The detection standards of activated carbon can be roughly divided into two parts: domestic standards and foreign standards.
Domestic standards include “Test Methods for Coal-Based Activated Carbon” and “Test Methods for Wood-Based Activated Carbon”. The coal-based carbon standards adopted include the 1987 standard (old standard) and the 2008 standard (new standard). The standards for wood-based charcoal also include the 1990 standard and the 1999 standard, and the new 2015 standard is also added.
Foreign standards include the US ASTM, the US ANSI/AWWA, the Japanese JIS, the Japanese JWWA, the French NF EN standard, the Korean KSM standard, etc. The most common foreign standards in China are the American ASTM and the Japanese JIS. The detection items of foreign activated carbon are different from those in China, and different foreign standards have different focuses on their detection items.
Different detection standards will detect different indicator values. Therefore, in trading applications, in addition to paying attention to the indicator values, we must also unify the standards. Let’s take a look at the meaning of various indicators of activated carbon.
Activated carbon adsorption capacity index
1. Iodine adsorption value
Refers to the amount of iodine absorbed by each gram of activated carbon when the residual (equilibrium) concentration of iodine in the solution is 0.02N/L. The unit of iodine value is mg/g. The diameter of iodine molecule is only 0.335nm, so iodine value is mainly used to characterize the degree of development of activated carbon micropores and the adsorption capacity of activated carbon for small molecules.
Standard distinction: Iodine value is the indicator that is most likely to cause disputes. The iodine value test results of coal-based carbon national standard, wood-based carbon national standard, American standard, and Japanese standard are different. Among them, the iodine value test results of coal-based carbon 2008 national standard and American standard ASTM are consistent.
2. Methylene blue value
Refers to the number of milligrams of methylene blue absorbed when 1.0g carbon reaches equilibrium with 1.0mg/L methylene blue solution. Common units are mg/g and ml/0.1g.
The molecular diameter of methylene blue is larger than that of iodine molecule, and the methylene blue value is usually used to characterize the number of pores in activated carbon. In practical applications, the methylene blue value is often used to represent the decolorization ability of activated carbon. The higher the methylene blue value, the better the decolorization is usually under the same unit weight.
Standard distinction: Coal-based activated carbon usually uses mg/g as the unit for detecting methylene blue, and wood-based activated carbon uses ml/0.1g.
3. Caramel decolorization rate
Refers to the decolorization ability of activated carbon on caramel test solution. Caramel decolorization rate is usually used to evaluate the decolorization ability of sugar-based activated carbon on sugar solution. Caramel decolorization rate characterizes the degree of macropore development of activated carbon. In practical applications, usually only wood powder charcoal will be tested for caramel decolorization rate, and other materials of charcoal rarely test caramel decolorization rate indicators.
In the actual application process, most people will have such a misunderstanding that the higher the adsorption index of activated carbon, the better it will be; the higher the price, the better it will be. In fact, the adsorption index of activated carbon is only used to measure the adsorption capacity of this type of carbon for a specific substance, and cannot represent its adsorption capacity for all substances. According to the specific application situation, we should still conduct corresponding selection tests to select suitable and cost-effective activated carbon products.
