Conversion Rate Of Glycerol Research Articles

Kinetic Study of Pd-Promoting Effect on Cu/ZnO/Al2O3 Catalyst for Glycerol Hydrogenolysis to Produce 1,2-Propanediol at Low Hydrogen Pressure

The promoting effect of Pd on a Cu/ZnO/Al2O3 catalyst for the aqueous glycerol hydrogenolysis process to produce 1,2-propanediol was studied. At a lower hydrogen pressure (2.07 MPa), using the Cu/ZnO/Al2O3 catalyst with 2 wt% Pd doped, could significantly improve the glycerol conversion (97.2%) and 1,2-propanediol selectivity (93.3%) compared with the unpromoted catalyst (69.4% and 89.7%, respectively). A power-law kinetic model, which took into account all the elementary reactions including glycerol dehydration and its reverse reaction, acetol hydrogenation, side reactions and ethylene glycol formation, was developed to comprehensively investigate the effect of Pd. Though the rate of glycerol dehydration using the Pd-promoted catalyst was found to be slightly lower, mainly due to the reduced number of acidic sites after adding Pd, the glycerol conversion rate was notably higher compared with using the unpromoted catalyst, mainly attributed to the enhanced activity of acetol hydrogenation by Pd. The rapid hydrogenation of acetol can inhibit the reverse reaction of glycerol dehydration, resulting in a higher glycerol conversion rate, so that glycerol dehydration is considered as the rate-determining step. In contrast, when the unpromoted catalyst was used, the rate of reverse glycerol dehydration was drastically increased due to the elevated acetol concentration, especially at a lower hydrogen pressure, resulting in a slower glycerol conversion rate; thus, acetol hydrogenation became the rate determining step. In addition, Pd can improve the reducibility of the catalyst, allowing the CuO to be reduced in situ during the reaction. Therefore, catalyst deactivation due to any potential oxidation of metallic copper during the reaction can be prevented.

Enhance glycerol conversion through co-etherification with isobutene and tert-butanol

tert-Butyl glycerol ethers obtained from etherification of glycerol with isobutene or tert-butanol are desirable fuel additives. While glycerol etherification with isobutene has high glycerol conversion and yield to the desired ethers, it undergoes intricate interphase mass-transfer and the rate is restricted by the low reactant concentration resulting from phase separation. On the contrary, although glycerol etherification with tert-butanol avoids phase separation, the conversion and yield are relatively low due to equilibrium limitation and/or the inhibition from the produced water. We proposed to etherify glycerol with isobutene and tert-butanol simultaneously (co-etherification) to enhance glycerol conversion. Multiphase chemical equilibrium was calculated to explore the phase states of reaction mixtures as well as the equilibrium conversions and yields under a wide range of conditions. The co-etherification was then demonstrated on NKC-9 catalyst, which validated that the solvation function of tert-butanol to the glycerol-isobutene mixture improved the glycerol conversion rate (up to twice). Isobutene addition raised glycerol conversion and yield to the poly-substituted ethers comparing with the etherification with tert-butanol. Co-etherification (G:IB:TBA = 1:3:1) yielded 0.573 poly-substituted ethers at 353 K, while the yield was only 0.069 in the G-TBA etherification (G:TBA = 1:4). Moreover, the presence of tert-butanol effectively hindered the undesired isobutene dimerization.

Synthesis of Hydrotalcites from Waste Steel Slag with [Bmim]OH Intercalated for the Transesterification of Glycerol Carbonate.

