No abstract

Carbon anodes for aluminium production are produced from calcined petroleum coke (CPC), recycled anode butts and coal tar pitch (CTP). The CO 2 produced during anode consumption contributes to a substantial amount of the CO 2 footprint of this industrial process. Charcoal from wood has been suggested to partly replace coke in anodes but high porosity, low electrical resistivity and high ash content contributes negatively to final anode properties.In this work, charcoal from Siberian larch and spruce was produced by heat treatment to 800 °C, 1200 °C and 1400 °C and acid-washed with H 2 SO 4 . Acid-washing resulted in reduced metal impurity and the porosity decreased with increasing heat treatment. Pilot anodes were made from CTP, CPC with some additions of spruce and larch charcoal. Another set of pilot anodes were produced using a green binder. Compared to reference anodes, the CO 2 reactivity of anodes containing larch was less affected compared to anodes containing spruce. The green binder was found to be highly detrimental for the anodes' CO 2 reactivity properties. Electrochemical consumption increased for anodes containing both green binder, larch and spruce compared to the reference anode.

The phenomenon of ‘gas migration’ during oil well cementing is believed to occur during the transition state between initial and final set of the cement. In order to evaluate the importance of pore openings and total porosity in the critical time gap, a suitable experimental technique was tested on some neat oil well cement slurries. The hydration was effectively stopped every 30 min at 20°C and every 20 min at 60°C by dropping plastic tubes containing the cement slurry into liquid nitrogen (i.e. quenching), cracking the tubes open and letting the frozen bits of paste thaw in ethanol. The change in porosity and pore size distribution was determined by helium pycnometry and mercury intrusion porosimetry as a function of time in the setting period for a plain API class G cement slurry (w/c = 0·50) at both 20°C and 60°C. These data were compared with the amount of chemically hound water in the same samples, and used to predict the total porosity at a given degree of hydration. The excellent correspondance of experimental and theoretical porosities validates the experimental procedure, which can also be used in explaining the variation in gas migration between commercial oil well cement slurries.

This paper presents partial phase relations for the systems NaF–CaF2, NaF–CaF2–CaO, NaF–CaF2–CaCO3, NaF–CaF2–NaCO3, and NaF–CaF2–Na2CO3–CaCO3. The data were obtained by thermal analysis (TA), thermodynamic calculations (FactSage), and X-ray diffraction (XRD) of quenched samples. There was particular emphasis on revealing the phase formations of CaO, CaCO3, and Na2CO3 in the eutectic composition of NaF–CaF2 for the development of a novel carbon capture technology. Therefore, a thermal analysis of the binary CaF2–NaF system was performed first. A eutectic point was found at 31.9 mol % CaF2 and 814.8 °C. The liquidus isotherms and phase regions of the Na–Ca//F–O and Na–Ca//F–CO3 systems were mapped using FactSage. In addition, some compositions in the NaF–CaF2–CaO and NaF–CaF2–Na2CO3–CaCO3 systems were studied by TA. XRD analysis of the quenched samples was applied for phase identification. Based on the FactSage simulation and the experimental data, the solubility of CaO increases with increasing CaF2 concentration in NaF melt. It was derived that carbonates (Na2CO3 and CaCO3) in NaF–CaF2 are present as intermediate compounds. The reactions of NaF and CaCO3 and the formation of complex carbonates are discussed. In general, there is good agreement between experimental data and simulations.

Aluminium is today commercially produced by the Hall-Héroult process using consumable carbon anodes. Consumable anodes have some concerns such as CO 2 emission, continuous anodecathode distance adjustments and replacements of anodes. Replacing the consumable anodes with inert anodes has been a topic for many decades without commercial success so far. Using porous inert anodes where natural gas or hydrogen take place in the anode reaction has been shown in laboratory tests to reduce the anode potential and reduce the CO 2 emission. However, formation of water results in evolution hydrogen fluorides which must be solved. Laboratory experiments using porous depolarized SnO 2 -based anodes with CH 4 and H 2 -gases have been performed with off-gas analysis and with special attention to hydrogen fluoride evolution. Some ideas of how the additional HF evolution is presented.