在凝胶干燥前，凝胶网络结构中充满了液体溶剂，随着干凝胶燥的进行，溶剂有部分挥发后，液体在凝胶网络的毛细孔中开始形成弯月面，产生附加压力。凝胶毛细孔的尺寸一般在1-100nm，若凝胶毛细孔的半径为20nm，当其中存在着乙醇液体时，理论计算所承受的压力约为3.2MPa。由液体表面张力形成的这样强烈的毛细管收缩力使毛细管孔径进一步变小，附加压力就进一步变大，这样就使粒子进一步靠近、聚集和收缩，使凝胶网络结构坍塌。
因此采用常规的干燥过程很难阻止凝胶的收缩和碎裂，只能得到碎裂、干硬、大尺度的多孔干凝胶。加入表面活性剂会引入杂质，目前消除液体表面张力对凝胶破坏作用的有效方法是在超临界流体条件下驱除凝胶孔隙中的液体即超临界干燥。
在超临界状态下的流体，气-液界面消失，表面张力不复存在，此时凝胶毛细孔中就不存在由表面张力产生的附加压力，因此在超临界流体条件下的干燥，就可以保持凝胶原先的分散结构，从而可以避免常温干燥和烘烤干燥等常规干燥技术在干燥过程中由于强烈的毛细管收缩作用造成的物料或纳米粒子的团聚和凝并，防止材料基础粒子变粗，比表面急剧下降以及孔隙大量减少等后果。
主要技术参数
凝胶干燥器：2L/30MPa，室温-85℃
分离器：1L/20MPa，85℃
制冷系统：:3100kcal/h，风冷水循环
储 罐：2L/16MPa
高压输送泵：50L/40MPa
变 频 器：2.2kW
流 量 计： 6.3L-63L/h
总 功 率：8kW
气源系统：
一般采用CO2为干燥介质，该系统为用户自备，若非国内气瓶供应或非气瓶直接供应，则需提供气源接入口规格尺寸，以便本装置接入系统正常运行。
制冷系统：
该系统为气源液化系统，在超临界干燥临界置换过程中，提供液态气源。风冷水循环，核心部件进口，保证装置制冷需要的稳定供应。
高压输送泵：
选用高压柱塞CO2泵作为动力源，确保干燥介质的稳定输送，泵头采用特殊材料，可对试验各阶段流体量的需求适时调节。常压～40MPa，50L/h。
流量计量系统：
采用气体质量流量计结合流量数显仪表对管路中的CO2气体进行计量，计量精度达到1%F.S.。
温度控制系统：
恒温水浴控温，热量充足，控温稳定，常温-90℃。
压力控制系统：
采用进口TESCOM精密背压调节阀进行控制。入口压力：≤32MPa
干燥反应釜：
容积2L，内部精密打磨处理，设计压力30MPa，室温-85℃，内部带有测温，外部设计保温隔热装置。干燥器的长径比根据凝胶样品制作的特殊性进行单独设计：为提高干燥装置的适用范围，满足不同干燥介质进行样品处理的要求，干燥器设计温度和压力均比较高，可在很大范围内对样品制作条件进行调节。
分离器：
分离装置是气液分离的主要场所，大部分液体在此得到有效回收，回收液收集后可再度循环利用，气体则通过上部的出口进入下一环节。分离容积：1L，分离压力：20MPa
安全保护装置：
高压泵出口配电接点压力表、设定工作压力、超压自动停泵保护。干燥反应釜、分离器、根据相应压力，分别配安全阀，超压自动泄压。
电气控制及箱体支架：
采用工业铝型材制作，人机操作环境，布置得体，与现代实验室搭配和谐。
Before gel drying, the gel network structure was filled with liquid solvent. With the progress of gel drying, after the solvent was partially volatilized, the liquid began to form meniscus in the pores of the gel network, resulting in additional pressure. Generally, the size of gel capillary is 1-100nm. If the radius of gel capillary is 20nm, when there is ethanol liquid in it, the theoretical calculation pressure is about 3.2MPa. Such a strong capillary contraction force formed by liquid surface tension further reduces the capillary pore size and increases the additional pressure, which makes the particles closer, gather and contract, and causes the gel network structure to collapse.
