Discussion of agglomeration mechanisms between hydrate particles in water in oil emulsions.

International audienceLine blockage due to gas hydrate formation in water/oil emulsions can be understood by considering the increase in the effective volume fraction of dispersed particles in the hydrate slurry. This increase is the result of an agglomeration process that takes place during hydrate formation. Two mechanisms of agglomeration reported in the literature are discussed. The first one is the contact-induced agglomeration mechanism for which the crystallization-agglomeration process is described as the result of the contact between a water droplet and a hydrate particle. The second one is the shear-limited agglomeration mechanism for which the balance between hydrodynamic force and adhesive force is considered. It is proposed to gather these two mechanisms in a unified model in order to predict the evolution of the viscosity of the slurry during hydrate formation. Such a model can be based on a Population Balance Model in which the agglomeration kernel is related to the contact-induced mechanism and the fragmentation kernel is related to the shear-limited mechanism

Cristallisation et agglomération de particules d'hydrate de fréon dans une émulsion eau dans huile : étude expérimentale et modélisation

207 pagesThis work deals with the problem of pipeline blockage by gas hydrates during oil production. Gas hydrates are crystals resulting from water and gas molecules association under high pressure and low temperature conditions. Such thermodynamical conditions are generally encountered in oil production, particularly for deep offshore fields or cold areas. Due to agglomeration process, hydrate occurrence leads to plug formation.The main objective of this study is to improve our understanding in the mecanisms involved in the agglomeration process, particularly for water in oil emulsions. Results have allowed us to supply a theorical model of agglomeration. A model system of Ice and Freon hydrates dispersed in xylene with asphaltenes as surfactant is used. As Freon hydrates form under atmospheric pressure at low temperature, it allows us to apply different techniques without being limited by pressure conditions. The Nuclear Magnetic Resonance (NMR) technique is mainly used. It makes the measurement of the ratio between solid hydrogene or fluorine in ice or hydrate and total hydrogen or fluorine in the sample possible - enabling to know the quantity of formed ice or hydrates. Thus, a kinetic study is realized, enabled to know the quantity of ice and hydrate formed. To complete this work, optical microscopy with cooling cell is used to get direct observations of agglomeration. The rheometry technique is also used. It enables us to study the evolution of the apparent viscosity of the system during ice or hydrate formation and plugging. These techniques can also be applied to study real systems like methane hydrates in crude oils under field conditions. Moreover, an interpretation, which couples rheology, crystallisation and agglomeration, is studied and leads to a model.Ce travail traite du problème du bouchage des pipelines par des particules d'hydrates de gaz dans la production de pétrole. Les hydrates de gaz sont des composés cristallins qui se forment à partir de l'association d'eau et de molécules de gaz à haute pression et basse température. De telles conditions thermodynamiques sont rencontrées pendant la production et le transport de pétrole, particulièrement en offshore profond ou dans des zones froides. A cause de ce processus d'agglomération, l'apparition d'hydrate peut mener à la formation de bouchons.Cette étude à pour but d'améliorer la compréhension de ce mécanisme d'agglomération, dans le cas d'une émulsion eau dans huile. Par conséquent, l'agglomération des particules de glace et d'hydrate est comparée. L'agglomération des particules de glace et d'hydrate de trichlorofluoromethane ou fréon (CCl3F) dispersées dans le xylène avec des asphaltènes comme tensioactif est choisie comme système modèle. Comme les hydrates de trichlorofluoromethane (CCl3F) sont stables à pression atmosphérique, ils permettent d'utiliser des techniques d'analyses sans être limité par les conditions de pression. La technique de Résonance Magnétique Nucléaire RMN est utilisée. La grande différence entre le temps de relaxation des solides et des liquides est utilisée afin de contrôler in situ le rapport entre la quantité d'entités (hydrogène ou fluor) solides et total en fonction du temps et des conditions contrôlées de cisaillement. Ainsi, une étude cinétique est réalisée, ce qui permet de connaître la quantité de glace ou d'hydrate formée ; La viscosité apparente du système, pendant la cristallisation et le bouchage, est également suivie grâce à des mesures rhéologiques afin de caractériser l'agglomération des particules. Pour compléter cette étude, des observations en microscopie optique avec une cellule thermostatée est utilisée afin d'obtenir des observations directes de l'agglomération. Cette approche expérimentale nous permet de discuter des différents mécanismes d'agglomération de la glace et de l'hydrate dans une phase hydrocarbure et de les modéliser

Cristallisation et agglomération de particules d'hydrate de fréon dans une émulsion eau dans huile (étude expérimentale et modélisation)

