Novel insights in dimethyl carbonate-based extraction of polyhydroxybutyrate (PHB)

Abstract

Background Plastic plays a crucial role in everyday life of human living, nevertheless it represents an undeniable source of land and water pollution. Polyhydroxybutyrate (PHB) is a bio-based and biodegradable polyester, which can be naturally produced by microorganisms capable of converting and accumulating carbon as intracellular granules. Hence, PHB-producing strains stand out as an alternative source to fossil-derived counterparts. However, the extraction strategy affects the recovery efficiency and the quality of PHB. In this study, PHB was produced by a genetically modified Escherichia coli strain and successively extracted using dimethyl carbonate (DMC) and ethanol as alternative solvent and polishing agent to chloroform and hexane. Eventually, a Life Cycle Assessment (LCA) study was performed for evaluating the environmental and health impact of using DMC. Results Extraction yield and purity of PHB obtained via DMC, were quantified, and compared with those obtained via chloroform-based extraction. PHB yield values from DMC-based extraction were similar to or higher than those achieved by using chloroform (≥ 67%). To optimize the performance of extraction via DMC, different experimental conditions were tested, varying the biomass state (dry or wet) and the mixing time, in presence or in absence of a paper filter. Among 60, 90, 120 min, the mid-value allowed to achieve high extraction yield, both for dry and wet biomass. Physical and molecular dependence on the biomass state and solvent/antisolvent choice was established. The comparative LCA analysis promoted the application of DMC/ethanol rather than chloroform/hexane, as the best choice in terms of health prevention. However, an elevated impact score was achieved by DMC in the environmental-like categories in contrast with a minor contribution by its counterpart. Conclusion The multifaceted exploration of DMC-based PHB extraction herein reported extends the knowledge of the variables affecting PHB purification process. This work offers novel and valuable insights into PHB extraction process, including environmental aspects not discussed so far. The findings of our research question the DMC as a green solvent, though also the choice of the antisolvent can influence the impact on the examined categories.

Ethylic Esters as Green Solvents for the Extraction of Intracellular Polyhydroxyalkanoates Produced by Mixed Microbial Culture

“…In alternative to chlorinated hydrocarbons, which are the best solvents for PHAs, many research studies address the use of green solvents, with low or no toxicity and possibly derived from biochemical conversion, to overcome ecological issues, limitations involving worker safety or stringent regulations on solvent traces in goods for particular applications [ 25 ]. Solvents characterized by low toxicity, including ethers [ 26 , 27 ], esters [ 25 , 27 , 28 , 29 ], carbonates [ 29 , 30 , 31 , 32 ] and ketones [ 28 , 33 , 34 ], have been identified as appealing alternatives to chlorinated hydrocarbons. Their suitability is evaluated by taking into account their recyclability, the need for biomass pretreatment, polymer recovery yield, the quality of the extracted polymer in terms of purity and possible molecular weight reduction, as well as process cost and environmental performances [ 35 , 36 ].…”

Optimization for the efficient recovery of poly(3-hydroxybutyrate) using the green solvent 1,3-dioxolane

“…On the other hand, the % purity from wet cells slightly decreased when scaled up from 40 ml to 1,000 ml. Therefore, our single step extraction process provided better efficiency than that reported in other reports (Manangan and Shawaphun, 2010;Fei et al, 2016;Aramvash et al, 2018;Mongili et al, 2021). Furthermore, solid-liquid separation by addition of water into PHB solubilized in 1,3-dioxolane provides PHB powder with off-white color.…”

“…Many researchers have tried to find cheap and environmentally safe solvents to replace the use of chloroform, such as sodium hypochlorite (Choi and Lee, 1997;Heinrich et al, 2012), linear and cyclic carbonates (Fiorese et al, 2009;Samorì et al, 2015;Fei et al, 2016), ethyl acetate (Riedel et al, 2013), and ionic liquids and supercritical fluids (Hampson and Ashby, 1999). those achieved by using chloroform (≥67%) (Mongili et al, 2021). PHB extraction using high-pressure CO 2 , enzymatic recovery, and 1,2-propylene carbonate has been demonstrated to achieve high yield and purity (Calleja Luque, 2020).…”

“…Recently, several green extraction processes have been proposed. For instance, dimethyl carbonate (DMC) and ethanol as alternative solvents to chloroform and hexane have been reported with PHB yield values similar to or higher than those achieved by using chloroform (≥67%) ( Mongili et al, 2021 ). PHB extraction using high-pressure CO 2 , enzymatic recovery, and 1,2-propylene carbonate has been demonstrated to achieve high yield and purity ( Calleja Luque, 2020 ).…”

Sustainable valorisation of renewables through dialkyl carbonates and isopropenyl esters

“…chloroform and hexane, observing comparable extraction yields. 116 DMC and DACs are suitable bio-sourced solvents for membranes manufacture. 117 For example, Pescarmona and coworkers evaluated the use of DACs as sustainable solvent alternatives in membranes fabrication, obtained from synthetic and artificial polymers.…”