Low-density Polyethylene Production Research Articles

Controlling Law of Flow and Mixing Behavior in an Autoclave for the Production of Low-Density Polyethylene

Controlling Law of Flow and Mixing Behavior in an Autoclave for the Production of Low-Density Polyethylene

Research on the transient dynamic characteristics of the low-density polyethylene compressors shaft system with operating pressure exceeding 180 MPa

The safe and stable function of hyper-compressors with operating pressures exceeding 180 MPa is a guarantee for the low-density polyethylene production process, and the transient dynamics of the compressor shaft system under stable operating conditions are an important concern for the design, maintenance, and fault detection of such compressors. Therefore, this paper presents a finite-element model of the hyper-compressor shaft system and analyzes the dynamic stress and fatigue life of the crankshaft, the connecting rod, the crosshead, and the plunger. In order to verify the accuracy of the model, all stages of the compressor's plunger stress and the torque of the crankshaft–motor connection end were tested in the field. The dynamic gas pressure of each stage cylinder was obtained by the tested stress of the corresponding plunger, then it was set as the load input of the finite-element model. The results show that: the average errors of the simulated plunger stress at two stages are 0.14% and 0.21%, respectively; the mean, peak, valley, and range errors of the torque at the crankshaft–motor connection end are 3.80%, 12.37%, and 3.49%, respectively; the simulated first-order torsional natural frequency of the shaft system is 78 Hz with an error of 8.3%. In the occurrence of the first-order torsional resonance, the maximum torsional stress appears at the crankshaft–motor connection end. The maximum dynamic stress alternating amplitude of the hyper-compressor shaft system under stable operating conditions is 103.7 MPa with a minimum life of 3.309 × 109, which occurs at the crankshaft–motor connection end and is converted into 31.48 years. The finite-element model, test, and simulation data presented in this paper can provide a reference for the fault detection and optimization design of hyper-compressors.

Effect of Surface Treatments on Zea mays Husk and the Behaviour of Husk/Low-Density Polyethylene Composites

(1) Background: The increasing generation of plastic and agricultural wastes is a critical environmental issue that requires urgent attention. Aiming to address this challenge, this study developed a sustainable waste-to-wealth system through the utilization of Zea mays husk as a reinforcing material in the production of green composites. (2) Methods: Delignification, de-hemicellulolysis, and bleaching were employed sequentially to improve the characteristics of the husk. Fourier-transform infrared spectroscopy and scanning electron microscopy confirmed the removal of lignin, hemicellulose, and impurities, and X-ray diffraction analysis determined the degree of crystallinity. Composites were made with treated and untreated husk and recycled low-density polyethylene (LDPE) at various husk-to-LDPE ratios. (3) Results: Mechanical characterization demonstrated that the treated husk composites exhibited superior tensile strength, flexural strength, and hardness compared to the untreated ones and pure LDPE. The treatment did not enhance the thermal stability of the composites, but it did lower their capacity for water absorption and improve their crystallinity. The economic assessment of the husk composite production indicated a total annualized cost of USD 0.9601 per kg, which is significantly lower than the estimated cost for LDPE (USD 1.2 to USD 1.4 per kg). Additionally, it has a much smaller carbon footprint compared to LDPE production. (4) Conclusions: The potential of utilizing treated Z. mays husk as a reinforcing agent in the development of sustainable and cost-effective green composites, improving their overall performance, was established. This approach offers a promising solution for the effective management of plastic and agricultural wastes, contributing to the transition towards a circular economy.

