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PubMed2004

Ceramic microreactors for heterogeneously catalysed gas-phase reactions.

The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components.

Aluminum Oxide↗
PubMed1998

Some critical issues and concerns related to research advances on toxicology of chemical mixtures.

This paper addresses some of the issues and concerns on research advances on the toxicology of chemical mixtures. Emphases will be selectively given to the following questions and answers: Can mechanistic studies be conducted on chemical mixtures? The fact that any studies, including mechanistic studies, of single chemicals are really the study of the parent chemical plus its metabolites underscores the relevance of mechanistic studies on chemical mixtures. Can predictions be made on the health effects of chemical mixtures? Some successes are already evident in the literature on simpler chemical mixtures. For more complex mixtures, it is possible and we propose an approach here. What can we learn from other disciplines (the importance of interdisciplinary collaboration)? Two aspects, the knowledge and methodologies available in clinical pharmacology and the latest advances in structure-oriented lumping in chemical engineering, are discussed in detail. Unrepeatable results: The possibility of magnification of biologic variability because of low-level exposures to chemical mixtures is suggested with special reference to some known examples, including the controversial study on synergistic interactions of endocrine disruptors. Is the driving force for scientific investigations on chemical mixtures the legislative and regulatory atmosphere? Two laws with chemical mixtures specifically in the language are quoted and discussed. Their implications regarding research funding and activities are described. What are the pitfalls of applying for research funding on investigating chemical mixtures? The dilemma at least one investigator faces in pursuing research funding is elaborated. The questions and issues listed above are not all inclusive, but they represent some of the aspects that need to be brought into the open in the scientific community for discussion and/or debate. Thus, the primary objective of this paper is to provide some momentum for the beginning of a fruitful and stimulating discussion.

Drug Interactions↗
PubMed2005

Linear mass balance equilibration: a new approach for an old problem.

Interval analyses are well known in the mathematics literature but have found few applications in control engineering. Based on the interval concept, we present here a methodology for data reconciliation and mass balance equilibration which is a very classical problem in mineral and chemical engineering. Indeed, this problem is solved with the view of inequality constraints which allows us to represent measurements by interval without particular knowledge and hypothesis about the density probability function of the measurement errors. As a main result, the paper gives a set of solutions for the reconciled data under an interval form and not only one solution as is the case with classical approaches.

Algorithms↗
PubMed2000

Use of bioassays for assessment of water-extractable ecotoxic potential of soils.

The characterization of contaminated soils is based on heterogeneous strategies considering chemical analyses or bioassays. In the report Bioassays for soils, test methods which are at an advanced state of development and standardization are recommended by the German DECHEMA (German Society for Chemical Apparatus, Chemical Engineering and Biotechnology e.V.). Following this report six soil samples contaminated with different organic and inorganic substances are applied to bioassays using the following organisms: Scenedesmus subspicatus, Daphnia magna, Vibrio fischeri, and Pseudomonas putida. Additionally, they are chemically analyzed. The test results demonstrate that toxic contaminants are present and bioavailable in water elutriates from two soils, indicating the necessity of bioassays and chemical analyses to predict potential risks from contaminated soils. Furthermore it is demonstrated that the described qualitative approach for the assessment of test results is not sufficient to quantify the risk potential of contaminated soils.

Animals↗
PubMed2005

Aquatic passive sampling of herbicides on naked particle loaded membranes: accelerated measurement and empirical estimation of kinetic parameters.

Water-sampler equilibrium partitioning coefficients and aqueous boundary layer mass transfer coefficients for atrazine, diuron, hexazionone and fluometuron onto C18 and SDB-RPS Empore disk-based aquatic passive samplers have been determined experimentally under a laminar flow regime (Re = 5400). The method involved accelerating the time to equilibrium of the samplers by exposing them to three water concentrations, decreasing stepwise to 50% and then 25% of the original concentration. Assuming first-order Fickian kinetics across a rate-limiting aqueous boundary layer, both parameters are determined computationally by unconstrained nonlinear optimization. In addition, a method of estimation of mass transfer coefficients--therefore sampling rates--using the dimension-less Sherwood correlation developed for laminar flow over a flat plate is applied. For each of the herbicides, this correlation is validated to within 40% of the experimental data. The study demonstrates that for trace concentrations (sub 0.1 microg/L) and these flow conditions, a naked Empore disk performs well as an integrative sampler over short deployments (up to 7 days) for the range of polar herbicides investigated. The SDB-RPS disk allows a longer integrative period than the C18 disk due to its higher sorbent mass and/or its more polar sorbent chemistry. This work also suggests that for certain passive sampler designs, empirical estimation of sampling rates may be possible using correlations that have been available in the chemical engineering literature for some time.

