Purification of water and preparation of ultrapure water

Purification of water and preparation of ultrapure water

Summary        This is an overview of the purification of water and the preparation of ultrapure water. Various techniques for purifying water and some recent advances are presented. Including distillation, ion exchange, electrodialysis, reverse osmosis and ultraviolet irradiation.
Important section    Purification of water    Ultra-pure water    Ion exchange    Electrodialysis    Reverse osm   
I. Introduction
The preparation of high-purity water has been discussed in detail in the monograph of Mr. Wen Ruimei et al. [1] . This article only wants to introduce some common sense and small experience related to chemical analysis and instrumental analysis water for reference.
Natural water usually contains five impurities: 1. Electrolytes, including charged particles, common cations are H + , Na + , K + , NH 4 + , Mg 2+ , Ca 2+ , Fe 3+ , Cu 2+ , Mn 2+ , Al 3+ , etc.; anions include F - , Cl - , NO 3 - , HCO 3 - , SO 4 -2 , PO 4 3- , H 2 PO 4 - , HSiO 3 - and the like. 2. Organic substances such as organic acids, pesticides, hydrocarbons, alcohols and esters. 3. Particulate matter. 4. Microorganisms. 5. Dissolved gases, including: N 2 , O 2 , Cl 2 , H 2 S, CO, CO 2 , CH 4 , and the like. The so-called purification of water is to remove these impurities. The more thoroughly the impurities go, the purer the water is.
National standards provide technical indicators for analytical laboratory water use [2] and electronic grade water [3] . The technical indicators for analyzing laboratory water use are shown in Table 1:
Table 1. Technical Specifications for Class I and II Laboratory Water (GB6682-92)
name
First level
Secondary
Third level
pH range (25 ° C)
--
--
5.0-7.5
Conductivity (25 ° C), mS / m. ≤
0.01
0.10
0.50
Oxidizable substance (in 0), mg/L <
--
0.08
0.4
Absorbance (254nm, 1cm optical path) ≤
0.001
0.01
--
Evaporation residue (105 ° ± 2 ° C), mg / L ≤
--
1.0
2.0
Soluble silicon (calculated as SiO 2 ) mg/L <
0.01
0.02
--
Primary water is used for analytical experiments with stringent requirements, such as water for liquid chromatography.
Secondary water is used for inorganic trace analysis, such as water for atomic absorption spectrometry.
Tertiary water is used for general chemical analysis experiments.
Supplementary to the national standard (GB6682-92): Since the true pH value of the primary and secondary water is difficult to determine, the pH range of the primary and secondary water is not specified.
The conductivity of the primary and secondary waters is determined online using freshly prepared water.
Because it is difficult to determine the oxides and evaporation residue under the purity of the first-order water, the national standard does not regulate the limit. Other conditions and preparation methods can be used to ensure the quality of the first-grade water.
1
The national standard has a clear regulation on the test methods for primary and secondary water conductance: the conductivity meter for the determination of primary and secondary water needs to be equipped with an online conductivity cell with an electrode constant of 0.01-0.1 cm -1 and an automatic temperature compensation function.
Electronic grade water has higher requirements for ion concentration levels in water. The national standard GB/T11446.1-1997 is divided into four levels, namely EW-I, EW-II, EW-III and EW-IV. The technical indicators are shown in Table 2:
Table 2. Technical indicators of electronic grade water
level
index
EW-I
EW-II
EW-III
EW-IV
Resistivity MΩ.cm (25°C)
18 or more
(95% time) no less than 17
15
(95% time) no less than 13
12.0
0.5
All silicon, maximum, μg/L
2
10
50
1000
>1μm particle meter, maximum, /m L
0.1
5
10
500
Number of bacteria, maximum, /m L
0.01
0.1
10
100
Copper, maximum, μg/L
0.2
1
2
500
Zinc, maximum, μg/L
0.2
1
5
500
Nickel, maximum, μg/L
0.1
1
2
500
Sodium, maximum, μg/L
0.5
2
5
1000
Potassium, maximum, μg/L
0.5
2
5
500
Chlorine, maximum, μg/L
1
1
10
1000
Nitrate, maximum, μg/L
1
1
5
500
Phosphate, maximum, μg/L
1
1
5
500
Sulfate, maximum, μg/L
1
1
5
500
Total organic carbon, maximum, μg/L
20
100
200
1000
*. Introduced the national standard GB/T 1144.6.1-1997
2. Method for purifying water
