blended by-product from the blending tank  101  to the homogenizer  104  for homogenization. After homogenization, the homogenized by-product mixture is delivered to a feedstock tank  201  of the by-product separator unit  200  (see  FIG. 3 ) for further separation process. 
     As shown in  FIG. 3 , the by-product separator unit  200  comprises the aforesaid feedstock tank  201 , a three-phase stack disc separator  202 , and two delivery pumps  203 . The homogenized by-product mixture obtained through the pre-treatment unit  100  and stored in the feedstock tank  201  is further separated into free fatty acid, crushed crystalloid potassium phosphoric acid, and a mixture of crude glycerol, water and methanol (hereinafter referred to as crude glycerol mixture). Because these three substances have different mass and specific gravity, they can be separated by means of a three-phase high-speed stack disc separator. 
     During actual operation, start the delivery pump  203  to deliver the homogenized by-product mixture from the feedstock tank  201  to the three-phase stack disc separator  202 , for enabling free fatty acid, crystallized potassium phosphoric acid and crude glycerol to be separated from the homogenized by-product mixture. Separated free fatty acid can be used as an animal feed additive, or added to a heavy oil as a fuel, crystallized potassium phosphoric acid can be sold to a fertilizer plant for making potassium phosphate fertilizer, and crude glycerol mixture is pumped to a storage of a next processing state as feedstock for further glycerol refining. 
       FIG. 4  is a schematic drawing showing the arrangement of the thin film evaporator unit according to the present invention. Crude glycerol mixture obtained from the aforesaid transesterification through the aforesaid by-product the pre-treatment unit  100  (see  FIG. 2 ) and by-product separator unit  200  (see  FIG. 3 ) contains methanol, water, crude glycerol (about 50˜85%) and MONG (matter of non organic). Because these substances have different distilled points, two thin film evaporators and two molecular evaporators are necessary for separating these substances under different working temperatures so as to obtain refined glycerol. The procedure is outlined hereafter: 
     At first, the thin film evaporator unit  300  for methanol recycling requires a feedstock blending tank  301 , a first delivery pump  302 , a feedstock adjustment tank  303 , a second delivery pump  304 , a pre-heater  305 , a wiper type thin film evaporator  306 , a heat exchanger  307 , a semi-finished product accommodation tank  308 , a methanol accommodation tank  309 , a third delivery pump  310 , methanol storage tank  311 , at least one gas-liquid separator  312 , a vacuum pump  313 , a thermal oil circulation pump  314 , a thermal oil heater  315 , an expansion tank  316 , a fourth delivery pump  317 , and related piping, thermostat means, fluid level control means, control valve means, operating wheel means and the like for system composition and component parts connection. Further, the thin film evaporator unit  300  is used with a functional public facility  700  that comprises a cooling tower  701  and water pumps  702 A/B/C/D and a water chiller  703  (see  FIG. 8 ). 
     Further, during operation, cooling water is guided into the thin film evaporator unit  300  to cool down the mechanical seal means of the wiper type thin film evaporator  306  and vacuum pump  313  and condensing coil means of the heat exchanger  307 . 
     During operation, the cooling tower  701  and the water pumps  702 A/B/C/D are started, and then the thermal oil circulation pump  314  is started to pump a thermal oil from the thermal oil heater  315  through the expansion tank  316  to the pre-heater  305  and the wiper type thin film evaporator  306  and then to the thermal oil heater  315  again, finishing one circulation cycle. Thereafter, set the thermal oil working temperature, and then start the thermal oil heater  315  to heat the thermal oil to about 140° C. 
     Thereafter, start the vacuum pump  313  to draw air from the related pipeline, the wiper type thin film evaporator  306 , the semi-finished product accommodation tank  308  and the methanol accommodation tank  309 , lowering the pressure of the whole feeding and catching pipeline system to below 100 mBar (0.1 bar). During this vacuum extraction process, gas is separated by the gas-liquid separator  312  and driven into the atmosphere by the vacuum pump  313  through an exhaust port. 
