Steam Cracking of Polyolefins in Fluidized Bed Systems: Influences of the Bed Materials on the Hydrogen Transfer Reactions

Plastic materials are crucial to the supply of everyday necessities, such as clothes, packaging, and building materials. Most plastic materials are disposed of after a short period of use due to their low cost of production. The linear use of plastics has resulted in high levels of plastic waste materials. In addition, the production of plastics is largely dependent upon fossil resources. A paradigm shift in relation to the production and management of plastic waste is necessary for the development of a sustainable plastic usage.Plastic waste is challenging to recycle, given its inherent heterogeneous nature. In this context, recycling using thermochemical processes is a promising approach towards fossil-free production of new plastics of original quality from the abundantly available plastic waste. For this application, steam cracking in a dual fluidized bed (DFB) reactor is a suitable process owing to its flexibility. This work focuses on strengthening the position of the DFB steam cracking technology in the recycling of plastic waste. Experimental studies were conducted on steam cracking of polyethylene, a polyolefin, and rapeseed oil, a polyolefin-like feedstock, in a laboratory reactor under operating conditions similar to that of a DFB system. The suitability of such feedstocks for the DFB steam cracking process is discussed with respect to the distribution of the obtained products. The influence of the bed material on the steam cracking reactions of polyolefins is also examined.The results presented in this thesis demonstrate that steam cracking in a DFB system is a suitable process for the recycling of polyolefin and polyolefin-type feedstocks. Steam cracking of such feedstocks yields a product distribution that is similar to that obtained from thermal cracking of petroleum naphtha. Experiments investigating the influences of the bed material on the steam cracking reactions reveal that the activity of the bed material towards the hydrogen transfer (C-H bond scission) reactions is a critical parameter for the process.An increase in the catalytic activity of the bed material towards the hydrogen transfer reactions results in either dehydrogenation or hydrogenation of the polyolefin feedstock. Dehydrogenation is associated with the oxidizing nature of the bed material, and results in the formation of compounds with H/C ratios <2. In contrast, hydrogenation promoted by the bed material leads to the enhanced formation of compounds with H/C ≥2. Hydrogenation was observed in the presence of a reduced bed material and was associated with the water dissociation and hydrogen transfer capabilities of the bed material. Extensive experimental results supporting these findings are discussed throughout the thesis

Transmission Lines For Ir Signal Routing

In this dissertation, the design, fabrication, and characterization of coplanar striplines, vias, and microstrip lines is investigated, from the point of view of developing interconnections for antenna-coupled infrared detectors operating in the 8- to 12-micron wavelength range. To our knowledge, no previous efforts have been made to study the performance of metallic-wire transmission lines at infrared frequencies. Both the design and fabrication of these structures present unique challenges. Because of attenuation and dispersion issues, the analytical formulas for transmission-line parameters that are valid below a few hundred GHz are not applicable in the infrared. Therefore, numerical modeling was performed to characterize the coplanar striplines and microstrip structures in terms of transmission-line parameters: characteristic impedance, attenuation constant and effective index of refraction. These parameters were extracted by fitting the computed impedance as a function of transmission-line length to the usual impedance transformation equation. The material properties used in the model are realistic, having been measured at the frequencies of interest by infrared ellipsometric techniques. The transmission-line parameters cannot be measured directly in the infrared, so experimental validation was carried out by measuring the response of a bolometer, which was connected to a dipole antenna by different lengths of both the coplanar and microstrip transmission lines. The modeled and measured responses for both types of transmission lines was in good agreement. A third type of signal-routing structure was also investigated, that of the vertical via, essentially a low-frequency connection that facilitates location of the bondpads away from the plane of the antenna. In the configuration studied, the vias pass vertically down through the SiO2 isolation layer and a groundplane, which provides electromagnetic isolation between the antenna and the structures that allow for signal-extraction from the bolometer. This type of interconnection will be useful for future detailed studies relating the angular antenna pattern to the spatial response of the antenna-coupled sensor

Thermochemical conversion of polyethylene in a fluidized bed: Impact of transition metal-induced oxygen transport on product distribution

Thermochemical conversion in dual fluidized bed (DFB) systems is a potential alternative to the recycling of abundantly available plastic waste. The development of oxygen transport in DFB systems is in most cases unavoidable due to the transition metal content of the bed material as well as the metal fraction in the waste stream. This work investigates the influence of transition metal oxide-induced oxygen transport on the thermochemical conversion of high-density polyethylene, a model plastic feedstock, in a bubbling fluidized bed reactor. Conversion in the reactor at 700 \ub0C was investigated using four different bed materials that had different concentrations of iron oxide. The share of carbon oxides among the gaseous products increased with an increase in the iron oxide content of the bed material. The yield of light olefinic and paraffinic compounds decreased with increased iron oxide content of the bed. The presence of iron oxide in the bed material significantly increased the formation rates of aromatic compounds and solid carbon deposits on the bed material. The observed shift in the product distribution due to oxygen transport follows a dehydrogenation-type reaction mechanism

