Preparetion Of Copper-Doped Carbon Material Ahd Its Application In Propylene/Propane Adsorption And Separation Process

Propylene is widely used in national defense,agriculture,transportation and daily life.At present,the production capacity of propylene mainly depends on catalytic cracking and steam cracking.Therefore,the development of an efficient and green separation process for propylene and propane system is of high commercial importance.There are two difficulties in this process.One is that the molecular properties of propylene and propane are similar,the difference of boiling point is only 1.5 K,and the relative volatility is only 1.14.The other is that the molecular size of propylene and propane is close,leading to the difficulty in the separation process.Adsorptive separation is an important method to separate propylene and propane,which has the advantages of low energy consumption and simple operation.In principle,adsorbents can distinguish guest molecules by size,shape,polarity and coordination ability.The development of suitable adsorbents is crucial to the successful implementation of adsorptive separation technology.In this paper,based on the π complex adsorption of propylene with Cu(Ⅰ),and considering the green economy of the adsorbent,a metal-doped carbon material with high affinity for propylene was prepared for the efficient separation between propylene and propane.Chitosan copper material was successfully prepared by using chitosan as carbon source.In the preparation process,the complex reaction between-OH and-NH2 in chitosan and Cu2+was used to fix Cu2+in chitosan molecular chain,and Cu(Ⅱ)was reduced to Cu(Ⅰ)by high temperature thermal reduction.Based on the coordination of Cu(Ⅰ)in carbon material,Cu(Ⅰ)was stable in the material.When the chitosan concentration is 20 g/L,the freezing temperature difference is 15℃-(-18℃),C(Cu2+)=0.025 mol/L,and the carbonization temperature is 700℃,the best propylene and propane adsorption and separation performance is obtained.The adsorption capacity for propylene is 39.41 cm3/g,while the adsorption capacity for propane is only 6.70 cm3/g,with extremely high selectivity.The experimental results showed that the adsorption of propylene was mainly related to the coordination structure formed by Cu(Ⅰ)and N-6,and the adsorption of propane was mainly linked to the specific surface area of the material.In order to further improve the selectivity of propylene and propane,gelatin was used as carbon source,which could form a close three-stage structure at high curing temperature.As a result,the specific surface area of the material and the adsorption of propane was reduced.The results show that the prepared series of materials have extremely low specific surface area(1-10 cm2/g),low propane adsorption(0.73-9.42 cm3/g),and exhibit extremely high propylene and propane selectivity.And when the concentration of gelatin is 20 g/L,m[Cu(NO3)2]=0.75 g,and the carbonization temperature is 700℃,the adsorption capacity of propylene is 24.78 cm3/g,and the adsorption capacity of propane is only 2.51 cm3/g,showing extremely high separation performance.Through Gauss,two common coordination forms of Cu(Ⅰ)-N2 and Cu(Ⅰ)-N4 were constructed to calculate the adsorption of propylene.It was found that the Cu(Ⅰ)-N4 configuration has almost no adsorption effect on propylene,and the adsorption energy is only-2.55 kJ·mol-1,while Cu(Ⅰ)-N2 has a greater adsorption effect on propylene,and the adsorption energy is-93.25 kJ·mol-1,and also the adsorption energy of propane on the Cu(Ⅰ)-N2 structure is only-12.20 kJ·mol-1.The results show that the coordination structure of Cu(Ⅰ)-N2 has adsorption effect on propylene.