With the development of aquaculture and the improvement of living standards,shellfish and egg have become common foods in life.Followed by the increasing amount of clamshell and eggshell waste,resulting in a large surplus.At present,the common disposal methods of clamshell and eggshell are discarded,landfill and incineration.Indiscriminate disposal of them is likely to breed bacteria and attract rodents and insects causing environmental health problems,and the gases produced by large amounts of incineration will pollute the environment.Clamshell and eggshell waste contain about 95%CaCO3,which is a good raw material of biomass carbonate.In fact,it is a waste of resources to treat it as garbage randomly,and the biomass carbonate also has the advantage of renewable.The climate problem caused by excessive CO2 emissions from the burning of nonrenewable fossil fuels has aroused wide concern,and green sustainability,energy conservation and emission reduction are the themes of development in the world today.CaO as CO2 adsorbent with excellent adsorption performance at high temperature,which generally comes from limestone and dolomite minerals,and excessive mining of minerals is easy to cause irreversible damage to the environment.In this study,renewable clamshell and eggshell wastes were used as carbon and calcium sources.The alkaline earth metal-induced hydrogenation skill was combined with mechanochemical method to avoid the release of CO2 during the experiment.At the same time,methane and CaO adsorbent were prepared,which was consistent with the concept of carbon neutrality.It is of great significance to environmental protection.The main research content and relevant conclusions of this paper are as follows:1.Hydrogenation of eggshell/clamshell to methane with the assistance of the alkaline earthmetalThe clamshell,eggshell powder obtained by ball milling and alkali earth metal(Ca,Mg,Ba)as raw materials were proportioned into the reaction vessel ball mill tank for mechanical and chemical reaction under hydrogen atmosphere.It was found that shell and eggshell waste(as a carbon source)could be selectively hydrogenated into CH4 fuel by a metal hydride intermediate product process.The gas products were analyzed by gas chromatography and fourier transform infrared spectrometer.The effects of milling speed,time,hydrogen pressure and doped transition metals(Fe,Co,Ni,Ru)on the methane yield were investigated.After milling at 550 rpm for 24 h,the methane yield of shell-Ca and eggshell-Ca systems was 45.04%and 33.30%,respectively.The methane yield increased to 52.62%(clamshell-Ca-Ru)and 54.76%(eggshell-Ca-Ru),respectively.This study provides a mechanochemical method for the hydromethanation of eggshell/clamshell at room temperature,and the solid product can be used for the later study of CO2 adsorption.2.Preparation of CaO-based carbon dioxide adsorbent by calcium-induced hydrogenation of shell and eggshell wasteClamshell,eggshell,and calcium were used as raw materials,and CaO adsorbent was prepared by mechanochemical and thermochemical methods.Firstly,the prepared solid adsorbent samples were characterized by XRD,FTIR,BET and SEM to explore their composition,pore size and morphological characteristics.CO2 adsorption experiments at different temperatures were carried out in TGA.Through the comparison of experimental data,it was found that the adsorption capacity of samples at 650℃ was higher.The adsorption capacity of BM-C-CaO sample and pure eggshell sample was up to 36.82%and 47.11%,respectively.The samples treated by ball milling have good dispersibility and can maintain good stability even in the cycle of CO2 absorption and desorption.In the preparation process of CaO-based adsorbent,we also produce methane,and eliminate shell wastes,conform to the concept of circular economy.3.Preparation of CaO based adsorbent and its properties for clamshell/eggshell hydrogenation induced by calcium and transition metalIn order to further improve the CO2 adsorption capacity of the adsorbent and the stability of the carbonization/calcination cycle,Ni and Ru were added by solid-phase mixing method.Firstly,the prepared adsorbent samples were characterized by XRD,FTIR,BET and SEM to explore its composition and morphological characteristics.After adding Ni and Ru,the adsorption capacity of the adsorbents was significantly improved,and the adsorption capacity of BM-C-CaO-Ni was up to 40.82%at 650℃(36%without doping).And it was also conducive to reducing the adsorption temperatures.In the carbonization/calcination cyclic adsorption experiment,it was found that after doping Ni and Ru,the adsorbent prepared with clamshell as raw material showed better adsorption performance,and after doping Ru,the adsorbent showed better cyclic stability,among which the activity loss rate of BM-E-CaO-Ru sample was only 6.50%.The main achievements of this research are removing clamshell or eggshell waste at the same time,obtaining clean fuel with certain economic value,and obtaining CaO based adsorbent with good adsorption performance. |