Silica Gel Is in Urgent Need of Quality Improvement     
  
By Liu Hongzhang   

Silica gel is a silicon dioxide xerogel with a three-dimension network structure and cellularity. Silica gel' unique characteristics of controllable specific surface area and pore volume enables it to serve as important desiccant, sorbent, catalyst carrier and super thermal insulation material.

Production status   

The technology for the production of staple silica gel categories in China, mainly including spherical silica gel, lump silica gel and indicator silica gel, has matured with a large scale and advanced technology, and as a result, a large volume of silica gel products are exported overseas. And currently, its production capacity has reached 300 000 t/a, with annual output of 250 000 tons, while its export volume covers 70%-80% of the total output. The main enterprises are located in Shandong province, of which, the output of Qingdao Haiyang Chemical Co., Ltd. (Qingdao Haiyang Chemical) and Qingdao Makall Group Inc. rank first in China.
    According to the preparation methods and product pore structure, the silica gel is grouped into the following categories:
    a. silica gel type A, i.e. fine pored silica gel, with an average pore diameter of 2-3 nm, including spherical silica gel & lump silica gel;
    b. silica gel type C, i.e. silochrom, with average pore diameter of around 8 nm, mainly including spherical silica gel, particle spherical silica gel and lump silica gel;
    c. silica gel type B whose pore property is between type A and type C.
    Based on type A, type B and type C, the silica gel can also be processed into highly value-added indicator silica gel, FNG waterproof silica gel as well as silica gel for chromatography. Silica-alumina gel is a new category developed in recent years. Qingdao Haiyang Chemical produces two categories, specifically, HY-H & HY-W, with aluminum content of 3% and 17% respectively. The latter one is a waterproof silica gel. Silica-alumina particle spherical silica gel is also available in the market.
    Other highly value-added silica gel products are micron-sized silica gel and aerogel, which are used as beer stabilizer, coatings dulling agent, sheet film anti-sticking agent, powder mass anti-caking agent, liquid carrier, a pre-coating agent for heliographic paper, color inkjet printing paper and digital photo paper, etc. These highly valued-added products have already been developed in China, but their grade and quality still need to be improved.

The problems currently existing    

1. Blind expansion   

In recent years, China's growth in silica gel capacity has been increasing too fast. The blind expansion in capacity has resulted in the domestic output of silica gel far exceeding demand in the domestic market, and hence the competition is severe, especially after the government has canceled its export rebate and with the price increase in raw materials. So profits have decreased dramatically.

2. Heavy pollution    

With the dramatic price rise of raw materials, the use of mirabilite as raw material has become a key means for enterprises to decrease feedstock costs. However, it is not a wise option. Firstly, for the production of sodium silicate, causticity to kiln & boiler is worse although its costs in raw material are decreased. Secondly, the technique using mirabilite alkali will generate severe pollution, and its costs for pollution treatment are much greater than the increment of profit achieved. And thirdly, the volume of alkali mud generated is in bulk, which results in increased impurities, decreased quality and a lower price for export.
    Due to the weak enforcement of environmental law in some places and price competition among enterprises in China, the production technique using mirabilite continues despite repeated prohibition, which hampers the technical advancement of the sodium silicate industry, and hence highly value-added silica gel products are difficult to produce.

3. Lack of highly value-added products   

In the silica gel industry, highly value-added and high-tech products are abundant, such as silica gel for chromatography, micron-sized silica gel, aerogel, etc. Though these products are also produced in China, their quality awaits improvement.
    For example, ethylene polymerization catalyst silica gel as catalyst carrier which is under research and produced by Sinopec Beijing Research Institute of Chemical Industry (BRICI), Qingdao Haiyang Chemical Co., Ltd. and Tianjin Research & Design Institute of Chemical Industry (TRICI) with an annual output only 100-200 tons currently, confronted with challenges and fierce competition from the catalyst silica gel catalyst carrier of multinational companies.
    The micron-sized silica gel and aerogel also face a similar problem. Up to now, the production history of silica gel used as beer stabilizer has been 10 years in China, but owing to a big gap in quality between the domestic products and those imported; they can be used only by some small-scale beer producers. It is the same with dulling agent, color inkjet printing paper and digital photo paper pre-coating agent; that is, their production is available in China, but their quality level is just equivalent to that of some multinational enterprises in the 1980s.