J.M.N. van Kasteren

Design of a process for steam gasification of PVC waste

One possibility for recycling of PVC waste is steam gasification in a bubbling fluidized bed reactor. The main products are syngas, employable for energy recovery and HCl that can be reused for PVC production in an oxychlorination plant. In this study the technical and economical feasibility of this process is investigated based on experimental data and the implementation of proven technology where possible. The design capacity is 50 kton waste/year. Mass and energy balances were determined by the simulation software package Aspen Plus. Equipment costs of the simulated equipment are estimated and the gate fee of the PVC waste is calculated with a discounted cash flow analysis. The produced syngas proves to have a heating value of 8.6 MJ/Nm3. Half of the chlorine, present in PVC waste, can be regained as pure HCl gas. The rest leaves the process as CaCl2 waste due to the presence of lime, added as a filler material to many PVC compounds. The total investment costs are 10 million EUR. The gate fee, needed to obtain an internal rate of return of 15%, is established at about 67 EUR. The gate fee proves to be very sensitive for variation in the investment costs and is strongly affected by the costs of CaCl2 disposal.

Determination of the pyrolytic degradation kinetics of virgin-PVC and PVC-waste by analytical and computational methods

Thermogravimetric curves of virgin- and waste-PVC in an atmosphere of nitrogen and nitrogen saturated with water vapour were recorded at several heating rates to determine degradation kinetics. The degradation curves of virgin-PVC showed two stages of considerable mass loss. Application of the Friedman method to the experimental data proved to be too inaccurate to determine the kinetics unambiguously. Numerical determination of the kinetics parameters resulted in a better description of the data. Two models were fitted to a set of degradation curves of virgin-PVC. Both models showed good reproducibility. The effects of addition of water vapour to the atmosphere were limited to very high temperatures. The degradation curves of rigid PVC-waste showed an additional mass loss between 950 and 1150 K, presumably caused by limestone conversion. The model proposed to describe the degradation of rigid PVC-waste fitted the experimental curves well. Samples from PVC-waste pipes proved to be too heterogeneous to fit the degradation curves with one set of parameters.

Elementary Reactions and Kinetic Modeling of the Oxidative Coupling of Methane

The oxidative coupling of methane is typically carried out at temperatures of 650–950°C, using a methane-rich mixture of methane and oxygen or air, and with an oxidic catalyst of low porosity. The process is very complex in the sense that reactions at the surface of the catalyst strongly interfere with reactions in the homogeneous gas phase.

Methane Oxidative Coupling Using Li/MgO Catalysts: The Importance of Consecutive Reactions

Summary The importance of consecutive catalytic reactions in the oxidative coupling of methane over Li/MgO catalysts has been elucidated by means of low pressure experiments (10 - 150 Pa). Ethane is converted a factor 4 faster than methane, primarily into ethylene. Ethylene in turn is oxidized a factor 2.6 faster than methane. The latter factor provides an upper limit to the C2+ yield, achievable with a catalyst like Li/MgO. The product selectivity (at 1 bar) can be modelled quite well using a rather simple consecutive reaction scheme. The kethylene/kmethane ratio can be used as a parameter determining the product selectivity. Depending on the catalyst system and the process conditions, this parameter may vary between 2.6 and 19, causing the C2+ yield to vary between 35 and 6%. It seems possible to reach C2+ yield values of >25%, with C2+ selectivities > 65% via optimization of the interaction of homogeneous and heterogeneous reactions. This opens the way for the production of ethylene via the catalytic oxidative coupling of methane.

Working Principle of Li Doped Mgo Applied for The Oxidative Coupling of Methane

The nature of the active compound in Li doped MgO was investigated by comparing the activity and deactivation of Li/MgO catalysts with that of Li 2 CO 3 supported on an inert carrier (ZrO 2 ). The conclusion is that Li 2 CO 3 itself is a very active catalyst (or a catalyst precursor). Also the role of the catalyst in the oxidative coupling of methane was determined: The selectivity of the active catalyst is mainly due to a very high production rate of methyl radicals.