Ca-Mg-Al hydrotalcites were prepared by coprecipitation from Type S95 steel slag of Shanghai Baosteel Group as supports of ionic liquid in this paper. Five basic ionic liquids [Bmim][CH3COO], [Bmim][HCOO], [Bmim]OH, [Bmim]Br and ChOH were prepared and their catalytic performance on the synthesis of glycerol carbonate by transesterification between dimethyl carbonate and glycerol was investigated. The characterization results indicated that [Bmim]OH is the best ionic liquid (IL) for the transesterification reaction of glycerol carbonate. The hydrotalcites before and after intercalation by ionic liquid were characterized by XRD, FTIR, SEM, EDS and the IL were characterized by FT-IR, 13C-NMR and basicity determination via the Hammett method. The analysis results implied that the dispersion of [Bmim]OH in hydrotalcites reduced the alkali density appropriately and facilitated the generation of glycerol carbonate. The yield of glycerol carbonate and the conversion rate of glycerol reached 95.0% and 96.1%, respectively, when the molar ratio of dimethyl carbonate and glycerol was 3:1, the catalyst dosage was 3 wt%, the reaction temperature was 75 °C and the reaction time was 120 min. The layered structure of hydrotalcites increased the stability of ionic liquid intercalated in carriers, thus the glycerol conversion and the GC yield still remained 91.9% and 90.5% in the fifth reaction cycle.

Niobium Enhances Electrocatalytic Pd Activity in Alkaline Direct Glycerol Fuel Cells

AbstractPdxNby/C binary electrocatalysts supported on Printex 6 L carbon black were prepared by using an adapted chemical reduction method with sodium borohydride. The electrocatalysts were characterized by using SEM, TEM, XRD, EDS, ICP‐MS, water contact angle and Raman spectroscopy. The best performance for the alkaline direct glycerol fuel cell (ADGFC) was obtained by using Pd1Nb1/C, which yielded a maximum power density of 27 mW cm−2 at 70 °C. Residues of products formed from the glycerol oxidation were analyzed by using FT‐Raman and high‐performance liquid chromatography (HPLC). The Pd1Nb1/C electrocatalyst exhibited a more negative onset potential for the CO oxidation reaction and a higher conversion rate of glycerol to carbonate. We suggest that the higher hydrophilicity, higher degree of disorder, and bifunctional effects enhanced the electrocatalytic activity of Pd, as Nb facilitated the oxidation of adsorbed CO in Pd and increased the transfer rate of electron from Pd to carbon black support Therefore, Nb is a promising co‐catalyst for Pd‐based electrocatalysts for ADGFCs.

Enhanced 1,3-propanediol production in Klebsiella pneumoniae by a combined strategy of strengthening the TCA cycle and weakening the glucose effect.

This study aimed to strengthen the reducing equivalent generation in Klebsiella pneumoniae for improving 1,3-propanediol (PDO) production. Disruption of the arcA gene activated the transcription levels of the TCA cycle genes and thus increased the NADH/NAD+ ratio by 54·2%, leading to the improved PDO titre and yield per cell from 16·1gl-1 and 4·0ggDCW-1 to 18·8gl-1 and 6·4ggDCW-1 respectively. Further ldhA gene deletion eliminated lactate accumulation and promoted the PDO titre to 19·9gl-1 . Finally, the glucose effect was weakened by deleting the crr gene to enhance the co-utilization of glucose and glycerol, resulting in the increased PDO production to 23·8gl-1 with the glycerol conversion rate of 59·5%. The PDO titre in bioreactor was promoted from 61·2 to 78·1gl-1 . Deletions of the arcA and the crr genes showed positive effects on the TCA cycle activity and the co-utilization of glucose and glycerol, leading to the strengthened reducing equivalent generation and the improved PDO titre by 47·8% in shaker. The PDO titre in the bioreactor was enhanced to 78·1gl-1 . This study provided novel information on generating reducing equivalent for the PDO biosynthesis by strengthening the TCA cycle and weakening the glucose effect in K. pneumoniae.

