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The combined mixture process variable approach for optimization and prediction of oil yield in co‐pyrolysis of polymeric wastes was investigated in this study using I‐optimal design. The components mixture investigated were low‐density polyethylene (LDPE), polystyrene (PS), and polyethylene terephthalate (PET), whereas the process variables were temperature and residence time. Thirty experimental runs were developed using the I‐optimality criterion to investigate the effect of interaction between the mixture and process parameters on oil recovery from co‐pyrolysis of the polymeric wastes. The data obtained were used to generate a model equation, and analysis of variance was used to estimate the significance of the model. The model was significant with a P value < 0.0001, the R2 value of 0.9980, adjusted R2 of 0.9949, and predicted R2 of 0.9201. Optimized oil yield showed close match between actual and predicted responses with a desirability factor of 0.999. The predicted mixture compositions and operating parameters for the optimum oil yield were 52.86% for LDPE, 47.15% for PS, and 0% for PET at 471.07°C and 115.25 minutes. The chemical compositions of the pyrolysis oil at the optimum conditions were hydrocarbons in the carbon range between C6 and C25, with physical properties comparable to conventional diesel.

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Chemical characterization of Portland limestone cement products collected across the nine existing cement manufacturing plants in Nigeria was conducted using Energy Dispersive X-ray Fluorescence Spectrometer (EDXRF) with the aim of determining conformity with global and local standards and investigating likely variation in quality resulting from differences in the sources of major raw materials, especially limestone used in production. The cement samples are composed essentially of CaO, SiO2, Al2O3, Fe2O3, MgO, Na2O, K2O and SO3 while P2O5, MnO and TiO2 were present in trace amount. In addition to oxide compositions, the mineralogical components: Alite (C3S), Belite (C2S), Celite (C3A), and Ferrite (C4AF), and other cement quality control variables such as Lime Saturation Factor, Silica Modulus and Alumina Modulus of all the nine cement samples analyzed in this study are in agreement with the specifications for Portland limestone cement published by the Standard Organisation of Nigeria (SON), the American Society for Testing and Materials (ASTM), and the British Standards Institution (BSI). The nine cement products also have their compositions in close proportion indicating none of the products is superior in quality irrespective of manufacturer or production site, a common misconception in the Nigerian cement market.