77 research outputs found
Graphene Oxide/Titanium Dioxide Membranes
No full textDuring recent years, graphene has been studied intensively because of itsunique characteristics, making it usable for a variety of applications. In order to produce graphene, it is rst necessary to oxidize graphite to grapheneoxide and then reduce it to graphene. Tests have shown that graphene oxidecould possibly be used as a membrane material for water treatment, as itsoxygen-rich functional groups provide high hydrophilicity, while the graphenestructure ensures excellent selectivity. A major limitation in membrane ltration is the fouling phenomena, which is why TiO2 could be of interest inmembrane usage. TiO2 is used to clean surfaces via its photocatalytic properties.The purpose of this project was therefore to investigate graphene oxide asa membrane material and incorporate TiO2. Dierent graphene oxide syntheses were tested and dierent GO/TiO2 ratios were also tested. The thermal treatment process for reducing graphene oxide was also tested in orderto nd optimal reduction time and temperature for stable membranes. Thethermal reduction was evaluated using X-ray diraction (XRD), dierentialscanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fouriertransform infrared spectroscopy (FT-IR). The surface characteristics were examined before and after UV-C irradiation, in order to see if the TiO2 providedsignicant changes. Surface characteristics were analyzed using drop shapeanalysis (DSA), zeta potential measurements and FT-IR. The vapor permeance of the membranes produced was tested with water, ethanol and hexane.Scanning electron microscopy (SEM) was also done in order to see any potential membrane damage as a result of UV-C irradiation. The membrane surfacecharacteristics and permeance were compared to that of two commercial membranes; Alfa Laval NF99HF and NFT50.By comparing the dierent syntheses via XRD and FT-IR, it was concludedthat the Tour's method was best suited for further experiments. From the reduction experiments done, it was found that reduction at 140◦C for one hourproduced the most stable and hydrophilic membranes. The optimal GO/TiO2ratio was found to be in the range of 15:1 - 30:1. The TiO2 added to thegraphene oxide membranes was found to signicantly enhance hydrophilicityand anti-fouling properties, caused by the formation of hydroxyl groups at thesurface. SEM tests were inconclusive as to whether the membrane is damaged by the photocatalytic activity of TiO2. The water vapor permeance wasfound to be close to unimpeded and at least 55% higher than the commercialmembranes teste
Development of an eco-sustainable solution for the second life of decommissioned oil and gas platforms:The mineral accretion technology
No full textWith the approaching end of the productive lives of offshore oil and gas platforms, the issue about decommissioning and what to do with existing structures arises. In this regard, this study aims to test solutions, at a preliminary level, for the eco-sustainable reuse of platforms at the end of their extraction phase. In particular, mineral accretion technology is applied by low-voltage electrolysis of seawater due to the precipitation of calcium carbonate on a cathode material in order to assess the protection capacity of the platforms against corrosion. This approach allows the extension of a platform’s “life” under a more sustainable purpose. The results, derived from laboratory and field experiments, will allow us to reduce uncertainties and define the best operating conditions to increase the efficiency of the mineral accretion technology in the marine ecosystem. The data collection on the main parameters that influence the process (i.e., temperature, salinity, and applied current) and the quantitative analysis of the collected material allowed us to acquire a better knowledge about mineral composition and deposition rate
Investigation of the Photocatalytic and Hydrophilic properties of the thermally reduced Graphene Oxide/TiO2 Membranes
No full textInvestigation of the cleaning effect of Stokbæk okkersø
No full textThis project treats the problem regarding an in increased amount of ferrous iron in aquatic environments inwestern Denmark. The problem is mainly due to oxidation of pyrite caused by farmers lowering the watertable, when draining arable land for cultivation as well as straightening of creeks and rivers.The study focuses specifically on establishing a way of measuring the actual residence time of water, in lakesmade for ocher cleaning, as well as describing the status of Stokbæk okkersø, regarding the water quality.This is done in order to find out, if there is a potential for establishing living conditions for aquatic life, suchas trout. As the biggest threat is the ferro iron, the cleaning effect is examined, by comparing water from theinlet to that of the outlet.An examination of Stokbæk creek, was performed downstream from the lake in order to find out, if thelocation of the lake secures, that all point sources of ferrous iron is lead through the lake.At last, testing of the lake sediments is