Co-Production of Ethanol and 1,2-Propanediol via Glycerol Hydrogenolysis Using Ni/Ce–Mg Catalysts: Effects of Catalyst Preparation and Reaction Conditions

Crude glycerol from biodiesel production is a biobased material capable of co-producing biofuels and chemicals. This study aimed to develop a line of Ni catalysts supported on cerium–magnesium (Ce–Mg) to improve the process efficiency of glycerol hydrogenolysis for ethanol and 1,2-propanediol (1,2-PDO). Results showed that catalytic activity was greatly improved by changing the preparation method from impregnation to deposition precipitation (DP), and by adjusting calcination temperatures. Prepared via DP, the catalysts of 25 wt % Ni supported on Ce–Mg (9:1 mol/mol) greatly improved the effectiveness in glycerol conversion while maintaining the selectivities to ethanol and 1,2-PDO. Calcination at 350 °C provided the catalysts better selectivities of 15.61% to ethanol and 67.93% to 1,2-PDO. Increases in reaction temperature and time improved the conversion of glycerol and the selectivity to ethanol, but reduced the selectivity to 1,2-PDO. A lower initial water content led to a higher conversion of glycerol, but lower selectivities to ethanol and 1,2-PDO. Higher hydrogen application affected the glycerol conversion rate positively, but the selectivities to ethanol and 1,2-PDO negatively. A comparison to the commercial Raney® Ni catalyst showed that the Ni/Ce–Mg catalyst developed in this study showed a better potential for the selective co-production of ethanol and 1,2-PDO from glycerol hydrogenolysis.

Synthesis of bioadditives of fuels from biodiesel-derived glycerol by esterification with acetic acid on solid catalysts

ABSTRACTIn this paper, glycerol esterification with acetic acid (AA) was studied on several solid acid catalysts: Al2O3, Al-MCM-41, HPA/SiO2, HBEA, Amberlyst 15 and Amberlyst 36 with the aim of determining the reaction conditions and the nature of the surface acid sites required to produce selectively triacetylglycerol (triacetin). The acidity of the catalysts (nature, density and strength of acid sites) was characterized by temperature-programmed desorption of NH3 and FTIR of adsorbed pyridine. Al2O3 (Lewis acidity) did not show any activity in the reaction. In contrast, highest activity and selectivity to the triacetylated product (triacetin) were obtained on catalysts with Brønsted acidity: Amberlyst 15 and Amberlyst 36. The effect of temperature and molar ratio of AA to glycerol was studied, and the results showed that both parameters have a significant impact on the production of the desired product. Glycerol conversion rate and selectivity to triacetin increased when temperature or AA to glycerol molar ratio were increased, reaching a triacetin yield on Amberlyst 36 of 44% at 393 K and AA to glycerol molar ratio of 6. Deactivation and reusability of Amberlyst 36 were evaluated by performing consecutive catalytic tests. The presence of some irreversible deactivation due to sulfur loss was observed. In addition, the feasibility of using crude glycerol from biodiesel production as reactant was also investigated. Conversion of crude pretreated glycerol yielded values of triacetin and diacetin similar to those obtained with the commercial pure glycerol although at a lower rate.

Synthesis, characterisation, and evaluation of stable, efficient modified nanocopper‐based glycerol hydrogenolysis catalysts

A series of CuO/SiO2 catalysts containing different modifiers were prepared via co-precipitation and used for glycerol hydrogenolysis. CuO–CeO2/SiO2 gave the best glycerol conversion rate (100%) and highest selectivity for 1,2-propanediol (up to 95%). Reactions were carried out under the following conditions: temperature, 220°C; H2 pressure, 0.5 MPa; glycerol concentration, 100 wt.%; and H2/glycerol molar ratio, 35:1. The catalysts were characterised by X-ray diffraction, NH3 temperature-programmed desorption, N2 adsorption, and scanning electron microscopy. The CuO–CeO2/SiO2 catalyst had smaller particle sizes, better dispersion, and greater specific surface area than the CuO/SiO2, CuO–phosphotungstic acid (PTA)/SiO2, and CuO–CeO2–PTA/SiO2 catalysts.

