Recycling of Wastes from the Production of Alumina-Based Catalyst ...

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Aug 12, 2016 - as industrial waste, requiring efficient recycling options, which are explored in this work. A range of physicochemical methods was applied to ...
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Recycling of Wastes from the Production of Alumina-Based Catalyst Carriers Anna N. Matveyeva,†,‡ Nikolai A. Pakhomov,†,‡ and Dmitry Yu. Murzin*,‡,§ †

Department of General Chemical Technology and Catalysis, St. Petersburg State Institute of Technology (Technical University), 26, Moskovsky Ave., St. Petersburg 190013, Russia ‡ Laboratory of Catalytic Technologies, St. Petersburg State Institute of Technology (Technical University), 26, Moskovsky Ave., St. Petersburg 190013, Russia § Laboratory of Industrial Chemistry and Reaction Engineering, Åbo Akademi University, 8, Biskopsgatan, Turku/Åbo 20500, Finland ABSTRACT: Preparation of microspherical chromia−alumina KDM-type catalysts for alkane dehydrogenation is based on utilization of an amorphous nanostructured hydroxide−oxide Al2O3−x(OH)2·nH2O (where x = 0−0.28, n = 0.03−1.8) prepared via the centrifugal thermal activation (CTA) of gibbsite. The fine fraction of this carrier is considered as industrial waste, requiring efficient recycling options, which are explored in this work. A range of physicochemical methods was applied to analyze the main properties (phase composition, morphology, reactivity, etc.) of pilot and industrial batches of gibbsite CTA products. It has been clearly shown that the properties of CTA products are dependent on the nature of gibbsite used. The largest amount of the active amorphous phase of alumina is formed using gibbsite made from concentrated nepheline. Regularities of rehydration of the CTA-products fine fraction in acidic/ alkaline media and dissolution in sulfuric acid of the fine fraction of gibbsite and the industrial CTA product were explored to prepare aluminum sulfate, which is a water purification coagulant.



INTRODUCTION Dehydrogenation processes are extensively used in the petrochemical industry. Unsaturated compounds, such as propylene, butadiene, isoprene, and isobutylene, are obtained from the corresponding alkanes by dehydrogenation. They are valuable monomers that are used in the production of synthetic rubber and plastics, as well as for synthesizing high-octane number components of gasoline (for example, methyl tert-butyl ether (MTBE) and alkylate) and other important chemical products. There are several industrial options for C3−C5 paraffin dehydrogenation, differing in both technology and catalyst type.1,2 Chromium oxide-based catalysts have been one of the most actively investigated formulations for dehydrogenation since the first report of Frey and Huppke in 1933.3 Dehydrogenation of butanes over a chromia/alumina catalyst was first developed in the 1940s at Leuna and independently at UOP by Ipatieff and co-workers.4,5 These catalysts have been applied to several processes for dehydrogenation of light olefins. Several challenges in utilization of these catalysts were repeatedly highlighted, namely, a certain health risk, when the plant operators are exposed to Cr(VI)-containing catalysts, and sintering at high temperatures. Despite these apparent drawbacks, more than half of the global market of industrial catalysts for the dehydrogenation of C3−C5 paraffins can be attributed to chromia−alumina systems; for example, the best © 2016 American Chemical Society

known process is CATOFIN, by Chicago Bridge & Iron Co. (CB&I, Lummus).5−8 In the Russian Federation, industrial processes of isobutane dehydrogenation are performed in fluidized-bed reactors with microspherical chromia−alumina catalysts. This fluidized-bed dehydrogenation (FBD) technology of Yarsintez, which was further developed and licensed by Snamprogetti, is similar to old fluidized catalytic cracking units with a continuous catalyst circulation between a fluidized-bed reactor and a regenerator.9,10 As a catalyst, chromium oxide on alumina in a microspherical form with an average particle diameter of 100 μm ≤40 μm >40 μm, ≤100 μm >40 μm, ≤100 μm

100 100 100 100 100 150 100

1 145 130 48 54 100 129

substantially. Such an increase, reaching more than 2 orders of magnitude, is dependent on the particle size and the amount of adsorbed water. It is known19 that amorphous aluminum compounds exhibit the highest reactivity, which decreases as the crystallinity increases. The highest reactivity among the tested materials was observed with the A-CTA product (R = 37.5%); the I-CTAproduct has a reactivity of 34.7%, and the B-CTA product has a reactivity of 30.5%. The reactivity provides an opportunity to quantitatively determine the phase composition of the CTA product by solving a system of two equations with two unknowns, x and y:19 R = 0.98x + 0.28y + 0.1a (2) x = 100 − y − a − b

Figure 4. Thermograms of the A-CTA and B-CTA products.

(3)

where x is the contribution of amorphous alumina (wt %), y the concentration of the χ-like alumina phase (wt %); a the amount of gibbsite (wt %, as determined via TGA), and b the amount of boehmite (wt %, as determined via TGA). In eq 1, the reactivity is calculated as summation of the reactivities of different phases. The respective constants (0.98, 0.28, and 0.1) in eq 1 are the reactivity values of pure phases

reflects the crystallization of amorphous alumina Al2O3· nH2O.21 Based on the weight loss, it can be stated that ACTA product (sample 1) contains, on average, 9 wt % gibbsite and 18 wt % boehmite. The fine fraction (0−40 μm) of this sample contains 7% less boehmite than its coarse fraction (sample 2). This difference can be attributed to the higher 9104

DOI: 10.1021/acs.iecr.6b00978 Ind. Eng. Chem. Res. 2016, 55, 9101−9108

Article

Industrial & Engineering Chemistry Research amorphous alumina, χ-Al2O3, and gibbsite, which were determined after their dissolution in HCl. In eq 1, the contribution of boehmite was not taken into account, since it does not dissolve in HCl. The phase composition, based on reactivity data, is shown in Table 4.

which larger coarse particles are formed. The larger the particle size, the closer their form to being spherical, the most optimal morphology for fluidized-bed processes.11 B-GB and B-CTA particles are aggregates of smaller threedimensional (3D) particles of irregular shape (see Figure 6). B-CTA product particles