Therefore, it is difficult to prevent the shrinkage and fragmentation of the gel by using the conventional drying process, and only a fragmented, hard and large-scale porous xerogel can be obtained. Adding surfactant will introduce impurities. At present, the effective method to eliminate the damage of liquid surface tension on gel is to drive out the liquid in the gel pores under the condition of supercritical fluid, that is, supercritical drying.
In supercritical fluid, the gas-liquid interface disappears, and the surface tension disappears. At this time, there is no additional pressure generated by the surface tension in the capillary pores of the gel. Therefore, the original dispersion structure of the gel can be maintained by drying under supercritical fluid conditions, thus avoiding the agglomeration and coagulation of materials or nanoparticles caused by strong capillary contraction during the drying process by conventional drying techniques such as normal temperature drying and baking drying, and preventing the basic particles of the material from becoming coarse, the specific surface rapidly decreasing and the pores greatly decreasing.
Main technical parameters
Gel dryer: 2L/30MPa, room temperature -85℃
Separator: 1L/20MPa, 85℃
Refrigeration system:: 3100kcal/h, air and cold water circulation.
Tank: 2L/16MPa
High pressure delivery pump: 50L/40MPa.
Frequency converter: 2.2kW
Flowmeter: 6.3L-63L/h
Total work rate: 8kW
Air supply system:
Generally, CO2 is used as the drying medium, and the system is provided by the user. If it is not supplied by domestic gas cylinders or directly by non-gas cylinders, the specification and size of the gas source access port shall be provided for the normal operation of the device access system.
Refrigeration system:
The system is a gas source liquefaction system, which provides a liquid gas source during the critical displacement of supercritical drying. Air-cooling water circulation and the import of core components ensure the stable supply of refrigeration needs of the device.
High pressure delivery pump:
High-pressure plunger CO2 pump is selected as the power source to ensure the stable transportation of drying medium, and the pump head is made of special materials, which can adjust the demand of fluid volume in each stage of the test in time. Atmospheric pressure ~ ～40MPa, 50 l/h.
Flow metering system:
The CO2 gas in the pipeline is measured by gas mass flowmeter combined with flow digital display instrument, and the measurement accuracy reaches 1% F.S..
Temperature control system:
Constant temperature water bath temperature control, sufficient heat, stable temperature control, normal temperature -90℃.
Pressure control system:
Imported TESCOM precision back pressure regulating valve is used for control. Inlet pressure: ≤32MPa
Drying reactor:
The volume is 2L, the internal precision grinding treatment, the design pressure is 30MPa, the room temperature is -85℃, the internal temperature is measured, and the external thermal insulation device is designed. The length-diameter ratio of the dryer is designed separately according to the particularity of gel sample preparation: in order to improve the application scope of the drying device and meet the requirements of sample treatment with different drying media, the design temperature and pressure of the dryer are relatively high, and the sample preparation conditions can be adjusted in a large range.
Separator:
The separation device is the main place for gas-liquid separation, where most of the liquid is effectively recovered, and the recovered liquid can be recycled again after collection, and the gas enters the next link through the upper outlet. Separation volume: 1L, separation pressure: 20MPa.
Safety protection device:
High-pressure pump outlet distribution contact pressure gauge, set working pressure, overpressure automatic pump stop protection. The drying reaction kettle and separator are respectively equipped with safety valves according to the corresponding pressures, and the overpressure can be automatically relieved.
Electrical control and box support:
It is made of industrial aluminum profiles, with man-machine operating environment, proper layout and harmonious collocation with modern laboratories.
南通立凯机电工程有限公司专业设计、制造、销售超临界流体设备和石油科研仪器。产品主要包括：
超临界二氧化碳萃取设备、超临界气凝胶干燥设备、超临界细微粒子制备装置、超临界清洗发泡装置、超临界抗溶剂结晶装置、高温高压磁搅拌反应装置、超临界相平衡仪等。
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