| IntroductionIn recent years, the most advanced molecular and functional imaging technology, PET, has been more and more applicated and spread in clinical diagnosis with the application of PET/CT imaging and positron emission tomography tracers. Because of the radioactive character of isotope 18F, 90 percent of positron medicine for PET(positron emission computed tomography) diagnosis is labeled by nuclide 18F and 18F-FDG is the most popularly used agent. The positron medicine labeled by 18F is most often synthesised by nucleophilic substitution reaction, the 18F nuclide is often got by bombarding oxygen-18 water in cyclotron ((18)O[p, n] 18F). The widespread application of positron medicine labeled by 18F leads to increasing consumption of oxygen-18 water and so oxygen-18 water is becoming to be a main raw material for the synthesis of positron medicine.Oxygen-18 water is composed of hydrogen and isotope oxygen-18, also named heavy-oxygen water, formula is H218O. On one hand, because the process of oxygen-18 water's manufacture is complicated and costs highly, the process of oxygen-18 water is limited, the large-scale application of nuclear-medicine diagnoses technology is conditioned by higher diagnoses expenditure for high-priced oxygen-18 water. On the other hand, radioactive isotope fluorin-18 will turn into oxygen-18 after disintegration and in the process of oxygen-18 water made for fluorin-18 and fluorin-18 labeled medicine, only little high-enrichment oxygen-18 Water is effectively used in nuclear-medicine diagnosis process, and more comes into being low-enrichment wasted oxygen-18 water. How to recycle these low-enrichment wasted oxygen-18 water is very important.At present, research on oxygen-18 water is mostly about industry-scale production, concerning improvement of industry-scale production technology, improvement of production efficiency, reduction of production cost, improvement of output quality etc. But it is hardly concerned that research on recycling the material of nuclear-medicine tracer reagent oxygen-18 water to hospital and PET diagnosis center. The research on recycling low-enrichment wasted oxygen-18 water from the PET center is carried out in this paper. High-purity recycling technique of the wasted oxygen-18 water includes two steps: first is purifying the wasted oxygen-18 water, second is enriching 18O up to high-enrichment for using as nuclear-medicine tracer reagent. By the research of purification and enrichment process, suitable recycling process of wasted oxygen-18 water will be chosen. Reusing oxygen-18 water is based on deep research on enrichment operation of isotope oxygen-18.Methods1. Removal of impurity in wasted oxygen-18 waterWasted oxygen-18 water that is totally 10500 grams for experimental use is made with the use of 2.25 kilogramS wasted oxygen-18 water collected from domestic PET center and 8.25 kilogram low-enrichment oxygen-18 water. Its isotope content of oxygen-18 water is approximately 35.04 percent (atom%)A small-scale purification device for wasted oxygen-18 water is built. To avoid the reduction of oxygen-18 enrichment and consumption of oxygen-18 water cotton core filtration, active carbon adsorption, ultraviolet oxidation, anti-osmosis filtration, ion exchange, and simple evaporation are in series for experiment. The experimental material is divided into 21 parts, and every part is 500 gram. Every process treates three parts. Every part flows through the above-mentioned process by dosing pump. After five recycling the value of conductance, TOC(total organic carbon), enrichment of oxygen-18 water will be separately measured under different process and different recycling times. And the statistics analysis was done with SPSS13.0 software pack. The purification procedure was further optimized on the basis of the conclusion.2. Enrichment of oxygen- 18 water after purificationBy PRO-Ⅱsimulation software the vapor-liquid equilibrium database about H216O-H217O-H218O and algorithm of enrichment of oxygen-18 water is developed to simulate the enrichment process of oxygen-18 water and chooses adaptable operation process.7500 grams oxygen-18 water whose enrichment is approximately 30 percent(atom%) after purification process are chosen as experimental material.The distillation column that consists of highly specific surface area Dixon pack is chosen. Then a constant-pressure two-column device is built up to operate under total reflux and part reflux and measure the enrichment of isotope oxygen-18 to further decide the purification procedure and parameter of that. ResultsIn the research of removal of wasted oxygen-18 water impurity anti-osmosis filtration and ion exchange is an efficient process of water purification, but the material is greatly consumed in the anti-osmosis filtration process and enrichment of oxygen-18 in the ion exchange process drops more. So two above-mentioned processes are not suitable for the treatment of wasted oxygen-18 water. Though there is great consumption at first steps of cotton core filtration and active carbon adsorption, consumption of latter steps are little. Material is hardly consumed in ultraviolet oxidation and simple evaporation. At the same time these processes have little influence on enrichment of isotope oxygen-18. So adaptable process of wasted oxygen-18 water purification is: ultraviolet oxidation, simple evaporation, or cotton core filtration, active carbon adsorption, ultraviolet oxidation, simple evaporation. With the validating experiment of cotton core filtration, active carbon adsorption, ultraviolet oxidation, simple evaporation, 1500 grams raw material are dealt with. The result: the value of conductance is below 3.0μs/cm, TOC is below 0.5mg/L, enrichment of oxygen-18 is 32.44%(atom%), consumption of raw material is 10.6%, enrichment of oxygen-18 drops 2.56%. The result proves that above-mentioned process meets the requirement of oxygen-18 water purification index.The vapor-liquid equilibrium database and algorithm about H216O-H217O-H218O is founded. By PRO-Ⅱsimulation software the result of simulation is close to the industrial data. It is proved that the vapor-liquid equilibrium database and algorithm about H216O-H2 17O-H2 18O can be used to predict and calculate the enrichment process about oxygen-18 water and provide reliable theoretical base for the separation and enrichment on oxygen-18 water.Usually the treatment quantity of wasted oxygen-18 water is small, it is applicable to adopt batch distillation. By simulation to get reusing oxygen-18 water (up to 95atom%) there are more than 200 theoretical plates. So general single-column batch distillation is not applicable.In the research it is applied a constant-pressure two-column device of enriching oxygen-18 water whose character is that two columns are fill with high-efficient Dixon packing. By connection of constant-pressure in series the process of two-column batch distillation will be carried out. Under the condition of two-column total reflux a single column can not provide enough theoretical plate, so enrichment of oxygen-18 only can be enriched from 30.0atom% to 60～63.5atom%,. When two columns work in series under the condition of overall reflux, 98atom% oxygen-18 sample will be achieved. Under the condition of experimental device after production extraction if the quantity of yield is more than 1.0g/h, it will be difficult to achieve qualified production. If production extraction is 0.5g/h it is easy to get＞95atom% oxygen- 18 production.ConclusionsHigh-purity recycling process of wasted oxygen-18 water includes two steps: first is purifying the wasted oxygen-18 water, second is enriching 18O up to high-enrichment.So adaptable process of wasted oxygen-18 water purification is: cotton core filtration, active carbon adsorption, ultraviolet oxidation, simple evaporation. This process can meet the demand of the purification index of wasted oxygen- 18 water.The vapor-liquid equilibrium database and algorithm about H216O-H217O-H218O can provide reliable theoretical base for the separation and enrichment on oxygen-18 water.Based on these a constant-pressure two-column batch distillation device is founded. Despite of the experimental data under different conditions it can be shown that the small constant-pressure two-column batch distillation device can fit for requirement of wasted low-enrichment oxygen-18 water, and suitable for recycling of wasted low-enrichment oxygen-18 water. At the same time it can improve the value of oxygen-18 water.
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