Fe-TAML® catalysts

Work is ongoing to quantify the relative importance of intermolecular pathways of Fe -TAML catalyst inactivation... 

Figure 1. Fe-TAML catalyst used in these studies...

End-of pipe effluent source. Effluent samples were taken from the El (first extraction stage) sewer of the bleach plant while the mill was processing Pinus radiata. Samples were stored at 4 °C. Treatment trials were carried out on filtered wastewater samples (25 mL) which had been adjusted to pH 11. The Fe-TAML catalyst (0.5 - 10 pM) was added simultaneously with H2O2 (2 - 30 mM) and stirred at 50 °C for a prescribed amount of time 30 - 300 minutes 34),... 

Initial trials with the Fe-TAML catalyst (0.5 pM) and H2O2 (16 mM) showed that the Fe-TAML/H202 methodology remove 41 % of color from the bleach plant wastewater after 30 minutes at 50 °C. Initial treatments also showed that adequate mixing of the wastewater was required for effective and consistent color removal. For example, when no mixing was used, color reductions varied from 9 to 42 % over seven repetitions, final color 495 68 CPU, whereas when mixing was used, the final color was 348 8 CPU. 

Aqueous solutions of Fe salts and H2O2 produce hydroxyl radical. To test the possibility that color removal using Fe-TAML/H202 could have resulted from reaction with free Fe /Fe derived from catalyst breakdown, reactions were investigated in which FeCIa replaced the Fe-TAML catalyst. The concentration of Fe was the same as the Fe-TAML catalyst concentration, 1 pM in this case. No effect from the added Fe was observed - control (0 pM Fe-TAML) 592 CPU, 1 pM Fe-TAML 348 CPU, and 1 pM FeClj 592 CPU all 26 mM H2O2. Thus the Fe-TAML-H202 combination must be decreasing the color. 

Based on the laboratory results described above a pilot facility was built at the Tasman mill for the treatment of El effluent (Pinus radiata feedstock) to test a real time application of the chemistry. The pilot facility consisted of two stirred reactor vessels where the effluent was pumped into the first vessel (200 L capacity, hydralic retention time (HRT) 1 h) at a rate of 3.3 L/min (4800 L/day), before flowing into the second one (800 L capacity, HRT 4 h). Temperature and pH were continuously monitored but were not adjusted. Solution samples were regularly collected from each vessel along with untreated effluent. The Fe-TAML catalyst and hydrogen peroxide were dosed into treatment vessel 1. 

In order to have a pulp slurry that was managable in terms of mixing of catalyst and H2O2, the consistency was reduced to 1%. This allowed for placing the pulp into glass bottles which could then be placed in a shaking incubator at 80 °C. In a mill situation, the Fe-TAML catalyst could be introduced just prior to the re-pulper where efficient mixing with the pulp could occur. 

In order to determine the impact of the Fe-TAML catalyst on the possible sources of color generated in the El process, the experiments outlined in Table 1 were devised. 

The results of the treatments under O2 are shown in Figure 4b. Like Figure 4a, the data are displayed in pairs in terms of die Trials depicted in Table 1. There are some significant differences between some of the color values under N2 and O2. First, the color values from the simulated Ep and Eop treatments in the absence of the Fe-TAML catalyst (Trials 3 in Figures 4a and 4b), are 177 and 221 CPU, respectively (Table 2). Eop effluents therefore are darker than Ep effluents by 20%. The majority of this additional color comes from the liquor which is 27 CPU higher when O2 is present (114 CPU N2 141 CPU O2). 

If step III in Scheme 6 is ignored, a simplification is reached that has been demonstrated to be reasonable with certain substrates (see below). As a consequence, then the 1 catalysts should oxidize targeted reductants in accordance with Eq. (13) (here [Fe-TAML] is the total concentration of all TAML iron in solution). Eq. (13) implies that the catalysis by 1 mimics the steady-state oxidation by peroxidase enzymes, where Compound I is much more reactive than Compound II (55). 

Several interesting bleach catalysts are described in recent patent literature and are currently under evaluation. Fe-TAML (tetraamido macrocyclic ligand), for example, was selected from a large number of similar tetraamido complexes, and has excellent dye transfer inhibition properties, as it selectively destroys many dyes dissolved in the wash liquor [37]. The catalyst is being tested in several applications, such as effluent bleaching, the pulp and paper industry, desulfurization of diesel, and decontamination [38]. 

Figure 3. Color of El effluent before and after 1 h Fe-TAML treatment on a production basis, 2 pM catalyst, 22 mM H2O2, pH 11.8, 60 C.

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