Life cycle assessment of agave bagasse management strategies: PLA biocomposites versus conventional waste disposal practices

Tequila production is one of Mexico's largest agro-industries, generating significant amounts of agave bagasse (AB) as its primary solid waste. Current AB management practices encompass composting, open dumps, and incineration. Life cycle analysis was developed to compare the environmental impact of these management scenarios with developing value-added agave fiber (AF) reinforced plastic biocomposites and generating biogas through anaerobic digestion. The assessment compares three molding methods for the PLA-AF biocomposite, with the environmental impact evaluated against pure PLA and low-density polyethylene (LDPE). Extrusion-injection molding was the most environmentally friendly molding method across all indicators, primarily due to the reduced inputs required for pretreating the fibers. Among the current management scenarios, composting was the least environmentally impactful for the global warming potential indicator. Nonetheless, composting requires substantial time and land use, posing challenges for some producers. Incineration displayed a significant trade-off on the fossil resource scarcity indicator by replacing natural gas. Anaerobic digestion displayed high impacts in all indicators as AB does not yield high methane potential. While the production of PLA-AF displays a significantly higher environmental impact, it remains a preferable option when compared to pure PLA and may further improve its sustainability through green chemistry principles. Notably, LDPE was less environmentally impactful than both bioplastic options assessed, due to the environmental impacts of PLA production and the widespread standardization of LDPE production processes. Context-specificity is critical to assess the environmental impact of circular bioeconomy pathways, which are not always inherently beneficial, while addressing SDG 12: Responsible Consumption and Production.

Orthogonal collocation based‐optimization of fouling resistance for industrial low‐density polyethylene production in a tubular reactor

AbstractIn tubular reactors, fouling issues are caused due to two reasons. One is the heating–cooling prerequisite, and the other is the exothermic nature of the low‐density polyethylene (LDPE) polymerization process. These issues must be considered while optimizing LDPE production to provide maximum productivity and a safe operation. However, it is not a simple process because the conversion of the monomer (XM) is generally related to significant profits. This conversion might be performed at high reaction temperatures, resulting in fouling formation. Therefore, in this research, a study of dynamic optimization to find the most efficient production of LDPE in the presence of fouling resistance (Rf) restrictions is conducted. An Rf is employed as a measure of fouling. To establish the highest reactor Rf , this study employs variations in the heat transfer coefficient (U) calculated from industry data. This dynamic optimization study addresses the optimization challenges using dynopt coded programming based on orthogonal collocation (OC) and sequential quadratic programming methodologies. Beforehand, the LDPE model is validated with industrial data. This study evaluates three possibilities to determine the most optimum reactor performance. The most optimum reactor output is determined from the constrained maximum conversion, which gave 32.15% conversion, while the was effectively met at 47.37cm2 s K/cal.

Development of environmentally friendly composite packaging films from safflower (Carthamus tinctorius L.) plant wastes

Safflower, a widely utilized industrial plant in the production of vegetable oil and biodiesel, generates safflower heads as waste during seed oil extraction, which is known to be rich in cellulose. In this study, the production and characterization of environmentally friendly biocomposite and nano-biocomposite packaging films with a reduction in the utilization of fossil-based materials were focused on. The materials of interest were cellulose (SC) and cellulose nanocrystals (SNC), which were derived from safflower head waste (SAW). The fillers SC and SNC were subjected to analysis to investigate changes in their chemical structure (FTIR), degree of crystallinity (XRD), and surface morphology (SEM and AFM). It was observed that SNC, obtained from SC, exhibited a higher crystallinity level (62%) compared to SC, and displayed mostly spherical morphology with an average diameter of approximately 100 nm. The production of low-density polyethylene (LDPE) based biocomposite and nano-biocomposite packaging films filled with SC (5%–20%) and SNC (0.1%–1.5%) was conducted in two stages: compound production using a twin-screw extruder and blown film extrusion. The incorporation of SC resulted in a 75% decrease in the mechanical properties of LDPE/SC biocomposite material. However, the addition of SNC proved to be relatively effective in maintaining the mechanical properties of LDPE/SC/SNC nano-biocomposite films. Furthermore, the LDPE/SC/SNC nano-biocomposite films exhibited increased crystallinity and gas permeability compared to LDPE, which can be attributed to the effective interaction between LDPE and the fillers (SC and SNC).

