Influence of graphene oxide additives on the NF separation of triazine-based H2S scavenging compounds using advanced membrane technology.

This work proposes an innovative approach for the membrane separation of spent and unspent H2S scavengers (SUS) derived from the application of MEA-triazine in offshore oil and gas production. Modified nanofiltration membranes were fabricated by incorporating graphene oxide (GO) and polyvinyl alcohol (PVA) into a thin film composite (TFC) to obtain a thin film nanocomposite (TFN) with enhanced permeability. In addition, various immobilization strategies for GO were investigated. The performance of the membranes and the effect of the GO loading were evaluated in terms of permeability, fouling propensity, and rejection of key components of the SUS, i.e., MEA-triazine (unspent scavenger), dithiazine (spent scavenger), and monoethanolamine, operating on a sample of SUS wastewater obtained from an offshore oil and gas platform. Various characterization techniques, such as contact angle, FTIR, XRD, SEM, TGA, and AFM, were employed to evaluate the structure, composition, and hydrophilicity of the membrane. The results show a remarkable increase in permeability (from 0.22 Lm-2 h-1 bar-1 for the TFC to 5.8 Lm-2 h-1 bar-1 for the TFN membranes), due to the enhanced hydrophilicity from GO incorporation. The strong interfacial interaction between GO and PVA within the TFN membrane results in negligible nanofiller leaching. The incorporation of GO moderately increases the rejection of the unspent scavenger (63%-73%, 62%-79%, 62%-80%, and 68%-76%), while drastically increasing the rejection of the spent scavenger, which is approximately null for the TFC membrane without GO and increases up to 58% in the TFN membrane with GO. Therefore, while the proposed membranes cannot be used for the selective separation of the unspent form the spent scavenger, they can achieve substantial recovery of all the key components contained in the SUS to avoid their discharge into the sea.

Reducing the environmental impact of offshore H2S scavenging wastewater via hydrothermal oxidation.

The discharge of H2S scavenging wastewaters, containing spent and unspent scavengers (SUS), into the marine environment is a large contributor to the environmental impact of offshore oil and gas production. Hydrothermal oxidation (HTO) can be a viable method for on-site treatment of the SUS before discharge, but the effect of the process on the ecotoxicity of the effluent has not been investigated so far. The aim of this study was to investigate the potential of the HTO technology in reducing the environmental impact by linking the chemical process design with ecotoxicity reduction. For this, we combined HTO experiments on a SUS sample from an oil and gas platform in the North Sea with whole effluent ecotoxicity evaluation before and after the treatment. The HTO process was carried out under excess of oxygen, for temperatures and pressures in the range 199 to 350°C and 83 to 228 bar, respectively, and for reaction times of 5 to 360 min. Initially, the SUS sample exhibited very high ecotoxicity, which was drastically reduced by the HTO process. More specifically, the ecotoxicity towards bacteria was reduced more than 90% for all HTO conditions, while the reduction in algal toxicity was in the range 48% to 66%, 59% to 86% and 60% to 82% at reaction temperatures of 199°C, 279°C, and 350°C, respectively. Furthermore, this work shows how typical wastewater chemical analyses, such as COD and TOC, and ecotoxicity tests towards different organisms provide complementary information, which should be used in combination to optimize operating conditions of the HTO process.

The effect of temperature on the catalytic conversion of Kraft lignin using near-critical water.

The catalytic conversion of suspended LignoBoost Kraft lignin was performed in near-critical water using ZrO2/K2CO3 as the catalytic system and phenol as the co-solvent and char suppressing agent. The reaction temperature was varied from 290 to 370°C and its effect on the process was investigated in a continuous flow (1kg/h). The yields of water-soluble organics (WSO), bio-oil and char (dry lignin basis) were in the ranges of 5-11%, 69-87% and 16-22%, respectively. The bio-oil, being partially deoxygenated, exhibited higher carbon content and heat value, but lower sulphur content than lignin. The main 1-ring aromatics (in WSO and diethylether-soluble bio-oil) were anisoles, alkylphenols, catechols and guaiacols. The results show that increasing temperature increases the yield of 1-ring aromatics remarkably, while it increases the formation of char moderately. An increase in the yields of anisoles, alkylphenols and catechols, together with a decrease in the yield of guaiacols, was also observed.