Due to the important role of ammonia as a fertilizer in the agricultural industry and its promising prospects as an energy carrier, many studies have recently attempted to find the most environmentally benign, energy efficient, and economically viable production process for ammonia synthesis. The most commonly utilized ammonia production method is the Haber-Bosch process. The downside to this technology is the high greenhouse gas emissions, surpassing 2.16 kgCO₂-eq/kg NH₃ and high amounts of energy usage of over 30 GJ/tonne NH3 mainly due to the strict operational conditions at high temperature and pressure. The most widely adopted technology for sustainable hydrogen production used for ammonia synthesis is water electrolysis coupled with renewable technologies such as wind and solar. In general, a water electrolyzer requires a continuous supply of pretreated water with high purity levels for its operation. Moreover, for production of 1 tonne of hydrogen, 9 tonnes of water is required. Based on this data, for the production of the same amount of ammonia through water electrolysis, 233.6 million tonnes/yr of water is required. In this paper, a critical review of different sustainable hydrogen production processes and emerging technologies for sustainable ammonia synthesis along with a comparative life cycle assessment of various ammonia production methods has been carried out. We find that through the review of each of the studied technologies, either large amounts of GHG emissions are produced or high volumes of pretreated water is required or a combination of both these factors occur.

A feature article describing the fundamental characteristics and emerging applications of micro technology in the field of synthetic chemistry.

Several inexpensive and non-toxic solvents with low vapour pressures were investigated for their suitability as alternative solvents for the absorption of carbon dioxide from flue gas. The solvents include poly(ethylene glycol)s, poly(ethylene glycol) ethers, poly(ethylenimine) and glycerol-based substances. Solvent properties such as thermal stability, solubility of carbon dioxide and selectivity over nitrogen were investigated in a systematic study using a thermogravimetric analyser. Absorption results are reported for pure carbon dioxide and nitrogen as well as a mixture of both gases. Desorption and long-term sorption behaviour are also discussed. Glycerol and poly(ethylene glycol)s show a high solubility of carbon dioxide. Due to the high viscosity of the solvent, carbon dioxide absorption in poly(ethylenimine) is very slow in spite of the presence of favourable amine groups. PEG 300 was found to be the best solvent in this study and shows a high carbon dioxide solubility as well as good selectivity over nitrogen. The advantages of high stability, low solvent loss and low desorption energy of PEG 300 may outweigh its lower absorption capacity compared to the state-of-the-art solvent monoethanolamine, making it a potentially advantageous solvent for industrial carbon dioxide absorption processes.

The vapour pressures of several ionic liquids, liquid polymers and derivatives of glycerol were investigated by thermogravimetric analysis (TGA). The experimental method is described and discussed. Vapour pressure data for various solvents with low vapour pressures are reported at 100–120 °C. The thermogravimetric method for vapour pressure measurement is useful for the rapid screening of solvents. Ionic liquids have a low but detectable vapour pressure at 100–120 °C. The vapour pressures of liquid polymers such as poly(ethylenimine) and polyethylene glycols are in the same range, which might make these substances a less expensive alternative to ionic liquids.

Carbon dioxide (CO₂) absorption in several imidazolium-based ionic liquids (ILs), pyridinium-based ionic liquids and a tetraalkylammonium-based poly(ionic liquid) (PIL), poly[(p-vinylbenzyl) trimethylammonium hexafluorophosphate] P[[VBTMA][PF₆], was studied. The trend of CO₂ solubility in all of the ILs increases dramatically with decreasing absorption temperature. Based on the same bis(triflamide) [Tf₂N] anion, imidazolium, pyridinium and trihexyltetradecylphosphonium-based ionic liquids all show relatively similar CO₂ solubilities, which were higher than for the [ES] anion. The highest CO₂ absorption was found in a poly(ionic liquid) P[[VBTMA][PF₆]], however, the monomer also showed higher CO₂ capacity than the other ionic liquids. The poly(ionic liquid) is remarkable in that it can adsorb 77% of its body weight of CO₂ with a selectivity over nitrogen of 70 : 1. The absorbed CO₂ gas can be readily desorbed from ionic liquids and poly(ionic liquid) and the selectivity for CO₂ over N₂ was consistent over repeated cycles. The materials can be reused several times for consecutive sorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial adsorbers.