Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Frederick M MacDonnell

Abstract

Speciation of Aluminum During the Formation of Aluminum Chlorohydrate: A Combined Kinetic and Mass Spectrometry Study Mohammad Fakrul Islam, Ph.D. The University of Texas at Arlington, 2019 Supervising Professor: Frederick M. MacDonnell Aluminum chlorohydrate (ACH) is synthesized in a heterogeneous reaction of aluminum ingots or pellets with aqueous hydrochloric acid. This exothermic reaction produces copious amounts of hydrogen gas and ultimately generates product grade aluminum chlorohydrate when the specific gravity of the solution reaches 1.33-1.35. Other product specifications include 3.5-4.0 pH, 7.9-8.4 wt.% chloride, 23-24 wt.% Al2O3, low turbidity (<50 NTU) and high basicity (>83%). A relative study of aluminum ingot with pellet shows that the reaction rate highly depends upon the size of the aluminum in terms of the surface area, as expected. The smaller the size of the aluminum solid, the higher the surface area to mass ratio, and the faster the rate of the ACH product formation. In a kinetic study of this reaction under commercial production conditions, we recorded the [Al3+] in the ACH solution versus time, using an ICP-OES to measure [Al3+], and observed that aluminum pellet (3.2 mm, 9.5 cm2/g surface area) reacts 6.5 times faster than the aluminum ingot (surface area 0.3 cm2/g, 2.27 kg bar) to produce specification grade ACH. The reaction is always run with an 150% excess of aluminum and calculations show that 60% of the aluminum added is now dissolved. In subsequent studies, we explored the role of trace metallic impurities, such as Fe, Co, Ni, and Cu in the kinetics of the ACH synthesis reaction. Experienced producers of ACH had long noted that if the aluminum was too pure the reaction would not ‘kick-off’, meaning take off and generate heat such that the reaction accelerated itself. Presumably the impurities in the aluminum play some role in the reaction kinetics. In a side-by-side study of ACH production in which aluminum with two different purities (99.99% and 99.82%) were used, we observed a substantial increase in the reaction rate (11.5 times) for those made with less pure Al. Additional studies show that a similar acceleration of the reaction can be accomplished by the deliberate addition of small quantities of these metal salts, including FeSO4.7H2O and NiSO4.6H2O, suggesting that the mechanism of catalysis is via lowering the reaction barrier to hydrogen formation, i.e. these metals serve as better hydrogen evolution sites (catalysts) than Al. We observe that Ni >> Fe, Co > Cu for accelerating the ACH reaction, which matches well with their overpotential for H2 evolution in acidic media.

Keywords

ACH, Aluminum, Coagulation, Antiperspiration

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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