Development and lifecycle assessment of various low- and high-density polyethylene production processes based on CO2 capture and utilization

This work focuses on the design and analysis of innovative environmentally friendly pathways to produce low-density polyethylene and high-density polyethylene, as the main feedstock of petrochemical industries, based on CO2 capture and utilization. For each polymer, the process development and simulation of the proposed pathways are performed using Aspen Plus. Each pathway includes the following units: CO2 capture from flue gas, hydrogen production via electrolysis of water, methanol production, olefin production, and polymerization of ethylene. Moreover, the greenhouse gas emissions of the proposed pathways are compared to those of the conventional method i.e., steam cracking. The midpoint and endpoint lifecycle assessment of each pathway are conducted using TRACI 2.1 and ReCiPe Endpoint (H, A) lifecycle impact assessment methods in the OpenLCA software, respectively, for various geographical locations, electricity sources and assessment scenarios for the incorporation of the by-products. The lifecycle assessment results show that the new pathway is an environmentally attractive option, particularly in regions where renewable (low-carbon) electricity is more prominent, such as Quebec and Ontario provinces in Canada. In such regions, negative CO2 emissions, as low as −6.1 kg CO2eq/kg polymer, can be achieved. However, in locations where coal or natural gas are the main sources of electricity generation, such as Alberta, lifecycle emissions increase to 20 times the emissions of the conventional method. Furthermore, the impact of incorporating alternative methanol production processes is evaluated. Results show that using the tri-reforming of methane as an effective syngas production technology from CO2 and natural gas can reduce the lifecycle greenhouse gas emissions by up to 94% and 62%, compared to the conventional high- and low-density polyethylene production pathways.

Fouling resistance study in industrial tubular reactor for low density polyethylene production

Fouling is the development and buildup of unwelcome elements on the surface of processing equipment. Fouling study in LDPE production via tubular reactor is very important with regard to safety, economic and productivity. However, the fouling study in LDPE production was rarely reported in the literature due to complex chemical reaction and reactor configuration. In this work, the overall heat transfer coefficient (U) computed by component’s physical properties (method 1) and log mean temperature difference of plant data (method 2) were studied. The U obtained from the correlation method is larger than plant data. The U variations obtained from industrial data were employed in this work to determine the maximum reactor fouling resistance Rfmax. The Rf reaction zone is significantly lesser than the Rf cooling zone.The fouling investigation utilized fouling resistance (Rf) as the fouling measurement. Rf is signified by the alteration of U dynamically over ten hours. The Rfmax achieved is 50.0 cm2.s.K/cal. The Rfmax value obtained were then applied as a constraint for the optimization study.

Climate and biodiversity impacts of low-density polyethylene production from CO2 and electricity in comparison to bio-based polyethylene

Plastics are essential materials for modern societies, but their production contributes to significant environmental issues. Power-to-X processes could produce plastics from captured CO2 and hydrogen with renewable electricity, but these technologies may also face challenges from environmental perspective. This paper focuses on environmental sustainability assessment of CO2-based low-density polyethylene (LDPE) compared to bio-based LDPE. Life cycle assessment has been applied to study climate impacts and land use related biodiversity impacts of different plastic production scenarios. According to the climate impact results, the carbon footprint of the produced plastic can be negative if the energy used is from wind, solar, or bioenergy and the carbon captured within the plastic is considered. In terms of biodiversity, land-use related biodiversity impacts seem to be lower from CO2-based polyethylene compared to sugarcane-based polyethylene. Forest biomass use for heat production in CO2-based polyethylene poses a risk to significantly increase biodiversity impacts. Taken together, these results suggest that CO2-based LDPE produced with renewable electricity could reduce biodiversity impacts over 96 % while carbon footprint seems to be 6.5 % higher when compared to sugarcane-based polyethylene.

