Application Of Activated Carbon In Cigarette Filter And Tobacco Processing Wastewater

In order to understand the application status of activated carbon in cigarette filters,8brands of cigarettes purchased from convenience stores were used to separate activatedcarbons from cigarette filters, and then employed as adsorbent materials for adsorption ofammonia, acetaldehyde, butyraldehyde, benzene, isoprene, acetone, carbon monoxide and nitricoxide. Their adsorption capacities were evaluated to understand the application status ofactivated carbon in cigarettes, and provide theoretical basis for selection of activated carbon.The activated carbons were characterized by particle size analysis, pore structure analysis, andFourier transform infrared spectroscopy （FTIR）. The results indicate no unified standardindicator for activated carbons used in cigarette filters, because the addition amounts, addingmodes, particle sizes, surface areas and pore structures of activated carbons were differentamong the8brands. The FTIR and particle size analysis indicated that the activated carbonsused for cigarettes were most physical ones, such as ZY, SH, SH-2, D, K, M and P; PQRcontained the most acidic oxygen groups, probably because it had been modified by chemicals.The adding mode of activated carbon affected its adsorption properties seriously. Comparedwith the ternary complex cigarette filter （SH）, the adsorption capacities of activated carbonsused in the binary composite cigarette filters （D, K, M and P） were poorer, probably because ofnumerous glyceryl triacetate on the surface of activated carbon used in the binary compositecigarette filters, which could block pore structures and form steric hindrance, and increase themass transfer resistance of the adsorbate molecules. Appropriately increasing the contents ofmespores, macropores and C=O structures in activated carbons were favorable for improvingthe ability to capture most adsorbates. All the activated carbons could not absorb CO.Activated carbons were prepared from almond shells by chemical activation with H₃PO₄orH₃PO₄-KH₂PO₄composite. The samples were characterized by N₂adsorption-desorption,iodine adsorption number determination, methylene blue adsorption number determination,elemental analysis and Boehm titration, and their textures and surface chemistry were studied.Then they were used as adsorbents in the cigarette filters and experiments were carried out toabsorb the heavy metals of Hg and Pb in cigarette main stream by DZJ single-channel smokingmachine. The results are first to show that: The pore size within0.852-1.096nm is conducive toHg adsorption, and the pore size within1.245-1.534nm is conducive to Pb adsorption. The poresize distributions are more important than the surface areas of activated carbons, as there is noobvious relationship between the surface areas and Hg/Pb adsorption amount. The surfaceacidic oxygen groups play an important role in the adsorption; improving the carboxyl groupcontents is favorable for adsorption of Hg and Pb, and Hg was competing with Pb for the sameactive sites during the adsorption. Four modified activated carbons （modified by ammonia, sulfur, iodine, or iron salt） wereprepared by impregnation, and almond shell-based activated carbon was used as raw materials.The modified activated carbons were characterized by N₂adsorption-desorption, elementalanalysis, FTIR, thermogravimetric analysis （TG）, X-ray diffraction （XRD） and X-rayenergy-dispersive spectrum （EDS）. It was the first time to reduce the harms of Hg and Pb incigarette stream smoke by adsorbents related with their modified methods and adsorptionproperties. The results show that: After the modification, the pore structure contents in bothammonia-modified and sulfur-modified activated carbons were improved to different degrees,while the pore contents and surface areas in both iodine-modified and iron salt-modifiedactivated carbons decreased to varying degrees. FTIR analysis showed that amino group wasintroduced onto the surface of ammonia-modified activated carbon; chemical reactions occurredamong activated carbon, KI and H₂SO₄, which led to the generation of two types of active sites（iodine and sulfuric acid group） on the surface of activated carbon. The TGA results indicatedthat the stabilities of sulfur-modified, KI/H₂SO₄composite modified and KI-modified activatedcarbons decreased, especially for KI/H₂SO₄composite-modified activated carbon; eachmodified activated carbon was stable below200℃, and it provided the preconditions formodified activated carbons to be used in cigarette filters. The XRD results show that the surfaceof iron salt-modified activated carbons was loaded with α-Fe₂O₃.The above four modified activated carbons were explored as adsorbents in cigarette filters,and experiments were carried out to absorb the Hg and Pb in cigarette main stream by DZJsingle-channel smoking machine, and their securities were evaluated. The results show that:The adsorption of Hg and Pb by non-modified activated carbon was weak and was mainlyphysical adsorption. Modification by ammonia could improve the N content in modifiedactivated carbons and lead to the generation of a new active site, so the adsorption efficiency ofammonia-modified activated carbons developed significantly. Compared with the blank sample,the contents of Hg and Pb in the cigarette stream smoke after adsorption by N-15decreased64.00%and80.00%, respectively. The adsorption on sulfur-modified activated carbons wasobviously chemical adsorption; the S on the surface of sulfur-modified activated carbons couldreact with Hg and Pb to produce HgS and PbS, which were deposited in the pores of theactivated carbons. S-11had the strongest adsorption capacity. Compared with the blank sample,the contents of Hg and Pb in the cigarette stream smoke after adsorption decreased84.00%and80.00%, respectively. A proper addition of H₂SO₄could transform KI to I₂and load on thesurface of activated carbon under the same preparation conditions, which greatly improved Hgand Pb adsorption capacities of modified activated carbons. There was no Hg in the cigarettestream smoke after adsorption by I-3and I-4. α-Fe₂O₃on the surface of modified activatedcarbons exhibited a strong affinity to Hg; the iron salt-modified activated carbons preferred toabsorb Hg and it was chemical adsorption. Pb adsorption by iron salt-modified activatedcarbons was influenced by the competitive adsorption of Hg and the content of micropores.Compared with the blank sample, Hg content and Pb content in the cigarette stream smoke afteradsorption by F-8decreased90.67%and70.12%respectively. Each modified activated carbon could reduce the TPM content in cigarette main stream to varying degrees. Because S, I and Featoms were introduced into activated carbons during modification, in order to prevent theparticles containing S, I and Fe from exiting through with cigarette stream smoke duringpumping, and to avoid secondary harm to health, the Cambrige filter films which adsorbedbefore and after were analyzed by EDS. The results showed no S, Na₂S, KI, I₂or Fe₂O₃particles on the Cambrige filter films after adsorption experiments, which ensured the safety ofmodified activated carbons to be used in cigarette filters.Finally, almond-shell-based activated carbon was reactivated or modified with steam, zincchloride and sodium bisulfate separately. Then the reactivated/modified activated carbons wereapplied for nicotine adsorption in the tobacco processing wastewater. The results show that:The nicotine adsorption experimental equilibrium data of reactivated/modified activatedcarbons could be described by Langmuir and Freundlich isotherm equations. Appropriatelyincreasing the reaction temperature could promote chemical adsorption. The static experimentaldata show that the saturated adsorption amount was best at45°C and nicotine initialconcentration was750mg/L by AC-H, which was355.68mg/g. The nicotine adsorptionamounts increased with the increasing phenolic hydroxyl content in activated carbons, butdecreased with the increasing carboxyl content.