Winfried Boenigk

Structural features and mesophase formation of coal-tar pitch fractions obtained by preparative size exclusion chromatography

Abstract High-temperature coal-tar pitch was fractionated by preparative size exclusion chromatography on Sephadex LH-20 in pyridine at 60 °C. The fractions obtained were characterized by elemental analysis, molecular weight determination (vapour pressure osmometry), i.r. spectroscopy, and TGA. The linear correlation observed between log molecular weight (range 200–2500 Dalton) and elution volume shows that fractionation of the pitch was mainly due to size exclusion and that interfering polar adsorption on the gel was essentially avoided. This is supported by the similarity between the i.r. spectra and elemental analyses of the fractions, respectively. The molecular weight distribution of the nitrogen-containing pitch constituents is also discussed. Selected samples were heat-treated using hot-stage microscopy. The reactivity of the fractions towards polymerization is lower than that of the unfractionated pyridine-soluble portion of pitch. This leads to a slower increase in viscosity of the fractions, thus allowing the formation of larger mesophase spheres. Addition of a small amount of a low molecular weight fraction to a high molecular weight fraction enhanced polymerization.

Pilot Anode Testing of Alternative Binder and CPC Raw Materials

The value of pilot anode testing for evaluating raw materials, anode recipes and mixing/forming changes has been well documented in previous studies. Since early 2013, RUTGERS and Rain CII have invested significant effort into developing a new pilot anode facility at Castrop-Rauxel, Germany. With the ability to mix and form paste at temperatures up to 300 °C and bake anodes at temperatures up to 1300 °C, this new facility is now being used actively across a wide range of carbon raw material R&D projects. Pilot-scale anode results will be presented to expand on previously reported work on low-PAH binder systems along with tests on different quality CPC raw materials. The good reproducibility of the pilot anode process allows better correlation of raw material properties and processing parameters on anode quality with a well targeted testing program.

Property Profile of Lab‐scale Anodes Produced with 180°C Mettler Coal Tar Pitch

The PAH-induced toxicity of coal tar pitch decreases with increasing softening temperature. The use of high- melting pitches is however restricted due to operational challenges. One critical limitation is high-temperature mixing. Temperatures up to 300 °C were now realized using a newly developed EIRICH mixer. A 180°C Mettler binder pitch resulted in lab-scale anodes having a higher baked density (+0.04 g/cm³). Electric resistivity and air permeability are reduced whereas compressive strength and Young’s modulus are increased. The significantly lower baking loss allows a faster carbonisation process in the low temperature range, potentially increasing the throughput of baking furnaces.

Pilot Anode Properties of Binder Pitches Softening Between 110 and 150 °C

Today there is a growing trend towards the use of higher melting binder pitches in the manufacture of prebaked anodes. Although 110–115 °C softening point Mettler (SPM) pitches are still the dominant quality for prebaked anodes, the use of 120 M pitches is growing and some anode producers are even using 130 M pitches on a routine basis. Due to their increased coking value, higher softening point pitches provide several property benefits over standard binders and total PAH levels are lower. Binders up to 150 M can be still produced with conventional distillation technology and processing as well as storage of these binders should be achievable in modern paste plants with relatively minor upgrades. Today’s generation of paste mixers are already capable of processing carbon paste up to 250 °C. The paper gives an overview of binder properties in the range of 112–150 M and presents the results of pilot anode testing with these binders.