Preparation Of Modified Porous Carbon For Toluene Adsorption From Liquid Paraffin

The annual demand of liquid paraffin recently was about 600,000 tons including theimport of about 150,000 tons.Since the end of last century,China's demand of liquid paraffin was increasing at an annual rate of about 7%the import growth rate at about13%a year,but it was still in short supply,which showed the world of liquid paraffin market has great prospects.The industry with the largest demand of liquid paraffin in2019 was the textile industry(32%).In addition,polystyrene(PS),adhesive ink,solvent oil,cosmetics and other industries demand was growing.Liquid paraffin can be divided into industrial/agricultural grades,cosmetics grades and medicine/food grades.Liquid paraffin is a complex petroleum distillate,which can be divided into mineral oil saturated hydrocarbon(MOSH)and mineral oil aromatic hydrocarbon(MOAH).MOAH is alkylation of aromatics mainly such as toluene and the aromatic hydrocarbon content can be up to 30-50%.Most aromatic hydrocarbons are carcinogens and they also cause chronic poisoning and harm to the nervous or hematopoietic systems.Therefore,liquid paraffin must undergo strict purification techniques to reduce or even eliminate aromatic compounds.Due to the advantages of easy operation and economy,liquid paraffin was purified by adsorption method,three kinds of porous carbon adsorption materials with different structures and properties were prepared by using biomass and pyrrole as carbon source with template method,activation method and self-doping method,The specific steps are:(1)Porous carbons derived from sodium lignin sulfonate were activated by four common metal salts(PCS-MCl_x).The samples exhibit distinct characteristic of irregular,sunflower-like,interconnected sheet and tine block morphologies with Na Cl,CaCl₂,ZnCl₂ and FeCl₃ impact,respectively.Surprisingly,the maximum and minimum specific surface area are 1524 and 44 m²/g responding to PCS-ZnCl₂and PCS-Na Cl,respectively.All the samples have plentiful functional groups,therein,PCS-Na Cl and PCS-FeCl₃ are detected with the highest O and S contents(11.85%,1.08%),respectively,which signifies sufficient active sites for adsorption.These porous materials were applied in toluene adsorption from paraffin liquid and matched the Langmuir isotherm models well.Thus,the activation mechanism was discussed in detail.PCS-MCl_x has completely different pyrolysis behaviors according to TG/DTG analysis.It is speculated that H[ZnCl₂(OH)]would have an etching effect on carbon structure of PCS-ZnCl₂,and HCl or H₂SO₄,resulting from FeCl₃ hydrolysis and reduction reaction,would be corrosive to SLS surface.Each metal salt plays a different role on activation.The devised method of synthesized porous carbons is green and economical which is suited to mass production.(2)A novel adsorbent was conveniently prepared by chemical activation of pre-carbonation sodium lignin sulfonate(SLS),namely,SLS based porous carbon with Na OH activation(SPCN).In this study,the effect of alkali dosage in the range of 0:1to 4:1(the ratio of Na OH to carbon)was investigated.The results showed the specific surface area(SSA)and porous structure could be tuned by adjusting the ratio of Na OH to carbon,which suggested the tendency of increasing first and then decreasing.The optimum ratio of Na OH to carbon was proved to be 1:1 and SPCN-1 had a large SSA of 710.4 m²/g compared to 316.2 m²/g of 0:1 and 518.3 m²/g of 4:1.Adsorption capacity was proportional to specific surface area and was calculated as 1684.74,2875.17 and1729.64 mg/g corresponding to 0:1,1:1 and 4:1,respectively.SPCN-1 not only had a better adsorption capacity than several commercial adsorbents but also maintained 92.5%adsorption efficiency after five adsorption and desorption cycles.In addition,the activation and adsorption mechanism were deeply discussed.For the former,the redox reaction consumed carbon and released gas,in which the pore structure was formed and the SSA was increased.And for the adsorption mechanism,it was considered to the synergy effects of pore filling,van der Waals'force,?-?interaction and electron-donor-acceptor interaction(EDA)combining the analysis of scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectra(Raman),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and N₂ adsorption desorption(BET).Overall,we proposed a facile and cheap method to remove the toluene from paraffin liquid with high cyclic stability and low pollution firstly,which provided a promising strategy for industrialization.(3)The polypyrrole based porous carbon(PPC)was prepared by the ZnCl₂ activation for toluene adsorption from paraffin liquid.The structure properties were adjusted by dosage of the activating agents and the carbonization temperature.The result,with the3:1 mass ratio of ZnCl₂/PPy at 600?,showed the highest micropore area and percentage of micropores volume as 1105 m²/g and 86.26%,respectively.In addition,the PPC surface was rich in functional groups and obtained high N-doped content from7.00 to 8.82%.The toluene adsorption behavior onto the PPC was comprehensively investigated including isotherm,kinetics and thermodynamics.The adsorption isotherm accorded with the Freundlich model well and the kinetic model was fitted more closely to the pseudo-second-order chemisorption.The thermodynamic research uncovered that the adsorption was spontaneous and endothermic process in essence.The devised way of synthesized microporous carbon is green and simple,which is suited to mass production for the adsorption of toluene from paraffin liquid and reducing environmental pollution.