Synthesis Method and its Influence Factors of Hydrotalcite-Like Compounds

Abstract

Hydrotalcite-like compounds are a class of anionic lays or layed double hydroxiods (LDHs) which consists of alkalescence, anion-exchanges and memory effect. The synthetic methods of LDHs include coprecipitation, hydrothermal synthesis, mirowave radiation, ion exchange, sol-gel method, roasting reduction method, instant synthesis, etc.The molar ratio of raw materials, pH value,reaction temperature,reaction time and so on have a greater impact on the purity and crystallinity of the LDHs.

Chemical Recycling of PET Wastes with Different Catalysts

“…Hydrotalcite catalyzed synthesis of polyethylene terephthalate was studied to clarify the effect of hydrotalcite properties on its catalytic activity [15]. Hydrotalcite was modified by various treatments to tune its activity as a polycondensation catalyst [14].…”

“…Replacement of the carbonate anions of hydrotalcite by more nucleophilic ones like hydroxide and alkoxide groups resulted in a faster polycondensation reaction. Hydrotalcite has two assembly orders: primary, lamination of sheets into plates, and secondary, agglomeration of plates into particles [14,15]. Hydrotalcite with larger sheet size showed lower activity.…”

“…Reuse of hydrotalcite after polycondensation followed by polycondensation resulted in a large activity enhancement [16]. Recently, the researchers at the Dow Chemical Company have patented HT-like compounds as safer, cheaper, and more efficient catalysts for PET production [15,16]. It is a hazardless material and can be applied in contact with food without any restrictions.…”

Back-to-monomer recycling of polycondensation polymers: opportunities for chemicals and enzymes

“…Dow Chemical Company has demonstrated the use of a hydrotalcite as an efficient catalyst for PET production. 12,64 Going one-step further, Vivek Sharma et al, studied the role of hydrotalcite as a depolymerisation catalyst especially for PET bottle chips. 45 Hydrotalcite was capable of degrading PET bottle chips up to 98% in 10 minutes using dimethyl sulfoxide (DMSO) as a solvent at 190 C. The products were mainly oligomers (tetramer), that required an additional step to hydrolyse the oligomers to DMT and EG using a strong base, for example sodium hydroxide.…”

Mg–Al Mixed Oxide Derived from Hydrotalcites Prepared Using the Solvent-Free Method: A Stable Acid–Base Bifunctional Catalyst for Continuous-Flow Transesterification of Dimethyl Carbonate and Ethanol

“…Layered double hydroxide (LDH) possesses brucite-like sheets and its formula is [M 1– x 2+ M x 3+ (OH) 2 ] x + [A x / n n – · m H 2 O] (M 2+ and M 3+ are octahedrally coordinated divalent and trivalent metal cations, respectively). Usually, LDH was synthesized by coprecipitation, urea hydrolysis, and sol–gel method. − The abovementioned methods have the disadvantages of time consumption and waste solutions produced in the process. Recently, mechanochemistry for the preparation of heterogeneous catalysts has attracted more attention because of various advantages such as environmental friendly solvent-free conditions, swiftness, and simplicity. − Perovskite, zeolites, , and metal oxides , prepared using solvent-free methods have unique properties compared with that of prepared using solvent-based routes.…”