     Thereafter, start the first delivery pump  302  to pump feedstock (crude glycerol mixture) from the feedstock blending tank  301  to the feedstock adjustment tank  303  for conditioning, and then start the second delivery pump  304  to pump the conditioned crude glycerol mixture from the feedstock adjustment tank  303  to the pre-heater  305  where the crude glycerol mixture is heated to above 58° C., and then to the inside of the cylinder of the wiper type thin film evaporator  306  where the wiper of the wiper type thin film evaporator is continuously rotated to apply the crude glycerol mixture to an inner cylindrical wall of the cylinder of the wiper type thin film evaporator evenly, forming a feedstock thin film of thickness about 4˜5/1000 mm (4μ˜5μ). Because 140° C. thermal oil is delivered through the space between the inner cylindrical wall and outer casing of the cylinder of the wiper type thin film evaporator  306 , the temperature of the feedstock thin film is then capable of being maintained. Further, because the working pressure inside the feeding and catching pipeline is kept under the negative pressure of 100 mBar, methanol molecules are evaporated from the feedstock thin film under this negative pressure environment before reaching 63° C. distillation temperature. Methanol steam goes through the pipeline into the heat exchanger  307  where methanol steam is condensed into fluid and guided into the methanol accommodation tank  309 . When the liquid methanol in the methanol accommodation tank  309  reaches a pre setting high level, the third delivery pump  310  is started to pump liquid methanol out of the methanol accommodation tank  309  to the methanol storage tank  311 . 
     The by-product that is not recycled, i.e., crude glycerol mixture is not distillable at 58° C. and therefore it falls along the inner cylindrical wall of the cylinder of the wiper type thin film evaporator  306  into the semi-finished product accommodation tank  308 . When the level of crude glycerol mixture in the semi-finished product accommodation tank  308  surpasses a pre setting range, the fourth delivery pump  317  is started to pump crude glycerol mixture out of the semi-finished product accommodation tank  308  to the next unit for dehydration. 
     When at 1 ATM, the distillation temperature of methanol is 63° C. However, methanol is evaporated at 58° C. when under the working pressure 100 mBar. This design avoids exposure of glycerol composition to a high temperature environment to affect its quality, and eliminates the risk of approaching of methanol steam to flash point. 
       FIG. 5  is a schematic drawing showing the arrangement of the crude glycerol mixture dehydrator unit according to the present invention. As illustrated, the crude glycerol mixture dehydrator unit  400  comprises a pre-heater  401 , a wiper type thin film evaporator  402 , a heat exchanger  403 , a semi-finished product accommodation tank  404 , a waste water reclaim tank  405 , a semi-finished product output pump  406 , a waste water reclaim tank  407 , an on-line gas-liquid separator  408 , a vacuum pump  409 , a thermal oil circulation pump  410 , a thermal oil heater  411 , a thermal oil expansion tank  412 , and related piping, thermostat means, fluid level control means, control valve means, operating wheel means and the like for system composition and component parts connection. Further, the crude glycerol mixture dehydrator unit  400  is used with the cooling tower  701  and water pumps  702 A/B/C/D of the aforesaid functional public facility  700  (see  FIG. 8 ). 
     Before operation, cooling water is guided into the crude glycerol mixture dehydrator unit  400  to cool down the mechanical seal means of the wiper type thin film evaporator  402  and vacuum pump  409  and condensing coil means of the heat exchanger  403 . 
     During operation, start the thermal oil circulation pump  410  to pump a thermal oil from the thermal oil heater  411  through the expansion tank  412  to the pre-heater  401  and the wiper type thin film evaporator  402  and then to the thermal oil heater  411  again, finishing one circulation cycle. Thereafter, set the thermal oil working temperature at 170° C., and then start the thermal oil heater  411  to heat the thermal oil to about 170° C. 
     Thereafter, start the vacuum pump  409  to draw air from the related pipeline, the wiper type thin film evaporator  402 , the semi-finished product accommodation tank  404  and the waste water reclaim tank  405 , lowering the pressure of the whole feeding and catching pipeline system to below 100 mBar. During this vacuum extraction process, gas is separated by the gas-liquid separator  408  and driven into the atmosphere by the vacuum pump  409  through an exhaust port. 
     When the level of crude glycerol mixture in the semi-finished product accommodation tank  308  of the last thin film evaporator unit  300  surpasses a pre setting range, the fourth delivery pump  317  of the thin film evaporator unit  300  is started to pump crude glycerol mixture out of the semi-finished product accommodation tank  308  through the pre-heater  401 , where the crude glycerol mixture is heated to above 95° C., and then to the inside of the cylinder of the wiper type thin film evaporator  402  where the wiper of the wiper type thin film evaporator is continuously rotated to apply the crude glycerol mixture to the inner cylindrical wall of the cylinder of the wiper type thin film evaporator evenly, forming a feedstock thin film of thickness about 4˜5/1000 mm (4μ˜5μ). Because 170° C. thermal oil is delivered through the space between the inner cylindrical wall and outer casing of the cylinder of the wiper type thin film evaporator  402 , the temperature of the feedstock film is then capable of being maintained. Further, because the working pressure inside the feeding and catching pipeline is kept under the negative pressure of 100 mBar, water is evaporated from the feedstock film at 95° C. under this negative pressure environment. At this time, steam goes through the output pipeline into the heat exchanger  403  where steam is condensed into water that is guided into the waste water reclaim tank  405 . 
