Views: 108 Author: Sam Lee Publish Time: 2019-04-02 Origin: Site
Cement is a very basic material in the construction industry and plays a very important role in the development of the national economy. China is a big cement producer. In 2011, China's cement output reached 2.09 billion tons, and cement production has exceeded in recent years. 8% of the speed increase. However, the energy consumption in the cement production process is high and the utilization rate is low, mainly due to the accumulation of fine powder particles during the grinding process, which causes the paste ball and the adhesive liner to reduce the grinding efficiency, so that about 80% to 90% % of the energy is consumed in the form of heat. In order to improve this situation, it is common in the industry to add a small amount of grinding aid to the grinding material to improve the grinding efficiency and reduce the grinding energy consumption. At the same time, grinding aids can also increase production (many studies have shown that grinding aids can increase cement production by 5 to 30 percent when it is added in the range of 1 in 10,000 to 10,000) and reduce environmental pollution ( Reduced emissions of CO2 and SO2 from dust and gaseous pollutants). As a processing aid for energy saving and consumption reduction in cement grinding, cement grinding aids have been recognized and valued by cement manufacturers, and now the focus of cement grinding aids is not only on grinding The role itself, and its enhancement of cement performance is also more concerned.
The cement grinding aid is composed of one or several kinds of surface active substances, and there are no more than one hundred kinds in the industry. However, the surface active ingredients in the cement grinding aid mainly have the following types: (1) Alcohol amine polar small molecules Such as triethanolamine, decylamine, etc.; (2) polyol polar polar molecules, such as ethylene glycol; (3) unsaturated fatty acids: such as stearic acid; (4) salts, such as sodium stearate (5) natural minerals such as talc; (6) macromolecules or macromolecules such as styrene copolymers, maleic anhydride derivatives, and the like. The first type of alcohol amine monomer contains hydroxyl groups in the molecule, which can better disperse cement during cement grinding and affect the physicochemical properties of cement. It is a common monomer used in compound grinding aids. At present, commercial cement grinding aids are mostly complexes of alcohol amines and polyols, such as organic compounds such as triethanolamine (TEA) and ethylene glycol. Therefore, three alcohol amine monomers, triethanolamine (TEA), triisopropanolamine (TIPA), and newly developed diethanol isopropanolamine (DEIPA) were compared.
Physicochemical properties and synthesis methods of three kinds of alcohol amine monomer cement grinding aids
Triethanolamine (TEA) is a colorless to pale yellow, amine-like viscous liquid. CAS No.: 102-71-6, relative molecular mass: 149.19, molecular formula: C6H15O3N, structural formula: N(CH2CH2OH)3, is a highly polar hydroxyl-(OH) nonionic surfactant.
At present, the most important ethanolamine production methods in the world and in China mainly use the ring-opening nucleophilic reaction of ethylene oxide (EO) and ammonia (NH3), and the excess ammonia in the case of ethylene oxide using water or alcohol ammonia as a catalyst. In the reaction, three active hydrogen atoms on the ammonia molecule are replaced one by one by hydroxyethyl groups, and MEA, DEA and TEA are successively formed, and three kinds of ethanolamine products are obtained by fractional distillation. The main technologies of this technology are American SD Company, Japan Mitsui East Pressure Company, German Dider Company, and Germany BASF Company. Most of the domestic technology is introduced, but Zhejiang University has made great breakthroughs in the research on ethanolamine reaction process. The liquid ammonia intermediate pressure reaction production process has been successfully developed, and the reaction is anhydrous.
Triisopropanolamine (TIPA) is an anhydrous white solid with a water-white, slightly viscous liquid. Its CAS number is: 122-20-3, the molecular weight is 191.3, the molecular formula: C9H21NO3, and the molecular structural formula: N(CH2CHOHCH2)3.
Similar to the production of ethanolamine, isopropanolamine is mainly produced by the reaction of propylene oxide (PO) and ammonia (NH3) to produce isopropanolamine, diisopropanolamine, and triisopropanolamine, and water is also used as a catalyst. High pressure supercritical fluid synthesis process.
1.3 diethanol monoisopropanolamine
Diethanol isopropanolamine (DEIPA) is a colorless, transparent, viscous liquid with an ammonia odor. The CAS number is 6712-98-7, the relative molecular mass is 163.21, and the molecular formula is C7H17NO3.
Diethanol monoisopropanolamine can be produced in three different ways. One is to react ammonia with EO and PO to synthesize DEIPA: first NH3 and PO to obtain isopropanolamine (MIPA), followed by MIPA EO is obtained in two steps; the second is developed on the basis of MIPA in the market, which reacts MIPA and EO to form DEIPA; and third, it is synthesized from diethanolamine (DEA) and PO. Since the first and second methods are step-by-step reaction methods, many operation controls and many by-products, and the DEA raw material market is sufficient, the third process route has great advantages.
