Aerogel performance is mainly determined by the nano hole structure, usually by sol-gel process to obtain nano holes required and the corresponding gel skeleton, due to the gel exist within the frame of solvent, surface tension, in ordinary dry conditions can cause skeleton to collapse, aerogel preparation technology of the core is to avoid in the process of drying nanometer hole structure collapse caused by capillary force.

According to the difference of drying process, it can be divided into two kinds: supercritical drying process and atmospheric pressure drying process, and vacuum freezing drying and subcritical drying are other technologies that have not been realized in batch production.

Supercritical drying technology is the first to realize mass production of aerogel technology, which has been relatively mature, and it is also the most widely adopted technology in domestic and foreign aerogel enterprises at present. The purpose of supercritical drying is to control the pressure and temperature so that the solvent reaches its own critical point in the drying process, forming a supercritical fluid. At present, the technology of batch production has been adopted carbon dioxide as the drying medium.

Atmospheric drying a new kind of aerogel preparation technology, which is the most active in current research and has the greatest development potential. The principle is to use hydrophobic groups to modify the gel skeleton, avoid the silicon-hydroxyl group on the surface of the gel holes to combine with each other and improve the elasticity. At the same time, low surface tension liquid is adopted to replace the water or ethanol with the original high specific surface area of the gel, so as to directly dry the aerogel materials with excellent performance under atmospheric pressure.

The following is a brief analysis and comparison of two technical routes:

Equipment: supercritical drying technology using core equipment for the autoclave, the general working pressure as high as 7 ~ 20 mpa, belongs to the special equipment of pressure vessel, complex equipment system, operation and maintenance costs are high, the current domestic existing can provide complete preparation of supercritical equipment manufacturers, but the number is not much, the owner's bargaining power is weak. The normal atmospheric drying technology adopts the normal atmospheric pressure equipment. Compared with supercritical drying, due to the absence of high pressure conditions, low equipment input and simple equipment system, most chemical equipment units can process and manufacture, and the owner has strong bargaining power.

Production cost: production cost of aerogel is mainly concentrated in silicon source, equipment depreciation and energy consumption. Silicon sources mainly include water glass and organic silicon. Organosilicon is relatively expensive, but with high purity and good process adaptability. It can be applied to both supercritical drying process and normal pressure drying process. At present, enterprises adopting supercritical drying process at home and abroad basically adopt organosilicon source. Water glass is low in price, but there are many impurities, and the process of removing impurities is complicated. In terms of equipment depreciation, due to high investment in supercritical drying equipment, the depreciation should be higher than normal pressure technology. In terms of energy consumption, the supercritical drying system consumes more electricity than the atmospheric pressure drying system. Therefore, generally speaking, the production cost of atmospheric drying technology is lower than that of supercritical drying.

Product performance: as far as silica dioxide aerogel is concerned, there is no significant or substantial difference between the current supercritical drying technology and the atmospheric pressure drying technology in the production of products. Basically, the supercritical technology can reach the technical indicators, and the atmospheric pressure drying technology can achieve both. In the preparation of non-silica aerogel, the supercritical drying process is much more mature, but has not been reported in mass production.

Technical threshold: contrast, supercritical drying technology of the production efficiency, safety, and process changes are dependent on the equipment system has higher, if equipment manufacturers to provide equipment system is relatively mature and reliable, the owner into the technical threshold is relatively low, it is also a lot of aerogel industry new entrants choose supercritical technology one of the reasons, but also are more constrained. The investment threshold of atmospheric pressure drying technology equipment is relatively low, but the technical threshold is relatively high, which has high requirements on the design of formula and process combination optimization. If the technology fails, not only the production cost may be higher than supercritical, but even the performance index cannot meet the requirements.

Room: as high pressure supercritical drying special equipment, if you want to expand the scale of production, fixed asset investment is huge, aerogel future if you want to meet the huge market of building insulation, such as the annual output of 500000 cubic meters (it is only at the current size of the small and medium-sized enterprise building materials), supercritical drying technology of equipment investment will be billions, very bad for aerogel enterprises bigger and stronger. However, with the expansion of scale, the input-output ratio will be further improved, and a larger production scale can be obtained with less investment, so it can better adapt to the needs of future large-scale production. In addition, limited by silicon source, the space of reducing raw material cost of supercritical is limited, which can only improve production efficiency by optimizing the system. However, atmospheric pressure drying has strong receptivity to cheap silicon source, and there are more degrees of freedom in process optimization, so there is more room for cost reduction.

Based on the above analysis, the author thinks that both supercritical drying technology and atmospheric pressure drying technology have advantages and rationality. However, just like the competition between plasma technology and liquid crystal technology in the field of display in the past, the two technologies were once close to each other. Till now, liquid crystal technology has won out completely. With the passage of time, the author believes that atmospheric pressure drying technology will finally win a landslide victory in the preparation and production of silica aerogel. Articles come from the Internet

Aerogel equipment