Foreword
Particulate matter and gas are two kinds of pollutants in the air. Particulate matter can be filtered out by using separate air filter media, such as melt-blown non-woven fabric, glass fiber, PTFE, etc. However, chemical gases need to be filtered by using substances with strong adsorption capacity. At present, commonly used adsorption materials mainly include activated carbon, activated alumina, zeolite, molecular sieve, ionic resin, etc.
Among them, the carbon fiber cloth made of activated carbon and non-woven fabrics by a specific production process. It can adsorb benzene, formaldehyde, sulfur dioxide, sulfur and hydrogen compounds, ammonia and other polluted gases, and can also filter particles in the air.
Characteristics of carbon fiber cloth
1) Carbon fiber cloth does not use the traditional columnar granular carbon, but uses crushed small granular carbon, which increases the total surface area of carbon particles while not increasing the carbon content, thus greatly improving its filtration efficiency and adsorption capacity for chemical gases.
2) Because the small particles of carbon are evenly distributed in the non-woven fabric and the gap is large enough, the resistance to air flow of carbon fiber cloth is small enough. Low differential pressure means lower energy consumption of the finished filter when it is used at the same air volume.
3) Easy processing and molding, high strength.
4) The service life is long, but it will be sour after long-term use.
Applications of carbon fiber cloth
Carbon fiber cloth is widely used in the following fields.
1) Air purifiers, such as household air purifier filter, vehicle purifier filter, national air purifier filter, oil smoke purifier filter, movable fresh air purifier filter and industrial waste gas purifier, etc. The author has a purifier at home, including a thick activated carbon filter, which is turned on whenever there is an odor in the home, and the effect is good.
2) Air conditioning, such as automobile air conditioning filter, household air conditioning filter, air conditioning system filter, air conditioning unit filter, etc. At present, there are few carbon fiber cloth used in ordinary household air conditioners, but there are still many filter elements used in automotive air conditioners.
3) Vacuum cleaners, such as dust industrial vacuum cleaner filter, industrial dust collector filter, mini household intelligent sweeper filter, vehicle-mounted handheld vacuum cleaner filter, wet and dry vacuum cleaner filter, etc. Most of the filter screens of vacuum cleaners we see in our life can't use carbon fiber cloth. At present, it's only necessary to filter particulate matter with a certain effect.
4) Fresh air fans, such as: mobile fresh air purifier filter, fresh air constant temperature constant oxygen air purifier filter, whole house intelligent oxygen fresh air purifier filter, HVAC duct air cleaning system filter, fresh air anti-haze dehumidifier filter, etc. Whether the carbon fiber cloth filter screen will be used in these occasions depends on the actual demand. In reality, more choices are: the combination of the filter screen for particle filtration and the filter element with activated carbon particles alone.
5) Clean filtration and purification system, such as industrial air filter element and ventilation pipe filter element of class 100/1000/10000 clean room purification system.
6) Other purification products and ventilation accessories, such as filter element of medical respirator, mist mask, projector/projector filter, artificial intelligence robot filter, etc.
Performance indicators that need attention
Carbon fiber cloth can filter both gas and particulate matter. Therefore, the gas filtration performance requirements of filter materials and filters can be tested according to ISO 10121-1 “Test method for assessing the performance of gas-phase air cleaning media and devices for general ventilation- Part 1: Gas-phase air cleaning media” and ISO11155-2 “Road vehicle – Air filters for passenger compartments – Part 2: Test for gaseous filtration”, and the particulate filtration performance requirements of filter materials and filters can be tested according to ISO 16890 “air filters for general ventilation”, ISO 29463 “high-efficiency filters and filter media for removing particles in air” and ISO 11155-1 “Road vehicle – Air filters for passenger compartments – Part 1: Test for particulate filtration”.
The mentioned test indexes are: gas removal efficiency, pollutant capacity, desorption, resistance, particulate matter filtration efficiency (including arrestance efficiency, fractional efficiency, etc.), air volume-resistance curve, dust capacity, etc. Specific indicators to be tested need to be determined according to the use of carbon fiber cloth.
Scince Purge used SC-13011CG chemical gas filtration performance tester to test the gas filtration performance of two carbon fiber cloth clips. Use the same gas type, gas concentration and flow rate for testing. See the following figure for the appearance and test results of the two samples.
From the test results, no matter the gas removal efficiency, pollution capacity or resistance, the No.2 sample is obviously better than the No.1 sample. From the appearance, the non-woven fabrics used in the surface layer of the two samples are different, and the amount, uniformity and particle size of activated carbon filled in the middle are also different. It can be seen that the above factors will affect the performance of carbon fiber cloth. The performance of carbon fiber cloth can be quantified, and we can optimize the product composition and process according to the test results and the application fields of carbon fiber cloth.
The above samples are from manufacturers with good quality, and in fact, there are more carbon fiber cloth tested. In fact, quite a few carbon fiber cloth manufacturers and filter screen manufacturers in the market don't have data support to know the performance of their carbon fiber cloth.
Factors affecting the performances
The main factor affecting the performance of carbon fiber cloth is the characteristics of activated carbon.
According to the different forces between activated carbon molecules and pollutant molecules in the adsorption process, the adsorption mechanism of activated carbon can be divided into physical adsorption and chemical adsorption (also called active adsorption). In the process of adsorption, when the force between activated carbon molecules and pollutant molecules is Van der Waals force (or electrostatic attraction), it is called physical adsorption; When the force between activated carbon molecules and pollutant molecules is a chemical bond, it is called chemisorption.
In the figure below, when the concentration of polluting gas in the air flow is greater than that in the activated carbon boundary layer, the gas will diffuse to the low concentration area. When entering the porous medium in the activated carbon, the gas molecules randomly hit the inner wall of the micropores of the activated carbon, and were "locked" by the pore channels by the Van der Waals force between the molecules.
According to the reported literature statistics, the adsorption capacity of activated carbon ranges from a dozen to several hundred mg/g, which depends on the physical and chemical properties of activated carbon, such as surface area, pore diameter, pore volume, chemical functional groups, molecular size and polarity of gas, etc. At the same time, the adsorption conditions such as temperature and humidity can't be ignored. Therefore, it is necessary to comprehensively consider various factors to judge in actual use, and then select the appropriate activated carbon.
Different types of gases are suitable for different adsorbents. As a gas adsorbent, activated carbon is mainly porous physical adsorption. Some manufacturers impregnate activated carbon, which increases the characteristics of chemical adsorption.
