An investigation of the temperature programmed desorption (TPD) of CO and D2 from Ni(111) has been carried out. It has been shown that a differential method for the extraction of the kinetic parameters, threshold temperature programmed desorption (TTPD), can be applied with accuracy near the limit of zero coverage. In this limit, agreement is found between integral and differential methods for kinetic parameter evaluation. The factors which limit the applicability of TTPD are explored and a method to verify its proper application is presented.

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The annual global production of plastics reached 335 million metric tons in 2016. Most waste plastics are landfilled or enter the natural environment in an uncontrolled manner. Pyrolysis can convert waste plastics, such as polyethylene (PE), to smaller hydrocarbons that can be used as fuels or chemicals. In this work, pyrolysis of PE was studied by thermogravimetric analysis (TGA) and in a fluidized‐bed reactor. A kinetic model based on two parallel first‐order random‐scission steps was developed on the basis of the TGA results. PE was pyrolyzed in a fluidized‐bed reactor over the temperature range of 500–600 °C and at residence times of 12.4–20.4 s. The yield of gas‐phase products increased from 8.2 to 56.8 wt %, and the yield of liquid‐phase products decreased from 81.2 to 28.5 wt % as the temperature increased from 500 to 600 °C. Detailed analysis of the gas‐ and liquid‐phase products revealed their potential as precursors for production of fuels and chemicals. Gas‐phase products included hydrogen, C1–C4 paraffins, C2–C4 olefins, and 1,3‐butadiene. The major liquid‐phase products were mono‐olefins and cycloalkanes/alkadienes with smaller amounts of n‐paraffins, isoparaffins, and aromatics. The carbon‐number distribution of the fluidized‐bed pyrolysis products suggested contributions of nonrandom reactions of random‐scission fragments at low conversion.

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