1. Distillation method, according to distillation vessels can be divided into glass, quartz distiller, metal materials are copper, stainless steel and platinum distiller. According to the number of distillations, it can be divided into one, two and multiple distillation methods. In addition, in order to remove some special impurities, some special measures are needed. For example, some potassium permanganate may be added in advance to remove the easy oxide; a little phosphoric acid may be added to remove the ferric iron; and a little non-volatile acid may be added to prepare the ammonia-free water. Distilled water can meet the water requirements of a general analytical laboratory. It is difficult to rule out the incorporation of carbon dioxide. Therefore, the resistivity of water is very low and cannot reach the MΩ level. Can not meet the needs of many new technologies.
2. The ion exchange method mainly has two preparation methods:
2
A. The double bed type, that is, the deionized water is connected according to the way of the sun bed - the Yin bed - the sun bed - the Yin bed - the mixed bed; this method is adopted in the early stage to facilitate the resin regeneration.
B, mixed bed type (2-5 series connected in series), mixed bed deionization effect is good. However, regeneration is not convenient.
The ion exchange method can obtain more than ten MΩ of deionized water. However, organic matter cannot be removed, and TOC and COD values ​​tend to be higher than raw water. This is because the resin is not good, or the pretreatment of the resin is not thorough, the oligomers, monomers, additives, etc. contained in the resin are not removed, or the resin is unstable, and the decomposition products are continuously released. All of this will be expressed in the form of TOC or COD indicators. For example, when the COD value of tap water is 2 mg/L, the deionized water obtained by deionization treatment often has a COD value of between 5 and 10 mg/L. Of course, good results can be obtained when using a good resin, otherwise ultrapure water cannot be prepared.
3. Electrodialysis, produced in 1950 [4] , is based on its low energy consumption and is often used as a pretreatment step in the ion exchange process. Under the action of an external DC electric field, the anion and cation exchange membranes are used to selectively allow the passage of the anion and cation, so that a part of the ions migrate through the ion exchange membrane to another part of the water, so that a part of the water is purified and the other part is concentrated. This is the principle of electrodialysis. Electrodialysis is one of the commonly used desalination techniques. The purity of the produced water can meet the needs of some industrial water. For example, 1.03 MΩ.cm (25 ° C) of produced water can be obtained with raw water having a resistivity of 1.6 KΩ·cm (25 ° C). In other words, when the total hardness of the raw water is 77 mg/L, the total hardness of the produced water is ∽10 mg/L.
Reverse osmosis [5] , it is currently the most widely used desalination technology. Although the reverse osmosis membrane was available in 1977, its large-scale production and widespread use in desalination have been a matter of recent years. The reverse osmosis membrane can remove inorganic salts, organic matter (molecular weight > 500), bacteria, heat sources, viruses, suspensions (particle size > 0.1 μm), and the like. The ability of the reverse osmosis membrane to remove impurities is shown in the table below.
Table 3: Removal of impurities by reverse osmosis membrane
ion
Removal rate (%)
ion
Removal rate (%)
ion
Removal rate (%)
Mn +2
96-99
SO 4 -2
90-99
NO 3 -
50-75
Al 3+
95-99
CO 3 -2
80-95
BO 2 -
30-50
Ca 2+
92-99
PO 4 3- , HPO 4 2- , H 2 PO 4 -
90-99
particle
99
Mg 2+
92-99
F -
65-95
bacterial
99
Na +
75-95
HCO 3 -
80-95
Organic matter (molecular weight >300)
99
K +
75-93
Cl -
80-95
NH 4 +
70-90
SiO 2
75-90
Common reverse osmosis membranes include cellulose acetate membranes, polyamide membranes, and polysulfone membranes. The pore diameter of the membrane is from 0.0001 to 0.001 μm. The power of reverse osmosis depends on the pressure difference (10-100 atmospheres). The ability to remove impurities is determined by the performance of the membrane and the ratio of influent to water. The ratio of influent and water is generally controlled to be around 10:6 or 10:7. The removal rate of such impurities should be between 95 and 99.7%. For example, when the resistivity of raw water is 1.6 KΩ.cm (25 ° C), the resistivity of produced water is about 14 KΩ.cm (25 ° C). This kind of water is now called pure water, which is the pure drinking water sold on the market.
3