Ce travail traite du problème du bouchage des pipelines par des particules d hydrates de gaz dans la production de pétrole. Les hydrates de gaz sont des composés cristallins qui se forment à partir de l association d eau et de molécules de gaz à haute pression et basse température. De telles conditions thermodynamiques sont rencontrées pendant la production et le transport de pétrole, particulièrement en offshore profond ou dans des zones froides. A cause de ce processus d agglomération, l apparition d hydrate peut mener à la formation de bouchons. Cette étude à pour but d améliorer la compréhension de ce mécanisme d agglomération, dans le cas d une émulsion eau dans huile. Par conséquent, l agglomération des particules de glace et d hydrate est comparée. L agglomération des particules de glace et d hydrate de trichlorofluoromethane ou fréon (CCl3F) dispersées dans le xylène avec des asphaltènes comme tensioactif est choisie comme système modèle. Comme les hydrates de trichlorofluoromethane (CCl3F) sont stables à pression atmosphérique, ils permettent d utiliser des techniques d analyses sans être limité par les conditions de pression. La technique de Résonance Magnétique Nucléaire RMN est utilisée. La grande différence entre le temps de relaxation des solides et des liquides est utilisée afin de contrôler in situ le rapport entre la quantité d entités (hydrogène ou fluor) solides et total en fonction du temps et des conditions contrôlées de cisaillement. Ainsi, une étude cinétique est réalisée, ce qui permet de connaître la quantité de glace ou d hydrate formée ; La viscosité apparente du système, pendant la cristallisation et le bouchage, est également suivie grâce à des mesures rhéologiques afin de caractériser l agglomération des particules. Pour compléter cette étude, des observations en microscopie optique avec une cellule thermostatée est utilisée afin d obtenir des observations directes de l agglomération. Cette approche expérimentale nous permet de discuter des différents mécanismes d agglomération de la glace et de l hydrate dans une phase hydrocarbure et de les modéliser.This work deals with the problem of pipeline blockage by gas hydrates during oil production. Gas hydrates are crystals resulting from water and gas molecules association under high pressure and low temperature conditions. Such thermodynamical conditions are generally encountered in oil production, particularly for deep offshore fields or cold areas. Due to agglomeration process, hydrate occurrence leads to plug formation. The main objective of this study is to improve our understanding in the mecanisms involved in the agglomeration process, particularly for water in oil emulsions. Results have allowed us to supply a theorical model of agglomeration. A model system of Ice and Freon hydrates dispersed in xylene with asphaltenes as surfactant is used. As Freon hydrates form under atmospheric pressure at low temperature, it allows us to apply different techniques without being limited by pressure conditions. The Nuclear Magnetic Resonance (NMR) technique is mainly used. It makes the measurement of the ratio between solid hydrogene or fluorine in ice or hydrate and total hydrogen or fluorine in the sample possible - enabling to know the quantity of formed ice or hydrates. Thus, a kinetic study is realized, enabled to know the quantity of ice and hydrate formed. To complete this work, optical microscopy with cooling cell is used to get direct observations of agglomeration. The rheometry technique is also used. It enables us to study the evolution of the apparent viscosity of the system during ice or hydrate formation and plugging. These techniques can also be applied to study real systems like methane hydrates in crude oils under field conditions. Moreover, an interpretation, which couples rheology, crystallisation and agglomeration, is studied and leads to a model.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

STUDY OF AGGLOMERATION OF ICE PARTICLES AND OF TRICHLOROFLUOROMETHANE HYDRATE PARTICLES SUSPENDED IN A HYDROCARBON PHASE

This work deals with the problem of pipeline plugging by gas hydrates during oil production. Gas hydrates are crystals resulting from water and gas molecules association under high pressure and low temperature conditions. Such thermodynamical conditions are generally encountered during oil production and transport, particularly in deep offshore fields or in cold areas. Due to an agglomeration process which is still debated, hydrate occurrence can lead to plug formation. This study aims at improving the understanding in this mechanism process, in the case of water-in-oil emulsions. Therefore, ice or hydrate particle agglomeration is compared. Ice or trichlorofluoromethane (CCl3F) hydrate particles dispersed in xylene with asphaltenes as surfactant is chosen as a model system. As CCl3F hydrates are stable under atmospheric pressure, it allows us to apply different techniques without being limited by high pressure conditions. The Nuclear Magnetic Resonance (NMR) technique is used. The very different relaxation rate for solids or liquids is used to monitor in situ the ratio between solid and total hydrogen or fluorine as a function of time with controlled shearing conditions. Thus, a kinetic study is realized, that enabled to know the amount of ice formed. The apparent viscosity of the system, during crystallization and plugging, is also followed with rheometry in order to characterize agglomeration. This experimental approach allows us to highlight that physico-chemistry of interface water/oil has an important role in agglomeration. It enables us to discuss different mechanisms of agglomeration of ice and hydrate particles in a hydrocarbon phase.Non UBCUnreviewe

