Synthesis method of high purity sodium gluconate and its role in concrete.What is the pH value? What are the functions in concrete?
Sodium gluconate is widely used in industry. Sodium gluconate can be used as high-efficiency chelating agent, steel surface cleaning agent, glass bottle cleaning agent, aluminum oxide coloring in electroplating industry, high-efficiency retarder and superplasticizer in construction, textile printing and dyeing, metal surface treatment and water treatment industries.
In industry, glucose containing substances (such as grains) are generally used as raw materials. Glucose acid is prepared from glucose by fermentation method, and then neutralized by sodium hydroxide to obtain sodium gluconate. It can also be synthesized by electrolysis and oxidation. Chemical oxidation – hypobromine oxidation is mostly used in China.
According to the different types of fermentation enzymes used, the fermentation method can be divided into two minutes. One is the enzyme of Aspergillus niger, and the other is acid. The latter method forms lactone by dehydrogenation of glucose, and then decomposes the ester
Sodium gluconate is also obtained by direct fermentation of glucose in the mouth. At this time, the composition of fermentation base can be: 250 ~ 350g / L glucose storage, 0.2 ~ 03g/l magnesium sulfate heptahydrate, 0.4 ~ 0.5g/l diammonium hydrogen phosphate or urea. This substrate must be sterilized. In the fermentation process, the temperature is controlled at 30-32 ℃, h is controlled at 55-65 by 30% ~ 50% sodium hydroxide, and the fermentation process lasts for 40 ~ 100h. Then, the microorganisms are removed by filtration and washing, activated carbon decolorization, re filtration, concentration or spray drying.The standard is between 7-8PH.
Electrolytic oxidation method: this method is to add a certain concentration of glucose solution into the electrolytic cell, then add appropriate electrolyte, and conduct constant current electrolysis at a certain temperature and current density. The determination of industrial parameters varies with the addition of electrolytes. For example, when sodium bromide is used as electrolyte, the glucose concentration is 23.5% (mass fraction), the temperature is controlled at 40 ℃, the current density is 1 a DM2, and the electrolyte concentration is 2% (mass fraction). Sodium carbonate can be added at one time in the electrolysis process. After electrolysis, the electrolyte is concentrated and crystallized to obtain sodium gluconate crystal. Although electrolytic oxidation method overcomes some shortcomings of biological fermentation method and homogeneous chemical oxidation method, it is rarely used in industrial production because of its high energy consumption and difficult to control.
Effect of sodium gluconate in concrete
- With sodium gluconate, the w / C ratio can be reduced, which can increase the strength of concrete. It is a high-quality concrete.
- Large and heavy grouting works are difficult to construct. Due to the addition of sodium gluconate, the improvement of concrete workability and the delay of setting time can avoid the contact surface on the structure, which can improve the structural strength.
- It is of great significance to keep the w / C ratio unchanged and improve the working performance in hot areas. A large amount of sodium gluconate was used in bridge construction in the Middle East.
- Adding sodium gluconate into the concrete mixture can delay the setting time, which is very important for long-time and difficult pouring.
- In the modern concrete industry, the ready mixed concrete is prepared at the central place and transported by mixer truck. In this case, it is very important to increase the workability and initial setting time.
- Reducing w / C ratio can make concrete with higher strength and durability, which can be achieved by sodium gluconate. This is very important for high strength reinforced concrete.
- The prefabricated masonry mortar must be used for a long time. The addition of sodium gluconate can prolong the working period.
- It is difficult to operate the oil well irrigation mud due to high temperature. After adding sodium gluconate, the concrete can work for several hours at 170 ℃
Effect of sodium gluconate content in pumping agent on concrete performance
In recent years, due to the construction of high-rise and super high-rise building projects, the traditional concrete construction technology can no longer meet its construction requirements. The use of pumped concrete has been very common in developed countries. Pumped concrete is widely used in Beijing and Tianjin, and the proportion of pumped concrete in other areas is also increasing year by year. Therefore, Admixtures such as water reducing agent and pumping agent are more and more widely used in engineering. However, after adding admixtures, the slump loss of concrete is more serious than that before adding admixtures. Especially after adding high-efficiency reducing agents, the slump of concrete can only be maintained for more than ten minutes to half an hour, which makes construction difficult. This problem is particularly prominent in commercial concrete and pumped concrete. Scholars from various countries have done a lot of work and achieved some results. In these achievements, there are two types of technical routes commonly used, one is the admixture addition method, and the other is the composite retarder. The method of compounding superplasticizer and retarder to solve the slump loss has been widely accepted. The theoretical basis of this method is to delay the formation of early hydration products of cement and inhibit the slump loss.
Generally, the pumping agent is composed of superplasticizer, retarder, air entraining agent and pump aid. The substances that can be used as retarders mainly include hydroxycarboxylic acids, polyhydroxycarbohydrates, lignosulfonate and humic acid water reducing agents and inorganic compounds. Molasses water reducing agent and calcium lignosulfonate water reducing agent are widely used in China. But there are problems. After the implementation of ISO standard, the fineness of cement increases, but it is not suitable for Retarders such as wood calcium and sugar. Due to the lack of research and application of hydroxycarboxylic acid retarders, more attention needs to be paid to this kind of retarders. Hydroxycarboxylic acid retarders include citric acid and sodium gluconate. The combination of sodium gluconate and superplasticizer can delay the setting time of concrete, reduce slump loss and improve the strength of concrete. However, some projects need to be over mixed with retarding and water reducing agent for construction, resulting in quality hidden dangers. In this paper, sodium gluconate (GNA), a hydroxyl carboxylic acid retarder, is selected to study the effect of its different content on the performance of concrete.Synthesis method of high purity sodium gluconate and its role in concrete.