Investigation of the chemistry of a diazo micromixing test reaction

Abstract

The azo coupling of I-naphthol with diazotized sulfanilic acid has been studied in detail focusing on the practical use of this reaction as a micromixing test reaction, as developed by Bourne and coworkers. The reaction is a fast, competitive, consecutive reaction whose final product distribution is affected greatly by mixing. Problems that occur in the isolation of the pure-dye products and quantification of the product distribution are addressed. Previously unreported in formation is given about the structure and properties of one of the products as well as the existence of an additional unknown product. The reaction was used to characterize the spatial heterogeneity of micromixing in a 14-L stirred-tank fermenter. Results show large differences in the product distribution dependent on the depth and radial position of the feed pipe in the tank. introductionIt has long been recognized (Danckwerts, 1958;Zwietering, 1959) that for nonfirst-order reaction kinetics the residence time distribution of a reactor is insufficient information to predict conversion. In such cases, it is necessary to consider the degree and intensity of segregation, defined by Danckwerts, which the molecules experience while undergoing chemical reaction. Ultimately, molecules are mixed by small-scale turbulent eddies whose size and velocity depend on the local rate of energy input. Consideration of mixing at the scale of the smallest turbulent eddies is usually termed micromixing. Micromixing becomes important particularly in the case of multiple simultaneous reactions where it can affect the selectivity of a desired product, Some general requirements for a reaction to display mixing sensitivity have been outlined by Bourne et al. (1977) and David and Villermaux (1987).Mixing effects are also seen in bioreactors, in which microorganisms aregrown (Dunlop and Ye, 1990; Tomaet al., 1991). For the purpose of oxygen transfer, these reactors are often highly agitated, which may lead to the assumption of "perfect" mixing in the design of bioreactors. However, changes in micro-organism productivity as a function of substrate injection Correspondence concerning this article should be addressed to E. H. Dunlop location (Hansford and Humphrey, 1966), stirrer speed (Torna et al., 1991), or grid generated turbulence (Fowler and Dunlop, 1989) suggest that the mixing is often less than perfect. Since micro-organisms are of the same length scale or smaller than the smallest turbulent eddies in a fermenter (Dunlop and Ye, 1990), micromixing concepts may be able to explain these effects. A micromixing test reaction, described below, is being used in the present study to measure micromixing in biochemical reactor systems.Although much work has been done to model the process of micromixing (see, for example, Baldyga and Rohani, 1987;David and Villermaux, 1987;Patterson, 1981), there still exists no way to predict its effects for an arbitrary reactor design and reaction kinetics. Micromixing effects, however, can be measured through the use of reactive tracers...

Micromixing effects in a two‐impinging‐jets precipitator

“…CR and C, in the sample mixture were then found by linear regression using previously determined specific molar absorbances. The conversion of B was generally found to be 95-97%, which compares with that typically reported by other researchers (Bourne et al, 1985;Tosun, 1987;Demyanovich and Bourne, 1989;Wenger et al, 1992;Iyer and Przybycien, 1994). The selectivity, X, calculated from the measured values of C, and C,, was determined as a function of jet Reynolds number for each condition listed in Table 1. cBO.…”

“…Bourne et al (1981) proposed an electrophilic aromatic substitution reaction between 1-naphthol ( A ) and diazotized sulfanilic acid ( B ) to produce monoazo dye ( R ) and bisazo dye (S). This system has been used commonly in recent mixing studies (Tosun, 1987;Mehta and Tarbell, 1987;Andrigo et al, 1988;Demyanovich and Bourne, 1989;Kusch et al, 1989;Bourne and Hilber, 1990;Wenger et al, 1992;Iyer and Pryzbycien, 1994) since the kinetics of this reaction are well characterized (Bourne et al, 1985). The rate constants are given as k , = 12,000 m3/mol-s and k, 2 m3/rnol.s at 25°C.…”

Protein precipitation: Effects of mixing on protein solubility

“…In the dye reaction, A is 1-naphthol, B is diazotized sulfanilic acid, R is 4-(4'-sulphophenylazo)-l-naphthol which is the monoazo dyestuff and S is 2,4-(4'-sulphophenylazo)-lnaphthol which is the bisazo dyestuff. The presence of a trace amount of a third dye product was ignored as reaction rate data for this product were not available for simulation (Wenger et al, 1992). The dye reactions were done in the same reactor in which the precipitation experiments were carried out.…”

Micromixing in a tubular flow reactor under simulated microgravity

“…The reaction can be adequately described by the competitive, consecutive scheme in Eq. 1 (Wenger et al, 1992):…”

“…The product distribution, defined by Eq. 2, was analyzed spectrophotometrically using the method described by Wenger et al (1992).…”