Environmental Monitoring↗
PubMed2002

Location of protons in anhydrous Keggin heteropolyacids H(3)PMo(12)O(40) and H(3)PW(12)O(40) by (1)H[(31)P]/(31)P[(1)H] REDOR NMR and DFT quantum chemical calculations.

HeteroPolyAcids (HPA's) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied acidic form of H(8-n)X(n+)M(12)O(40), X = Si, P and M = Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (R(P-H) = 520 +/- 20 pm) in H(3)PMo(12)O(40) and in the terminal oxygen positions (R(P-H) = 570 +/- 20 pm) in H(3)PW(12)O(40), REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.

Journal Article↗
PubMed1986

Occupation and risk of cutaneous melanoma.

Occupational mortality from cutaneous malignant melanoma was evaluated for deaths occurring in British Columbia from 1950-1978 by using age standardised proportional mortality ratios (PMR). For males, significantly elevated PMRs for melanoma were seen in managers and owners, accountants, architects, chemical engineers, and gardeners and nursery workers. Female school teachers were also at elevated risk of death from cutaneous melanoma.

British Columbia↗
PubMed2005

Real-time nonlinear feedback control of pattern formation in (bio)chemical reaction-diffusion processes: a model study.

Theoretical and experimental studies related to manipulation of pattern formation in self-organizing reaction-diffusion processes by appropriate control stimuli become increasingly important both in chemical engineering and cellular biochemistry. In a model study, we demonstrate here exemplarily the application of an efficient nonlinear model predictive control (NMPC) algorithm to real-time optimal feedback control of pattern formation in a bacterial chemotaxis system modeled by nonlinear partial differential equations. The corresponding drift-diffusion model type is representative for many (bio)chemical systems involving nonlinear reaction dynamics and nonlinear diffusion. We show how the computed optimal feedback control strategy exploits the system inherent physical property of wave propagation to achieve desired control aims. We discuss various applications of our approach to optimal control of spatiotemporal dynamics.

Bacteria↗
PubMed2002

[Tissue engineering].

Tissue engineering is a fast developing multidisciplinary field. Both from a medical and social point of view, there is great need to safe tissues and organs to overcome the shortage of donor organs and to reduce the health care cost. At the same time, progress made in the field of molecular sciences as well as in biomaterials and chemical engineering, offers great possibilities to manipulate cells, growth factors and carrier materials in such a way that growth of tissues can be achieved.

Bone Regeneration↗
PubMed1992

Basic aspects and future trends in the freeze-drying of pharmaceuticals.

Freeze-drying, as a unit operation in chemical engineering, is a complex multistage process which has to be carefully adjusted to each individual case. Its essential feature, drying from the frozen state, makes it particularly attractive for the stabilization of labile hydrated organic compounds of biological origin. However, it offers equal opportunities for the preparation of three-dimensional porous matrices for diversified physical and chemical applications. As such it is both an advanced technology for the long term preservation of unstable material and a refined operation for the development of new structures. Since freeze-drying, also called lyophilization, has been known for almost a century, and has given rise to numerous publications, this paper will not attempt to give a comprehensive review of its evolution but will focus on some of its basic requirements and potential trends.

Biological Products↗
PubMed2005

Optimization of Fenton's oxidation of chemical laboratory wastewaters using the response surface methodology.

Establishing a treatment process for practical and economic disposal of laboratory wastewaters has become an urgent environmental concern of the Department of Chemical Engineering of the Universidade Estadual de Maringá (State University of Maringá), Brazil. Fenton and related reactions are potentially useful oxidation processes for destroying toxic organic compounds in water. In these reactions, hydrogen peroxide is combined with ferrous or ferric iron in the presence or absence of light to generate hydroxyl radicals (.OH). The feasibility of Fenton's reagent to treat waste chemicals from an academic research laboratory was investigated in this study. A response surface methodology was applied to optimize the Fenton oxidation process conditions using chemical oxygen demand (COD) removal as the target parameter to optimize, and the reagent concentrations, as related to the initial concentration of organic matter in the effluent, and pH as the control factors to be optimized. Maximal COD removal (92.3%) was achieved when wastewater samples were treated at pH 4 in the presence of hydrogen peroxide and iron in the ratios [COD]:[H2O2]=1:9 and [H2O2]:[Fe2+]=4.5:1. Under these conditions, it was possible to obtain simultaneously maximal COD removal and minimal chemical sludge after treatment, which is a residue that needs further processing.

Brazil↗
PubMed2003

Artificial cells for replacement of metabolic organ functions.

