DATA ADJUSTMENT FOR NON-REACTIVE BATCH OR STEADY-STATE PROCESSES

An analytical method was developed to adjust inconsistent process data by a least-sum-of-squares technique to “best” meet all material balance constraints. One complete data set composed of “M” stream flow rates with “N” components in each stream was used from either batch or steady-state non-reactive processes to define an unconstrained sum-of-squares adjustment function

Derivatives of the unconstrained sum-of-squares adjustment function with respect to each variable were set to zero yielding a set of non-linear algebraic equations. The entire non-linear set was solved by converging on only M— 2 search variables as compared to conventional methods requiring N(M — 1) — 1 search variables.     

Chemical composition and bond structure of aerosol particles of amorphous hydrogenated silicon forming from thermal decomposition of silane

Aerosol particles of amorphous hydrogenated silicon resulting from thermal decomposition of silane were investigated by hydrogen evolution, IR-, EPR-, NMR spectroscopy, and transmission electron microscopy.

The experimental data show that aerosol particles contain to a various extent {SiH₂}_n polymer structures and two types of monohydride groups SiH- “clustered” and “dilute” monohydride groups. The hydrogen atoms of the “clustered” monohydride groups are located close to each other. The “clustered” monohydride groups are inaccessible to the ambient because they are embedded in the amorphous network. The “dilute” monohydride groups are relatively isolated from each other. The majority of “dilute” monohydride groups are open to the ambient. They are located on the surface of preferentially interconnected microchannels and microvoids.

Interaction between the “dilute” SiH groups and atmospheric oxygen results in formation of OSiH groups in which hydrogen and oxygen are bonded to a common silicon atom. Evidently, the interaction occurs throw the oxygen reaction with weak bonds associated with “dilute” monohydride groups. There is no interaction between oxygen and both “clustered” SiH groups and {SiH₂}_n chain because the former are inaccessible to atmospheric oxygen and the latter has presumably no weak bonds in the chains.     

Modification of faujasites to generate novel hosts for “ship-in-a-bottle” complexes

Zeolites X, Y, and DAY have been modified by a post-synthetical dealumination procedure to generate mesopores that are completely surrounded by micropores. In these novel host materials several bulky transition metal salen complexes have been occluded via the “ship-in-a-bottle” synthesis approach. Both the host materials and the “ship-in-a-bottle” catalysts have been characterized by FTIR spectroscopy and nitrogen adsorption. Additionally, the “ship-in-a-bottle” catalysts have been characterized by thermogravimetric analysis and ICP-AES spectroscopy. The catalysts have been tested in the stereoselective epoxidation of R-(+)-limonene and (−)--pinene with molecular oxygen as oxidant. The best results so far — 100% conversion, 96% selectivity and 91% de — were achieved with the immobilized (R,R)-(N,N′)-bis(3,5-di-tert-butylsalicylidene)-1,2-diphenylethylene-1,2-diaminocobalt complex in the epoxidation of (−)--pinene.     

The effect of flexible substrates on pressure-sensitive adhesive performance

The adhesive fracture energy (fracture toughness) of tapes during globally elastic unpeeling is often calculated from the relation “G=P/b(1−cos θ)”. We show that while this expression is correct for elastic peeling from rigid substrates, it gives misleading results when peeling from reversible flexible substrates. A two-dimensional analysis is presented for peeling from non-linear elastic substrates that give consistent fracture energies from experimental data.     

A GRAPHICAL DESIGN METHOD FOR A PARTIAL SOLAR DRYER FOR CORN

This paper presents the application of a design method for a partial solar heating system of polyvalent modular dryers called “GJ-ABAQUE” to the drying of thick layers of grains.

This method is based on the use of charts or polynomial correlations. In the actual case where the drying air is not recycled, we only need one chart which allows one to determine the fraction of the monthly heating load supply by solar energy as a function of two dimensionless parameters. The latter implies the use of monthly average radiation data, the collector surface and estimates of drying loads.

The “GJ-ABAQUE” method was applied for drying 777 kg of corn, corresponding to 1 m³ of fresh product, in a thick layer in each modular dryer.     

