Model-Based Analysis of the Limiting Mechanisms in the Gas-Phase Oxidation of HCl Employing an Oxygen Depolarized Cathode

The electrochemical oxidation of HCl to Cl2 plays an important role in the production of polycarbonates and polyurethanes. Recently, the gas-phase oxidation of HCl proved to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. In experimental investigations of this gas-phase reactor, a limiting current can be observed that is so far not understood but impedes the overall reactor performance. In the present work, a nonisothermal multiphase agglomerate model is developed to investigate the underlying reasons for this limiting behavior in more detail. It is shown that the thermal management of the cell plays a significant role and that minor changes to its thermal resistance lead to the limiting behavior being caused by either flooding of the cathode or dehydration of the membrane and anode. An optimization of operational and structural parameters of the cell based on these insights leads to an increase in the limiting current by more than 90%. Interestingly, under these conditions a third phenomenon, the rate determining Tafel step in the microkinetic reaction mechanism of the HCl oxidation, limits the overall reactor performance. These insights harbor the potential for enormous energetic savings in this industrially highly relevant process

Automation of Operation Control of the Human Centrifuge

Human centrifuge is a motion platform used to artificially achieve transient and sustained G-load intended for physiological pilot training under controlled conditions. This paper presents the successful modernization and upgrade of the control system of the human centrifuge. Due to the need for system redundancy, in addition to the new automatic control system, the previously used manual control system had to be maintained, which is provided by the usage of a switch selector. Human centrifuge speed and positioning control algorithms are based on the implementation of a digital PI and P controller

Rheoencefalographic study of the cerebrovascular circulation in human lead poisoning

Cerebralna cirkulacija je ispitivana reoencefalografskom (REG) metodom na grupi od 34 radnika u kojih je kliničkim i laboratorijskim ispitivanjem dokazano trovanje olovom. Kontrolna grupa se sastojala od 24 osobe, približno iste starosti, koje u svojoj profesionalnoj aktivnosti nisu bile eksponirane olovu. U osoba trovanih olovom nađeno je signifikantno produženje trajanja anakrotske faze reograma uz morfološke alteracije reografskih talasa, koje ukazuju na smanjenu rastegljivost i povećan tonus cerebralnih arterija, pretežno arteriola. U 7 ispitanika nađene su reografske promene koje govore u prilog difuznih promena na cerebralnim arterijama. Autori smatraju da je glavobolja pri trovanju olovom vaskularne geneze.Cerebral circulation was investigated by the REG method in a group of thirty-four workers in whom lead poisoning had been proved by clinical and laboratory examinations. A control group consisted of twenty-four subjects of approximately the same age, with no previous occupational exposure to lead. The duration of the anacrotic phase was significantly longer in lead poisoned subjects. In addition, morphological alterations of REG waves in these subjects indicated a decreased distensibility and increased tonus of cerebral blood vessels, primarily arterioles. Seven subjects showed REG changes which reflected diffuse alterations of the cerebral artery. The authors consider that headache in subjects poisoned by lead is of vascular origin

Thromboelastographlc research of blood clotting in rats chronically exposed to X-rays

Autori su izvršili kroničnu ekspoziciju rendgenskim zrakama dvije grupe od po 30 albino štakora kroz 14 i 15 nedelja. Sveukupna primljena doza iznosila je 280-300 r. Pramene u zgrušavanju krvi ispitivane su pomoću tromboelastografije. Tom metodom dobiveni rezultati pokazuju da nije bilo značajnih pramena.Two groups of 30 albino rats were chronically exposed to X-rays during 14 and 15 weeks. The integral dose received was 280-300 r. The changes in blood clotting were foil owed by thromboelastographic method. The results obtained indicate that no changes could be registered by the method applied

Opasnost za zdravlje u proizvodnji i primjeni pesticida

The results of a long-term survey of working conditions and health status of workers in a pesticide industry in Serbia are presented. The survey has been completed with ophthalmological findings as well as with a description of ten cases of intoxication in pesticide applicators. The difficulties in assessing health hazards in the course of simultaneous exposure to products known for different toxicodynamic properties are pointed out. In conclusion the authors suggest further improvement of preventive measures as well as a more systematic investigation of the combined effects of pesticides in which ophthalmological examinations should be included.Prikazani su rezultati višegodišnjeg praćenja radnih uvjeta i zdravstvenog stanja radnika jedne industrije pesticida u Srbiji. Izvještaj obuhvaća i podatke oftalmoloških pretraga jednog dijela izloženih radnika kao i deset slučajeva otrovanja u toku primjene pesticida. Istaknute su teškoće pri ocjeni opasnosti kada se radi o istodobnoj izloženosti komercijalnim pripravcima različita mehanizma djelovanja. U zaključcima su dani prijedlozi za djelotvorniju preventivu profesionalnih otrovanja kao i za temeljitiji studij mogućih kombiniranih učinaka pesticida pri kojem se, po mišljenju autora, valja koristiti i oftalmološkim nalazima

