Author : Kang Gao
Publisher :
ISBN 13 :
Total Pages : 218 pages
Book Rating : 4.:/5 (129 download)
Book Synopsis Sustainable Valorization of Coal Fly Ash Waste in Conventional/intensified Glycerol Steam Reforming for Green Hydrogen Production by : Kang Gao
Download or read book Sustainable Valorization of Coal Fly Ash Waste in Conventional/intensified Glycerol Steam Reforming for Green Hydrogen Production written by Kang Gao and published by . This book was released on 2022 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: Among renewable fuels, hydrogen is an appealing energy carrier for mitigating climatechange arising from the anthropogenic emissions of CO2. Most hydrogen is currentlyproduced by steam reforming (SR) from fossil fuels. For specific applications, hydrogenyield/purity can be enhanced via the integration of steam reforming and sorptionintensification in a single step/reactor (SESR). However, the high and unceasingconsumption of fossil fuels results in the exhaustion of finite resources and negative effectson the environment. With a scenario of green-economic sustainable development, there is agrowing interest in the recycling and valorization of a variety of industrial wastes and residualmaterials to a broad spectrum of value-added products. In particular, hydrogen productionfrom renewable byproduct substrates is widely recognized and investigated as a promisingapproach to mitigate energy and environmental crises. The booming of biodiesel productionhas resulted in the increase of glycerol (C3H8O3), byproduct, which can represent however apotential feedstock candidate to be adopted in green technologies for conversion intohydrogen. On the other side, another industrial waste, coal fly ash (FA), is vastly generatedfrom coal combustion in thermal power plants. Due to its high thermal stability and the factthat it contains several metal oxides, FA can act as potential alternative solid support and/orpromotor for developing heterogeneous catalysts. The hydrogen production (SR and/or SESR)presents therefore opportunities to valorize glycerol and FA wastes in a green approach(GSR/SEGSR).In the context of the importance of turning wastes into value-added products, this thesis dealswith a combined valorization of two important industrial residues (namely, FA for developingefficient Ni-based catalysts (yNi-FAx) and bifunctional catalyst-sorbent materials (Ni-CaO-FA), and glycerol as potential alternative feedstock) for sustainable green hydrogenproduction by GSR and SEGSR processes. More specifically, the main objectives of our workwere 1) investigating the influence of FA types, Ni loading, and reforming temperature onthe catalytic performance of yNi-FAx catalysts, 2) proposing a novel method for improvingthe properties of raw FA by adjusting the physicochemical properties using acid/alkalitreatments, and 3) developing bifunctional Ni-CaO-FA catalyst-sorbent materials for multi-cyclic SEGSR/regeneration operation.(1) FA supported Ni catalysts (Ni-FA) were synthesized via solid-state impregnation method.The effect of different parameters including (i) types of FA, (ii) Ni loading (2.5 - 15 wt.%),and (iii) reforming temperature (530 - 730 °C) on the catalytic performance of yNi-FAxcatalysts over GSR was investigated. The best performance in terms of activity (glycerolconversion to gas = 98 %, hydrogen yield = 78.8 %) and stability (40 h, with a low rate ofcoke formation and sintering 2.44 mgcoke•g−1catalyst•h−1) was achieved for 7.5 wt.% Ni-FA4 catalyst at 630 °C. This performance was attributed to a higher dispersion of Ni° active sitesand stronger interaction with the support, due to the higher surface area of FA4 and theexistence of nepheline (providing vacancy sites for anchoring Ni particles) and thermostablemullite.(2) In light of the catalytic performance of Ni-FAx catalyst (1), simple acid/alkali treatmentswere carried out to improve a low-efficiency FA (as support of Ni-based catalyst) byregulating its properties via one-step (HNO3 or NaOH) or two-step (NaOH/HNO3 orHNO3/NaOH) leaching-partial-dissolution (LPD). The influence of the treatment sequenceon the activity of the developed catalysts was highlighted. The results show that the catalyticactivity of Ni-FA(treated) catalysts for GSR was significantly improved compared to theuntreated materials. Alkali-LPD is more effective than acid-LPD in both improving FA’ssurface area and adjusting FA’s elemental distribution. Ni-FA(HNO3/NaOH) has the bestperformance with glycerol conversion to gas of 99.2 % and hydrogen yield of 74.5 %,attributed to (i) the removal of sulfur-containing species via acid-LPD, (ii) improvement ofspecific surface area, iron exposure, and Ni dispersion via alkali-LPD, (iii) reduction of cokeformation by acid/alkali-LPD sequence treatment, and (iv) enhancement of catalytic stabilitydue to the formation of NiFe alloys. (3) To synthesize bifunctional catalyst-sorbent materials, an attempt was initially made tomodify a CaO-based sorbent by adding different types of FA (FAx (x = 1 to 12)) to develophighly efficient and economical CaO-based sorbents for CO2 removal at high temperatures.The results showed that CaO-FA5 (90 wt.% CaO) sorbent offered the most stable CO2 captureactivity over 20 cycles, with a CO2 capture capacity of 0.58 gCO2•gsorbent-1 at the 1st cycle and 0.45 gCO2•gsorbent-1 at the 20th cycle. This was attributed to the relatively high amounts of SiO2 and mullite (inert materials) in FA5 compared to the other FAx samples. The presence of these inert materials helps to enhance the sorbent stability by hindering their aggregation andsintering. This sorbent was then chosen to further synthesize a bifunctional catalyst-sorbentmaterial for highly pure hydrogen production via SEGSR. The Ni-CaO-FA5 bifunctionalmaterial exhibited a stable hydrogen purity of ~ 97 % and yield of ~ 90 % for 30 min (pre-breakthrough period). These results highlight the high potential of FA5 as a low-coststabilizer for improving the stability of CaO-based sorbents.In conclusion, through the valorization of both liquid (glycerol) and solid (coal fly ash)residual materials, the results presented in this thesis provide an economic and environmentalapproach to hydrogen production by GSR as well as the simultaneous CO2 capture and high-purity hydrogen production by SEGSR. Even though not all kinds of as-received (raw) FAmaterials are suitable for serving as catalytic support, simple acid/alkali treatments could leadto low-calcium/sulfur FA supports with superior physicochemical features. As for differentresidual liquid substrates, using solid wastes to catalytically produce hydrogen is anenvironmentally favorable and economically sustainable strategy. With the growing energycrisis, this aspect is becoming more important and pushing forward new attempts to convertmore wastes to value-added products