| Coal pyrolysis staged conversion poly-generation technology is key utilization direction encouraged in China.Coal pyrolysis poly-generation process would produce a lot of gas and tar,and the pitch accounts for half of the coal tar.To increase value added of coal tar pitch(CTP),this paper prepared high-performance activated carbon monoliths(ACMs)from the pitch,and the adsorption performance of toluene steam and CO2 were studied respectively.The main work and research results are as follows:(1)The carbon precursors were prepared from CTP at different vacuum distillation final temperatures(VDFTs)and different pre-carbonization temperatures.And the influence of their carbonization degree on the pore structure of activated carbons(ACs)was investigated.Results indicate that appropriate carbonization degree,which can be presented by the proper amount of the volatile matter,the H atoms,the surface functional groups in carbon precursors as well as the appropriate structure arrangement,is beneficial to the KOH activation process.In general,CTP with VDFT of 440 ℃ is suitable for preparation of high performance AC directly activated with KOH,which has the highest specific surface area and relatively high yield,up to 2599 m~2/g and 63.5%respectively.(2)With toluene as model pollutant,the experimental study of preparation of high-performance ACMs and its adsorption and desorption performance of VOCs were carried out.The orthogonal test was designed to optimize the preparation conditions of ACs.The suitable preparation parameters are as follows:KOH/C mass ratio is 3,activation temperature is 850 ℃ and activation time is 90 min.The static adsorption capacity of toluene is as high as 1109 mg/g.And in toluene dynamic adsorption experiments,the equilibrium adsorption capacity increased with the increase of toluene concentration,but when it increased to a certain extent,equilibrium adsorption capacity remained unchanged at about 800 mg/g.The adsorption isotherm of toluene at 25 ℃ is in good agreement with the Langmuir model.The ACMs were prepared from powdered ACs added with 10%sodium carboxymethyl cellulose(CMC).Compared to the powdered ACs,the specific surface area and pore volume of ACMs decrease slightly,the dynamic adsorption rate of toluene was slower and the static saturated adsorption capacity of toluene is about 979 mg/g and decreased slightly,too.As desorption temperature increased,desorption rate of ACMs with toluene rose,and the desorption rate reached 95%at 250 ℃ for 20 min.(3)The preparation of high performance ACMs based on CTP and its adsorption and regeneration performance for CO2 were discussed.The single factor experiments show the optimum conditions for preparing ACs with high CO2 adsorption capacity are:KOH/C mass ratio of 1.5,activation temperature of 750℃ and activation time of 60 min.The CO2 equilibrium adsorption capacity of powdered ACs is 3.19 mmol/g at 35℃,while the ACMs prepared by adding 10%CMC is 2.80 mmol/g with compressive strength of 4.92 MPa.The ACMs prepared by CO2 activation after coal tar pitch direct compression molding are relatively compact,so its intensity is as high as 21.13 MPa.However,the pore size distribution is relatively wide with the CO2 adsorption capacity of 1.33 mmol/g and t the yield of 38.7%.Both of the ACMs show good CO2 temperature desorption regeneration performance.Compared with three conventional adsorbents,commercial granular activated carbon,mesoporous silica gel MCM-41 and zeolite 13X,the ACM activated with KOH shows better comprehensive performance.Therefore,ACMs prepared from poly-generation coal tar pitch activated with KOH,and then bonded with CMC have good CO2 adsorption application value.(4)It is found that there is a significant difference between pore structure and adsorption capacity of different adsorbates on the prepared ACs.Toluene adsorption capacity enhances with the increase of specific surface area and total pore volume of ACs,and has a good linear correlation with the theoretical effective pore volume of 0.67-7.77 nm.While CO2 adsorption capacity has no obvious relationship with specific surface area and total pore volume,but is very relevant with pore volume of less than 1 nm.Therefore,for different adsorbates,the best preparation conditions are also very different. |
