Views: 4 Author: Site Editor Publish Time: 2022-09-09 Origin: Site
According to incomplete statistics, the current global production of non-ionic cellulose ether has reached more than 500,000 tons, and hydroxypropyl methyl cellulose accounted for 80% to more than 400,000 tons, China in recent two years a number of companies have expanded production to rapidly expand the capacity has reached about 180 000 tons, about 60 000 tons for domestic consumption, Of this, more than 550 million tons are used in industry and about 70 per cent are used as building additives.
Due to the different uses of the products, the ash index requirements of the products can also be different, so that the production can be organized according to the requirements of different models in the production process, which is conducive to the effect of energy saving, consumption reduction and emission reduction.
1 hydroxypropyl methyl cellulose ash and its existing forms
Hydroxypropyl methylcellulose (HPMC) is called ash by industry quality standards and sulphate or hot residue by pharmacopoeia, which can be simply understood as an inorganic salt impurity in the product. The main production process by the strong alkali (sodium hydroxide) through the reaction to the final adjustment of pH to neutral salt and raw materials originally inherent in the sum of inorganic salt.
Method for determination of total ash; After a certain amount of samples are carbonized and burned in a high temperature furnace, the organic substances are oxidized and decomposed, escaping in the form of carbon dioxide, nitrogen oxides and water, while the inorganic substances remain in the form of sulfate, phosphate, carbonate, chloride and other inorganic salts and metal oxides. These residues are ash. The amount of total ash in the sample can be calculated by weighing the residue.
According to the process using different acids and will produce different salts: mainly sodium chloride (generated by the reaction of chloride ions in chloromethane and sodium hydroxide) plus other acids neutralization can produce sodium acetate, sodium sulfide or sodium oxalate.
2. Ash requirements of industrial grade hydroxypropyl methyl cellulose
Hydroxypropyl methyl cellulose is mainly used as thickening, emulsification, film forming, protective colloid, water retention, adhesion, anti-enzyme and metabolic inert and other uses, it is widely used in many fields of industry, which can be roughly divided into the following aspects:
(1) Construction: the main role is water retention, thickening, viscosity, lubrication, flow aid to improve cement and gypsum machinability, pumping. Architectural coatings, latex coatings are mainly used as protective colloid, film forming, thickening agent and pigment suspension aid.
(2) Polyvinyl chloride: mainly used as dispersant in the polymerization reaction of suspension polymerization system.
(3) daily chemicals: mainly used as protective supplies, it can improve the product emulsification, anti-enzyme, dispersion, adhesion, surface activity, film formation, moisturizing, foaming, forming, release agent, softener, lubricant and other properties;
(4) Pharmaceutical industry: in the pharmaceutical industry is mainly used for preparation production, used as solid preparation of coating agent, hollow capsule material, binder, used for slow release pharmaceutical skeleton, film forming, pore-forming agent, used as liquid, semi-solid preparation thickening, emulsification, suspension, matrix application;
(5) Ceramics: used as a binder forming agent for ceramic industry billet, dispersing agent for glaze color;
(6) paper making: dispersion, coloring, strengthening agent;
(7) Textile printing and dyeing: cloth pulp, color, color extender:
(8) Agricultural production: in agriculture, it can be used to treat crop seeds, improve germination rate, protect moisture and prevent mildew, keep fruit fresh, slow release agent of chemical fertilizers and pesticides, etc.
According to the feedback of the above long-term application experience and the summary of the internal control standards of some foreign and domestic enterprises, only some products of polyvinyl chloride polymerization and daily chemicals are required to control the salt less than 0.010, and the pharmacopoeia of various countries requires to control the salt less than 0.015. And other uses of salt control can be relatively wider, especially construction products in addition to the production of putty, paint salt has certain requirements, the rest can control the salt < 0.05 can basically meet the use.
3 hydroxypropyl methyl cellulose process and salt removal method
The main production methods of hydroxypropyl methyl cellulose at home and abroad are as follows:
(1) Liquid phase method (slurry method) : the fine powder of cellulose to be crushed is dispersed in about 10 times organic solvent in a vertical or horizontal reactor with strong agitation, and then quantitative lye and etherifying agent are added for reaction. After the reaction, the product was washed, dried, crushed and sieved with hot water.
(2) Gas-phase method (gas-solid method) : The reaction of cellulose powder about to be crushed is completed in the semi-dry state by directly adding quantitative lye and etherifying agent and a small amount of low boiling point by-products in a horizontal reactor with strong agitation. No additional organic solvents are required for the reaction. After the reaction, the product was washed, dried, crushed and sieved with hot water.
