ABSTRACT
In this paper, we propose an improved hydroisomerization process, making use of membrane reactor technology. Linear alkanes are selectively supplied from a hydrocarbon feed (consisting of branched and linear alkanes) through an inert tubular membrane to a packed bed of catalyst. The results indicate that n-, mono- and di-branched components in a gas mixture can be separated with a selectivity factor of greater than 20 with a zeolite membrane under dedicated parameter settings. The RON-value of the product was calculated to be as high as 90 in a single pass reactor, which is 50 points higher than the feed value. The flux through the membrane could be optimized to give a STY/ATY ratio for the reactor of 877 m-1, which falls within the limits of technical feasibility.
Subject(s)
Alkanes/chemistry , Alkanes/isolation & purification , Chemical Industry/methods , Hydrocarbons/chemistry , Hydrocarbons/isolation & purification , Membranes, Artificial , Feasibility Studies , Isomerism , Technology/methodsABSTRACT
A novel tandem quadrupole mass spectrometer is described that enables gaseous collision-induced dissociation (CID) and surface-induced dissociation (SID) experiments. The instrument consists of a commercially available triple quadrupole mass spectrometer connected to an SID region and an additional, orthogonal quadrupole mass analyser. The performance of the instrument was evaluated using leucine-enkephalin, allowing a comparison between CID and SID, and with previous reports of other SID instruments. The reproducibility of SID data was assessed by replicate determinations of the collision energy required for 50% dissociation of leucine-enkephalin; excellent precision was observed (standard deviation of 0.6 eV) though, unexpectedly, the reproducibility of the equivalent figure for CID was superior. Several peptides were analysed using SID in conjunction with liquid secondary-ion mass spectrometry or electrospray; a comparison of the fragmentation of singly protonated peptide ions and the further dissociation of y-type fragments was consistent with the equivalence of the latter fragments to protonated peptides. Few product ions attributable to high-energy cleavages of amino acid side-chains were observed. The SID properties were investigated of a series of peptides differing only in the derivatization of a cysteine residue; similar decomposition efficiencies were observed for all except the cysteic acid analogue, which demonstrated significantly more facile fragmentation.
Subject(s)
Mass Spectrometry/instrumentation , Amino Acid Sequence , Angiotensinogen/chemistry , Bradykinin/analogs & derivatives , Bradykinin/chemistry , Cysteine/chemistry , Dynorphins/chemistry , Enkephalin, Leucine/chemistry , Fibrinopeptide A/chemistry , Mass Spectrometry/methods , Molecular Sequence Data , Molecular Structure , Peptide Fragments/chemistry , Reproducibility of Results , Sensitivity and Specificity , ThermodynamicsABSTRACT
The structural and performance characteristics (for n- and i-butane separation) of self-supported silicalite-membranes, were optimised by fine-tuning their syntheses by screening a total of nine silica sources and many reaction conditions. The mass balances indicate that membrane thickness is a function of both the synthesis volume and the silica source used. The excellent properties of the final membrane are demonstrated by its high permselectivity of 31 for n-butane combined with a n-butane flux of 10 mmol m(-2)s(-1), indicating perfect performance. For 50/50 mixtures (of n and i) the selectivity for nbutane was 48 and its flux was 3.8 mmol m(-2)s(-1). For the given selectivities, in relation to the membrane thickness, the theoretical fluxes are the highest values ever reported, underlining the point that high structural integrity is essential to achieve superior functionality.