Developing a parametric system model to describe the product distribution of steam pyrolysis in a Dual Fluidized bed

Steam pyrolysis is a thermochemical process that converts carbon-based materials into valuable gases. In general, the products of the reaction are syngas (H2,CO,CO2), low-molecular-weight hydrocarbon gases (methane, ethylene, and propylene), pyrolytic gasoline and oils, monoaromatic and polyaromatic species (tar), and carbonaceous residues (char) with ashes. However, the intricacy of the reactions comprising the process, the diversity of the product species, and the constraints linked to the sampling and measurement equipment, create a highly complex system. In this work, a method for data representation is presented based on a special Parametric System Model (PSM) that portrays product species measurements in a way that provides relevant information and valuable insights into the process. The method incorporates generic knowledge of the chemical nature of the reactions to create a constrained system in which the data can be expressed in parametric terms with meaningful statistical functions. The evaluated data were obtained from a high-temperature steam pyrolysis process performed in the 2–4-MW Dual Fluidized Bed reactor at Chalmers University using polyethylene as feedstock. The quantities of the hydrocarbon species detected in the gas product were taken for the PSM as a probabilistic system that can be described with a set of distribution functions. The carbon, hydrogen and oxygen balances were taken into account to build a constrained set of equations to find the parameters of the functions. The resulting model was proven to be useful as a prediction tool to quantify unmeasured carbon group species and to estimate process variables, such as the oxygen transport of the bed material. Also, it was demonstrated the potential of the model as a method to identify and estimate inconsistencies in the measurements, which improve the quality of the characterization data. The modeĺs outcomes find application in providing critical information for the control and evaluation of pyrolysis process and downstream operation of biorefineries

Unraveling the hydrocracking capabilities of fluidized bed systems operated with natural ores as bed materials

Hydrocracking represents an alternative to the recycling of abundantly available plastic waste. Hydrocracking of polyethylene in a fluidized bed, at 750 \ub0C and 1 atm, was investigated in this work. Water dissociation, through the steam-iron reaction, was used as the source of hydrogen. Bauxite and olivine, containing reduced iron, were used as the bed materials in the reactor to drive the water dissociation reaction. The hydrogen-to-carbon (H/C) ratios of the products were compared to assess the hydrocracking potential. It was discovered that conversion of polyethylene on the surface of reduced bauxite effectively increased the H/C ratios of the products, as compared to bauxite in its oxidized form. Reduced olivine was ineffective at increasing the H/C ratios of the products in the presence of water dissociation. It is concluded that hydrocracking through hydrogen donation by steam is feasible in fluidized beds, provided that the bed material has the ability to transfer the hydrogen atoms to the hydrocarbon species

Fluidized bed steam cracking of rapeseed oil: exploring the direct production of the molecular building blocks for the plastics industry

Fossil-based production of plastics represents a serious sustainability challenge. The use of renewable and biogenic resources as feedstocks in the plastic industry is imminent. Thermochemical conversion enables the production of the molecular building blocks of plastic materials from widely available biogenic resources. Waste cooking oil (WCO) represents a significant fraction of these resources. This work provides insights into the thermochemical conversion of the fatty acids present in WCO, where rapeseed oil is used as the source of fatty acids. The experimental results reveal that fluidized bed steam cracking of rapeseed oil in the temperature range of 650-750 degrees C yields a product distribution rich in light olefins and mono aromatics. Up to 51% of light olefins, 15% of mono aromatics, and 13% of light paraffins were recovered through steam cracking. This means that up to 70% of the carbon in rapeseed oil was converted into molecular building blocks in a single step. The main conclusion from this study is that WCO and vegetable oils represent viable biogenic feedstocks for the direct production of the molecular building blocks, where the conversion is achieved through steam cracking in fluidized beds

Effect of biomass ash on preventing aromatization of olefinic cracking products in dual fluidized bed systems

