No abstract

C8-D), dodecylamine-N,N-bis(methylenephosphonate) (DBMP, C12-D), with carbon steel surfaces are studied by XPS at pH = 3.0. Structurally, they all possess two methylenephosphonate moieties connected to a single N atom. The third substituent on N is a non-polar, variable-length alkyl chain, -(CH 2 ) x CH 3 , where x = 0 (C1-D), 1 (C2-D), 3 (C4-D), 5 (C6-D), 7 (C8-D), and 11 (C12-D). XPS studies (on pristine solid diphosphonate samples and also on carbon steel specimens, immersed in aqueous solutions), indicate significant deprotonation of the diphosphonic acid molecules upon interaction with the 2 metallic surface. They also prove that this surface interaction results in adsorption on the surface via the deprotonated phosphonic acid moieties. The adsorption of inhibitors on the metal surface was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes detected in the charge transfer resistance (R ct ) and constant phase element (CPE) independently confirm inhibitors adsorption on metal surface. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy was used to investigate the nature of deposited film. Small alkyl chain diphosphonates (C1-D, C2-D and C4-D) exhibited lower corrosion resistance due to the thin, porous and/or incomplete layer formed on carbon steel surface. Longer alkyl chain molecules (C6-D, C8-D and C12-D) were found to adsorb more efficiently and form a more organized and thicker layer. The best results were obtained in the case of C8-D (lower corrosion current, higher R ct and surface coverage). In the presence of C8-D the corrosion rate was reduced by a factor of 6.

Organophosphonates are well-known to strongly interact with the surfaces of various minerals, such as brucite, gypsum, and barite. In this work, we study the influence of six systematically varied organophosphonate molecules (tetraphosphonates and diphosphonates) on the dissolution process of the (10.4) surface of calcite. In order to pursue a systematic study, we have selected organophosphonates that exhibit similar structural features, but also systematic architectural differences. The effect of this class of additives on the dissolution process of the calcite (10.4) surface is evaluated using in situ dynamic atomic force microscopy. For all of the six organophosphonate derivatives, we observe a pronounced restructuring of the (10.4) cleavage plane of calcite, demonstrated by the formation of characteristically shaped etch pits. To elucidate their specific influence on the dissolution process of calcite (10.4), we vary systematically the number of functional end groups (two for the tetraphosphonates and one for the diphosphonates), the spacing between the functional ends through separating methylene groups (2, 6, and 12), as well as the pH of the solution (ranging from 2.6 up to 11.7). For each of the two groups of the organophosphonate derivatives, we observe the very same formation of etch pits (olive-shaped for the tetraphosphonate and triangular-shaped for the diphosphonate molecules), respectively. This finding indicates that the number of functional ends decisively determines the resulting calcite (10.4) surface morphology, whereas the size of the organophosphonate molecule within one group seems not to play any important role. For all of the molecules, the restructuring process of calcite (10.4) is qualitatively independent of the pH of the solution and, therefore, independent of the protonation/deprotonation states of the molecules. Our results reveal a general property of organophosphonate derivatives to induce surface restructuring of the calcite (10.4), which seems to be very robust against variations in both, different molecular structures and different protonation/deprotonation states.

No abstract

Organophosphorus-based scale inhibitors (SIs) have been widely used in the petroleum industry for several decades. Among them, aminomethylenephosphonates (possessing at least one −NH+–CH2–PO3H– moiety) have shown outstanding inhibition efficiency against carbonate and sulfate oilfield scales. However, one of the main drawbacks of aminomethylenephosphonate-based SIs with multiple phosphonate (−PO3H2) groups is their poor tolerance against high-calcium brines. In this work, the calcium tolerance of aminomethylenephosphonates was improved by reducing the number phosphonate groups in the inhibitor backbone to less than three and introducing a variable-length non-polar alkyl side chain while maintaining acceptable inhibitory efficiency levels. Hence, we synthesized a series of variable-length alkyl chain-based amino-di(methylenphosphonate) [(H2O3P–CH2)2–N–(X)] inhibitors, (X = methyl, ethyl, propyl, butyl, hexyl, octyl, and dodecyl). In addition, we also studied the role of the alkyl side-chain length in the diphosphonate structure backbone on the scale inhibitory activity. All newly synthesized aminomethylenediphosphonates were evaluated as SIs for calcium carbonate (calcite) and barium sulfate (barite) in brines based on the Heidrun oilfield using a high-pressure dynamic tube blocking rig at 100 °C and 80 bar. Furthermore, we investigated the calcium compatibility of all aminomethylenediphosphonate SIs at several levels of calcium stresses. The new aminoalkyldiphosphonate inhibitors possessing shorter alkyl chain lengths (X = methyl, ethyl, propyl, butyl, and hexyl) gave better calcite scale inhibition performance and outstanding calcium compatibility of up to 1000 ppm of Ca2+ compared to the commercial benchmark ATMP SI [amino-tris(methylenephosphonate)] and longer alkyl-chain diphosphonates, that is, octylamine-N,N-di(methylenephosphonate) (ODMP, C8-D) and dodecylamine-N,N-di(methylenephosphonate) (DDMP, C12-D). Moreover, we tested the thermal stability (at 130 °C for one week) of the best-performing additive (based on calcite inhibition and calcium tolerance performances), and it was found that methylamine-N,N-dimethylenephosphonate (MDMP, C1-D) was thermally stable under these harsh conditions without any loss of its inhibition performance. The Ca-C8-D “complex” was deliberately synthesized and structurally characterized. It appears that the major factor for its poor Ca tolerance is the tight packing of the octyl side-chain groups.