Abstract
Macroalgal blooms are environmentally problematic and costly to remediate, but they also represent a vast untapped resource for the production of renewable chemicals and fuels. The responsible exploitation of such marine resources will become increasingly prominent in the transition away from the crude oil economy that currently dominates global productivity. However, crude oil-derived plastic pollution is now a ubiquitous presence in the marine environment, which hampers the effective conversion of marine feedstocks. If the full potential of macroalgae is to be realized, any large-scale industrial process will need to accommodate the presence of this plastic. This study, for the first time, aimed to assess the effect of several common marine plastic pollutants on the hydrothermal liquefaction (HTL) of four UK macroalgae species and determine the impact on the major HTL products and biocrude oil quality. Co-liquefaction of polyethylene and polypropylene with L. digitata, U. lactuca, F. serratus, and S. mu...
Highlights
There is a pressing need to decarbonize global energy production systems, and biofuels compatible with current refinery and transportation infrastructure are a vital component of the transition
Co-liquefaction of PE with Spirulina was found to decrease the oxygen content of the biocrude products,[27] while we have previously demonstrated that coliquefaction of Vietnamese Ulva intestinalis with PE gave biocrudes with decreased nitrogen levels and increased higher heating value (HHV),[28] an overall improvement in fuel properties
Liquefaction of NY at Hydrothermal liquefaction (HTL) temperatures (340 °C) led to the conversion of 6.6% of the polymeric material to chloroform-soluble “biocrude” product and 10.9% to watersoluble material. Polycondensation polymers such as NY are susceptible to thermal degradation, and NY has been shown to depolymerize by hydrolysis at subcritical conditions to form monomeric ε-caprolactam via an ε-aminocaproic acid intermediate.[38]
Summary
There is a pressing need to decarbonize global energy production systems, and biofuels compatible with current refinery and transportation infrastructure are a vital component of the transition. With increasing PP blend levels, degradation between 400 and 500 °C becomes less pronounced, suggesting that unreacted PP is present This suggests that while more of the polymers break down under HTL conditions with macroalgae present, a significant proportion of the plastic retains some of its macrostructure and remains in the solid phase. Mn(II), and Cr(III) chlorides, as well as Mg(OH)2.53 Macroalgal ash contains a wide range of metals, the composition of which varies depending on the metals present in the marine environment, but macroalgae of the genus Ulva are considered to be good metal bioaccumulators and are often used as indicators of aqueous metal pollution.[54] It is likely that U. lactuca contained higher levels of catalytic transition metal species, which activated nylon depolymerization, while the content of the relevant metals in L. digitata may have been lower. The interplay between the many hundreds of individual reactions occurring under HTL conditions between biomass and plastics is complex and merits further study
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