Catalyst and Process Design for the Continuous Manufacture of Rare Sugar Alcohols by Epimerization– Hydrogenation of Aldoses

Sugar alcohols are applied in the food, pharmaceutical, poly- mer, and fuel industries and are commonly obtained by reduc- tion of the corresponding saccharides. In view of the rarity of some sugar substrates, epimerization of a readily available monosaccharide has been proposed as a solution, but an effi- cient catalytic system has not yet been identified. Herein, a mo- lybdenum heteropolyacid-based catalyst is developed to trans- form glucose, arabinose, and xylose into less-abundant man- nose, ribose, and lyxose, respectively. Adsorption of molybdic acid onto activated carbon followed by ion exchange to the cesium form limits leaching of the active phase, which greatly improves the catalyst stability over 24 h on stream. The hydro- genation of mixtures of epimers is studied over ruthenium cat- alysts, and it is found that the precursor to the desired polyol is advantageously converted with faster kinetics. This is ex- plained by density functional theory on the basis of its more favorable adsorption on the metal surface and the lower energy barrier for the addition of a hydrogen atom to the pri- mary carbon atom. Finally, different designs for a continuous process for the conversion of glucose into mannitol are stud- ied, and it is uncovered that two reactors in series with one containing the epimerization catalyst and the other containing a mixture of the epimerization and hydrogenation catalysts in- creases the mannitol/sorbitol ratio to 1.5 from 1 for a single mixed-bed reactor. This opens a prospective route to the effi- cient valorization of renewables to added-value chemicals

Methanol-essential growth of Escherichia coli

Methanol represents an attractive substrate for biotechnological applications. Utilization of reduced one-carbon compounds for growth is currently limited to methylotrophic organisms, and engineering synthetic methylotrophy remains a major challenge. Here we apply an in silico-guided multiple knockout approach to engineer a methanol-essential Escherichia coli strain, which contains the ribulose monophosphate cycle for methanol assimilation. Methanol conversion to biomass was stoichiometrically coupled to the metabolization of gluconate and the designed strain was subjected to laboratory evolution experiments. Evolved strains incorporate up to 24% methanol into core metabolites under a co-consumption regime and utilize methanol at rates comparable to natural methylotrophs. Genome sequencing reveals mutations in genes coding for glutathione-dependent formaldehyde oxidation (frmA), NAD(H) homeostasis/biosynthesis (nadR), phosphopentomutase (deoB), and gluconate metabolism (gntR). This study demonstrates a successful metabolic re-routing linked to a heterologous pathway to achieve methanol-dependent growth and represents a crucial step in generating a fully synthetic methylotrophic organism.ISSN:2041-172

Knowledge Transfer in Support of the Development of Oxygen Concentrators in Emergency Settings During the COVID-19 Pandemic

The COVID-19 pandemic simultaneously disrupted supply chains and generated an urgent demand in medical infrastructure. Among personal protective equipment and ventilators, there was also an urgent demand for chemical oxygen. As devices to purify oxygen could not be manufactured and shipped rapidly enough, a simple and accessible oxygen concentrator based on pressure swing adsorption was developed at ETH Zurich in spring 2020. Instead of building devices locally and shipping them, it was decided to educate others in need of oxygen. The implementation encompassed education on process chemistry, material choice, and assembly and optimization of the concentrator and was realized using synchronous teaching tools, such as video call, and asynchronous ones, such as a website and video streaming. The project gained traction and interaction with engineering teams from universities and non-Governmental Organizations (Red Cross and the UN Development Program) in developing countries and emerging market economies, including Ecuador, Mexico, Somalia, and Peru. At the end of the project, the teams were surveyed regarding their experience in the educative knowledge transfer. It was reported that the learning experience prepared these groups well to build the device and to teach others as well. Major challenges were accessing some parts of the device and optimizing its performance. While synchronous communication is expected to be a very effective teaching method, the survey results showed that explanations via a website and video streaming have contributed the most to the implementation of the oxygen concentrator and thereby provide autonomous and sustainable education tools.ISSN:0021-9584ISSN:1938-132