carried out, in order to find out, whether the sediment can be usedas fertilizer on fields, or whether the amount of heavy metals excess the amounts, which can be used for thatpurpose. At the same time any potential patterns in sedimentation is sought.The main findings of the study have been obscured, by the fact, that the autumn of 2019 has brought thelargest amount of precipitation on record, so that the flow through the lake, exceeds its capacity. It ishowever concluded, that under the given conditions, the cleaning effect of the lake on ferrous iron is at 18%,which is among the lowest observed values since the establishment of the lake.By applying small amounts of sodium chloride to the inlet, and measuring the differences of conductivity, anapproximate residence time, was found to be approximately 5 hours. This low value corresponds well to thelow cleaning effect and is low compared to the theoretically calculated residence time of 7 hours 40 minutes.When analyzing the iron content in in- and outlet by ICP, a negative cleaning percentage was measured. Thisobservation was made on water samples collected shortly after an intense downpour. There were indicationsof a possible inlet of water from a drainpipe, with a high iron content, that may have been the cause of thenegative cleaning. No direct measurements were performed on the inlet of drain water, as the inlet waslocated under the water table.The quality of the data obtained from sediment samples was not good enough to find any significantdifferences between the sedimentation contents in different parts of the lake. The chosen significance levelwas 0.05. There were, however some indications, that there is a difference between the amount ofprecipitated metals between the northern and southern part of the lake.While investigating possible point sources of iron downstream from the lake, 3 sources was located. Thisindicates the need of either blocking off the sources or making an additional cleaning facility furtherdownstream
Kinetic modeling and rate constant determination of Vacuum-UV oxidation of BAM in Danish groundwater
No full textVariable screening of pyrolysis of composted Cattle Manure in a semi-batch reactor: Thermochemical degradation of biomass
No full textEnergy consumption is increasing globally; fossil fuel resources are diminishing and polluting. However,substituting fossil fuels is difficult due to their participation in almost all facets of human existence in oneform or another. It may be possible to substitute some of the fossil fuel demand by utilizing biomass.Pyrolysis is a method of thermochemical degradation in an inert atmosphere at elevated temperatures, thatproduces biochar, biooil, and pyrolytic gas. These products have numerous applications, including fertilizers,value added chemicals and fuels. Composting cattle manure may be used to reduce the water content of thecattle manure, making it feasible to perform pyrolysis on this biomass. The effects of temperature, hold timeand the use of CO2 as the atmosphere was investigated via a variable screening design for numerous differentanalyses of the biochar and biooil. Increasing the temperature changes the chemical composition of both thebiochar and the biooil, as well as the yields of the different product phases. Notably the biochar carboncontent increases, leading to an increased temperature for thermal mass loss, as well as a higher grosscalorific value. The biooil composition changes dramatically in relation to the temperature, leading to morephenolic oil, due to enhanced lignin decomposition. The biooil composition is also affected by theatmosphere, as a longer hold time in CO2 increases the content of aliphatic and cyclic content, whiledecreasing the aromatic content. This effect is not seen when the process is run in a nitrogen atmosphere.From PCA, it is possible to determine that 39.76% of the total variance is due to the variation of thetemperature level. The pyrolysis products should not be applied as fuels, due to the immense energy costs ofpyrolysis, but utilizing it as a fertilizer may be feasible based off the heavy metal contents
Fly ash-based geopolymer cement as alternative to ordinary Portland cement in oil well cementing operations
No full textOne of the challenges when drilling, especially in a HPHT(High Pressure High Temperature) environment [1], is the well integrity as far as the cement is concerned. It is well known that cement has a tendency to degrade in corrosive environment and high temperatures. Due to chemical attacks and formation movements and the consequent mechanical failure that was experienced in many cases many oil and gas companies decided to search for potential material for oil well cementing operations [2]–[5] . Alumino-silicates that are industrial waste and powdered residue from the combustion of coal having pozzolanic properties such as fly ash [6] and have geopolymerization potential have attracted scientific attention the last 10 years. In order to have a positive environmental impact combined with the use of a new material, it is important to seek materials that are