Comparison of the effects of two kinds of alcohol amine monomer cement grinding aids on the grinding and performance of Portland cement
2.1 Impact on cement grinding
Since most of the energy consumption of cement production is in the grinding process, the impact on cement production is mainly compared with the grinding aid effect of the three grinding aids. Many studies and actual production have verified that TEA is a good and widely used grinding aid, which can increase the grinding efficiency by about 20% when the dosage is 0.01% to 0.03%; Katsiot et al. Human studies have found that triethanolamine and triisopropanolamine (TIPA) have increased the specific surface area and brittleness of cement. Li Guohua studied the effects of three blends of TEA, TIPA and DEIPA on the distribution of cement particles. It was found that all three made 80μm, and the 45μm sieve was greatly reduced, indicating that it has a good grinding effect. However, the changes in the curves of the three are similar, and the impacts are roughly similar. Studies by CheuIlg and Josephine et al. have shown that DEIPA can effectively reduce the formation of tiny bubbles in the cement clinker grinding process, thereby reducing the microscopic pores on the cement surface, making the cement particles surface more uniform and improving the grinding performance of the cement.
Research on the grinding mechanism. It is generally believed that all three contain both a hydroxyalkyl group and an amine group, and are easily adsorbed on the surface of the particles and in the gaps of the particles, reducing the surface energy of the cement particles, and at the same time, the charge is weakened, thereby being easily broken. At the same time, it also reduces the phenomenon of static electricity accumulation, thereby reducing the phenomenon of over-grinding, reducing the fine particles in the cement, and the particle size distribution is concentrated.
Since all three are tertiary amines with hydroxyalkyl groups, the amine nitrogen atoms are respectively connected to three hydroxyalkyl groups, resulting in a low degree of bare pair of electrons on the nitrogen atom, which has strong electronegativity and powder. The steric hindrance of bulk adsorption is large, and the hydroxyalkyl group can be adsorbed on the surface of cement particles; the electronegativity of nitrogen makes it electrostatically repulsive, and the newly generated surface has different charges due to the breakage of bonds after particle breakage. The two can be neutralized to avoid re-aggregation of the new surface and increase the dispersion of the material. Therefore, the three grinding aids can improve the fluidity of the cement. The longer the hydroxyalkyl carbon chain is, the stronger the ability to adsorb with cement particles. Since the angles of repose of TEA, DEIPA and TIPA are getting smaller and smaller, it can be inferred that the ability to increase the fluidity of cement is: TEA < DEIPA < TIPA.
2.2 Influence on cement performance
TEA is already a mature early-strength agent, and research and production have proved that the strength of d1 and d3 is greatly increased, but the later d28 is lower than the blank, and the optimum dosage should not exceed 0.02%. . TIPA's research and application are reversed, with no increase in early strength, but can significantly increase the late strength of the milled cement, which can exceed 10%.
Li Guohua's experimental results show that under the same dosage, all three can improve the compressive strength of d1/d3, but the improvement ability is: TIPA<DEIPA<TEA, the highest TEA of d1 is 19.5%, the worst The TIPA increase is not obvious. D3 compression growth rate of up to 5%, the lowest 0.3%; while adding TEA d28, d90 compressive strength growth rate decreased, up to 5%; add DEIPA, TIPA d28, d90 compressive strength growth rate, both It is about 10%. Therefore, the strength increase ability of the three in the late stage is: TEA<DEIPA<TIPA is the highest. It can be seen that DEIPA is a good balance of grinding aids that can balance both early strength and late strength (both can exceed 10%). TEA and TIPA are better compatible with other additives. . This is of great significance for the practical application of DEIPA in grinding aids. Increasing the compressive strength of the whole age can increase the replacement of clinker, reduce the amount of clinker and increase the amount of mixed materials, which has great economic value.
