Bis 2-hydroxyethyl Research Articles

Conversion of polyethylene terephthalate (PET) plastic particles in a microwave-assisted heating reactor

Abstract With the rapid economic development, PET (polyethylene terephthalate) plastic is widely used in various fields, i.e., clothing, food, housing and transportation. However, PET has a very strong chemical inertia, which makes it difficult to be degraded by microorganisms, thereby occupying a lot of space. Therefore, the recycling of waste PET has become one of the most important topics of environmental protection. Glycolysis requires the most mild and safe reaction environment among chemical recycling methods, and the ethylene glycol used in the reaction can be reused. Using glycolysis to recycle PET undoubtedly conforms to the green and sustainable concept, and glycolysis recycling is undoubtedly a low-cost, low-consumption and low-harm path for PET recycling. The heating and glycolysis characteristics of microwave-assisted PET glycolysis, and the energy analysis of glycolysis were studied. The aim was to produce BHET (bis(2-hydroxyethyl) terephthalate) as the target product from PET waste. In this study, the effects of reaction temperature, reaction time, and PET particle size on the performances of PET conversion rate, oligomeric BHET yield, and BHET yield were examined, and the energy efficiency and recovery efficiency also were presented. The results showed that the optimal conditions for microwave-assisted PET glycolysis were reaction temperature of 180 °C, reaction time of 30 min, and PET particle size of 75 μm, and the maximum PET conversion rate was 66.71 ± 9.71 wt%, the maximum yield of BHET was 48.08 ± 0.68 wt% and the maximum BHET yield was 19.83 ± 5.40 wt%. The energy efficiency and recovery efficiency were 11.88 % and 17.89 %, respectively.

Expression, purification and characterization of a novel bis (hydroxyethyl) terephthalate hydrolase from Hydrogenobacter thermophilus

PET (polyethylene terephthalate) is one of the most important petrochemicals that is widely used in mineral water bottles, food and beverage packaging and textile industry. Because of its stability under environmental conditions, the massive amount of PET wastes caused serious environmental pollution. The use of enzymes to depolymerize PET wastes and upcycling is one of the important directions for plastics pollution control, among which the key is the depolymerization efficiency of PET by PET hydrolase. BHET (bis(hydroxyethyl) terephthalate) is the main intermediate of PET hydrolysis, its accumulation can hinder the degradation efficiency of PET hydrolase significantly, and the synergistic use of PET hydrolase and BHET hydrolase can improve the PET hydrolysis efficiency. In this study, a dienolactone hydrolase from Hydrogenobacter thermophilus which can degrade BHET (HtBHETase) was identified. After heterologous expression in Escherichia coli and purification, the enzymatic properties of HtBHETase were studied. HtBHETase shows higher catalytic activity towards esters with short carbon chains such as p-nitrophenol acetate. The optimal pH and temperature of the reaction with BHET were 5.0 and 55 ℃, respectively. HtBHETase exhibited excellent thermostability, and retained over 80% residual activity after treatment at 80 ℃ for 1 hour. These results indicate that HtBHETase has potential in biological PET depolymerization, which may facilitate the enzymatic degradation of PET.

Removal of Zn2+ from glycolytic monomers of the polyethylene terephthalate based on electrodeposition

The usage of zinc-containing catalysts in glycolysis causes the residue of Zn2+ in the polyethylene terephthalate (PET) degradation monomer bis-hydroxyethyl (BHET), which limits the high-value utilization of BHET. This work first used electrodeposition combined with one-time recrystallization to purify BHET. Electrodeposition was suitable for dealing the Zn2+ concentrations of degradation solutions within 50–100 ppm, and decreased the content of Zn2+ in BHET from 141.30 to 2.41 ppm, which reached the standard of repolymerization into PET bottles. The removal rate of Zn2+ was 90 % for the degradation solutions, which decreased the concentration of Zn2+ in wastewater from 100 to 8.97 ppm. Meanwhile, the Zn2+ removed from the degradation solutions was deposited on cathode, which obtained metal Zn materials and realized the recycling of Zn resources from Zn(OAc)2. Therefore, electrodeposition could realize the purification of BHET, recycling of Zn(OAc)2, reducing the environmental pollution caused by the emission of Zn2+ and the protection of human health, simultaneously. Electrodeposition had less water consumption, lower loss rate of BHET (from 60 % to 10 %) and shorter processing time, compared with six-times recrystallizations. This study first proposed the formation of quadridentate between BHET and Zn2+, and put forward a new three-steps electrodeposition mechanism of Zn2+: the addition of electric field destroyed the dissociation equilibrium of quadridentate and made it shift to release free Zn2+; the free Zn2+ gathered to form ionic groups and they migrated to copper; Zn2+ reduced on copper, of which the first step was the speed limited step.

A new continuous assay for quantitative assessment of enzymatic degradation of poly(ethylene terephthalate) (PET)

Enzymatic degradation of poly(ethylene terephthalate) (PET) has emerged as a promising route for ecofriendly biodegradation of plastic waste. Several discontinuous activity assays have been developed for assessing PET hydrolyzing enzymes, usually involving manual sampling at different time points during the course of the enzymatic reaction. In this work, we present a novel, compartmentalized UV absorbance assay for continuous detection of soluble hydrolysis products released during enzymatic degradation of PET. The methodology is based on removal of the walls separating two diagonally adjacent wells in UV-transparent microplates, to ensure passage of soluble enzymatic hydrolysis products between the two adjacent wells: One well holds an insoluble PET disk of defined dimensions and the other is used for continuous reading of the enzymatic product formation (at 240 nm). The assay was validated by quantifying the rate of mixing of the soluble PET degradation product BHET (bis(2-hydroxyethyl) terephthalate) between the two adjacent wells. The assay validation also involved a simple adjustment for water evaporation during prolonged assays. With this new assay, we determined the kinetic parameters for two PET hydrolases, DuraPETase and LCCICCG, and verified the underlying assumption of steady-state reaction rates. This new continuous assay enables fast exploration and robust kinetic characterization of PET degrading enzymes.