High Purity Hydrogen Production By Chemical Looping Methane Decomposition And Orientational Modification Of Activated Carbon Carrier

At present,we are facing climate change and the greenhouse effect,and we need to find clean energy without greenhouse gases such as CO₂.Hydrogen energy is one of the most promising options;currently,hydrogen energy demand is increasing,and hydrogen production is usually produced by methane steam reforming technology,but its hydrogen production process is accompanied by a large amount of COx.To solve this problem,methane decomposition is used to produce hydrogen,and the product is only solid carbon and H₂,and the solid carbon is easily separated to obtain high-purity H₂.In order to achieve continuous high-purity hydrogen production,chemical looping methane decomposition for hydrogen production has been proposed.Activated carbon is usually used as a multifunctional carrier to achieve functions such as heat transfer,catalysis,and carbon loading,but it faces the serious deactivation problem.In this paper,activated carbon was regenerated and modified in order to make the activated carbon have better functional characteristics.The production process of high-purity H₂ via chemical-looping methane catalytic decomposition with activated carbon as a catalyst is an advanced process for reducing COx formation.AC has a reasonable catalytic activity,but it is highly susceptible to rapid deactivation.The spent AC catalyst by the steam deep regeneration can eliminate its deactivated state,which sacrifices a part of the AC;in addition,the endothermic decomposition reaction in this system usually requires external heating.To solve this problem,H₂O+O₂ is used as a deep regeneration method for reagents,which can overcome the problem of maintaining catalytic deactivation and generate heat that can satisfy the endothermic reaction.The experimental results shown that 30%or more of the deep regeneration can completely activate the spent AC catalyst and generate sufficient heat for methane decomposition.Characterization analysis shown that deep regenerated AC catalyst could maintain its physical properties within a certain number of cycles.Based on the experimental results,Aspen Plus^?was used to simulate and optimize the catalytic process of chemical-looping methane decomposition.The results shown that heat and mass balance can be achieved.The AC temperature difference between the decomposer and the regenerator was 262°C,which enabled the process to run automatically.In the system of methane decomposition for hydrogen production system,the catalytic performance of activated carbon and carbon black shows opposite deactivation behavior over time.AC has a high initial activity but poor activity stability.While,CB has low catalytic activity,but good activity stability and a certain increment in its activity.Experimental results suggested that the different catalytic properties of AC and CB were related to the morphology,derivation direction and chemical structure of carbon deposits on the surface.Out-growth tapered graphene layers and tubular nanostructures were key factors in maintaining catalyst porosity and activity;the reason for different deposition of carbon is probably due to irregular,cross-linked graphene layers and CB spherical graphene layers.By analyzing the reasons for their different properties,an AC modification method was proposed.Due to the different catalytic properties of AC and CB,this thesis improved the activity stability of AC by adding a certain amount of CB.The experimental results illustrated that the catalytic stability of AC/CB is improved;The activity stability of mixed materials increased with the increase of CB component,and the 2AC_20-50/6CB had the best activity stability.Characteristic analysis shown that AC_20-50 can form a few tubular nanostructures,and CB mainly formed tip structures;their mixed materials stick together on the contact surface,and its carbon deposit structure near the contact faces is similar to CB;these carbon deposits had a similar chemical structure with a layer spacing of approximately 3.7?.This enabled AC_20-50/CB to exhibit both catalytic properties of activated carbon and carbon black,resulting in higher activity stability.This indicated that the addition of CB to AC could improve the catalytic activity stability of AC.