Conversion of Polypropylene into Light Hydrocarbons and Aromatics by Metal Exchanged Zeolite Catalysts

Polyolefins can be converted into C2-C5 hydrocarbons and benzene-toluene-xylene (BTX) aromatics as high-demand petrochemical feedstocks via catalytic pyrolysis on acidic zeolites. Bro̷nsted and Lewis acid sites are responsible for cracking polyolefins into olefins and subsequent aromatic formation. In this study, we have subjected the parent HZSM-5 zeolite to postsynthetic partial metal exchange with Fe, Co, Ni, Cu, and Ce cations to perturb Bro̷nsted/Lewis acidity. We have investigated these metal-modified HZSM-5 on the catalytic pyrolysis of polypropylene (PP) in a micropyrolyzer connected to a two-dimensional gas chromatograph coupled to a time-of-flight mass spectrometer and flame ionization detector (Tandem Pyrolyzer-GC × GC-TOF-MS/FID setup). Whereas Fe-, Co-, Cu-, and Ce-exchanged zeolites (with 2.5, 2.3, 1.9, and 0.8 wt % metal, respectively) had comparable product yields with the parent zeolite, Ni-exchanged zeolites with Ni content of 0.5 to 2 wt % were associated with enhanced BTX formation (28-38 wt %) compared to that of the parent zeolite (22 wt %). Pyridine-FTIR indicated that the Bro̷nsted/Lewis acid ratio of the parent zeolite decreased upon metal ion exchange. According to Pyridine-TPD, the parent zeolite's medium-strength acid sites were redistributed into weak and strong acid sites in Ni-exchanged zeolites. The higher amount of carbon deposits on Ni-exchanged zeolites compared to the parent and other metal ion exchanged zeolites was attributed to the enhanced aromatization activity by the simultaneous decrease in the Bro̷nsted/Lewis acid ratio and emergence of strong acid sites.

Programmable heating and quenching for efficient thermochemical synthesis

Conventional thermochemical syntheses by continuous heating under near-equilibrium conditions face critical challenges in improving the synthesis rate, selectivity, catalyst stability and energy efficiency, owing to the lack of temporal control over the reaction temperature and time, and thus the reaction pathways^1-3. As an alternative, we present a non-equilibrium, continuous synthesis technique that uses pulsed heating and quenching (for example, 0.02 s on, 1.08 s off) using a programmable electric current to rapidly switch the reaction between high (for example, up to 2,400 K) and low temperatures. The rapid quenching ensures high selectivity and good catalyst stability, as well as lowers the average temperature to reduce the energy cost. Using CH₄ pyrolysis as a model reaction, our programmable heating and quenching technique leads to high selectivity to value-added C₂ products (>75% versus <35% by the conventional non-catalytic method and versus <60% by most conventional methods using optimized catalysts). Our technique can be extended to a range of thermochemical reactions, such as NH₃ synthesis, for which we achieve a stable and high synthesis rate of about 6,000 μmol g_Fe^-1 h^-1 at ambient pressure for >100 h using a non-optimized catalyst. This study establishes a new model towards highly efficient non-equilibrium thermochemical synthesis.

Catalytic co-pyrolysis of LDPE and PET with HZSM-5, H-beta, and HY: experiments and kinetic modelling

This study determines interaction effects and conducts kinetic modeling for catalytic co-pyrolysis of LDPE and PET with multiple zeolite frameworks.

Analytical Py-GC/MS of Genetically Modified Poplar for the Increased Production of Bio-aromatics

Genetic engineering is a powerful tool to steer bio-oil composition towards the production of speciality chemicals such as guaiacols, syringols, phenols, and vanillin through well-defined biomass feedstocks. Our previous work demonstrated the effects of lignin biosynthesis gene modification on the pyrolysis vapour compositions obtained from wood derived from greenhouse-grown poplars. In this study, field-grown poplars downregulated in the genes encoding CINNAMYL ALCOHOL DEHYDROGENASE (CAD), CAFFEIC ACID O-METHYLTRANSFERASE (COMT) and CAFFEOYL-CoA O-METHYLTRANSFERASE (CCoAOMT), and their corresponding wild type were pyrolysed in a Py-GC/MS. This work aims at capturing the effects of downregulation of the three enzymes on bio-oil composition using principal component analysis (PCA). 3,5-methoxytoluene, vanillin, coniferyl alcohol, 4-vinyl guaiacol, syringol, syringaldehyde, and guaiacol are the determining factors in the PCA analysis that are the substantially affected by COMT, CAD and CCoAOMT enzyme downregulation. COMT and CAD downregulated transgenic lines proved to be statistically different from the wild type because of a substantial difference in S and G lignin units. The sCAD line lead to a significant drop (nearly 51%) in S-lignin derived compounds, while CCoAOMT downregulation affected the least (7–11%). Further, removal of extractives via pretreatment enhanced the statistical differences among the CAD transgenic lines and its wild type. On the other hand, COMT downregulation caused 2-fold reduction in S-derived compounds compared to G-derived compounds. This study manifests the applicability of PCA analysis in tracking the biological changes in biomass (poplar in this case) and their effects on pyrolysis-oil compositions.

Evaluation of alkaline pretreatment temperature on a multi-product basis for the co-production of glucose and hemicellulose based films from lignocellulosic biomass

Cotton stalks were subjected to alkaline pretreatment for the co-production of glucose and hemicellulose based films with a multi-product approach. Three pretreatment temperatures (25, 60 and 90 °C) were evaluated for their effects both on the glucose yield and on the properties of hemicellulose based films. Compared to untreated cotton stalks, the glucose yields were enhanced 3.9, 4.1 and 4.2 times for pretreatments conducted at 25, 60 and 90 °C, respectively. The pretreatment temperature of 90 °C was detrimental in terms of film formation. Tensile energy to break values of the films obtained after pretreatments conducted at 25, 60 and 90 °C were 1.1, 0.8, and 0.4 MJ/m3, respectively. The hemicellulosic part of the process, which considers the production of hemicellulose based films, should govern the pretreatment temperature since it was more responsive to the changes in the pretreatment temperature compared to the cellulosic part that accounts for glucose production.