Method for preparing ultrapure water
The conventional pure water method cannot produce ultrapure water, and the theoretical conductivity of pure water (liquid H 2 O) is 18.3 MΩ·cm. The pure water produced by people is not up to the theoretical value, but 18 MΩ.cm seems to
It is achievable. For this kind of water, some are called high-purity water, and some are called ultra-pure water. There is no systematic definition yet. There is no hierarchy, and from a commercial point of view, ultrapure water seems to be better than high purity water. The author thinks that it is more accurate to look at the conductivity index.
The current method for preparing ultrapure water is to scientifically combine various new technologies for purified water, which not only produces ultrapure water, but also becomes very easy. The currently commercially available ultrapure water is a successful example. It is very convenient to tap the tap water into the ultrapure water. And the service life is getting longer and longer.
The principle and steps of preparing ultrapure water in ultrapure water are as follows:
1. Raw water: tap water or ordinary distilled water or ordinary deionized water can be used as raw water.
2. Mechanical filtration: Filter out mechanical impurities such as rust and other suspended materials through sand core filter plates and fiber columns.
3. Activated carbon filtration: Activated carbon is a broad-spectrum adsorbent that can adsorb gas components, such as residual chlorine in water; adsorb bacteria and certain filter metals. Chlorine gas can damage the reverse osmosis membrane, so it should be exhausted.
4. Reverse osmosis membrane filtration: It can filter out more than 95% of electrolytes and macromolecular compounds, including colloidal particles and viruses. Due to the removal of most ions, the service life of the ion exchange column is greatly extended.
5. Ultraviolet digestion: By means of short-wave (180nm-254 nm) ultraviolet irradiation, small organic compounds that are not easily adsorbed by activated carbon, such as methanol and ethanol, are decomposed into CO 2 and water to reduce the TOC index.
6. Ion exchange unit: A known mixed ion exchange bed is a decisive means of removing ions from water. It is not difficult to obtain ultrapure water by means of a multistage mixed bed. But the TOC indicator of water is mainly from the resin bed. High quality ion exchange resins are therefore the key to success. The so-called high-quality resin is a resin which is particularly good in chemical stability, does not decompose, and does not contain oligomers, monomers and additives. The so-called "nuclear industrial grade resin" probably belongs to this type of resin. The requirement for the resin is that the higher the quality, the better. It is a pity that few people in China have worked hard in this area and are satisfied with the production route.
7.0.2μm filter membrane is filtered to remove the particulate matter in water. One milliliter per milliliter (the water produced by the above steps is less than 0.2μm. The water produced by the above steps is ultrapure water. It should be able to meet various instrumental analysis, high purity analysis. Requirements for trace analysis, etc., approach or meet the requirements of electronic grade water.
4. Special pure water:
1. Thermal power plants require pure water without silicon, and silicon is often present in the form of hydrated silica (SiO 2 · H 2 O) in water, which is non-ionic and difficult to remove. However, hydrated silica also has a small degree of ionization, and by virtue of lengthening the length of the ion exchange bed or repeatedly circulating in a mixed ion exchange bed, it is still possible to obtain ultra-pure water free of silicon. Silicon-free water is not available with a glass or quartz distiller because the container contains silicon.
2. Pure water without heat source (ie endotoxin), water for injection requires no heat source. So as not to cause an allergic reaction. The best way to remove the heat source today is by distillation. There are also adsorption columns in addition to heat sources.
3. Pure ammonia without ammonia, the preparation method is two, one of the distillation methods, pre-added non-volatile acid in water, can fix the ammonium salt in the raw water. The second is to pass the pure water through the cation exchange bed again. It should be noted that the anion exchange resin has the possibility of decomposing to generate trace amounts of ammonia, and it is not suitable to remove ammonia by a mixed bed.