Metabolic engineering of Klebsiella pneumoniae J2B for the production of 1,3-propanediol from glucose

The production of 1,3-propanediol (1,3-PDO) from glucose was investigated using Klebsiella pneumoniae J2B, which converts glycerol to 1,3-PDO and synthesize an essential coenzyme B12. In order to connect the glycolytic pathway with the pathway of 1,3-PDO synthesis from glycerol, i.e., to directly produce diol from glucose, glycerol-3-phosphate dehydrogenase and glycerol-3-phosphate phosphatase from Saccharomyces cerevisiae were overexpressed. Additionally, the effect of expression levels and the use of isoforms of these two enzymes on glycerol and 1,3-PDO production were studied. Furthermore, to prevent loss of produced glycerol, the glycerol oxidation pathways were disrupted. Finally, the conversion rate of glycerol to 1,3-PDO was increased via homologous overexpression of glycerol dehydratase and 1,3-PDO oxidoreductase. The resultant strain successfully produced 1,3-PDO from glucose at a yield of 0.27mol/mol along with glycerol at 0.52mol/mol. Improvement of the engineered K. pneumoniae J2B to further increase conversion of glycerol to 1,3-PDO is discussed.

Repeated biotransformation of glycerol to 1,3-dihydroxyacetone by immobilized cells of Gluconobacter oxydans with glycerol- and urea-feeding strategy in a bubble column bioreactor

Some inorganic nitrogen sources and amino acids instead of yeast extract, which resulted in trouble of product purification, were introduced for 1,3-dihydroxyacetone (DHA) production by biotransformation with Gluconobacter oxydans. The results showed that urea is an optimal nitrogen source. Furthermore, the effects of glycerol- and urea-feeding strategies for DHA production by immobilized cells in a home-made bubble column bioreactor were optimized. Cells immobilization was prepared by cultivation in the bioreactor packed with porous ceramics, and then the broth was removed. Then, repeated biotransformation by continuous-feeding of glycerol and urea was developed. Up to 96.4±4.1g/L of average DHA concentration with 94.8±2.2% of average conversion rate of glycerol to DHA was achieved after 12 cycles of run. Near colorless DHA solution with few impurities was obtained and the production cost could be decreased.

A comprehensive kinetic model for Cu catalyzed liquid phase glycerol hydrogenolysis

Hydrogenolysis of biomass-derived glycerol has been investigated as an alternative route for the production of value-added chemicals, such as 1,2-propanediol, also commonly denoted as propylene glycol (PG). Intrinsic glycerol hydrogenolysis kinetics have been acquired experimentally on a stable, commercial copper-based catalyst in an isothermal trickle-bed reactor at 463–513K, hydrogen pressures from 6.5 to 8MPa and space times (W/FG0) from 25 to 340kgsmol−1 resulting in glycerol/PG conversions from 1 to 75mol%. The selectivity to PG amounts to at least 90%. For a given conversion, the lowest selectivity is observed at the highest temperature. Glycerol is predominantly dehydrated to acetol which is subsequently converted to PG. Co-feeding reaction products, i.e., PG and water, does not affect the rate of glycerol conversion. Additionally, glycerol can lead to minor side reactions forming products such as 1,3-propanediol, ethylene glycol while PG can degrade to ethanol, methanol and propanol. A comprehensive kinetic model accounting not only for the formation of main reaction products but also of side products was constructed. The activation energy of the rate-determining step for glycerol dehydration towards acetol was estimated at 84kJmol−1, exceeding that of the rate-determining step of the consecutive hydrogenation into PG by about 25kJmol−1. The high selectivity towards PG is attributed to (1) the relatively lower surface reaction rates for the parallel and the consecutive side reactions and (2) its low affinity for adsorption on the catalyst surface compared to glycerol at the investigated experimental conditions.

Palladium catalysed oxidation of glycerol—Effect of catalyst support

The activity and selectivity of Palladium catalysts on various supports, for the liquid-phase oxidation of glycerol in basic condition, have been studied. Activated carbon (AC), SiO2, Al2O3 and TiO2 were the supports studied. The catalysts were characterized using a variety of techniques (TEM, BET, Pulse-Chemisorption, TPD, TPR and XPS). The support is shown to have a significant effect on both rate and selectivity of the reaction, with the best rate of glycerol conversion, as well as selectivity to glyceric acid, being obtained for activated carbon (AC) among all the supports studied. The results have been interpreted in terms of known concepts of metal-support interactions. It is concluded that the electronic interactions between the metal and support, as well as acidic/basic properties of catalyst, play a vital role in product selectivity and activity.