CO oxidation over CuOx-CeO2-ZrO2 catalysts: Transient behaviour and role of copper clusters in contact with ceria

The effects of ZrO₂ content on the CO oxidation activity in a series of CuO_x/Ce_xZr_1−xO₂ (x = 0, 0.15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H₂, i.e. preferential CO oxidation—PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an “oxidized” towards a “reduced” state of the catalyst under the simulated PROX reaction conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures.     

ESTIMATION OF FUNCTIONS IN DRYING EQUATIONS

In drying problem, particularly for drying foodstuff, modelling is very difficult. Many physical effects have to be taken into account for mass transfer ; then mass transfer coefficient varies

In different models unknown functions must be estimated. It is particularly the case in simple models of drying using average values of water content, where the mass transfer varies versus mean water content in falling rate period. On the other hand in the “diffusion model” we have the same problem concerning the diffusion coefficient which must be also estimated

The method we propose in this paper for these two models : simple and “diffusion model” of drying consists from measurements of temperature and water content of the product to search a numerical approach of the unknown function. This method uses optimization techniques on computer and least squares criterion between model values and experimental data

Results are given for the “diffusion model” applied to shelled corn drying to find the diffusion coefficient and for a simple 11107 del applied to plum drying to find the mass transfer coefficient.     

RESHEX: An interactive software package for the synthesis and analysis of resilient heat-exchanger networks—I Program description and application

RESHEX is an interactive software package for the synthesis and analysis of resilient heat-exchanger networks (HENs). An overview of the program structure, features and functions is presented. A case study describing the revamp of a refinery feed preheat train illustrates the versatility and effectiveness of RESHEX. The case study demonstrates the ease with which a designer can generate (by semi-automatic synthesis and/or evolutionary development) several economically attractive networks which also satisfy practical requirements (such as the revamp network resembling the existing network as much as possible, constraints on the number and location of stream splits and resilience to anticipated changes in operating conditions).

Scope—Over the last decade many techniques for synthesis and analysis of HENs have been developed [e.g. 1–4]. However, the “pencil-and-paper” techniques are awkward for the large-size problems encountered in practical industrial situations, and the “automatized” computer techniques have limited capabilities to accommodate the special requirements of the design engineer. RESHEX is a prototype program where the computer techniques are significantly enhanced in terms of versatility to meet the practical needs of the design engineer. All functions including utility and area targeting, network synthesis, evolutionary network development, resilience analysis and economic optimization are available.

Conclusions and Significance—Figure 2 outlines the typical steps taken by an engineer when designing or revamping an HEN. RESHEX allows these complex needs to be served in a comprehensive manner. The power and versatility of RESHEX is illustrated through a revamp study of a refinery crude preheat train. the revamp study demonstrates the power of RESHEX to allow the engineer to influence the shape of the synthesized network by constraining the number and location of stream splits and exchangers. The study also demonstrates the versatility of RESHEX to suggest what piping changes should be made or where area should be added when revamping the network.     

A CRITICAL EVALUATION OF THREE EQUATIONS OF STATE FOR DENSE GASES AGAINST OBSERVED DATA

The van der Waals, the Benedict-Webb-Rubin, and a virial equation of state predictions for dense gases are evaluated against observed “integral” properties (p, ρ, T) and “slope” properties like the speed of sound [(∂p/∂p)^1/2₃], isothermal compressibility coefficient [(∂ In ρ /∂p)_T], and few other thermodynamic properties directly derived from the observed data. The documented procedure thus constitutes a stringent test methodology to evaluate the applicability of these equations of state to dense gases which may also be followed for appraising any other equation of state. The graphical comparisons between the predictions and the observed data are presented and discussed critically     

CataIyst Poisoning

The literature of catalysis is vast, reflecting the industrial importance of the subject. For the sake of curiosity, we undertook a computerized search of Chemical Abstracts to trace the number of publications per year, using the generic form “Cataly” and, for catalyst poisoning, the simultaneous occurrence of the generic forms “Cataly” and “Poison” beginning with the year 1967 and ending with 1978, the last reasonably complete computer file at the time of this writing.     