(3) Homogeneous method (dissolution method) : The horizontal can be added directly after crushing of cellulose with a strong stirring reactor scattered in naoh/urea (or other solvents of cellulose) about 5 ~ 8 times of water freezing solvent in solvent, then adding quantitative lye and etherifying agent on reaction, after the reaction with acetone precipitation reaction good cellulose ether, It is then washed in hot water, dried, crushed and sieved to get the finished product. (It is not yet in industrial production).
The reaction end no matter use which kinds of methods mentioned above have a lot of salt, according to different process can produce are: sodium chloride and sodium acetate, sodium sulfide, sodium oxalate, and so on mix salt, need through the desalination, the use of salt in the water solubility, generally with plenty of hot water washing, now the main equipment and way of washing are:
(1) belt vacuum filter; It does this by slurping the finished raw material with hot water and then washing the salt by spreading the slurry evenly over a filter belt by spraying hot water on it and vacuuming it below.
(2) Horizontal centrifuge: it by the end of the reaction of the crude material into the slurry with hot water to dilute the salt dissolved in hot water and then through centrifugation separation will be liquid-solid separation to remove salt.
(3) with the pressure filter, it by the end of the reaction of the crude material into the slurry with hot water, it into the pressure filter, first with steam blown water and then with hot water spray N times with steam blown water to separate and remove salt.
Hot water washing to remove dissolved salts, because need to join the hot water, washing, the more the more the lower the ash content, and vice versa, so its ash is directly related to how much the amount of hot water, the general industrial product if ash control under 1% USES hot water 10 tons, if control under 5% will need about 6 tons of hot water.
Cellulose ether waste water has a chemical oxygen demand (COD) of more than 60 000 mg/L and a salt content of more than 30 000 mg/L, so it is very expensive to treat such waste water, because it is difficult to directly biochemical such high salt, and it is not allowed to dilute according to the current national environmental protection requirements. The ultimate solution is to remove salt by distillation. Therefore, one ton more boiling water washing will generate one ton more sewage. According to the current MUR technology with high energy efficiency, the comprehensive cost of each ton of washing concentrated water is about 80 yuan, and the main cost is the comprehensive energy consumption.
Effect of 4 ash on water retention rate of industrial hydroxypropyl methyl cellulose
HPMC mainly plays three roles in water retention, thickening and construction convenience in building materials.
Water retention: to increase the opening time of the material water retention, to assist its hydration function fully.
Thickening: Cellulose can be thickened to play a suspension, so that the solution to maintain uniform up and down the same role, resistance to flow hanging.
Construction: Cellulose lubrication, can have a good construction. HPMC does not participate in how the chemical reaction, only plays an auxiliary role. One of the most important is water retention, the water retention of mortar affects the homogenization of mortar, and then affects the mechanical properties and durability of hardened mortar. Masonry mortar and plaster mortar are two important parts of mortar materials, and the important application field of masonry mortar and plaster mortar is masonry structure. As a block in the application in the process of the products is in the dry state, in order to reduce the dry block of strong water absorption of mortar, construction adopts the block before prewetting, to block certain moisture content, keep moisture in the mortar to block material excessive absorption, can maintain normal hydration internal gelling material such as cement mortar. However, factors such as block type difference and site pre-wetting degree will affect the water loss rate and water loss of mortar, which will bring hidden dangers to the overall quality of masonry structure. The mortar with excellent water retention can eliminate the influence of block materials and human factors, and ensure the homogeneity of mortar.
The effect of water retention on mortar hardening performance is mainly reflected in the effect on the interface area between mortar and block. With the rapid water loss of mortar with poor water retention, the water content of mortar at the interface part is obviously insufficient, and the cement cannot be fully hydrated, which affects the normal development of strength. The bond strength of cement-based materials is mainly produced by the anchorage of cement hydration products. The insufficient cement hydration in the interface area reduces the interface bond strength, and the hollow bulging and cracking of mortar increase.
Therefore, choosing the most sensitive to water retention requirement building K brand three batches of different viscosity, through different ways of washing to appear the same batch number two expected ash content, and then according to the current common water retention test method (filter paper method) on the same batch number different ash content of the water retention of three groups of samples the specific as follows:
4.1 Experimental method for detecting water retention rate (filter paper method)
4.1.1 Application of instruments and equipment
Cement slurry mixer, measuring cylinder, balance, stopwatch, stainless steel container, spoon, stainless steel ring die (inner diameter φ100 mm× outer diameter φ110 mm× high 25 mm, fast filter paper, slow filter paper, glass plate.