TEA can form a soluble complex with Al3+ and Fe3+ in a highly alkaline solution, thereby promoting the initial hydration of the aluminate phase in the cement and accelerating the reaction between gypsum and aluminate. At the same time, the complexation of TEA The reaction reduces the concentration of Ca2+ and Al3+ in the liquid phase, further promotes the hydration of C3S, accelerates the formation of ettringite, accelerates the setting of cement slurry, and inhibits the hydration of C3S and β-C2S. This property is beneficial to the early stage of cement. The development of strength. However, the adsorption of TEA affects the full effect of TEA: when silicate hydrates to form CH in cement, TEA adsorbs to the surface of the crystal, preventing the complexation reaction of TEA. This makes TEA unable to show a late reinforcement effect on the cement. Compared with TEA, TIPA has the advantage of being highly dispersible and not easily adsorbed to the surface of crystals or particles, so it can not promote the hydration of cement minerals, so the early strength is not improved. However, Gartner et al. believe that TIPA can mainly complex with Fe3+ and promote the hydration of C4AF. This enhancement of TIPA Portland cement is due to the fact that TIPA can maintain a high concentration throughout the hydration process, thus enabling free sulfuric acid. After the calcium is fully hydrated, it forms iron. The TIPA complex further promotes the hydration of C4AF, so TIPA can increase the late strength of cement mortar. The transition zone theory of Perez et al. believes that TIPA does not improve the mechanical properties of hydrated Portland cement paste, but TIPA forms a complex between the slurry and aggregate interface, thus changing the properties of the interfacial transition zone (ITZ). According to Gartner et al., C4AF hydration produces a certain amount of iron ions (including similar aluminum ions), and will continue to form iron hydroxide gel, covering the surface of hydrated minerals to delay hydration; when TIPA is present, generate The iron ions can form a water-soluble complex with TIPA under high pH conditions, avoiding the enrichment of iron ions and causing the gel to cover the surface of the reactants and delay the hydration, so that TIPA promotes the ettringite orientation. The rate of conversion of low-sulfur calcium aluminate increases the subsequent hydration strength of the cement. When TIPA is present, more low sulfur type calcium aluminate (Afm) phase can be produced, which is the main reason for the increase of compressive strength of cement 28d.
The grinding aid containing TEA accelerates the hydration process of C3A to make the cement setting time slightly shorter; the grinding aid containing TIPA delays the setting time, and has a retarding effect at the initial stage of hydration, which improves the performance of the slurry.
There is no research or theory on the mechanism of DEIPA, and only experiments have shown that it can be enhanced.
From the above information, we can draw the following conclusions:
(1) TEA, TIPA and DEIPA are all good cement grinding aids, which have good grinding effect.
(2) TEA has excellent improvement of early strength, but it can not even weaken the late strength of cement; TIPA can not promote the early strength of cement, but can improve the characteristics of late strength; DEIPA has the advantages of both, for early strength And the late strength has been significantly improved.
(3) Due to the prevalence of chloride salt early strength agents and triisopropanolamine compared with triethanolamine, there are many advantages in terms of dispersibility, age enhancement, application conditions and relative cost, so the application is gradually increasing. , an increasingly widespread replacement of triethanolamine.
(4) Diethanol monoisopropanolamine has a strong advantage in strength of early strength and strength, and will replace triethanolamine and triisopropanolamine. At the same time, due to its low toxicity, DEIPA will not pollute the environment during use. It is in line with the development trend of low-carbon and environmental protection of cement grinding aids, and it is a new type of grinding aid for green environmental protection. In addition to its good compatibility with other additives, industrial applications will inevitably become more and more.
3 Development of three kinds of alcohol amine monomer cement grinding aids
As China's cement production capacity accounts for half of the world's production, the market for cement grinding aids is huge. Foreign well-known cement grinding aid companies such as Fosroc, Grace, Mapei and other companies have already entered China to share this market cake. They have strong technical strength, many independent intellectual property rights patents and many years of production and management experience, and comprehensive technical services, product coverage, professionalization and serialization, and have great technical and competitive advantages in the market. Although the domestic cement grinding aid enterprises are numerous in number, due to the low industry threshold, most of them do not have the technical strength they deserve. There is no independent research and development institution, but simple compounding, and product quality and technical support cannot Meet the needs of cement production companies. With the gradual compression of the profit margin of cement grinding aid enterprises, market competition is increasingly relying on product quality, technical service and cost performance, and more and more relying on grinding and grinding new product research and development, the domestic cement additives industry will face more and more The challenge. How to deal with the challenges, I believe that Chinese companies only need to increase investment in scientific research, and strive to develop and apply more at the forefront of technology. The two development directions should be worthy of attention.
(1) Research and application of modified triethanolamine and similar alternative products. Although DEIPA and TIPA have a tendency to replace TEA, due to TEA's long history of application and greater market supply, TEA's market share has been a long-standing market for a long time. Therefore, domestic enterprises should continue to increase the optimization of TEA and replace the research and development of alternative products, and develop new and efficient products, thereby reducing the multi-process and stable quality control of the compounding. Wang Bin and Zhao Jihui found that the modification of triethanolamine as cement grinding aid is better than triethanolamine. Due to the reduction of the relative amount of triethanolamine added by the same amount of other groups, the modified triethanolamine as a monomer has a great feasibility and considerable economic benefit in compounding an excellent cement grinding aid. However, we must be aware of the current challenges of ethanolamine products, that is, the toxicity of ethanolamine products. The “Emissions and Transfer Registration System” of developed countries in Europe and the United States has restricted the use of ethanolamine as a hazardous substance. Animal experiments and human clinical trials have shown that long-term repeated exposure to such products may cause liver and kidney damage. With the increasing awareness of environmental protection at home and abroad, the new alternative to TEA production