Artificial cells are being actively investigated for use in the replacement of cell and organ functions, especially related to metabolic functions. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion. Implantation of encapsulated cells are being studied for the treatment of diabetes, liver failure, kidney failure and the use of encapsulated genetically engineered cells for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients with as much as 20 units infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. Artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering and medicine.

Artificial Organs↗
PubMed1999

Degradation of pentachlorophenol aqueous solutions using a continuous flow ultrasonic reactor: experimental performance and modelling.

The degradation of aqueous solutions of pentachlorophenol (PCP) in a three-stage sonochemical reactor operating in the continuous flow mode has been investigated. The experimental reactor may be considered as a series of three high-frequency ultrasonic units. The influence of several parameters such as ultrasonic power, reactor volume and volumetric feed flow rate on the reactor performance is reported. Application of classical basic chemical engineering principles leads to a model that enables us to predict the PCP concentration within the reactor. In steady state, experimental conversion rates are shown to be in good agreement with model predictions.

Models, Chemical↗
PubMed2004

Artificial cells for cell and organ replacements.

The artificial cell is a Canadian invention (Chang, Science, 1964). This principle is being actively investigated for use in cell and organ replacements. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion for use in the removal of drugs, and toxins and waste in uremia and liver failure. Encapsulated cells are being studied for the treatment of diabetes, liver failure, and kidney failure, and the use of encapsulated genetically-engineered cells is being investigated for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients, with as much as 20 units being infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. The artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering, and medicine.

Artificial Organs↗
PubMed1998

Tissue engineering in facial plastic and reconstructive surgery.

Current biomaterials technology meets some of the needs of the facial plastic and reconstructive surgeon. However, there is a genuine need for improvement in the area of tissue replacement. The principle of tissue engineering provides a natural way to generate needed tissue using the patient's own cells as building blocks, coupled with biodegradable polymers which have been used safely in [figure: see text] patients for decades. This technology enables the creation of complex structures which ultimately have no immunogenicity. Current obstacles to human clinical trials for auricular repair are being pursued for resolution, and the number of new tissues which it may be possible to generate in this fashion continues to expand. Through continued experimentation and collaboration among surgeons, chemical engineers, and materials scientists, we are certain that the barriers to widespread clinical use for this emerging technology will be overcome.

Animals↗
PubMed1976

[Fatal arsenic trichloride poisoning (author's transl)].

Report on a 24-year-old chemical engineer who committed suicide by means of arsenic trichloride. The clinical course and the autopsy findings are discussed briefly. The results of the toxicological examination leave no doubt as to an acute arsenic poisoning. In addition to this, extreme corrosion was found, especially in the region of the oesophagus. If an anamnesis on this patient had not been present one would probably have been satisfied with a diagnosis of acid poisoning and the possibility of intoxication by arsenic would not have been taken into consideration. This case indicates that especially where persons come into contact professionally with chemical and drugs, the chemo-toxicological examinations cannot cover too braod a spectrum.

Adult↗
PubMed1986

"Inborn errors of metabolism" and "chemical individuality", two ideas of Sir Archibald Garrod briefly revisited 50 years after his death.

Two ideas of Sir A. Garrod, "chemical individuality" (1902) and "inborn errors of metabolism" (1908) have proved fundamental for the development of medical knowledge. The latter idea was more fortunate than the former which, however has been extremely heuristic. On the other hand the two ideas are not entirely independent of each other: in fact, a third Garrodian concept, "inborn factors in disease", represents a significant link between them. "Inborn errors of metabolism" revived the laws of genetics and opened the way to interpretation of the molecular diseases with all their inherent practical modern implications (neonatal screening, prenatal diagnosis, and in perspective, genetic engineering). "Chemical individuality" still constitutes a valid premise for knowledge of biological individuality (in other words, the "biological ego") fundamentally programmed for conservation of self and for continuous discrimination of self versus non-self.

Adult↗
PubMed2000

Artificial cell biotechnology for medical applications.

Artificial cells are prepared in the laboratory for medical and biotechnological applications. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion. Implantation of encapsulated cells are being studied for the treatment of diabetes, liver failure and the use of encapsulated genetically engineered cells for gene therapy. We recently found that daily orally administered artificial cells containing a genetically engineered microorganism can lower the elevated urea level in uremic rats to normal levels and increase the survival of the animal. Furthermore, this can remove potassium, phosphate, uric acid and other waste metabolites from uremic plasma. Blood substitutes based on modified hemoglobin are already in phase-III clinical trials in patients with as much as 20 units infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trials in hereditary enzyme deficiency diseases and other diseases. Artificial cells are also being investigated for drug delivery and other uses in biotechnology, chemical engineering and medicine.

Animals↗