Study On Methanol Reforming By Gliding Arc Plasma Catalysis For Efficient Hydrogen Production

Due to the dwindling oil resource and increasing energy demand,many countries in the world pay much attentions to development of hydrogen fuel cell vehicles.However,the lack of economic,safe and reliable hydrogen delivery and storage technique makes it difficult to build a hydrogen distribution network.One possible solution is on-demand hydrogen generation at distributed hydrogen stations or vehicles by reforling of methanol,which is easy to storage and contains high hydrogen content.Compared with traditional catalytic reforming technique.plasma reforming has the advantages of fast response and compact structure and therefore make it promising for distributed and on-board hydrogen production in small and medium scale.However,it has drawbacks such as low energy efficiency,low product selectivity and high energy cost.Plasma catalytic reforming technique combines the advantages of plasma and catalytic techniques,providing a feasible route for efficient hydrogen production from methanol reforming.In this paper,hydrogen production from methanol reforming by gliding arc plasma catalysis is studied for distributed and on-board hydrogen production.For distributed hydrogen production for a stationary source,methanol pyrolysis reforming in gliding arc plasma and methanol pyrolysis-steam reforming in gliding arc plasma catalysis are studied.Moreover,to meet the particular requirement of low energy cost for on-board hydrogen production,studies of methanol oxidative-pyrolysis reforming in gliding arc plasma and plasma chain catalytic oxidative-pyrolysis-steam reforming of methanol are carried out.The contents and main results are summarized as follows:1.Methanol pyrolysis reforming in gliding arc plasma is studied with gasified methanol and water as the feeding gas.Within the investigated range,when the composition in feed gas is unchanged,methanol conversion mainly depends on specific energy input(SEP).With a fixed SEL methanol concentration shows significant effect on product selectivity:at low methanol concentration(high water concentration),HZ,CO and CO2 are main products;with the increase of methanol concentration.selectivities of CO and hydrocarbons increase while CO2 selectivity decreases sharply.The gliding arc plasma at various lethanol concentrations is diagnosed by optical emission spectra(OES).It is found that the arc channel temperature and electron density barely change with methanol concentration,and they are estimated to be 2500 K and 3～4×1014 cm’3,respectively.Thermodynamic-equilibrium(TE)product distribution of methanol pyrolysis reforming at arc channel temperature is calculated by using commercial software(HSC v7.0).The TE results are very close to the experimental results within the range of methanol concentration,indicating that methanol reforming mainly occurs in arc channel.Mechanism of methanol reforming in gliding arc plasma is discussed combining the radiation species detected by OES and the product distribution2.To solve the low conversion and energy efficiency of hydrogen production from methanol pyrolysis reforming in gliding arc plasma.methanol pyrolysis-steam reforming using gliding arc plasma coupling with catalyst is investigated for distributed hydrogen production in a heat-insulation reactor which has no external heating.Effect of power input and gas hourly space velocity(GHSV)are examined.The Fe-Cu/Al2O3 catalyst used in experiment can be auto-reduced during reaction process,and methanol steam reforming and water gas shift reaction occur over the catalyst.With the catalyst of 20 g,steam to methanol(S/C)ratio of 1.5,input power of 140 W and flow rate of 2.5 SLM.compared with plasma alone,the methanol conversion and energy efficiency increase fron 48%and 67%to 94%and 84%,respectively;the energy cost decreases from 1.69 kWh/Nm3 to 0.85 kWh/Nm3 and the CO selectivity reduces from 82%to 22%.3.To meet the demand of low energy cost for on-board hydrogen production,methanol oxidative-pyrolysis reforming using gliding arc plasma(without catalyst)is studied.The introduction of oxygen(using air as oxygen source)in methanol reforming system makes the gliding arc plasma run stably at a lower SEI,therefore reduces the electrical energy demand to maintain the plasma.Increase of oxygen to methanol(O2/C)ratio can promote more methanol converted via pyrolysis reforming,therefore significantly increases methanol conversion.Increase of S/C ratio and SEI decrease energy efficiency and increase energy cost.Under the conditions of O2/C=0.30,S/C=0.5,SEI=24 kJ/mol,energy efficiency of 74%and energy cost of 0.45 kWh/Nm3 with methanol conversion of 88%are achieved.4.In order to take full advantage of the heat from gliding arc plasma and partial oxidation reaction of methanol,a heat-insulated plasma chain catalytic reactor with two-stage feed is designed for methanol reforming.According to the stoichiometric ratio of methanol autothermal reforming and experimental results of plasma alone,composition and flow rate of the two feedings are optimized.Two-stage catalysts of high-temperature C1(Ni-Cu/Al2O3,5 g)and medium-temperature C2(Fe-Cu/Al2O3,27 g)for methanol reforming are sequentially coupled with the gliding arc plasma.Under the condition of input power of 60 W,total flow rate of 4.8 SLM,O2/C=0.16 and S/C=0.7 in the total feeding gas,methanol and water conversion of 92%and 42%are achieved,respectively.The utilization of hydrogen atom and dry-basis concentration of H2 are 88%and 59 vol.%,respectively.A high energy efficiency of 91%and a low energy cost of 0.22 kWh/Nm3 are achieved.Combined with the results,the individual contribution of plasma,C1 and C2 catalyst for the plasma chain catalytic reforming of methanol are discussed.