Study On Preparation Of Walnut Shell Based High Specific Surface Area Activated Carbon And Its Methane Adsorption Capacity

In recent years, the consumption of natural gas has gradually grown into the stage of diversified development and efficient usage. Adsorption of Natural Gas（ANG） is an effective method for low-pressure adsorption storage of natural gas at room temperature, in which high specific surface activated carbon is considered as the most valuable special adsorbent for natural gas adsorption storage with prosperous future promotion and applications.In this paper, walnut shell was uesed as the raw material, KOH and K₂CO₃ were used as activators, to prepare high specific surface area activated carbon for natural gas adsorption. Experiment has been carried out to attain optimal process conditions, the methane absorption kinetics of the produced activated carbon have simulated and the methane adsorption performance of the produced activated carbon have tested.（1） Walnut-shell high specific surface area activated carbon preparation with KOH activation. Through single factor experiments, this paper explores the influence of carbonization time, activation time, activation temperature, ratio of KOH and walnut shells（material ratio） on the yield, Iodine adsorption value of the activated carbon, pore volume and pore size distribution as well as methylene blue adsorption values. The results have shown three factors are of the most importance: activation time, activation temperature and material ratio, which have been selected for orthogonal experiments.Conclusively, the optimal process conditions for activated carbon preparation using walnut shells with KOH activation is: the mass ratio of KOH and walnut shell is 1:1, 60 min at 350 oC carbonization, 30 min at 850 oC activation. The product activated carbon has BET specific surface area of 1798m2/g, Langmuir specific surface area of 2168m2/g, average pore size of 1.82 nm, t-Plot meso-micropore volume of 0.5342cm3/g which accounts for 68% in total pore volume.（2） Walnut-shell high specific surface area activated carbon preparation with K₂CO₃ activation. The optimal process condition for activated carbon preparation using walnut shells with K₂CO₃ activation is: the material ratio of K₂CO₃ to walnut shell is 2:1, 60 min at 350 oC carbonization, 90 min at 850 oC activation. The product activated carbon has a BET specific surface area of 1674m2/g, Langmuir specific surface area of 2058m2/g, average pore size of 2.03 nm, t-Plot meso-micropore volume of 0.4315cm3/g which accounts for 55% of total distributed capacity.（3） The methane adsorption kinetics of AC-KOH has simulated by using Langmuir model and Freundlich model, first and second order equation simulation. The results show that Langmuir isotherm could describe the experimental data best, the correlation coefficient is 0.99963.（4） Using Carboxymethylcellulose（CMC） as adhesive to form activated carbon, the optimal ratio of adhesive was 10%. The results showed that formed AC-KOH has 6% increase in CH4 volume adsorption, which is 137.8 v/v at 25 oC, 3.46 MPa.（5） Methane adsorption properties of the product AC-KOH in single column have been tested, the breakthrough curves under different pressures and temperatures have been studied. The results showed that relationship between pressure and breakthrough time is linear growth, while breakthrough time and operating temperature show a negative linear relation, therefore, different breakthrough time have been used to determine respective breakthrough volume under different circumstances. In the end, the experiment of single column pressure swing cycling adsorption of AC-KOH was carried out, the experimental results showed that the product methane concentration is 42.52% compared to the 30% original concentration after cyclic desorption, the improvement is 12.52%, and the recovery is 73.14%.