Overexpressions of xylA and xylB in Klebsiella pneumoniae Lead to Enhanced 1,3-Propanediol Production by Cofermentation of Glycerol and Xylose.

1,3-Propanediol (1,3-PD) is a valuable platform compound. Many studies have shown that the supplement of NADH plays a key role in the bioproduction of 1,3-PD from Klebsiella pneumoniae. In this study, the xylA and xylB genes from Escherichia coli were overexpressed individually or simultaneously in K. pneumoniae to improve the production of 1,3-PD by cofermentation of glycerol and xylose. Compared with the parent strain, the xylose consumption was significantly increased by the introduction of these two genes. The 1,3-PD titers were raised from 17.9 g/l to 23.5, 23.9, and 24.4 g/l, respectively, by the overexpression of xylA and xylB as well as their coexpression. The glycerol conversion rate (mol/mol) was enhanced from 54.1% to 73.8%. The concentration of 2,3-butanediol was increased by 50% at the middle stage but drastically decreased after that. The NADH and NADH/NAD(+) ratio were improved. This report suggests that overexpression of xylA or xylB is an effective strategy to improve the xylose assimilation rate to provide abundant reducing power for the biosynthesis of 1,3-PD in K. pneumoniae.

Multi-objective optimization of a continuous bio-dissimilation process of glycerol to 1, 3-propanediol

This paper deals with multi-objective optimization of continuous bio-dissimilation process of glycerol to 1, 3-propanediol. In order to maximize the production rate of 1, 3-propanediol, maximize the conversion rate of glycerol to 1, 3-propanediol, maximize the conversion rate of glycerol, and minimize the concentration of by-product ethanol, we first propose six new multi-objective optimization models that can simultaneously optimize any two of the four objectives above. Then these multi-objective optimization problems are solved by using the weighted-sum and normal-boundary intersection methods respectively. Both the Pareto filter algorithm and removal criteria are used to remove those non-Pareto optimal points obtained by the normal-boundary intersection method. The results show that the normal-boundary intersection method can successfully obtain the approximate Pareto optimal sets of all the proposed multi-objective optimization problems, while the weighted-sum approach cannot achieve the overall Pareto optimal solutions of some multi-objective problems.

Development of a two-step process for production of 3-hydroxypropionic acid from glycerol using Klebsiella pneumoniae and Gluconobacter oxydans.

In this work, a two-step process was developed for the production of 3-hydroxypropionic acid from glycerol. In the first step, glycerol was converted to 1,3-propanediol by Klebsiella pneumonia. In the second step, the 1,3-propanediol was converted into 3-hydroxypropionic acid by Gluconobacter oxydans. In a 7.0 L bioreactor, the whole process took 54 h, consumed 480 g glycerol and produced 242 g 3-hydroxypropionic acid. The conversion rate of glycerol to 3-hydroxypropionic acid was 50.4 % (g g(-1)). The final concentration of 3-hydroxypropionic acid arrived 60.5 g L(-1). The process was effective for 3-HP production from glycerol and it might provide a new approach to the biosynthesis of 3-HP from a cheap starting material. Moreover, in this paper, it was first reported that the by-product of 3-hydroxypropionic acid production from 1,3-propandeiol was acrylic acid.

