CO₂-Free Hydrogen Production by Catalytic Pyrolysis of Hydrocarbon Feedstocks in Molten Ni–Bi

Abstract

The catalytic decomposition of methane, propane, benzene, and crude petroleum was investigated between 900 and 1000 °C in molten metal bubble column reactors. The conversion to gas phase products and solid carbon was measured after introducing the gas phase reactants into a bubble column reactor containing a catalytic molten mixture of 27 mol % Ni and 73 mol % Bi. The conversions of propane, benzene, and crude oil are 100% at temperatures >950 °C at a reactor residence time of ∼1 s. Equilibrium selectivity of 100% H 2 and carbon was not achieved in the short residence time, but can be achieved at longer residence times. The solid carbon products obtained from methane pyrolysis were more graphitic than those produced from the other, highermolecular weight reactants; the latter were more amorphous, as measured by Raman spectroscopy and electron microscopy and resembled carbon black. A model is proposed for carbon formation in bubble column reactors, in which amorphous carbon products are derived from the gas-phase decomposition and graphitic carbon products are formed from dissolution and reprecipitation of carbon into and out of the molten metal.

Methane Pyrolysis for Zero-Emission Hydrogen Production: A Potential Bridge Technology from Fossil Fuels to a Renewable and Sustainable Hydrogen Economy

“…This kind of reactor operates with molten media, such as molten metals (Ti, Pb, Sn, Ga), molten metal alloys (Ni−Bi, Cu−Bi) or molten salts (KBr, NaBr, NaCl, NaF, MnCl 2 , KCl). 29,31,[253][254][255][256][257][258][259][260][261][262][263]268 Molten metals and salts act as heat transfer fluids 254,256,259,263 and avoid temperature losses or gradients along the reactor. 263 Furthermore, they could also serve as potential catalysts for the reaction.…”

“…A reactor design that is gaining importance for methane pyrolysis in recent years is the liquid bubble column reactor (Figure D). This kind of reactor operates with molten media, such as molten metals (Ti, Pb, Sn, Ga), molten metal alloys (Ni–Bi, Cu–Bi) or molten salts (KBr, NaBr, NaCl, NaF, MnCl 2 , KCl). ,,− , Molten metals and salts act as heat transfer fluids ,,, and avoid temperature losses or gradients along the reactor . Furthermore, they could also serve as potential catalysts for the reaction. ,, The main advantage of liquid bubble column reactors is the easy separation of the carbon byproduct from the liquid medium due to density differences .…”

Hydrogen Evolution from Hydrocarbon Pyrolysis in a Simulated Liquid Metal Bubble Reactor

“…The kinetics needs to be improved by selection of suitable catalysts. In light of this, Palmer et al, 38 in their very recent work on catalytic pyrolysis of hydrocarbon feedstocks including benzene, have stated that Ni 0.27 Bi 0.73 molten alloy delivers fast kinetics, achieving 100% benzene decomposition (T: 950 °C), while methane decomposition was limited to 8%. While it is interesting to explore the catalytic benefits, the present modeling is limited to only noncatalytic scenarios.…”

“…The present study develops a novel modeling effort to explore all ranges of hydrocarbon fuels in an LMBR. More insights into the experimental findings and relevance of the recent work of Palmer et al 38 will be discussed in section 2.3.…”

“…Although there are studies that deal with the pyrolysis of hydrocarbons, which includes gaseous higher hydrocarbons such as ethane, propane, and butane − and liquid fuels, crude oils, and various petroleum fractions, − the molten metal pyrolysis investigations are scarce. Very recently, an experimental study on catalytic pyrolysis of hydrocarbon feedstocks such as propane, benzene, crude oil, and coal was explored by Palmer et al The same molten alloy combination of Upham et al (Ni 0.27 Bi 0.73 ) is investigated. The paper establishes the concern of the practicality of using feedstocks other than methane arising from high raw material cost and the limitation in the amount of hydrogen extraction per mole of feedstock due to low H/C ratio input.…”