Chinese coal adsorbents: technologies and applications? 

I often hear that Chinese sorbents are just a cheap analogue, well, activated carbon and carbon. In reality, everything is much more interesting and complex. If you dig deep, it turns out that over the last ten years a whole industry has grown there with its own approaches, and not everything depends only on price. I’ll try to sort it out based on what I’ve encountered in practice.

Not just “activated carbon”: what is it really about?

When people say “Chinese coal adsorbents,” they usually mean products based on coal or coke. But here it is important to separate. There is classic granular activated carbon (GAC) for water or gas treatment, and there are, for example, molded carbon adsorbents for capturing organic vapors - this is a different story regarding technology. Many people get confused, hence some of the skepticism.

I personally observed how one of the enterprises in the Moscow region purchased a batch of Chinese GAU for wastewater treatment, expecting that it would quickly be exhausted. But in fact, its iodine capacity turned out to be even higher than that of the usual European one, although the mechanical strength was slightly lower. I had to adjust the regeneration modes - no worse, just different. This is to the question that the specifications need to be read carefully, and not just look at the country of origin.

Another nuance is raw materials. In China, local coals with a high volatile content are often used, which affects the pore structure. Therefore, their adsorbents can show phenomenal activity in some applications (say, for benzene) but average results in others (for some heavy metals). Generalizing is dangerous.

Activation technologies: steam versus chemistry

The main method, of course, is steam-gas activation. Chinese manufacturers have brought it to a high level of automation, which gives it a price advantage. But there is a subtlety: many large factories, especially in the provinces of Shanxi or Ningxia, combine it with pre-processing of raw materials. I saw a line where raw coal in front of the activation furnace goes through the stage of “compaction?” - I don’t know what to call it more precisely - which reduces the percentage of small items at the output.

Chemical activation (phosphoric acid, zinc chloride) is also used, but more often to obtain powder sorbents or specific brands. I heard from colleagues who worked withChengdu Yizhi Technology Co., that they focus on deep processing and can offer products with a given ratio of micropores and mesopores. This is no longer a mass market, but for a specific task. Their websiteyzkjhx.ruit is useful to dig specifically to understand the spectrum - it shows that this is not just trade, butdesign institutewith a registered capital of 120 million yuan, established by Huaxi Technology. Such structures are usually closer to R&D.

The problem we encountered: sometimes the documentation does not fully disclose exactly the activation method and the promoters used. This can backfire upon contact with certain environments, for example, high acidity. Once there was a story about washing out the remains of the activating agent in the first hours of work - we had to organize intensive washing on site. Now this is the first question for the supplier.

Key Applications: Where They're Really Strong

1.Flue gas cleaningfrom SO2, Hg (mercury) and fly ash. Here, Chinese developments are perhaps one of the most advanced in the world, and this is logical - environmental problems in the industrial regions of China stimulated R&D. Not just coals are used, but impregnated sorbents (with the addition of iodine and sulfur). I saw the operation of such a system at a thermal power plant - the efficiency of mercury capture was 98%, but the sorbent itself is quite specific and required special transportation conditions (low humidity).

2.Water treatment in the chemical industry. Here they often buy inexpensive brands of GAU for preliminary or final cleaning. Their advantage is predictability. I ordered 100 tons with certain characteristics and received exactly the same thing six months later. Quality control at large factories is now at the level. The downside mentioned above is sometimes the durability. For devices with a moving bed or frequent backwashing, you need to carefully select the brand.

3.VOC (Volatile Organic Compound) Vapor Capture

in coal adsorbers. Molded cylindrical or spherical carbon granules are often used here. Chinese manufacturers have learned to make them with a very high rate of adsorption of benzene, toluene, and xylene vapors. But there is a nuance regarding desorption: some brands give higher abrasion losses during steam regeneration than, say, their Japanese counterparts. This needs to be factored into the economics of the process.