VOLUME-BASED THERMODYNAMICS GLOBAL PHASE STABILITY ANALYSIS

In this study we propose a method for phase stability analysis at pressure and temperature specifications, in the frame of a “volume-based” thermodynamics. The formulation of the tangent plane distance (TPD) criterion in terms of the Helmholtz free energy is used in this work for testing phase thermodynamic stability at p-T conditions, using component molar densities as primary variables. The phase stability problem is non-convex; the TPD function may exhibit multiple local minima and saddle points, the use of global optimization methods for its minimization being appropriate. For the unconstrained minimization of the TPD function we use the tunneling global optimization method, which has shown its ability in efficiently solving difficult non-convex, highly nonlinear problems. The method is tested for a variety of mixtures ranging from binaries to mixtures with many components, with emphasis on difficult conditions. The proposed method proved to be an efficient and reliable tool for phase stability analysis.     

Kinetics of the selective catalytic reduction of NO by NH3 on a Cu-faujasite catalyst

The kinetics of the selective catalytic reduction (SCR) of NO by NH₃ in the presence of O₂ has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<T_R<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O₂, and essentially 0 with respect to NH₃. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH₃ was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) Cu^I is oxidized by O₂ to “Cu^II-oxo”, (ii) “Cu^II-oxo” reacts with NO to yield “Cu^II-N_xO_y”, and (iii) finally “Cu^II-N_xO_y” is reduced by NH₃ to give N₂, H₂O, and the regeneration of Cu^I (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that Cu^I or “Cu^II-oxo” species constitute the rate-determining active center.     

The Mechanical Behaviour of Polyimide/Copper Laminates Part 2: Peel Energy Measurements

The mechanical peel behaviour of laminates consisting of polyimide films adhered to copper foil using a modified acrylic adhesive has been studied over a wide range of test rates and temperatures. The laminates were prepared from polyimide films which had been subjected to either a “high-thermal history” or a “low-thermal history” treatment during the production of the film. The measured peel energies of the laminates could be superimposed to give a master curve of peel energy versus the reduced rate of peel test, Ra_T, where R is the rate of peel test and a_T is the time-temperature shift factor. The appropriate shift factors were a function of the test temperature and were mainly deduced from tensile tests conducted on the bulk adhesive. The “high-thermal history” laminates gave higher peel energies and the locus of failure of the laminates was mainly by cohesive fracture through the adhesive layer. At low values of log₁₀ Ra_T, i.e. Low rates of peel and high test temperatures, the “low-thermal history” laminates also failed in the adhesive layer and possessed similar peel energies to those measured for the “high-thermal history” laminates. However, at high log₁₀ Ra_T values, the peel energies measured for the “low-thermal history” laminates were lower and showed a wider scatter. These arose from a different locus of failure occurring in these “low-thermal history” laminates when tested under these conditions. Namely, it was found that most of these laminates failed in a weak boundary layer in the outer regions of the “low-thermal history” polyimide film.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d_s and γ^d_l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d_s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^-2 K^-1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d_s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d_s and d(γ^d_s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

Fractals in Heterogeneous Catalysis

In a recent review on the influence of particle size on catalytic properties of supported metals [l], evidently a most important aspect of heterogeneous catalysis by any account, the authors end on a fairly discouraging note since they suggest doing even more work — with ever more sophisticated techniques and methods as well as normalized procedures — on top of an already formidable amount of literature. At such a state of the art it may be appropriate to reflect and to ask whether full pursuit of reductionism as scientific method needs fresh thinking in order to progress more effectively. Perhaps the difficulties are rooted in emphasis on mere data collection, the lack of a good empirical guiding principle, inappropriate models; in brief, the frequent simplification of a vastly complicated object — the real catalyst — into the sum of phenomena of better-understood idealized subsets. It might even be argued that a thorough knowledge of a well-characterized prototype or a particular model catalyst would be actually of little help in seeing the real world where catalysts are of irregular shape, suffer sintering, become poisoned; in other words, lose their ideal state after some time of operation. Also, we realize that a change in “quantity” often engenders a change in “quality”: For instance, a material with a BET area of hundreds of square meters per gram can hardly be considered to have a surface like a huge tennis court or ball field: it is rather “convoluted” in some very irregular fashion, having a shape that is difficult to realistically construct as a linear combination of planar portions.     

GAS HOLDUP IN UNIFORMLY AERATED BUBBLE COLUMN REACTORS

Conditions of the stable performance of gas distributing plates were studied and the effect of plate geometry on gas holdup of uniformly aerated gas-liquid beds was investigated. The ratio of plate holes opened for gas passage was determined as a function of gas hole velocity and critical values of gas hole velocity corresponding to the onset of stable performance of distributing plates were obtained.