One-pot oxydehydration of glycerol to value-added compounds over metal-doped SiW/HZSM-5 catalysts: Effect of metal type and loading

A one-pot oxydehydration of glycerol to value-added compounds was carried out over metal-doped SiW/HZSM-5 catalyst at low temperature (90°C) and ambient pressure. Effects of metal types (Co, Ce, Ni and V) and loadings (0–8wt.%) on catalyst properties and catalytic activity were explored. Doping different types of metal and loading on the surface of SiW/HZSM-5 catalyst affected surface chemistry and textural chemistry as well as the catalytic activity for glycerol conversion and product yield distribution. The V at 6% loading most effectively enhanced the activity of SiW/HZSM-5 for a one-pot oxydehydration of glycerol to value-added compounds. The presence of V6-SiW/HZSM-5 catalyst can enhance the glycerol conversion up to 99.67% with the yields of glycolic acid, formic acid, acetic acid, acrolein, acrylic acid, and propionic acid of 19.45%, 12.03%, 23.62%, 0.25%, 36.23% and 7.06%, respectively with less than 1.5% of glycerol converting to some undesired products. The kinetic studies of a one-pot oxydehydration of glycerol over this catalyst (V6-SiW/HZSM-5) showed the rate of glycerol conversion depended upon the glycerol concentration according to the pseudo-first order kinetic rate and about the zero order with respect to the H2O2 concentration. The Eley–Rideal model, assuming the reaction between a non-dissociative adsorption of H2O2 and glycerol molecule provided the best fit with the experimental results.

Biohydrogen production from crude glycerol by two stage of dark and photo fermentation

Hydrogen production from crude glycerol by two-stage processes of dark fermentation using Klebsiella sp. TR17 and photo fermentation using Rhodopseudomonas palustris TN1 (Rps. palustris TN1) was investigated in batch experiments. In dark fermentation, the cumulative hydrogen production and hydrogen yield was 64.24 mmol H2/L and 5.74 mmol H2/g COD consumed, respectively with 80.21% of glycerol conversion rate. The dark fermentation effluent (DFE) was employed for photo fermentation. Effect of DFE concentrations (0–5 times dilution), with and without supplementation of yeast extract (2.3 g/L) + NaHCO3 (0.63 g/L), and glutamate (2–8 mM) were optimized. The optimal conditions for hydrogen production from Rps. palustris TN1 were 5 times dilution of DFE without the supplement of yeast extract + NaHCO3, and 2 mM glutamate. Under the optimum conditions, the cumulative hydrogen production of 3.12 mmol H2/L and hydrogen yield of 0.68 mmol H2/g COD consumed was obtained. The total hydrogen yield of two-stage processes was estimated to be 6.42 mmol H2/g COD consumed which was 10.4% of the theoretical yield.

Sorption enhanced aqueous phase reforming of glycerol for hydrogen production over Pt-Ni supported on multi-walled carbon nanotubes

In this study, multi-walled carbon nanotubes supported Pt and Pt-based bimetallic catalysts were prepared and their catalytic activities were investigated to screen effective and economical catalyst for H2 production in catalytic aqueous phase reforming (CAPR) of glycerol. Nickel promoted Pt catalyst with optimized Ni:Pt molar ratio afforded highest glycerol conversion rate (81.21%) and carbon conversion to gas (15.3%) although hydrogen gasification ratio (7.2%) was poorer than that of noble metals promoted Pt-based bimetallic catalysts. Adding CaO significantly enhanced the fraction and selectivity of H2 over Pt-Ni catalyst and those of CH4 were reduced to a negligible level, which was possibly attributed to the facilitated water-gas shift reaction and inhibited methanation through in-situ CO2 sorption via carbonation. Results suggested that Pt-Ni bimetallic catalysts improved dehydrogenation–decarboxylation and dehydration–hydrogenation reactions, leading to high glycerol conversions. Introducing CaO further favored C–C bond cleavage towards high H2 yield. The catalytic performance can be completely recovered after regenerating the catalyst and adding sacrificial CaO. In terms of reduced consumption of precious metal catalyst, excellent catalyst performance and hydrothermal stability, combination of Pt-Ni bimetallic catalyst and CaO additive was identified as an effective catalytic system for H2 production in CAPR of glycerol.

