Lithium Silicate Applied For Hydrogen Production In Sorption-enhanced Steam-methane Reforming

Hydrogen as clean energy and chemical resources,with high calorific value of combustion,combustion products are water,zero pollution,renewable and other advantages,are widely used in synthetic ammonia,petrochemical and other industrial fields.With the increasingly depletion of natural energy and increasingly stringent environmental rules,people's demand for high-purity hydrogen is also increasingly urgent.At present,the most important hydrogen production method in the industry is natural gas(methane)steam reforming,but the process is complicated and the high temperature reaction during the reforming stage often leads to the deactivation of the catalyst.With the advancement of industrial technology and the continuous improvement of energy saving requirements,recently a research topic has been conducted on the in-situ removal of the produced CO2 from SMR and WGS reactions by a sorbent mixed with a reforming and shift reaction catalyst to enhance the yield and purity of hydrogen,which is so-called"Sorption-Enhanced Reaction Process(SERP)".This can lead to SMR and WGS reactions taking place at the same time,breaking the original chemical equilibrium reaction limit,so that the reaction can be carried out in depth at a relatively low temperature(550? or so).which makes a low energy consumption as well as to the simplification of the process.Based on the preliminary research work of the research group,in this thesis,hydrogen production via SMR and WGS in combination with SERP has been studied systematically,in which conventional catalysts are unsuitable and lithium-based CO2 sorbents Li4SiO4 with improved CO2 capture properties should be developed.So a study from the following two aspects was carried out.1)Preparation of high temperature CO2 solid absorbent Li4SiO4 by soft chemical method.The results show that the Li4SiO4 prepared by wet grinding has a faster absorption rate and a higher absorption capacity.Under the low CO2 partial pressure,the absorption capacity and the absorption rate of the Li4SiO4 are almost unchange.It is generally believed that the difference of CO2 uptake capacity is related to the migration rate of the internal ions of the crystal.From the Li4SiO4 bulk structure,the absorption process of CO2 in the lithium-based material is accompanied by the migration of Li+ and O2-the rate of Li+ and O2-migration directly determines the rate of CO2 absorption in the lithium-based absorber.According to this,Li4SiO4 with good CO2 absorption performance can be successfully prepared by wet milling,and it can be effectively used to improve the yield of H2 in the reaction of absorption and promotion(SERP)methane steam reforming.In addition,the sorption-enhanced reaction process is required to provide a catalyst that still has high stability and high catalytic activity at the optimum operating temperature of the absorbent.As the reaction process,from the absorbent alkali metal species will contact with the traditional Ni-based catalyst,resulting in loss of catalyst activity.It is reported that MgSi03 and alkali metal ions are weak,as a carrier preparation of Ni-based catalyst,which has a good resistance to alkali poisoning.In view of this,we prepared 20 wt.%Ni/MgSiO3 with alkali-resistant poisoning catalyst,which is mixed with CO2 absorber Li4SiO4,and still showed normal catalytic activity and stability under the experimental conditions.2)The prepared high temperature CO2 absorber Li4SiO4 was mixed with 20 wt.%Ni/MgSiO3 catalyst for absorption and enhanced methane steam reforming.It was found that the hydrogen concentration was higher than 80 mol%.While the same conditions,without the addition of absorbent when the maximum concentration of hydrogen only 70 mol%.The feasibility of high temperature CO2 absorbing agent Li4SiO4 for absorption and promoting reaction was proved.