     The by-product that is not recycled, i.e., crude glycerol mixture is not distillable at 95° C. and therefore it falls along the inner cylindrical wall of the cylinder of the wiper type thin film evaporator  402  into the semi-finished product accommodation tank  404 . When the level of crude glycerol mixture in the semi-finished product accommodation tank  404  surpasses a pre setting range, the semi-finished product output pump  406  is started to pump crude glycerol mixture out of the semi-finished product accommodation tank  404  to the next unit for further refining. 
     The distillation temperature of water is 100° C. However, water is evaporated at 95° C. when under the working pressure 100 mBar. This design avoids exposure of glycerol composition to a high temperature environment and emulsification of glycerol by steam, thereby maintaining the product quality. 
       FIG. 6  is a schematic drawing showing the arrangement of the industrial grade glycerol molecular distillatory unit according to the present invention. As illustrated, the industrial grade glycerol molecular distillatory unit  500  is adapted for refining industrial grade glycerol of purity over 95%, comprising a pre-heater  501 , a wiper type molecular still  502 , a cold well  503 , a semi-finished product accommodation tank  504 , a semi-finished product output pump  505 , a by-product accommodation tank  506 , a by-product buffer tank  507 , a by-product output pump  508 , a vacuum buffer tank  509 , an on-line gas-liquid separator  510 , a vacuum pump  511 , a thermal oil circulation pump  512 , a thermal oil heater  513 , a thermal oil expansion tank  514  and related piping, thermostat means, fluid level control means, control valve means, operating wheel means and the like for system composition and component parts connection. Further, the industrial grade glycerol molecular distillatory unit  500  is used with the cooling tower  701  and water pumps  702 A/B/C/D of the aforesaid functional public facility  700  (see  FIG. 8 ). 
     Before operation, cooling water is guided into the industrial grade glycerol molecular distillatory unit  500  to cool down the condensing coil means of the wiper type molecular still evaporator  502  and the mechanical seal means of the vacuum pump  511 . 
     During operation, add clean water and ethylene glycol to the water chiller  703  of the functional public facility  700  at the ratio that the amount of ethylene glycol is about 65% of the total water amount, and then start the water chiller  703  to make chilled water, enabling produced chilled water to be pumped by the internal chilled water pump of the water chiller  703  to the condensing loop of the cold well  503  and the mechanical seal means cooling loop  516  of the wiper type molecular still  502  and then to the chilled water tank of the water chiller  703 , forming a circulation loop. This chilled water circulation process is repeated again and again till that the temperature of the chilled water in the pipeline reaches −10° C. 
     Thereafter, start the thermal oil circulation pump  512  to pump a thermal oil out of the thermal oil heater  513  through the expansion tank  514 , the pre-heater  501  and a sandwich structure of the wiper type molecular still  502  and then the thermal oil heater  513  again, finishing one circulation cycle. Thereafter, set the thermal oil working temperature at 240° C., and then start the thermal oil heater  513  to heat the thermal oil to 240° C. 
     Thereafter, start the vacuum pump  511  to draw air from the related pipeline system of the industrial grade glycerol molecular distillatory unit  500 , the wiper type molecular still  502  and the semi-finished product accommodation tank  504 , lowering the pressure of the whole feeding and catching pipelines  517 ,  518  to below 40 Pa. During this vacuum extraction process, gas is separated by the gas-liquid separator  510  and driven into the atmosphere by the vacuum pump  511  through an exhaust port. 