4. Iron-free water, iron is known to be ubiquitous, and the anti-boiling point of FeCl 3 is only 315 ° C. Therefore, it is difficult to remove iron ions by distillation. This can be achieved by adding a drop of phosphoric acid to the raw water. Of course, with ultra-pure water, there is no need to remove iron.
5. Estimate the concentration level of ions in water from the conductivity of pure water:
4
The ion concentration of ultrapure water is extremely low, and the sensitivity of many analytical methods is not achieved. The average user lacks special detection means. Someone [6] has done calculations in this area for reference:
Table 4. Ion calculated concentrations of several pure waters with different resistivities
Concentration μg/L
ion
18.2 M Ω
18.0 M Ω
17.5 M Ω
15 M Ω
Na +
0.8
1.3
1.8
1.6
Cl -
<0.1
0.15
0.5
2.1
Fe 2+
2.0
2.4
2.0
5.4
Na + + Cl - +SO 4 2-
<0.1
0.3
1.1
5.4
Na + + Cl -
<0.1
0.2
0.9
5.0
For example, water with a resistivity of 15 MΩ has a total concentration of sodium, chlorine and sulfate ions of 5.4 μg/L. Such impurity levels should meet the requirements of various trace analysis and high purity analysis. Don't have to worry. Also do not measure the pH value in this case, because even if all ions are H + , one PH unit cannot be changed. Don't be tempted by yourself. Abnormal data will appear unless there is a problem with the conductivity meter or the PH meter. As pointed out in the national standard for laboratory water use (GB6682-92), ultra-pure water is more difficult to accurately measure for the first and second grade waters.
There are some ultra-pure water products on the market. Now take the products of Shanghai Racing Pigeon Company as an example. The introduction is as follows:
SPW series of ultra-pure water purifiers of Shanghai Racing Pigeon Company are divided into basic type and multi-purpose type. The technical indicators are relatively advanced. The combination of membrane filtration and ion exchange technology enables on-line automatic detection and control of water quality, and can obtain high-quality water stably for a long time. The main technical indicators are as follows:
Outlet water resistivity: 18.2 megohm / cm
★ Total organic carbon: TOC≤10ppb
★ Low heat source content: ≤0.02Eu/ml
Micro-imparting particles: (<0.22μm) ≤1/ml
Microbial content: ≤1cfu/ml
Using ordinary tap water or distilled water as raw water, it is convenient to produce ultra-pure water in one step. According to the output, it can be divided into 10 liters, 20 liters, 30 liters, 40 liters and 50 liters per hour, namely 10T, 20T, 30T, 40T and 50T. There are several models to choose from, consumables are cheaper and easier to buy.
references
[1]. Wen Ruimei, edited by Wang Zaizhong, preparation and inspection technology of high purity water, Science Press, 1999, Beijing
[2]. National Standard of the People's Republic of China, GB6682-92, "Analysis Laboratory Water Specifications and Experimental Methods"
[3]. National Standard of the People's Republic of China, GB/T11446.1-1997, "Electronic Water Specifications and Experimental Methods"
5
[4].W.Juda and WAMcrae, J.Am.Chem.Soc.,72,1044,1950
[5].S.Sourira, Reverse Osmosis and Synthetic Membrane, Engineering National Research Council of canada, 1997
[6].S.Whitehead, J.Chromatogr.770:115,1997
[7].MAAccomazz, Swiss Contamination Control, 3, 136, 1990
The Purification of Water and the Production of Ultrapure Water
Ma Huichang Zan baozhen Liou Xinghan
(Beijing Epoch Electronic Instruments Co., Beijing, 100085)
Abstract This is a review on the purification of water and the production of ultrapure water.Various techniques of water includedion exchange, reversed osmosis and electronic dialysis method and some recent development are introduced.
Key words Purification of water Ultrapure water Ionexchange
Reversed osmosis Electronic dialysis

For flower type operation lamp, it has two types of lamp head, one is big one, it has 64 LED bulbs which from Germany osram, another small one, it has 45 LED bulbs, also from Germany. the surgical lamps bulb can last long for 8 hours, that is one of the reasons which our surgical lamp has low maintainance rate. for Double Dome Surgical Lamp, can constituted by one big+one big lamp head, one big+one smal lamp head and one small+ one small lamp head, it can be choosed depends on users' requirment; 

the flowet type OT lamp has functions of Bright and Uniform illumination; Outstanding color temperature control performance; Supramaximal effective light field;Electric focusing system;

Led Operation Lamp 25

Double Dome Flower Ot Lamp

Double Dome Flower Ot Lamp,Double Dome Ot Lamp,Double Dome Operation Lamp,Double Dome Surgery Light

Shandong Lewin Medical Equipment Co., Ltd. , https://www.operatinglight.nl