Activated carbon to remove odor

The common odors of waste come from sulfur and nitrogen compounds. We selected five kinds of odorous waste gases and studied their adsorption capacity and desorption efficiency using activated carbon. The selected gases include polar gases (hydrogen sulfide H2S and ammonia NH3, and non-polar gases acetaldehyde, methanethiol, and trimethylamine. Activated carbon has non-polar and hydrophobic properties of the micro-pore, mesoporous and macroporous. As a result of these characteristics, activated carbon is widely used in BTEX series VOC gas adsorption research. In general, activated carbon has a high adsorption capacity for VOCs and other non-polar gases.

Activated Carbon adsorbent

In order to study the removal efficiency of waste gas, granular activated carbon adsorbent was purchased with the size of 3.0-4.0 mm. The material was dried at 110 ° C for 24 hours before the experiment. The adsorbents were analyzed by industrial analysis, element analysis (EA) and N 2 adsorption/desorption performance. For approximate analysis, dry adsorbent carbon was placed in a furnace and heated at 950 ° C for 7 minutes, followed by heating at 750 ° C for 10 hours. Sample products, including ash, volatile and fixed carbon content, measured as a percentage of total weight. EA was performed at 900 ° C for 12 minutes using an elemental analyzer to determine the concentrations of carbon, hydrogen, oxygen, nitrogen and sulfur. The surface morphology of activated carbon can be observed in the microscopic world by Scanning electron microscope analysis (SEM) . The SEM image in Figure 1a shows that the activated carbon consists of small pieces with many pores and is well developed on the surface. The well-developed mesopore in SEM images has relatively high BET surface area and pore size distribution. TGA and FT-IR Fourier transform were used to observe the weight loss and the changes of active functional groups on the surface of the adsorbents. The thermal stability of activated carbon was studied by TGA analysis, as shown in Figure 1b. The TGA curve showed that the weight of the activated carbon began to decrease slowly. In the process of weightlessness, until 130 ° C decomposes to carboxyl group, in the process of gradual weightlessness until 600 ° C decomposes to lactone and phenol group. At 800 ° C, weight loss occurs due to the decomposition of ether and quinone groups. After about 1000 ° C, the weight of activated carbon remains about 51.6% of the initial weight. The FT-IR spectra of activated carbon are shown in Fig. 1c. The functional groups of activated carbon show three main peaks at 1022cm-1,1583CM-1 and 1659cm-1, which participate in the stretching of CO and C = O bond in the carboxyl group, respectively. The C-C triple bond in bis-substituted alkynes can be deduced from 2250-2400 cm -1. However, no hydroxy (OH) , asymmetric or symmetric stretching bands were found in the range of 2500 ~ 4000cm -1.

Figure 1: (a) Scanning electron microscope (SEM) image, (b) TGA weight percentage curve, and (C) spectrum of activated carbon.

Adsorption performance of activated carbon for odor exhaust gas

In order to evaluate the effective adsorption capacity of activated carbon for different exhaust gases, its adsorption capacity should be studied. The odour threshold and stimulation level of the exhaust gas are at the billionth level. The total adsorption capacity of the adsorbent is difficult to use as a design factor for equipment to remove waste gases from waste. Therefore, we calculated the effective adsorption capacity of less than 1 ppm according to the breakthrough point. The breakthrough column experiment was carried out in a 304 stainless steel tubular reactor with a total flow rate of 1 l/min, including hydrogen sulfide (H2S) , ammonia (NH3) , acetaldehyde (AA) , methanethiol (MM) and trimethylamine (TMA) , as shown in Figure 2. The breakthrough curves were H2S, NH3, AA, MM and TMA. Compared with exhaust gas, TMA has better dynamic adsorption performance because it has longer breakthrough time and correspondingly larger effective adsorption capacity (& LT; 1 ppm) .

Figure 2: Breakthrough Curve of exhaust gas on activated carbon.

The effect of SV on NH3 gas and the effective adsorption capacity of activated carbon on ammonia are affected by the variation of SV in gas phase. Flow rate increased from 0.1 L/min to 10 L/min. The results show that the contact time is long enough for the gaseous ammonia to flow through the pores and reach the stagnation zone and adhere to the adsorbent bed. The higher flow rate contrasts with the fact that most ammonia can escape from sites on the surface of the adsorbent because it has a high input load at the entrance. This indicates that the kinetics of the ammonia captured on the adsorbent should be controlled.

Desorption of ammonia at different concentrations (40 ppm and 1000 ppm) and flow rates (10,20, and 30 L/min) was analyzed as shown in Figure 3. The maximum desorption concentration varies according to the adsorption concentration. However, the results show that ammonia is desorbed after 10 times concentration. A concentration of 40 ppm of adsorbent was used to check the desorption rate according to the desorption flow rate. Approximately 60% of the adsorbed ammonia is desorbed after about 1.8 hours at a flow rate of 10 L/min, and approximately 79% of the adsorbed ammonia is desorbed after 1.5 hours at a flow rate of 20 l/min. At a maximum desorption flow rate of 30 l/min, about 81% of ammonia is desorbed after 1.4 hours. The results show that there is a trailing phenomenon, in which the desorption will take place at a low flow rate for a long time due to the insufficient energy needed for desorption. At the concentration of 1000 ppm, the desorption rate increases and the desorption time decreases with the increase of desorption flow rate. With an initial feed concentration of 1000 ppm, the adsorption time required for desorption of 50% , 79% and 80% is 2.4,2.3 and 1.4 hours, respectively. The results show that, regardless of the adsorption concentration, the desorption amount increases with the flow rate, because the desorption amount is proportional to the desorption energy.

Figure 3: effect of desorption flow rate on adsorption of (a)40 ppm and (B)100 ° C on activated carbon at 1000 ppm concentration.

In the study of activated carbon’s ability to treat odors, the effective adsorption capacity of the adsorbents was evaluated using five types of waste gases, including hydrogen sulfide, ammonia, acetaldehyde, methanethiol and trimethylamine. In order to compare the effective adsorption capacity of exhaust gas, activated carbon was used as adsorbent. The effective adsorption capacity of trimethylamine, methyl mercaptan, acetaldehyde, ammonia and hydrogen sulfide is proportional to the molecular size, polar gases (hydrogen sulfide and ammonia) result in lower effective adsorption capacity than non-polar gases (acetaldehyde, methanethiol and trimethylamine) . Experiments were carried out under each adsorption condition of the polar gas ammonia. The effective adsorption capacity of activated carbon is inversely proportional to SV, and the effective adsorption capacity increases with the increase of supply concentration. On the contrary, the effective adsorption capacity decreases with the increase of flow rate. In addition, the supply of high concentrations at low flow rates during the adsorption process results in a high effective adsorption capacity. The desorption rate is proportional to the desorption flow rate and desorption temperature. At 150 ° C, 100% of the adsorbed ammonia is desorbed. In conclusion, experiments were carried out under different adsorption/desorption conditions to remove odors from the waste. The results show that activated carbon is a kind of good environmental protection material for odor treatment. The activated carbon produced by Jiasheng Water Purification Material Co. , Ltd. has good deodorization adsorption effect, welcome your inquiry!