     When the level of crude glycerol mixture in the semi-finished product accommodation tank  404  of the crude glycerol mixture dehydrator unit  400  surpasses a pre setting range, the semi-finished product output pump  406  is started to pump crude glycerol mixture out of the pre-heater  501 , where the crude glycerol mixture is heated to above 195° C., and then to the inside of the cylinder of the wiper type molecular still  502  where the wiper of the wiper type molecular still is continuously rotated to apply the crude glycerol mixture to the inner cylindrical wall of the cylinder of the wiper type molecular still evaporator evenly, forming a feedstock thin film of thickness about 4˜5/1000 mm (4μ˜5μ). Because 240° C. thermal oil is delivered through the space between the inner cylindrical wall and outer casing of the cylinder of the wiper type molecular still  502 , heat is rapidly transferred to the oil membrane of the feedstock to keep its temperature at a range above 195° C. Further, because the working pressure inside the feeding and catching pipelines  517 ,  518  is kept under the negative pressure of 40 Pa, glycerol is evaporated from the oil membrane of the feedstock at 195° C. under this negative pressure environment. At this time, glycerol molecules start to fly. When touched the internal condenser of the wiper type molecular still evaporator  502 , glycerol steam is condensed into fluid, which flows along the pipeline into the semi-finished product accommodation tank  504 . When the level of the fluid in the semi-finished product accommodation tank  504  reaches a pre setting high level, the semi-finished product output pump  505  automatically pumps the semi-finished product out of the semi-finished product accommodation tank  504  to the next unit for further glycerol refining. 
     The by-product that is not recycled is a fluid mixture of flock-like solid matter, animal gel and inorganic substance. Because of heavy molecular weight, the molecular free path of this mixture cannot reach the internal condenser of the wiper type molecular still  502 . Therefore, this fluid mixture falls to the bottom side of the wiper type molecular still  502  and collected by a collector board  520  and then guided to the by-product buffer tank  507 . When the level of the fluid mixture in the by-product buffer tank  507  reaches a pre setting high level, the by-product output pump  508  is immediately started to pump the fluid mixture out of the by-product buffer tank  507  to an external storage tank for sale. On the other hand, the semi-finished glycerol that falls to the semi-finished product accommodation tank  504  has a purity over 95%, and therefore it can be sold as industrial grade glycerol, or used as feedstock for refining into medial grade glycerol. According to the present preferred embodiment, when the level of the fluid in the semi-finished product accommodation tank  504  reaches a pre setting high level, the semi-finished product output pump  505  automatically pumps the semi-finished product out of the semi-finished product accommodation tank  504  to the next unit for further refining into medical grade glycerol. 
     Further, a part of the glycerol composition of the material that is delivered to the first glycerol refinery process that has a light molecular mass cannot be condensed by the internal condenser of the wiper type molecular still  502  during molecular distillation, and will escape out of the wiper type molecular still  502  and fly to the inside of the shade of the cold well  503 . Because the temperature of the fog-like glycerin molecules is as high as 195° C., very low temperature chilled water therefore is used to make a heat exchange with the internal condenser of the cold well  503 , enabling these light mass glycerol molecules to be condensed and guided into the vacuum buffer tank  509 . Therefore, the water chiller  703  must pump chilled water into the condenser pipeline of the cold well  503  continuously for heat exchange with the residual glycerol molecules that are not condensed in the wiper type molecular still  502  and that escape out of the wiper type molecular still  502 . 
     Under atmospheric pressure, the distillation temperature of glycerol is about 250˜290° C. However, because the working pressure in the wiper type molecular still  502  is below 40 Pa, glycerol start to evaporate at 195° C. This design avoids exposure of glycerol composition to a high temperature environment to affect its quality. 
       FIG. 7  is a schematic drawing showing the arrangement of the medical grade glycerol molecular distillatory unit for refining medical grade glycerol according to the present invention. The medical grade glycerol molecular distillatory unit  600  is adapted for processing the industrial grade glycerol thus obtained from the aforesaid the industrial grade glycerol molecular distillatory unit  500  into a medical grade glycerol having a purity over 99.75%. 
     This equipment of the medical grade glycerol molecular distillatory unit  600  is same as the aforesaid the industrial grade glycerol molecular distillatory unit  500 . The feedstock for this refining process is a high purity industrial glycerol, and the product of this refining process is a medical grade glycerol having a purity over 99.75%. 
     As illustrated, the medical grade glycerol molecular distillatory unit  600  comprises a pre-heater  601 , a wiper type molecular still  602 , a cold well  603 , a by-product accommodation tank  604 , a by-product output pump  605 , a finished product accommodation tank  606 , a finished product output pump  607 , a vacuum buffer tank  608 , an on-line gas-liquid separator  609 , a vacuum pump  610 , a thermal oil circulation pump  611 , a thermal oil heater  612 , a thermal oil expansion tank  613 , and related piping, thermostat means, fluid level control means, control valve means, operating wheel means and the like for system composition and component parts connection. Further, the medical grade glycerol molecular distillatory unit  600  is used with the cooling tower  701  and water pumps  702 A/B/C/D of the aforesaid functional public facility  700  (see  FIG. 8 ). 