Aqueous phase reforming of glycerol over Re-promoted Pt and Rh catalysts

The potential of Re promotion for carbon-supported Pt and Rh nanoparticles was investigated for aqueous phase reforming (APR) of glycerol as a model compound for biobased feedstock. Upon alloying with Re, the overall conversion rate of glycerol was substantially increased for both metal catalysts. Whereas Pt/C is more active than Rh/C in glycerol APR, the RhRe/C catalyst outperforms PtRe/C. The overall APR catalytic performance strongly correlates with the activity trend for the gas-phase water–gas shift (WGS) reaction. RhRe/C exhibited the highest activity in APR and WGS reactions. A very strong synergy between Rh and Re and Pt and Re is observed in the model WGS reaction. The role of Re in the bimetallic catalysts is to facilitate water dissociation, effectively increasing the WGS activity. During APR, this results in lower steady-state CO coverage and increased glycerol conversion rates. In terms of selectivity, the yield of renewable hydrogen is increased. The use of Re as a promoter also results in significant changes in the product selectivities during glycerol APR. Although gas-phase acetaldehyde decomposition measurements evidenced that alloying with Re increased C–C bond cleavage activities of Pt/C and Rh/C, the increased acidity due to acidic hydroxyl groups bound to Re resulted in a more substantial increase of dehydration reactions. Whereas Rh/C is more selective for formation of products involving C–C bond cleavage than Pt/C, the product mixtures of their alloys with Re reflect a much increased ratio of C–O vs. C–C bond cleavage reaction rates.

Flux analysis of the Lactobacillus reuteri propanediol-utilization pathway for production of 3-hydroxypropionaldehyde, 3-hydroxypropionic acid and 1,3-propanediol from glycerol.

BackgroundLactobacillus reuteri converts glycerol to 3-hydroxypropionic acid (3HP) and 1,3-propanediol (1,3PDO) via 3-hydroxypropionaldehyde (3HPA) as an intermediate using enzymes encoded in its propanediol-utilization (pdu) operon. Since 3HP, 1,3PDO and 3HPA are important building blocks for the bio-based chemical industry, L. reuteri can be an attractive candidate for their production. However, little is known about the kinetics of glycerol utilization in the Pdu pathway in L. reuteri. In this study, the metabolic fluxes through the Pdu pathway were determined as a first step towards optimizing the production of 3HPA, and co-production of 3HP and 1,3PDO from glycerol. Resting cells of wild-type (DSM 20016) and recombinant (RPRB3007, with overexpressed pdu operon) strains were used as biocatalysts.ResultsThe conversion rate of glycerol to 3HPA by the resting cells of L. reuteri was evaluated by in situ complexation of the aldehyde with carbohydrazide to avoid the aldehyde-mediated inactivation of glycerol dehydratase. Under operational conditions, the specific 3HPA production rate of the RPRB3007 strain was 1.9 times higher than that of the wild-type strain (1718.2 versus 889.0 mg/gCDW.h, respectively). Flux analysis of glycerol conversion to 1,3PDO and 3HP in the cells using multi-step variable-volume fed-batch operation showed that the maximum specific production rates of 3HP and 1,3PDO were 110.8 and 93.7 mg/gCDW.h, respectively, for the wild-type strain, and 179.2 and 151.4 mg/gCDW.h, respectively, for the RPRB3007 strain. The cumulative molar yield of the two compounds was ~1 mol/mol glycerol and their molar ratio was ~1 mol3HP/mol1,3PDO. A balance of redox equivalents between the glycerol oxidative and reductive pathway branches led to equimolar amounts of the two products.ConclusionsMetabolic flux analysis was a useful approach for finding conditions for maximal conversion of glycerol to 3HPA, 3HP and 1,3PDO. Improved specific production rates were obtained with resting cells of the engineered RPRB3007 strain, highlighting the potential of metabolic engineering to render an industrially sound strain. This is the first report on the production of 3HP and 1,3PDO as sole products using the wild-type or mutant L. reuteri strains, and has laid ground for further work on improving the productivity of the biotransformation process using resting cells.