Zinc dithiophosphates (ZnDTPs) are ubiquitous lubricating oil additives in today's passenger car motor oils, providing the important functions of wear and oxidation inhibition. However, the molecular-level mechanism by which these materials reduce wear is not understood. As a first step in developing an understanding of this mechanism, we used ab initio quantum chemical methods to examine the structures, vibrations, and energetics of these systems. The results show that the two phosphorus-sulfur bonds of the dithiophosphate of ZnDTPs are equiValent and have character intermediate between single and double bonds. This contrasts with the paradigm of one double bond (PdS) and one single bond (P-S) often used. Vibrational studies of DTP systems lead to a strong IR transition at about 650 cm -1 and a weak transition at about 530 cm -1 . We find modes in good agreement with experiment, where the high-frequency mode is antisymmetric PS stretch (not PdS), while the lower mode is symmetric PS stretch (not P-S). On the basis of the ab initio calculation results, we used the biased Hessian method to develop a vibrationally accurate force field (FF) for ZnDTPs. This FF can be used to examine the binding of DTPs to metal and metal oxide surfaces.

Zinc dithiophosphate (DTP) molecules have long been used as wear inhibitor oil additives for automotive engines. In order to obtain an atomistic understanding of the mechanism by which these molecules inhibit wear, we examined the geometries, energetics, and vibrations of an oxidized iron surface [(001) surface of α-Fe2O3] using the MSX force field (FF) based on ab initio quantum chemistry (QC) calculations. The DTP molecules studied include (RO)2PS2 with R = methyl, isobutyl, isopropyl, and phenyl. The α-Fe2O3 surface is described using the generalized valence bond (GVB) model of bonding. The geometries, binding energies, and vibrational frequencies from ab initio calculations on simple clusters are used with the biased Hessian method to develop the MSX FF suitable for describing the binding of DTP molecules to the surfaces. We find that the cohesive energies for the self-assembled monolayers (SAM) of the DTP molecules on the Fe2O3 surface correlate with the antiwear performance observed in experimental engine tests. This suggests that the search for more effective and environmentally benign wear inhibitors can use the cohesive energies for SAM formation as a criterion in selecting and prioritizing compounds for experimental testing.

In previous studies of dithiophosphate [DTP = S2P(OR)2] wear inhibitors bound to an oxidized iron surface, we found that the cohesive energy of the self-assembled monolayers (SAM) for DTP molecules with various organic R groups correlates with the wear inhibition observed in full engine experiments. In this paper we expand these calculations to consider dynamics at 500 K and then use the SAM model to predict new candidates for wear inhibitors. Using molecular dynamics (MD) simulations at 500 K, we show that the SAM has one DTP per two surface Fe sites of iron oxide. At this coverage we find that the cohesive energy of the SAM at 500 K is in the sequence 2-alkyl > 1-alkyl > aryl (e.g., iPr > iBu > Ph) which again correlates with wear inhibitor performance observed in engine tests. We then considered 7 novel DTPs and predict that R = cyclo-hexyl, nPr, and benzyl may perform as well as iPr. We then used the SAM wear inhibitor model to assess the likely performance of 11 novel classes of potential wear inhibitors. On the basis of this model we selected dithiocarbamates (DTC) as the best candidate to supplement DTP. We then considered a number of possible alkyl substitutions for DTC. The SAM model suggests that iC5 and nC3 are the best candidates, followed closely by iC3.

No abstract

Laboratory studies were conducted to find the best surfactant for generating CO2 foam in the presence of residual oil for two dolomite reservoirs. Conventional anionic and nonionic surfactants did not foam very well in core tests at reservoir conditions. The poor performance was attributed to the oil-wet nature of the dolomite cores. A new surfactant formulation was developed that alters wettability and has much better oil tolerance. CO2 foams were generated easily with the new formulation and were more stable. Field tests are planned to demonstrate improvement of sweep efficiency using the new surfactant. Evaluation of surfactants for mobility control applications involved a series of tests that measured brine compatibility, bench foam height, flow resistance in corefloods, and adsorption on reservoir rock. Bench foam tests, often used for surfactant screening, were unable to predict the effects of oil in the corefloods. Even the low oil saturation remaining after immiscible or miscible CO2 injection was detrimental to foam generation. The new surfactant formulation works over a wide range of brine salinities, controls CO2 mobility better than conventional surfactants, and has moderately low adsorption on dolomite rock. Introduction Oil production from CO2 flooding is increasing steadily in the U.S. despite marginal oil prices. There are many field-wide projects under way in West Texas, and new projects are planned for the mid-90's. CO2 is injected continuously or alternated with water if there is channeling and gravity override. The need for better CO2 mobility control grows as the older projects mature because of declining oil production and increasing CO2 recycling costs. The use of foam-forming surfactants to improve sweep efficiency and reduce CO2 breakthrough has received extensive laboratory evaluation but only limited field testing with mixed results. A large field demonstration of CO2 foam is planned for 1992 that should define better the potential of this promising technology. This paper describes the evaluation of foam-forming surfactants for two dolomite reservoir applications. The objective for Reservoir A was to find a suitable surfactant to improve the performance of immiscible cyclic CO2 treatments. For Reservoir B, surfactant would be used in a CO2 drive to improve the injection profile and control in-depth CO2 mobility under miscible conditions. Both reservoirs are challenging applications for foam because the dolomite rock tends to be oil-wet, which inhibits in-situ foam generation. Residual oil saturations are higher in Reservoir A than in Reservoir B because the CO2 is injected well below the minimum miscibility pressure. Our strategy in evaluating surfactants was to select a few commercial products that were identified previously as good foaming agents. These products were passed through a series of screening tests that measured brine compatibility, bench foam height, adsorption on reservoir rock, and foam performance in corefloods at reservoir conditions. The corefloods were a critical part of our evaluation because they modeled reservoir behavior more accurately than bulk foam, glass bead pack, or sand pack tests. P. 215^

To understand antiwear phenomena in motor engines at the atomic level and provide evidence inselecting future ashless wear inhibitors, we studied the thermal stability of the self-assembled monolayer(SAM) model for dithiophosphate (DTP) and dithiocarbamate (DTC) molecules on the iron oxidesurface using molecular dynamics. The interactions for DTP, DTC and Fe2O3 are evaluated based on aforce field derived from fitting to ab initio quantum chemical calculations of dimethyl DTP (and DTC)and Fe(OH)2(H2O)2-DTP (DTC) clusters. MD simulations at constant-NPT are conducted to assesrelative thermal stabilities of the DTP and DTC with different pendant groups (n-propyl, i-propyl, npentyl.and i-pentyl). To investigate frictional process, we employ a steady state MD method, in whichone of the Fe2O3 slabs maintained at a constant linear velocity. We obtain the time averaged normaland frictional forces from the interatomic forces. Then, we calculated the friction coefficient at theinterface between SAMs of DTP and the confined lubricant, hexadecane, to assess the shear stability ofDTPs with different pendant groups.

No abstract

Ketone werden mit Lithiumdiisopropylamid (LDA) in ihre Enolate übergeführt, die mit Eisen(III)‐chlorid oxidiert werden.