     During actual practice, make sure that the cooling tower  701  and water pumps  702 A/B/C/D of the aforesaid functional public facility  700  have been started, and cooling water has guided into the mechanical seal means and condenser of the wiper type molecular still  602  and the mechanical seal means of the vacuum pump  610 , and the cooling loop of the water chiller  703 . 
     Make sure that the water chiller  703  has been started to make chilled water, the chilled water pump of the water chiller  703  has been started to pump chilled water to the condensing loop of the cold well  603  and the mechanical seal means cooling loop  616  of the wiper type molecular still  602  and then to the chilled water tank of the water chiller  703 , forming a circulation loop. 
     Thereafter, start the thermal oil circulation pump  611  to pump a thermal oil from the thermal oil heater  612  through the expansion tank  613 , the pre-heater  601  and a sandwich structure of the wiper type molecular still  602  and then the thermal oil heater  612  again, finishing one circulation cycle. Thereafter, set the thermal oil working temperature at 240° C., and then start the thermal oil heater  612  to heat the thermal oil to 240° C. 
     Thereafter, start the vacuum pump  610  to draw air from the related pipeline system of the medical grade glycerol molecular distillatory unit  600 , the wiper type molecular still  602  and the finished product accommodation tank  606 , lowering the pressure of the whole feeding and catching pipelines  617 ,  618  to below 40 Pa. During this vacuum extraction process, gas is separated by the gas-liquid separator  609  and driven into the atmosphere by the vacuum pump  610  through an exhaust port. 
     When the level of the fluid in the semi-finished product accommodation tank  504  reaches a pre setting high level, the semi-finished product output pump  505  automatically pumps the semi-finished product out of the semi-finished product accommodation tank  504  through the pre-heater  601  where the feedstock, industry glycerol from the previous process is heated to above 195° C., and then to the inside of the cylinder of the wiper type molecular still  602  where the wiper of the wiper type molecular still is continuously rotated to apply the crude glycerol mixture to the inner cylindrical wall of the cylinder of the wiper type molecular still evaporator evenly, forming a feedstock thin film of thickness about 4˜5/1000 mm (4μ˜5μ). Because 240° C. thermal oil is delivered through the space between the inner cylindrical wall and outer casing of the cylinder of the wiper type molecular still  602 , heat is rapidly transferred to the oil membrane to keep the oil membrane temperature above on 195° C. Further, because the working pressure inside the feeding and catching pipelines  617 ,  618  is kept under the negative pressure of 40 Pa, glycerol is evaporated from the oil membrane of the feedstock at 195° C. under this negative pressure environment. At this time, glycerol molecules start to fly. When touched the internal condenser of the wiper type molecular still  602 , glycerol steam is condensed into fluid, which flows along the pipeline into the finished product accommodation tank  606 . When the level of the finished product in the finished product accommodation tank  606  reaches a pre setting high level, the finished product output pump  607  automatically pumps the finished product out of the finished product accommodation tank  606  to external storage means for further packaging for sale. 
     The by-product that is not recycled is a fluid mixture of flock-like solid matter, gel and/or inorganic substance. Because of heavy molecular weight, the molecular free path of this mixture cannot reach the internal condenser of the wiper type molecular still  602 . Therefore, this fluid mixture falls to the bottom side of the wiper type molecular still  602  and collected by a collector board  620  and then guided to the by-product buffer tank  604 . When the level of the fluid mixture in the by-product buffer tank  604  reaches a pre setting high level, the by-product output pump  605  is immediately started to pump the fluid mixture out of the by-product buffer tank  604  to an external storage tank for sale. On the other hand, the finished product that falls to the finished product accommodation tank  606  has a purity in exceed of 99.75%, reaching the requirement for medical application. Further, a part of the glycerol composition of the material under this glycerol refinery process that has a light molecular mass cannot be condensed by the internal condenser of the wiper type molecular still  602  during molecular distillation, and will escape out of the wiper type molecular still  602  and fly to the inside of the shade of the cold well  603 . Because the temperature of the fog-like glycerin molecules is as high as 195° C., very low temperature chilled water therefore is used to make a heat exchange with the internal condenser of the cold well  603 , enabling these light mass glycerol molecules to be condensed and guided into the vacuum buffer tank  608 . Therefore, the water chiller  703  must pump chilled water into the condenser pipeline of the cold well  603  continuously for heat exchange with these fog-like glycerol molecules to have these fog-like glycerol molecules be condensed. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.