4.1.2 Materials and reagents
Ordinary Portland CEMENT (425#), STANDARD SAND (SAND WITHOUT MUD WASHED BY WATER), PRODUCT SAMPLE (HPMC), CLEAN WATER FOR EXPERIMENT (TAP WATER, MINERAL WATER).
4.1.3 Experimental analysis conditions
Laboratory temperature: 23±2 ℃; Relative humidity: ≥ 50%; The laboratory water temperature is the same as room temperature 23 ℃.
4.1.4 Experimental methods
Put the glass plate on the operating platform, put the weighed chronic filter paper (weight: M1) on it, then put a piece of fast filter paper on the slow filter paper, and then put a metal ring mold on the fast filter paper (the ring mold shall not exceed the circular fast filter paper).
Accurately weigh (425#) cement 90 g; Standard sand 210 g; Product (sample) 0.125g; Pour into stainless steel container and mix well (dry mix).
Use cement mixer (mixing pot and leaves are clean and dry, thoroughly clean and dry after each experiment, set aside). Use a measuring cylinder to measure 72 ml of clean water (23 ℃), first pour into the stirring pot, and then pour the prepared material, infiltrate for 30 s; At the same time, raise the pot to the mixing position, start the mixer, and stir at low speed (i.e., slow stirring) for 60 s; Stop for 15 s and scrape the slurry on the wall and blade into the pot; Continue to whisk quickly for 120 s to stop. Pour (load) all the mixed mortar into the stainless steel ring mold quickly, and time from the moment when the mortar touches the fast filter paper (press the stopwatch). After 2 min, the ring mold was turned over and the chronic filter paper was taken out and weighed (weight: M2). Do blank experiment according to the above method (the weight of chronic filter paper before and after weighing is M3, M4)
The calculation method is as follows:
Where, M1 -- the weight of the chronic filter paper before the sample experiment; M2 -- weight of chronic filter paper after sample experiment; M3 -- weight of chronic filter paper before blank experiment; M4 -- weight of chronic filter paper after blank experiment.
(1) the clean water temperature must be 23 ℃, and the weighing must be accurate;
(2) after stirring, remove the stirring pot and stir evenly with a spoon;
(3) the mold should be installed quickly, and the mortar will be tamped flat and solid while installing;
(4) Be sure to time the moment when the mortar touches the fast filter paper, and do not pour the mortar on the external filter paper.
4.2 the sample
Three batch numbers with different viscosities of the same K brand were selected as: 201302028 viscosity 75 000 mPa·s, 20130233 viscosity 150 000 mPa·s, 20130236 viscosity 200 000 mPa·s through different washing to obtain the same batch number of two different ash (see Table 3.1). Strictly control the moisture and pH of the same batch of samples as much as possible, and then carry out the water retention rate test according to the above method (filter paper method).
4.3 Experimental Results
The index analysis results of the three batches of samples are shown in Table 1, the test results of water retention rates of different viscosities are shown in Figure 1, and the test results of water retention rates of different ash and pH are shown in Figure 2.
(1) The index analysis results of the three batches of samples are shown in Table 1
Table 1 Analysis results of three batches of samples
Water / %
(2) The water retention test results of the three batches of samples with different viscosities are shown in Figure 1.
FIG. 1 Test results of water retention of three batches of samples with different viscosities
(3) Water retention rate detection results of three batches of samples with different ash content and pH are shown in Figure 2.
FIG. 2 Detection results of water retention rate of three batches of samples with different ash content and pH
Through the above experimental results, the influence of water retention rate mainly comes from viscosity, high viscosity relative to its high water retention rate will be poor on the contrary. The fluctuation of ash content in the range of 1%~5% almost does not affect its water retention rate, so it will not affect its water retention performance.
In order to make the standard more applicable to reality and conform to the increasingly severe trend of energy conservation and environmental protection, it is suggested that:
The industrial standard of industrial hydroxypropyl methyl cellulose is formulated in the ash control by grades, such as: level 1 control ash < 0.010, level 2 control ash < 0.050. In this way, the producer can choose to let the user also have more choices. At the same time, the price can be set based on the principle of high quality and high price to prevent the confusion of the market. The most important thing is that energy conservation and environmental protection make the production of products more friendly and harmonious with the environment.