In this work, the effect of ash activated olivine on olefinic products cracking and aromatization was assessed. The experiments were carried out in the Chalmers 2–4 MWth dual fluidized bed gasifier, where the feedstock was cracked using steam as fluidization agent, at a reaction temperature of ca. 780–790 \ub0C. Three activation states of the olivine, representing three consecutive days of the campaign, were evaluated. The changes of the permanent gas composition along with the reduction in aromatic species with the time of exposure to biomass ash demonstrate a clear effect of the ash activated olivine on the conversion of olefinic cracking products. The ash activation of the olivine clearly promoted the reactions involving steam. As a consequence, higher yields of permanent gases, mainly H2, CO and CO2, were produced at expenses of the yields of the total aromatic compounds and C4 hydrocarbons and larger. It is concluded that the biomass ash activated olivine promotes the steam reforming path of the C4 and larger hydrocarbon fragments, while avoiding the alternative aromatization route. The results presented here provide useful insights on the opportunities and limitations of ash activated materials in DFB systems when steam cracking linear hydrocarbon feedstocks, e.g., polyolefin-based materials

Vertical-via interconnection for infrared antennas

The authors present fabrication process details and test data for a vertical-via. interconnection suitable for low-frequency signal extraction from infrared antenna-coupled sensors. Electrical readout of the signal from an antenna-coupled bolometer was accomplished using two 300 nm diameter Au via structures that extended 300 nm in the vertical direction. These vertical vias passed through two isolation layers of SiO2 and through a 1500 X 600 nm(2) cutout in a ground plane. Electromagnetic, isolation of the antenna from its associated electrical-readout bondpads at 28.3 THz in the infrared was demonstrated by mapping the two-dimensional spatial response of the antenna and comparing it to spatial response data from a similar structure without the intervening ground plane. (c) 2006 American Vacuum Society

Clinical Challenges in the Management of Malignant Ovarian Germ Cell Tumours

Nonepithelial ovarian cancers (NEOC) are a group of rare malignancies, including germ cell tumours (GCT) and sex cord-stromal tumours (SCST), along with small-cell carcinomas and sarcomas. GCTs represent 2-5% of ovarian cancers, with a yearly incidence of 4:100,000, and they usually affect young women and adolescents. Precursory germ cells of the ovary form the basis of GCT. They are histologically classified into primitive GCT, teratomas, and monodermal and somatic-type tumours associated with dermoid cysts. A primitive GCT can be either a yolk sac tumour (YST), dysgerminoma, or mixed germ cell neoplasm. Teratomas are either mature (benign) or immature (malignant). Given that malignant GCTs occur rarely compared to epithelial ovarian tumours (EOC), greater focus is required in their diagnosis and treatment. In this article, we review the epidemiology, clinical manifestations, diagnosis, and molecular biology, along with the management and therapeutic challenges

Identification of AnnexinA1 as an endogenous regulator of RhoA, and its role in the pathophysiology and experimental therapy of type-2 diabetes.

Annexin A1 (ANXA1) is an endogenously produced anti-inflammatory protein, which plays an important role in the pathophysiology of diseases associated with chronic inflammation. We demonstrate that patients with type-2 diabetes have increased plasma levels of ANXA1 when compared to normoglycemic subjects. Plasma ANXA1 positively correlated with fatty liver index and elevated plasma cholesterol in patients with type-2 diabetes, suggesting a link between aberrant lipid handling, and ANXA1. Using a murine model of high fat diet (HFD)-induced insulin resistance, we then investigated (a) the role of endogenous ANXA1 in the pathophysiology of HFD-induced insulin resistance using ANXA1−/− mice, and (b) the potential use of hrANXA1 as a new therapeutic approach for experimental diabetes and its microvascular complications. We demonstrate that: (1) ANXA1−/− mice fed a HFD have a more severe diabetic phenotype (e.g., more severe dyslipidemia, insulin resistance, hepatosteatosis, and proteinuria) compared to WT mice fed a HFD; (2) treatment of WT-mice fed a HFD with hrANXA1 attenuated the development of insulin resistance, hepatosteatosis and proteinuria. We demonstrate here for the first time that ANXA1−/− mice have constitutively activated RhoA. Interestingly, diabetic mice, which have reduced tissue expression of ANXA1, also have activated RhoA. Treatment of HFD-mice with hrANXA1 restored tissue levels of ANXA1 and inhibited RhoA activity, which, in turn, resulted in restoration of the activities of Akt, GSK-3β and endothelial nitric oxide synthase (eNOS) secondary to re-sensitization of IRS-1 signaling. We further demonstrate in human hepatocytes that ANXA1 protects against excessive mitochondrial proton leak by activating FPR2 under hyperglycaemic conditions. In summary, our data suggest that (a) ANXA1 is a key regulator of RhoA activity, which restores IRS-1 signal transduction and (b) recombinant human ANXA1 may represent a novel candidate for the treatment of T2D and/or its complications