Preparation method of starch sulfate and application of starch sulfate as cement additive

Abstract

The invention relates to a preparation method of starch sulfate and application of the starch sulfate as a cement additive. The invention relates to the technical field of fine chemical engineering and concrete admixtures. For the first time, the starch sulfate is prepared by taking sodium hydrogen sulfate or sulfuric acid or a composition aqueous solution of sodium hydrogen sulfate and sulfuric acid as a sulfonating agent by a semi-dry method, and synthesis raw materials comprise starch, the sulfonating agent and an inorganic alkali. The synthesis process comprises the following steps: preparing the sulfonating agent; mixing the sulfonating agent with the starch; heating and esterifying the mixture; and performing esterification product base neutralization. The method disclosed by the invention is different from a method for preparing the starch sulfate by taking concentrated sulfuric acid, chlorosulfonic acid, sulfur trioxide and the like as sulfonating agents in the prior art; the method has the advantages of simple preparation process, no emission of three wastes, low raw material cost, low equipment requirements and the like. The product prepared by the invention can be directly used as a super-retarding superplasticizer or retarder, and has the advantages of high water reducing rate, good retarding effect, strong cohesiveness, bleeding resistance, segregation resistance and the like; and if the starch sulfate is compounded with polycarboxylate superplasticizers and the like, an obvious synergistic effect can be generated.

Description

technical field [0001] The invention relates to the technical fields of fine chemicals and concrete admixtures, in particular to a preparation method of starch sulfate and its use as a cement admixture. Background technique [0002] Starch sulfate, also known as sulfonated starch, is the introduction of sulfonic acid groups (-SO 3 H) and a starch derivative prepared. Starch sulfate has a variety of characteristics different from other modified starches, and has good applications in many fields, especially in food, medicine and concrete admixtures. [0003] Water reducer is a concrete admixture, one of its main functions is to improve the fluidity of concrete while keeping the water-binder ratio and water consumption unchanged, so as to meet the transportation and distribution requirements of ready-mixed concrete in various projects . The high-performance water reducers used in my country's water reducer market are mainly polycarboxylate water reducers. This type of water...

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Problems solved by technology

However, this type of water reducer also has the following disadvantages in the process of use: (1) The prepared ready-mixed concrete is very sensitive to water consumption. Usually, a slight increase in the water content will cause serious bleeding of the concrete, and it is very easy to appear stones. Bad phenomena of stacking and bottoming

A high content of mud in the aggregate will absorb more polycarboxylate water-reducing agents, resulting in reduced water-reducing dispersion performance of such water-reducers and poor slump retention effect; and in this case, increasing the polycarboxylate water-reducing agent The amount of additives is usually not obvious for improving the fluidity of concrete. In many cases, the fluidity has not met the requirements and the concrete has begun to bleed.

(4) Used in combination with other traditional water reducing agents, no superimposed effect

(2) Enhance cohesion, inhibit segregation and bleeding: One of the main shortcomings of polycarboxylate water reducers is that the cohesion of ready-mixed concrete is poor, and segregation and bleeding are prone to occur.

This method has many disadvantages: the one, the strong corrosivity of chlorosulfonic acid or hypertoxicity, have high requirement to production process or equipment

The second is that a large amount of chloride ions will be introduced into the synthetic crude product. If it is not purified, it will cause corrosion of the steel bars in the concrete; if it is purified, it will lead to an increase in product cost.

Third, the price of chlorosulfonic acid itself is high, and it is difficult to recycle the unreacted part

Fourth, the recycling of organic solvents is also a problem

The piperidine or pyridine used in the method are expensive and toxic, and the recovery of solvent dimethyl sulfoxide or pyridine is difficult

(4) take urea-sulfuric acid as sulfonating agent (CN109306021A), adopt dry method and solvent method to prepare starch sulfate water-reducer, the main deficiency of this method one is that a large amount of heat that produces in the reaction process is difficult to control, has increased industrialization cost and difficulty; the second is that a large amount of sulfate by-products are produced in the product, especially the high content of sodium sulfate, which is easy to precipitate and crystallize from the aqueous solution in cold seasons, resulting in blocked pipes in pumping of ready-mixed concrete; third, the urea in the reaction system cannot recycling, increased cost

Although the maximum degree of substitution of the product sulfonic acid group has been improved in this method, the cost of the sulfonating agent and solvent used is relatively expensive, and the pyridine used is also highly toxic, so it is difficult to have industrialization potential

[0007] In conclusion, although there are patents and literature reports on the preparation of starch sulfate and its use as a water reducer, no industrialized commercial product has come out.

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