Two regimes of bubbling were observed under conditions of stable uniform gas distribution; the regions of their existence being determined by the values of gas flow velocity and distributing plate parameters. Considerable increase of gas holdup was observed in the region of “foam” bubbling compared to the “turbulent” bubbling regime commonly encountered in bubble column reactors. The character of the bed and hence its gas holdup value were affected by the geometry of distributing plates in the “foam” bubbling region while no such effect was observed under “turbulent” bubbling conditions.     

GAS MICROEMBOLI—DETECTION, QUANTITATION AND ELIMINATION

The need for removing gas microemboli (GE) from The returned blood during extracorporeal circulation is well recognized. One of the methods used to safeguard against the perfusion of GE is the employment of arterial line filters. These devices separate and eliminate solid as well as GE from the extracorporeal blood stream. The major difficulty in any determination of the number or size of GE, is that bubbles may coalesce or divide and may even dissolve or be released from the blood. Thus to study filter “efficiency” comparison of bubble “counts” upstream and downstream of the filter is not meaningful; more pertinent is the proportion of gas volume that passes the filter. This paper reviews factors involved in the design of effective arterial filters for the elimination of gas microemboli, identifies possible areas of improvement, and presents evaluation methods and laboratory data obtained with several filters currently in use.     

ON CHARACTERIZATION AND MITIGATION O F COMBUSTION HAZARDS INVOLVED IN THE HANDLING OF PARTICULATE MATERIALS: A REVIEW OF THREE BOOKS

The three publications reviewed herein deal with the complex of hazards which may derive from the agricultural and commercial handling of combustible particulate and gaseous materials. The principal thrusts of each book differ substantially from those of the other two. This review first attempts to consider the essential combustion processes which underlie the hazards of common concern in all three works. Each of the three books is then considered on an individual basis. The three publications are designated Books (1)- (3) respectively and are listed below:

(1) “User Guide to Fire and Explosion Hazards in the Drying of Particulate Materials.” 1977. Institution of Chemical Engineers. Warwick Printing Company Limited, England.

(2) “Prevention of Grain Elevator and Mill Explosions.” 1982. NAS-NRC Publication NUB 367-2. National Academy Press, Washington, D. C.

(3) “Guidelines for the Investigation of Grain Dust Explosions.” 1983. NAS-NRC Publication NMAB 367-4, National Academy Press, Washington, D. C.     

The Fracture Mechanics of the Pin and Collar Test for High Temperature Anaerobic Adhesives

A mechanical test method for the studies of high-temperature anaerobic adhesives has been established, based on fracture mechanics, by modifying the standard test method of collar and pin test. Linear Elastic Fracture Mechanics approach was applied to the establishment of the relationship between adhesive fracture surface energy “R”, fracture load and crack length. Hence, from the joints containing a given artificial flaw the adhesive fracture surface energy can be determined; alternatively, from the strength of the joints without artificial flaws the inherent flaw size “a_i” can be calculated to account for the decrease of joint strength.

The experimental techniques were applied to examine the mechanical behaviour of the joint system based on high temperature anaerobic adhesives. It was found that the joints cured at room-temperature had higher adhesive fracture surface energy but lower joint strength than the joints postcured at high temperatures. The “a_i” data explained this interesting phenomenon. The joints cured at room-temperature had extraordinarily large “a_i”, which was found to be formed by the uncured adhesive near the edges of the joints and the adhesive further cured in the postcure processes to reduce the “a_i”. Also, the growth of intrinsic flaw was found to be responsible for the deterioration of the joints in a short-term, high-temperature ageing process.     

Book Reviews

“lssledovaniya v oblasti poverkhnostnykh sil” (“Research on surface forces”) B. V. Deryagin, editor. Nauka Publ., Moscow 1967.544 pp. Rubles 3.00.

G. D. Andreevskaya, “Vysokoprochnye Orientirovannye Steklo-plastiki” (“High-strength Oriented Glass-Plastics”). Nauka Publ., Moscow 1966. 370 pp., Rubles 2.12.

A. D. Zimon, “Adgeziya pyli i poroshkov” (“Adhesion of dust and powders”) Khimiya Publ., Moscow 1967.372 pp. Rubles. 1.51.

J. J. Bikerman, “The Science of Adhesive Joints”. Academic Press, New York 1968.349 pages. $16.00.