in abundance locally. The current project aims at identifying any viable combinations of waste/residues that can result in a binder capable of withstanding chemical attacks and high temperatures while being strong enough to sustain formation stresses. In Denmark fly ash from power plants is an inexpensive source of aluminosilicates. There are two ways to produce cement/binder from aluminosilicate source. The oldest and most conventional (zeolitic method) is user-hostile while the user-friendly (geopolymerization) method yields less Uniaxial Compressive Strength (U.C.S.) [7]. The safety of the end-user is of utmost importance and the U.C.S. values do not give the actual point of failure of the placed cement [8]. Therefore, both methods were tested and a hybrid one too. For the geopolymerization method, an additional material is needed (electric arc furnace slag-EAFS was chosen over the frequently tested Ground Granulated Blast Furnace slag) that is not locally abundant (in Denmark) but is rather inexpensive and transportable through neighboring countries e.g. Germany. The main use of the new binder under test is oil well cementing applications. However, in order for a new product to be commercialized and achieve industrial acceptance must have characteristics that extend beyond the boundaries of oil industry. The Ordinary Portland Cement(OPC) with the addition of certain reagents can be applied in areas ranging from tunnel construction to oil well cementing operations. An OPC alternative must have the same versatility. One basic advantage that is widely recognized is the lower CO2 footprint (compared to OPC) of the geopolymerized/alkalinated binder manufacture [9]–[16]. Ultimately, the new binder must achieve similar performance in popular OPC applications (if not better).At Chapter 1 a literature review is provided so the reader would get accustomed to the terminology regarding cementing operations, history, process and the potential of geopolymerization method (and the conventional method too). A brief introduction of the application of cement in oil wells in also provided.Chapter 2 is dedicated to experimental procedures (materials, mix designs, preparation, test methods and test analysis).The experimental results are the topic of the Chapter 3 where the properties of the binder, Uniaxial Compressive Strength (U.C.S.) tests, pH and rheology measurements, penetrometer tests, durability tests, Differential Scanning Calorimetry measurements and X-Ray Diffractometry analysis are presented.Next, at Chapter 4 discussion of the results presented is done where the effects of some test parameters e.g. curing temperature is analysed.Finally, Chapter 5 concludes the current study with the reached conclusions and some topics for further/future investigation
Geopolymers as alternative to Portland Cement in P&A
No full textWhen oil and gas wells reach the end of their production life, they need to be permanently plugged and abandoned. Due to the maturity of the fields in the North Sea, in the next decades many of the wells will have to be permanently plugged and abandoned therefore, Plug and Abandonment (P&A) has become a major focus in the petroleum industry. P&A is the last phase of the life cycle of a well and hence no return of capital from it is expected. Furthermore, the responsibility of the operators for the abandoned well lasts long after the wellbore has been plugged, therefore an efficient plugging procedure will be the main goal for any permanent abandonment. The requirements for a permanent barrier state that it must cover the entire cross-section of the wellbore, including all annuli, sealing permanently that region avoiding any fluid leakages through the barrier itself. This thesis evaluates fly-ash based geopolymers as an alternative sealant material for establishing a cross-sectional barrier instead of the commonly used Portland cement which presents some weaknesses when exposed to well conditions, mainly high temperatures and corrosive environments. In order to investigate the reliability of fly-ash based geopolymers, a series of experiments were conducted using fly ash-based geopolymers which were produced by the alkali-activation of fly ash. Several different recipes were prepared using different molarities and activators. Uniaxial Compressive Strength tests were performed to compare the results for each recipe and those results showed that higher concentrations of alkali solutions developed higher compressive strength. In addition, durability tests were performed to evaluate the resistance of geopolymers in corrosive environments. In this case, a solution of 15% HCl was used and geopolymers revealed a better resistance when in contact with this corrosive substance. The promising results showed that there is a great potential in geopolymers usage. Moreover, if geopolymers make less of an impact to the environment, geopolymers might be regarded as a good alternative for the industry
Sol-gel Processes for Development of Nanomaterials for Ceramic and Photocatalytic Applications
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