Cleaner Chemical Engineering最新文献

Interest in hemp as a viable cellulosic fibre for clothing has increased, driven partly by its economic benefits and the importance of natural renewable materials in emerging circular economies. However, the coloration and chemical finishing of lignocellulosic fibres such as hemp typically require large quantities of water and chemicals. Argon plasma pretreatment provides a way of modulating the physical properties of hemp fibres to improve the coloration process without compromising other bulk properties such as tensile strength. Such plasma treatments may contribute to alleviating the negative environmental impacts associated with liquid pretreatments, heating, or the use of auxiliary chemicals. Dyeing of hemp fibres is particularly challenging due to its crystalline chemical structure. In this study, low-pressure argon plasma-assisted surface modification of woven hemp fabrics up to 600 s at 40 and 80 Hz was explored for enhanced dyeability, resulting in enhanced dye-fibre bonding. Fourier-transform infrared spectroscopy and Raman spectroscopy of argon plasma pretreated hemp fabrics produced no noticeable changes in the functional groups of the fibres, but a physiochemical modification was observed in terms of the density of polar groups. Scanning electron microscopy (SEM) images revealed marked morphological changes including nano-etching of the fibre surface at certain argon plasma process conditions. The pretreatment process increased fibre hydrophilicity, and enhanced reactivity of the surficial –OH groups towards fibre-reactive and vat dyes, resulting in higher colour strength in dyed woven hemp fabrics. Overall, we envisage such plasma pretreatments may impact positively on the material and energy efficiency of the hemp fabric dyeing process.

Catalytic upgrading of plastics to valuable fuels and chemicals is an attractive route to valorize waste plastics. Herein, catalytic pyrolysis of polypropylene was performed over γ-Al₂O₃ as a heterogeneous catalyst to produce fuel-grade hydrocarbons. The use of an inexpensive γ-Al₂O₃ catalyst and mild reaction conditions led to high liquid yield selectively in gasoline-range hydrocarbons which stands out from most of the work reported in the literature for polypropylene pyrolysis. The reaction conditions of pyrolysis were optimized by the Box-Behnken Design approach utilizing the response surface methodology. The highest liquid yield of 88.1 wt.% was obtained at 470 °C temperature, with 2 wt.% of catalysts and 5 h reaction time. The amount of solid carbon was insignificant (0.7 wt.%) and the gas yield was 11.2 wt.%. The γ-Al₂O₃ showed high efficiency and stability for converting polypropylene to liquid fuels. The catalyst was highly stable, reusable, and showed similar catalytic activity for 3 recycles. These features and the highly selective conversion of PP to gasoline range fuels are crucial for large-scale applications. The GC–MS analysis revealed that the liquid fuel produced mostly contained C8 to C15 hydrocarbons encompassing mostly gasoline and a small fraction of diesel fuel and higher hydrocarbons. The GC–MS data was also supported by SimDist analysis, which exhibited the boiling point ranging from 100 °C to 260 °C for the liquid fuel product. The reaction temperature and time had a significant impact on the liquid yield. The higher temperature favored the formation of the gaseous product of C1-C3 hydrocarbons. The NMR analysis showed that the liquid products mostly contained the highest amount of paraffins followed by olefins and a small fraction of aromatics. The presence of mild acidity in the γ-Al₂O₃ catalyst and optimum reaction condition provides favorable conditions to produce the highest yield of transportation fuel grade hydrocarbons without over-cracking into gases.

Sustainable liquid fuels are essential for decarbonization of various means of transportation which are challenging to address through electrification or hydrogen use. A possible method for producing low-carbon liquid fuel is through the thermochemical biomass to liquid (BTL) process. In this study, we conduct a technoeconomic-environmental analysis of two processes which take advantage of integration of natural gas reforming and biomass gasification, with the objective of improving the economics. By integrating H₂-rich syngas (a mixture of H₂/CO) obtained from natural gas reforming with carbon-rich syngas from biomass gasification, we harness synergistic effects. This combination allows us to achieve the optimal H₂/CO ratio required for methanol synthesis, while also ensuring efficient carbon utilization. In the first design, natural gas is reformed in an autothermal reformer (ATR) to produce syngas. A Solid Oxide Electrolysis Cell (SOEC) is utilized to supply the O₂ for both gasification and reforming processes. The H₂ produced by the SOEC adjusts the H₂ content in the syngas before the methanol synthesis reactor. In the second design, natural gas is reformed in a gas-heated-reformer (GHR) before an ATR, while an Air Separation Unit (ASU) produces the O₂ for the process. As a benchmark, the economics and flexible operation of both processes are compared to a conventional BTL process. In addition, the techno-economic impact of operating in biomass-only or natural gas-only modes are investigated. For a 134 MW_th plant with 50 % of entering carbon from biomass, the levelized cost of methanol (LCOMeOH) of ATR+SOEC case is 34 % higher than the BTL reference case, while that of ATR+GHR case is 24 % lower than the BTL reference case. A lifecycle analysis (LCA) is conducted for these designs. Utilizing renewable electricity and 50 % biogenic carbon, the ATR+SOEC case emits 908 kgCO_2e /tonne MeOH for a 100-year Global Warming Potential (GWP), while the ATR+GHR case emits 721 kgCO_2e /tonne MeOH. For a 20-year GWP, these emissions are 1055 and 915 kgCO_2e /tonne MeOH, respectively. These emissions correspond to more than 50 % reduction in LCA emissions when compared to natural gas based LCA emissions.

Film-like carbon is expected to have various applications, and establishing a method for its mass production is highly desirable. Although there have been reports of obtaining film-like solid carbon using thermal plasma, knowledge about the growth behavior of this film-like carbon has not been sufficient. We analyzed the products and their growth behavior by pyrolysis experiments of C2 hydrocarbons with thermal plasma and investigated the pyrolysis behavior of C2 hydrocarbons with thermal plasma by numerical analysis. Solid products with different residence times were sampled from a sampling port in the reactor, observed by electron microscopy, and analyzed for crystallinity by Raman spectroscopy and X-ray diffraction. The solid products collected by a filter at the reactor outlet were measured by pyrolysis gas chromatography-mass spectrometer (GC/MS). The pyrolysis of acetylene yielded particulate carbon as in the pyrolysis in the electric furnace, whereas the pyrolysis of ethylene yielded a film-like carbon. The HRTEM image of ethylene pyrolysis products, however, shows lines indicating a stacked graphite structure of several tens of nanometers, indicating a different structure. In the pyrolysis GC/MS of ethylene pyrolysis products, various compounds were detected, whereas in the pyrolysis of acetylene, polycyclic aromatic hydrocarbons (PAHs) from three to seven rings were not detected. Reaction kinetic calculations using electron collision reactions were performed to examine the important reactions. The amount of ions produced tends to be larger for the pyrolysis of ethylene than for the pyrolysis of acetylene, indicating that the electron collision reaction is more likely to occur with ethylene in this calculation.