Kinetic studies of liquid phase ethyl tert-butyl ether (ETBE) synthesis using macroporous and gelular ion exchange resin catalysts

Biodegradation and fate of ethyl tert-butyl ether (ETBE) in soil and groundwater: A review

This review summarises the current state of knowledge on the biodegradation and fate of the gasoline ether oxygenate ethyl tert-butyl ether (ETBE) in soil and groundwater. Microorganisms have been identified in soil and groundwater with the ability to degrade ETBE aerobically as a carbon and energy source, or via cometabolism using alkanes as growth substrates. Aerobic biodegradation of ETBE initially occurs via hydroxylation of the ethoxy carbon by a monooxygenase enzyme, with subsequent formation of intermediates which include acetaldehyde, tert-butyl acetate (TBAc), tert-butyl alcohol (TBA), 2-hydroxy-2-methyl-1-propanol (MHP) and 2-hydroxyisobutyric acid (2-HIBA). Slow cell growth and low biomass yields on ETBE are believed to result from the ether structure and slow degradation kinetics, with potential limitations on ETBE metabolism. Genes known to facilitate transformation of ETBE include ethB (within the ethRABCD cluster), encoding a cytochrome P450 monooxygenase, and alkB-encoding alkane hydroxylases. Other genes have been identified in microorganisms but their activity and specificity towards ETBE remains poorly characterised. Microorganisms and pathways supporting anaerobic biodegradation of ETBE have not been identified, although this potential has been demonstrated in limited field and laboratory studies. The presence of co-contaminants (other ether oxygenates, hydrocarbons and organic compounds) in soil and groundwater may limit aerobic biodegradation of ETBE by preferential metabolism and consumption of available dissolved oxygen or enhance ETBE biodegradation through cometabolism. Both ETBE-degrading microorganisms and alkane-oxidising bacteria have been characterised, with potential for use in bioaugmentation and biostimulation of ETBE degradation in groundwater.

Insight into the active site nature of zeolite H-BEA for liquid phase etherification of isobutylene with ethanol

The nature of active acid sites of zeolite H-BEA with different Si/Al ratios (15–407) in liquid phase etherification of isobutylene with ethanol in a continuous flow reactor in the temperature range 80–180 °C has been explored. We describe and discuss data concerning the strength and concentration of acid sites of H-BEA obtained by techniques of stepwise (quasi-equilibrium) thermal desorption of ammonia, X-ray diffraction, low-temperature adsorption of nitrogen, FTIR spectroscopy of adsorbed pyridine and solid-state ²⁷Al MAS NMR. The average values of the adsorption energy of NH₃ on H-BEA were experimentally determined as 63.7; 91.3 and 121.9 mmol g⁻¹ (weak, medium, and strong, respectively). In agreement with this, a correlation between the rate of ethyl-tert-butyl ether synthesis and the concentration of weak acid sites (E_NH3 = 61.6–68.9 kJ mol⁻¹) has been observed. It was concluded that the active sites of H-BEA for this reaction are Brønsted hydroxyls representing internal silanol groups associated with octahedrally coordinated aluminum in the second coordination sphere.

The active sites of H-BEA zeolites for ETBE synthesis are the weak Brønsted acid sites representing internal silanol groups.

Catalytic activity dependence on morphological properties of acidic ion-exchange resins for the simultaneous ETBE and TAEE liquid-phase synthesis

Resin acid capacity and specific volume of the swollen polymer are the key properties that determine its catalytic activity.

Adsorption–desorption of ethanol on sulfonated resin catalysts for ethyl-tert-butyl ether synthesis

Ethanol adsorption on sulfonic resins of different morphological types, such as gel, macroporous sulfonic resin, mixed sample (1:1 mixture of gel-type sulfonic resin with aerosil) and sulfonic resin loaded on wide-porous mineral carrier was studied using the methods of quasi-equilibrium thermal desorption and quartz crystal microbalance. It has been observed that the faster ethanol adsorption proceeds on the macroporous sulfonic resin and the slower ethanol adsorption on the gel-type one. It is due to different swelling ability. It was found that the transfer of the ethanol molecules through the gel phase of sulfonic resin proceeds by means of the adsorption–desorption mechanism. The ratio of ethanol adsorption on sulfonic resin is one molecule per one acid site. During the ethanol adsorption on the gel and mixed sulfonic resin, one type of adsorbed complex is formed, whereas on the macroporous and loaded samples two adsorbed complexes with different energies are formed. This is probably because of the different localization of the acid sulfonic groups.

Current uses and trends in catalytic isomerization, alkylation and etherification processes to improve gasoline quality

Due to the growing restrictions on the content of aromatic compounds by the European legislation in motor fuels and at the same time the need for higher quality fuels (minimizing the presence of contaminants and hazardous products to health), it has become necessary to increase processes that can maximize the number of octane in gasoline. This manuscript is aimed to provide current trends and processes related to isomerization, alkylation and etherification processes to improve gasolines as final product. Examples provided include the isomerization of light n-alkanes into iso-alkanes or the alkylation, in which the preferred olefin is the methylbutilene and i-butane to produce a high octane number gasoline. Currently, there are two main commercial processes for alkylation processes (hydrofluoric and sulfuric acid technologies). Other incoming suitable process is the etherification of iso-olefins to bio-ethers (the European Union have as a minimum target of biofuel content in fuels of 10% in 2020). The refiners are recently investing in the production of bio-ETBE (ethyl tertiary butyl ether) and other products as additives using bio-ethanol and olefins. Commercial and new potential catalysts for all these processes are currently being used and under investigation.