Increase of the softening point of a petroleum pitch by heat-treatment in the presence of a nitrogenated resin

Abstract

Carbon fibres (CF) can be prepared from very different pitch with a low softening point, a low carbon yield precursors like PAN, rayon, resins and pitches [1]. In (SP5384 K, carbon yield540 wt.%) and a very good particular, pitch is readily available in large quantities and spinnability (tested in a monofilament spinneret). The first low costs because it is a by-product of the distillation of two characteristics make the material not useful for petroleum, coal or natural asphalt. The preparation of preparation of CF because the stabilisation is extremely carbon fibres from petroleum or coal pitches consists of difficult. The nitrogenated material used was a commercial different steps: firstly, a pitch treatment, secondly the aminoformaldehyde resin (s-176, Nipon Carbide Industries spinning, followed by stabilisation and carbonisation steps. Co.), that is a condensation product of melamine (2,4,6Finally, depending on the further application of the materitriamino-1,3,5-triazine) and formaldehyde. This melamine al, additional steps are needed, like activation for manufacresin was chosen due to its high nitrogen content (47 turing porous solids or doping with heteroatoms to modify wt.%) and its structure, presented in Fig. 1. the chemical properties of the carbon fibres or graphitisaThe resin and the pitch were physically mixed at tion for manufacturing high performance materials. different ratios in a mortar to ensure a homogeneous In the case of petroleum and coal tar pitches, a precontact between particles. To choose the treatment temtreatment is necessary to obtain a material with an perature, the thermal history of the resin was studied by adequate viscosity to be spun and a sufficiently high thermogravimetry (SDT 2960, TA instruments) (Fig. 2). softening point (SP) or a sufficiently high reactivity to be An important weight loss at around 648 K occurs which easily stabilised. During the last years, big efforts have corresponds with the decomposition of the melamine been made to develop suitable methods that permit the use monomer units. Then, temperatures around this value, of low softening point pitches. Three possibilities have ranging between 623 and 723 K, were used for the heat been analysed: (i) a heat treatment in air to increase the treatment of the pitch / resin mixtures. The mixture was softening point [2,3], (ii) the use of gases, like NO [4] or then heat-treated in a fixed bed reactor under He flow (100 2 halogens [5], during the stabilisation of pitch fibres, and ml /min), using a heating rate of 5 K/min and maintaining (iii) the modification of the chemical composition of the the treatment temperature for 30 min. pitch to increase its reactivity [2,6]. The effect of the pitch / resin ratio and the heat treatment In this work, the blending of a low softening point temperature was analysed by spinning tests and DSC (DSC petroleum pitch and a nitrogenated resin is analysed, 2920, TA Instruments). Fig. 3 presents the DSC curves for paying attention to the changes occurring on the resulting the materials prepared. The figure includes the SP values. pitch from the point of view of the preparation of carbon For a given pitch / resin ratio and different heat treatment fibres. The main purpose of the present method is to transform the initial pitch, not useful for preparation of carbon fibres, into a material with a high softening point and appropriate viscosity, able to be spun and stabilised. We also seek to prepare N-doped carbon fibres that have shown to be of interest to modify their catalytic or adsorptive properties [7]. The study was done with a standard binder petroleum