Preoperative use of anti-TNF therapy and postoperative complications in inflammatory bowel diseases: A meta-analysis

International audienceBackground and aims: About one-third of inflammatory bowel disease (IBD) patients still require surgery. A growing number of them receive anti-tumor necrosis factor (TNF) therapy before surgery. The present meta-analysis studied the risk of postoperative complications in IBD patients treated with anti-TNF.Methods: MEDLINE was searched (up to January 2012) to identify observational studies reporting the prevalence of postoperative complications in IBD patients. The prevalence of overall, infectious, and non-infectious postoperative complications was extracted for all studies, and according to preoperative anti-TNF treatment where reported. Pooled prevalence, as well as odds ratios (ORs), with 95% confidence intervals (CIs) was calculated.Results: The search identified 86 citations. Twenty-one studies, containing 4251 subjects, reported the prevalence of postoperative complications according to preoperative anti-TNF treatment. Pooled prevalence of any postoperative complication was 21%, 35%, and 26% in Crohn's disease (CD), ulcerative colitis (UC) or inflammatory bowel disease unspecified (IBD-U) and IBD, respectively. The prevalence of any postoperative complication was increased in IBD patients who underwent preoperative anti-TNF therapy (OR: 1.25; 95% CI: 1.02–1.53). Pooled prevalence of infectious postoperative complications was 16%, 17%, and 15% in CD, UC/IBD-U and IBD, respectively. The prevalence of infectious postoperative complications was increased in CD patients who underwent preoperative anti-TNF therapy (OR: 1.45; 95% CI: 1.03–2.05). The confounding effect of concomitant therapies could not be studied.Conclusions: Preoperative anti-TNF use slightly increases the occurrence of overall postoperative complications in IBD patients, and particularly infectious complications in CD patients. Postoperative complications are not increased in UC

Enterocolitis due to immune checkpoint inhibitors: a systematic review

International audienceImmune checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) and programmed death-1 (PD-1)/ ligand are increasingly used to treat several types of cancer. These drugs enhance antitumour T-cell activity and therefore induce immunerelated adverse effects (irAE), of which gastrointestinal (GI) irAE are among the most frequent and severe. This systematic literature review summarises the clinical manifestations, management and pathophysiology of GI irAE due to immune checkpoint inhibitors. GI irAE induced by anti-CTLA-4 are frequent, potentially severe and resemble IBD, whereas those induced by PD-1 blockade seem to be less frequent and clinically more diverse. Baseline symbiotic gut microbiota is associated with an enhanced antitumour response to immune checkpoint inhibitors and an increased susceptibility to developing enterocolitis, in patients treated with anti-CTLA-4. These findings open new perspectives for possible manipulation of the gut microbiota in order to better identify responders to immune checkpoint inhibitors and to increase their efficacy and safety

Trough levels and antibodies to infliximab may not predict response to intensification of infliximab therapy in patients with inflammatory bowel disease.

Background: Infliximab is effective for the treatment of refractory inflammatory bowel disease (IBD). Nevertheless, up to 40% of patients lose response to infliximab over time. The aim was to assess the clinical value of measuring infliximab trough levels and antibodies to infliximab (ATI) concentrations in IBD patients who lost response to infliximab therapy. Methods: We retrospectively studied records of IBD patients who lost response to infliximab therapy. We first assessed clinical responses of different therapeutic strategies that were applied when patients lost response to infliximab and then we looked at the correlation between clinical response and infliximab trough levels and ATI concentrations. Results: Seventy-six IBD patients were included. 31/76 patients (41%) continued infliximab therapy without any modification, 39 patients (51%) had an intensification of infliximab therapy, five patients (7%) had switched to adalimumab therapy, and one patient (1%) underwent surgery. Clinical response was observed in 27 patients (69%) with an intensification of infliximab therapy. There was no significant difference in mean infliximab trough level at inclusion in patients who responded to intensification of infliximab therapy (3.3 +/- 4.1 mu g/mL) as compared with patients who did not respond (2.3 +/- 2.2 mu g/mL, P = 0.85). In all, 16/76 patients (22.4%) presented detectable ATI in the serum. Ten ATI-positive patients had an intensification of infliximab therapy and six (60%) demonstrated a clinical response. After intensification of infliximab therapy the ATI concentration decreased in five patients. Conclusions: In patients with IBD who lose response to infliximab, clinical improvement may occur upon intensification of infliximab therapy, irrespective of infliximab serum concentration or presence of ATI. (Inflamm Bowel Dis 201