Arjan van der Linden

Phospholyl catalysts for olefin polymerization

Abstract Seventeen different phospholyl ligands were incorporated in a total of 22 zirconium complexes, (Phos) 2 ZrCl 2 , (Phos)(C 5 H 5 )ZrCl 2 , investigated in propylene polymerization catalysis using methylaluminoxane as cocatalyst. Atactic polypropylene with M n varying from 450 to >20 000 and vinylidene end groups (CH 2 C(Me)R) was obtained with activities up to 170 kg/g Zr·h. For the 11 diphospholyls of structure (2,5-R 2 C 4 H 2 P) 2 ZrCl 2 , catalytic activity was highest with substituents of moderate bulk adjacent to phosphorus (e.g., c -Pr, Ph), whereas complexes with two small (H) or two large (CMe 3 , SiMe 3 ) ligand substituents were inactive. It is hypothesized that optimum activity with MAO requires selective blocking of phosphorus lone pair coordination to aluminum, whilst allowing free propylene approach to the active site. The degree of polymerization increased steadily in the series of 2,5-disubstituted phospholyl complexes, dialkyl M n .

New, Highly Efficient Work‐Up Protocol for Sulfonated Diphosphines

Isolation of a series of sulfonated diphosphines via a new highly efficient method is described. The work-up procedure involves the precipitation of the sulfonated ligand prior to neutralization, and subsequent removal of the sulfuric acid by filtration and washing. Great advantages of this procedure are its simplicity and easiness to scale-up while co-production of large amounts of sulfate salts is avoided.

Cationic ansa-(eta(5)-cyclopentadienyl)(eta(6)-arene) complexes of titanium

The half-sandwich titanium trimethyl complex (η5-C5H4CMe2Ar)TiMe3 (Ar = 3,5-Me2C6H3) reacts with the Lewis acid B(C6F5)3 to give the ionic TiIVansa-cyclopentadienyl-arene complex [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3]. In bromobenzene solvent, addition of more B(C6F5)3 leads to C6F5/Me exchange and, subsequently, to formation of an unusual dimeric TiIII dicationic species, {[(η5,η6-C5H4CMe2Ar)Ti(μ-Br)]2}[B(C6F5)4]2, which was structurally characterized. Its formation involves reduction of the transition-metal center, solvent C–Br cleavage and perfluoroaryl-group scrambling.

Defining the Brittle Failure Envelopes of Individual Reaction Zones Observed in CO2-Exposed Wellbore Cement

To predict the behavior of the cement sheath after CO2 injection and the potential for leakage pathways, it is key to understand how the mechanical properties of the cement evolves with CO2 exposure time. We performed scratch-hardness tests on hardened samples of class G cement before and after CO2 exposure. The cement was exposed to CO2-rich fluid for one to six months at 65 °C and 8 MPa Ptotal. Detailed SEM-EDX analyses showed reaction zones similar to those previously reported in the literature: (1) an outer-reacted, porous silica-rich zone; (2) a dense, carbonated zone; and (3) a more porous, Ca-depleted inner zone. The quantitative mechanical data (brittle compressive strength and friction coefficient) obtained for each of the zones suggest that the heterogeneity of reacted cement leads to a wide range of brittle strength values in any of the reaction zones, with only a rough dependence on exposure time. However, the data can be used to guide numerical modeling efforts needed to assess the impact of reaction-induced mechanical failure of wellbore cement by coupling sensitivity analysis and mechanical predictions.

Stress And Pore-pressure Dependence of Sound Velocities In Shales: Poroelastic Effects In Time- Lapse Seismic

We have measured the stress, stress-path, and pore-pressure dependence of p-wave velocities of different shales. In good approximation, for small deformations, vertical velocity changes are proportional to changes in vertical effective stress. For low-permeability, undrained formations such as shales, it has been well established that pore pressures change as a function of mean-total stress changes and deviatoric stress changes. Analytical and finite-element geomechanical modeling, for a linear-elastic, isotropic half space, demonstrate that a ubiquitous porepressure increase in the low-permeability non-producing formations accompanies depletion of an adjacent reservoir. This pore pressure increase results in positive seismic timelapse time shifts in the overand underburden and may nearly cancel the negative time shifts due to archinginduced total vertical stress increase in the sideburden. Thus, poroelastic effects might offer an alternative explanation for the observation of mostly positive time shifts in time-lapse seismic, which was previously attributed to an asymmetric velocity-strain dependence for loading and unloading.

Rock Physical Controls on Production-induced Compaction in the Groningen Field

Advancing production from the Groningen gas field to full depletion generates substantial, field-scale deformation, and surface subsidence. Quantifying associated risk requires understanding physical processes in the subsurface, in particular those related to deformation of the Permian sandstone reservoir. Here, we report the results of a large experimental study, using fresh core material taken from the center of the field. By subjecting the material to depletion and slight unloading, complemented with a range of rock property measurements, we determine what rock physical properties control production-induced compaction in the material. Our results show that, although a large part of the deformation can be explained by classical linear poroelasticity, the contribution of inelastic (permanent) deformation is also significant. In fact, it increases with progressing pressure depletion, i.e. with increasing production. Utilizing univariate and multivariate statistical methods, we explain the additional inelastic deformation by direct effects of porosity, packing, and mineral composition. These proxies are in turn related to the depositional setting of the Permian reservoir. Our findings suggest that field-scale subsidence may not only be related to the often-used rock porosity, but also to packing, and composition, hence the local depositional environment. This motivates alternative assessments of human-induced mechanical effects in sedimentary systems.