The effect of D-penicillamine on experimental silicosis in rats

Istraživali smo uticaj d-penicilamina na silikozu u pacova. Tri grupe od po 10 pacova dobile su intratrahealnim putem po 50 mg silicijum dioksida. Četvrta grupa od 10 pacova ostavljena je kao kontrola. Od eksponovanih Si02 jedna grupa služila je kao kontrola, bez tretmana d-penicilaminom. Druga grupa dobivala je svakog dana u vodi za piće lek Metalkaptazu firme »Pliva« 10 mg po pacovu. Treća grupa primala je, takođe, Metalkaptazu u vodi za piće po 5 mg po pacovu svakog dana. Životinje su žrtvovane 7 meseci posle početka primene penicilamina, odnosno, 15 meseci od ekspozicije Si02. Pored makroskopskog pregleda, merena je telesna težina pacova na početku eksperimenta i posle 1, 3, 8 i 15 meseci. Merena je i težina pluća. Poseban značaj ima težina pluća treće grupe pacova koja su lakša od čiste silikotičarske grupe za 0,5 g. Međutim, histološki nalaz pluća i limfnih čvorova medijastinuma ukazuje da su nastupile promene koje govore da je pod uticajem d-penicilamina došlo do regresije, odnosno, do razgradnje kolagena naročito u grupi koja je primila manju dozu penicilamina. Na osnovu našeg histološkog nalaza i težine pluća pacova zaključili smo da penicilamin, u manjim dozama, utiče na razgradnju kolagena.The effect of D-penicillamine on silicosis was studied in 40 rats divided into four groups, ten in each group. Three groups received 50 mg of silicon dioxide intratracheally. The fourth group served as control. Among the exposed groups one was not treated with D-penicillamine and served as positive control. The rats in the second group were each given 10 mg D-penicilIamine (Metalcaptase »Pliva«) in drinking water every day. The third group was also treated with D-penicillamine and received about 5 mg per rat in drinking water every day. The rats were killed seven months after the first administration of penicillamine, i. e. after 15 months of SiO2 exposure. The rats were weighted at the beginning of the experiment and after 1, 3, 8 and 15 months. The lungs were also weighted. The lungs of rats in the third group weighted less, by 0.5 g, than those in the silicotic group. However, a histological analysis of the lungs and lymph nodes from the mediastinum showed some changes which proved that under the influence of D-penicillamine a regression i. e. decomposition of the collagen fibre took: place, especially in the group of rats which received a lower dose of penicillamine. On the basis of the histological analysis and the weight of the lungs we concluded that penicillamine in smaller doses causes decomposition of the collagen fibre

Electrochemical gas phase oxidation of hydrogen chloride to chlorine: Model-based analysis of transport and reaction mechanisms

The electrochemical conversion of hydrogen chloride to chlorine plays a significant role within major industrial processes like the polyurethane or polycarbonate production. Our recent studies demonstrated that the direct electrolysis of gaseous HCl in combination with novel strategies for product purification leads to significant exergetic savings (36–38%) compared to the Bayer UHDENORA state-of-the art process, which employs aqueous hydrochloric acid as a feedstock. Furthermore, we showed that despite of the improvements in the efficiency of the electrochemical reactor, it still has by far the greatest exergy demand of all process units. While the oxygen depolarized cathode (ODC) utilized in both process variants has been investigated in great detail in the scientific literature, the oxidation reaction of gaseous HCl (HClOR) has not yet received much attention and is hence the major subject of this work. In earlier experimental investigations of the HClOR, a limiting current was observed that has the potential to critically reduce the performance of the overall reactor. In the past, membrane dehydration and mass transfer resistances on the anode side were suggested as possible reasons. In order to shed light on this phenomenon, a dynamic, one dimensional agglomerate model of the gas phase HCl oxidation half-cell, considering detailed micro kinetics, as well as the mass transfer of HCl in the different cell parts, is developed. The modeling results suggest that neither mass transfer resistance nor membrane dehydration but a kinetic limitation is the underlying reason for the observed limiting behavior. This has a significant impact on the strategy for further reactor optimizations and harbors the potential of major energy savings in an industrial application of this highly relevant process