Malcolm A. Kelland

A New Class of Kinetic Hydrate Inhibitor

Abstract: Low dosage hydrate inhibitors (LDHI) offer a recently developed hydrate control technology that can be more cost‐effective than traditional practices, such as the use of thermodynamic inhibitors (e.g., methanol and glycols). One class of LDHI, called kinetic inhibitors, is already being successfully used in the field. This paper describes efforts to develop a new class of kinetic inhibitor that shows various improvements over existing commercial technology. The polymer chemistry of the inhibitors and experiments carried out in high pressure cells and wheel/loops is described.

Experiments Related to the Performance of Gas Hydrate Kinetic Inhibitors

Abstract: (1) The hydrate formation process and growth is described through three different stages: (a) an induction period (nucleation), (b) a slow growth period prior to (c) a final stage described by a catastrophic, fast growth rate. In this paper the effect of kinetic hydrate inhibitors (KI) is characterized by the total delay of the catastrophic growth process at given subcooling ratios at given pressures. (2) The effects of a 20,000 Mw PVCap on a structure I (sI) ethane hydrate and a sII synthetic natural gas (SNG) hydrate have been examined in sapphire cells. A baseline was first established for each of two hydrate forming systems to describe the respective induction periods, slow growth periods, and initial growth rates. Without inhibitor, at similar subcoolings, and at similar pressures a longer induction period and a slower growth rate were observed prior to the catastrophic stage for the sII hydrate system as compared to the sI hydrate system. By the addition of 5,000 ppm PVCap to the aqueous phase the total delay of the catastrophic growth stage increased by a factor 12 for the sII SNG‐hydrate system and by a factor 5 for the sI ethane‐hydrate system. (3) The effect of different kinetic hydrate inhibitors (KI) at various pressures ranging from about 65 bar and up to about 200 bar has been examined in high pressure sapphire cells using a sII hydrate forming condensate‐SNG‐synthetic sea water system (SSW, 3.6% salt). For all the experiments reported the degree of subcooling (ΔT) with respect to the hydrate equilibrium properties of the fluid system used was kept at a similar magnitude. This was done to examine KI effects at similar degrees of subcooling within the different pressure regions. The experiments at constant ΔT showed that the KI effect (i.e., total delay of the catastrophic growth stage) decreased with increasing pressure and that a dramatic decrease was observed for increasing pressures above 90 bar. The true driving force of a hydrate forming system is described through a chemical potential, Δμ, which is a function of pressure (i.e., fugacity) and absolute temperature (K). At a given ΔT the chemical potential is greater in the high‐pressure region than in the low‐pressure region.

Formation of three-vertex metallaboranes from monoborane precursors: X-ray crystal structures of the molybdenum and ruthenium complexes [Mo(η-C5H5)2H(η2-B2H5)] and [Ru(η-C5Me5)(PMe3)(η2-B2H7)]

The novel three-vertex metallaborane [Ru(η–C5Me5)(PMe3)(η2-B2H7)](1) has been synthesised by reaction of [Ru(η-C5Me5)(PMe3)Cl2] with NaBH4; homologation is also observed in the reaction of [Mo(η-C5H5)2H2] with BH3·THF, which forms [Mo(η-C5H5)2H(η2-B2H5)](2); X-ray crystal structures of compounds (1) and (2) are reported.

Terminal substitution and cage incorporation of an η-cyclopentadienyl ring into borane cage structures; crystal structures of [Mo (η-C5H5)(η5:η1-C5H4)B4H7] and [Mo(η-C5H5)(η3:η2-C3H3)C2B9H9]

The synthesis and crystal structure of the molybdaborane [Mo(η-C5H5)(η5:η1-C 5H4)B4H7](1) and of the molybdacarbaborane [Mo(η-C5H5)(η3:η2-C3H3)C2B9H9](2) formed via cyclopentadienyl ring activation are reported.

Alkyl-chain disorder in tetraisohexylammonium bromide.

Tetraisohexylammonium bromide [systematic name: tetrakis(4-methylpentyl)azanium bromide], C(24)H(52)N(+)·Br(-), is a powerful structure II clathrate hydrate crystal-growth inhibitor. The crystal structure, in the space group P3(2)21, contains one ammonium cation and one bromide anion in the asymmetric unit, both on general positions. At 100 K, the ammonium cation exhibits one ordered isohexyl chain and three disordered isohexyl chains. At 250 K, all four isohexyl chains are disordered. In an effort to reduce the disorder in the alkyl chains, the crystal was thermally cycled, but the disorder remained, indicating that it is dynamic in nature.

Synthesis of small nido-ferrapentaboranes; a novel borane-capped nido-diferrapentaborane

Pentaborane(9) reacts with [Fe(PMe3)3(η2-CH2PMe2)H] to give [2,3-{Fe(PMe3)2}2(µ-H)B4H9](1) and [2-{Fe(PMe3)3}B4H8](2) in yields of up to 1 and 22% respectively; the X-ray crystal structure of (1) shows a nido-pentaborane(9) structure in which a BH3 fragment caps the Fe2B face.