Phasertng: directed acyclic graphs for crystallographic phasing

Crystallographic phasing strategies increasingly require the exploration and ranking of many hypotheses about the number, types and positions of atoms, molecules and/or molecular fragments in the unit cell, each with only a small chance of being correct. Accelerating this move has been improvements in phasing methods, which are now able to extract phase information from the placement of very small fragments of structure, from weak experimental phasing signal or from combinations of molecular replacement and experimental phasing information. Describing phasing in terms of a directed acyclic graph allows graph-management software to track and manage the path to structure solution. The crystallographic software supporting the graph data structure must be strictly modular so that nodes in the graph are efficiently generated by the encapsulated functionality. To this end, the development of new software, Phasertng, which uses directed acyclic graphs natively for input/output, has been initiated. In Phasertng, the codebase of Phaser has been rebuilt, with an emphasis on modularity, on scripting, on speed and on continuing algorithm development. As a first application of phasertng, its advantages are demonstrated in the context of phasertng.xtricorder, a tool to analyse and triage merged data in preparation for molecular replacement or experimental phasing. The description of the phasing strategy with directed acyclic graphs is a generalization that extends beyond the functionality of Phasertng, as it can incorporate results from bioinformatics and other crystallographic tools, and will facilitate multifaceted search strategies, dynamic ranking of alternative search pathways and the exploitation of machine learning to further improve phasing strategies.

Coupling Solvent Extraction Units to Cyclic Adsorption Units

The possibility of regenerating the solvent of extraction units by cyclic adsorption was analyzed. This combination seems convenient when extraction is performed with a high solvent-to-impurity ratio, making other choices of solvent regeneration, typically distillation, unattractive. To our knowledge, the proposed regeneration scheme has not been considered before in the open literature. Basic relations were developed for continuous and discontinuous extraction/adsorption combinations. One example, deacidification of plant oil with alcohol, was studied in detail using separate experiments for measuring process parameters and simulation for predicting performance at different conditions. An activated carbon adsorbent was regenerated by thermal swing, making cyclic operation possible. When extracting the acid with methanol in a spray column, feed = 4 L min−1, solvent = 80 L min−1, feed impurity level 140 mmol L−1, and extract concentration 7.6 mmol L−1, the raffinate reaches a purity of 1.2 mmol L−1, the solvent being regenerated cyclically in the adsorber (364 kg) to an average of 0.7 mmol L−1. Regeneration of the solvent by cyclic adsorption had a low heat duty. Values of 174 kJ per litre of solvent compared well with the high values for vaporization of the whole extract phase (1011 kJ L−1).

Extraction of aromatic solvents from reformates and paint solvent wastes during ionic liquids

The work conducted in this study comprised three aspects: syntheses, characterizations, and multi-component liquid-liquid extractions. The main objectives of the project were: (1) to evaluate the efficacy and efficiency of ionic liquids to extract aromatic components from catalytic reformates and paint solvent wastes, and (2) to validate the method(s) used in this project to qualitatively and quantitatively analyze the aromatic molecules (BTEX) in multi-component mixtures. Therefore, this research critically investigated the major effects of the chosen ionic liquids as extractive solvents for the recovery of BTEX components from model and industrial organic mixtures. The project was concerned with the nature of solvents currently used in most industries for the separation by extraction of aromatic hydrocarbons from non-aqueous or organic mixtures. Most solvents currently employed for this purpose are highly volatile; hence they contribute significantly towards environment pollution. In addition, the extraction efficiency of these conventional solvents is limited only to mixtures containing aromatic hydrocarbons of 20% or more. Furthermore, conventional solvents are organic compounds which are generally toxic, flammable, and expensive to recover or regenerate from extract phases due to methods which involve several steps. In addition, they demand high energy input for the distillation steps. used in the analysis of aromatic components were evaluated for validity. According to the literature no such work was carried out by previous researchers. The study targeted four ionic liquids, namely, 1-ethyl-3-methylimidazolium ethyl sulphate [EMIM][ESO4], 1-ethyl-3-methylpyridinium ethyl sulphate [EMpy][ESO4], 1- Butyl-1-methyl-2-pyrrolidonium bromide [BNMP][Br], and 1,1-Dimethyl-2- pyrrolidonium iodide [MNMP][I] in an attempt to address this concern. These ionic liquids were synthesized and characterized in our laboratories using previously accepted methods. After synthesis and purification, they were characterized by techniques including FTIR, 1H-NMR, and 13C-NMR. The densities and moisture content of both the synthesized and standard ionic liquids were also determined using density meters and Karl-Fischer apparatus, respectively. The extractions were carried out on both the model and industrial mixtures using ionic liquids. Each ionic liquid was mixed with a target mixture in a water-jacketed vessel and then stirred vigorously at constant temperature achieved by a thermostatically controlled water-bath. After a selected period of time the operation was stopped and the resulting mixture was left to stand overnight to allow phase equilibration to be reached. The two phases were then separated and analyzed for the content of individual aromatic components in each phase using GC-FID calibrated with external standards of the components present in the mixtures being investigated. According to the results obtained from the synthesis and characterization methods the percentages yield of ionic liquids were reasonably high (> 95%). In addition, spectral studies showed high purity with fewer traces of impurities based on the observed relative intensities. Results from GC-FID indicated a relatively lower concentration of aliphatic hydrocarbons in the extract phase. On the other hand, the concentrations of aromatic II components in the extract phase were relatively higher than those of aliphatic hydrocarbons. The results obtained from the three extraction stages showed the total recovery of greater than 50% for the aromatic components. This suggests that at least six extraction stages would be required in order to achieve a total recovery of 100% aromatic components which is an indication of good efficiency. Also noticeable was that the first extraction stages for all ionic liquids recovery values were much higher than those values obtained from successive stages which showed approximately the same extraction results. In most experiments, 1-ethyl-3-methylpyridinium ethyl sulphate gave higher recovery values than the other three ionic liquids. It was also noted that the recovery values obtained from the extractions performed on model mixtures of the entire concentration range (0.5 – 25%) of individual aromatic components did not show any significant difference. Proportional difference in recoveries occurred across the entire concentration range of model mixtures. The results also indicated that the solubility of aromatic hydrocarbons in the ionic liquids decreases in the order: benzene > toluene > ethyl benzene >xylenes. This phenomenon is attributed to a decrease in π-π, cation- π, cation- anion interactions occurring between the ionic liquid and each of the aromatic molecules in this order. The recovery values for BTEX ranged from 80 to 120 % by volume for the three extraction stages. This is in line with results previous research studies carried out on liquid-liquid extractions involving ternary systems containing only one aromatic component in each mixture. Therefore this study shows that ionic liquids are capable extraction solvents for simultaneous recovery of the aromatic components from any organic mixtures containing low to high BTEX concentrations. In addition, the outcomes of this project have proved that ionic liquids are economically viable as potential extraction solvents since they can be easily recycled and reusable many times without any noticeable degradation. The results of this study are envisaged to make significant contributions to the current research efforts aimed at achieving greener environments and minimization of global warming. The findings of this project are also geared to boost the economy of our country through job creation using economically viable methods.