START-UP TIME IN TUBULAR REACTORS WITH AXIAL DISPERSION

In the modeling of nonideal reactors the axial dispersion model is one of the most used (Butt, 1980). Boundary conditions for a tubular reactor with axial dispersion were extensively analyzed (Danckwerts, 1953, Wehner and Wilhelm, 1965, Van Cauwen-berghe, 1966, Choi and Perlmutter, 1976, Deckwer and Mahlmann, 1976) Similarly, the steady state behaviour of the reactor when simple or complex reactions take place was also studied by several authors (Deckwer et al. 1972, Wan and Ziegler, 1973). However, the transient behaviour was only analyzed for simple kinetics expressions (Fan and Ahn, 1963, Sawinsky artd Hunek, 1977, Godslave and Chang, 1980)

In the present work, the time necessary to reach the steady state or start-up time is determined for single and complex reversible reactions. The analysis presented is also valid in case there is a change in feed concentration (feed upset, etc.)     

Influence of lead(II) carbonate films of non-antimonial grids on the deep discharge cycling behaviour of maintenance-free lead/acid batteries

The role of hydrocerussite (i.e., 2PbCO3.Pb(OH)2) on the deep discharge cycle-life of non-antimonial lead/acid battery cells was assessed using aged grids comprising deliberately invoked 2PbCO3. Pb(OH)2, and it is shown that, when compared to the untreated grid cells, the aged grid cells required half as many cycles to reach 67% of their initial discharge capacity. The initial specific energy of cells employing aged grids is 40% higher than their untreated grid counterparts; this is attributed to the improved adhesion of the active material to grids containing large amounts of hydrocerussite. A mechanism involving the hydrocerussite-induced formation of a barrier layer in the grid corrosion layer is proposed to explain the premature capacity loss of non-antimonial battery cells.     

PURIFICATION AND CHARACTERIZATION OF AN ENDOPEPTIDASE FROM PSEUDOMONAS FLUORESCENS ATCC 948

Intracellular, ca 55 kDa monomeric endopeptidase (PsPepO) from Pseudomonas fluorescens ATCC 948 was purified to homogeneity by chromatography on Q-Sepharose, Sephacryl 200, Phenyl-Superose and Mono Q. It was strongly inhibited by the metalloproteinase inhibitor, 1,10 phenanthroline and by dithiothreitol, but less strongly by EDTA; it was stimulated by Co²⁺. Activity was optimal at pH 7.0 and 40–45C, with considerable activity at pH 5.0 and 12C. The enzyme was relatively heat-stable with a D_80Cvalue of 1.2 min. It did not hydrolyze α_s1-, β-or κ-casein (CN) and peptides with less than 5 amino acids but readily hydrolyzed α_s1-CNfl-23, α_s1-CN f157-164, α_s1-CN f165-199 and various β-CN fragments and peptide hormones. On α_s1-CN fl-23, α_s1-CN f165-199, insulin B-chain and bradykinin, it mainly catalyzed the hydrolysis of peptide bonds in which a hydrophobic amino acid (most commonly Phe or Leu) residue occupied the P'₁position. β-CN f193- or 194-209, which are the source of bitter peptides in cheese ripening, were hydrolyzed slowly or not at all. β-CN fragments from the sequence 58-70 were degraded or did not inhibit the endopeptidase activity as well as β-CN f193-209. The characteristics of the endopeptidase of Ps. fluorescens ATCC 948 were compared with those of lactococcal endopeptidases.