Pareto Optimization of Low‐Density Polyethylene in a Tubular Reactor Using a Hybrid Strategy

AbstractMulti‐objective optimization (MOO) to produce low‐density polyethylene (LDPE) in a tubular reactor is performed for three different purposes, namely, maximizing the monomer exchange rate, lowering operational costs, and increasing the productivity. The ASPEN simulator is used to resolve optimization problems. Here, MOO of particle swamp optimization (MOPSO), non‐dominated sorting genetic algorithm (NSGA‐II), and a hybrid strategy of NSGA II‐MOPSO are employed as a model‐based optimization for LDPE production in a tubular reactor. The results demonstrated that the hybrid strategy of NSGA II‐MOPSO is the most effective MOO strategy. Using the hybrid strategy, the discovered solution set provides the utmost precision and diversity along the Pareto front.

A novel alternative to free oil remediation and recovery: Foamy absorbents designed from low molecular paraffinic waste

This study focuses on preparing porous, hydrophobic, and oleophilic hydrocarbon-based foams applicable for removing free oils from water surfaces. Paraffinic waste material generated during industrial production of low-density polyethylene (Qatar Petrochemical Company) was used for the preparation of foamy, elastic structures through crosslinking of short aliphatic chains by dicumyl peroxide and foaming by 1,1′-azobiscarbamide. The porosity of the foam determined by computer microtomography was 58.9%, and the bulk density was 0.42 g.cm−3. The sorption ability of the foam was tested using diesel oil, motor oil, and heavy crude oil. The absorption capacity of foam was characterized as the ratio between the mass of oil absorbed by the foam and the mass of a neat foam (Sw) and as the ratio between the volume of oil absorbed by the foam and the volume of a neat foam (Sv). The absorption capacities of the new foam reported in this study (referred to here as Qwax foam) are 6.6 ± 0.3 g/g, or 3.3 ± 0.2 cm3/cm3 for diesel oil, 3.9 ± 0.4 g/g or 1.9 ± 0.3 cm3/cm3 for motor oil, and 3.4 ± 0.2 g/g or 1.4 ± 0.4 cm3/cm3 for crude oil. To compare the sorption ability of Qwax foam with some standard foams, the absorption capacities of highly porous commercial polyurethane (PU) and melamine (MA) foams were investigated under the same conditions. These foams showed much higher sorption capacity considering the Sw parameter as a reference; however, there was a lower sorption capacity compared to parameter Sv. In the last paragraph, the suitability and the relevancy of parameters Sw and Sv for a comparison of the absorption capacity of foams were theoretically analyzed.

In vitro degradation of low-density polyethylene by new bacteria from larvae of the greater wax moth, Galleria mellonella

Three bacterial species isolated from whole body extracts of the greater wax moth larvae, Galleria mellonella, were evaluated for their ability to utilize low-density polyethylene (LDPE) as a sole carbon source invitro. These bacteria were identified as Lysinibacillus fusiformis, Bacillus aryabhattai, and Microbacterium oxydans. Their ability to biodegrade LDPE was assessed by growth curves, cell biomass production, polyethylene (PE) weight loss, and the presence of LDPE hydrolysis products in the growth media. Consortia of these bacteria with three other bacteria previously shown to degrade LDPE (Cupriavidus necator H16, Pseudomonas putida LS46, and Pseudomonas putida IRN22) were also tested. Growth curves of the bacteria utilizing LDPE as a sole carbon source revealed a peak in cell density after 24h. Cell densities declined by 48h but slowly increased again to different extents, depending on the bacteria. Incubation of LDPE with bacteria isolated from greater wax moth larvae had significant effects on bacterial cell mass production and weight loss of LDPE in PE-containing media. The bacterial consortia were better able to degrade LDPE than were the individual species alone. Gas chromatographic analyses revealed the presence of linear alkanes and other unknown putative LDPE hydrolysis products in some of bacterial culture media.

Dynamic optimization of low-density polyethylene production in tubular reactor under thermal safety constraint

A commercial low-density polyethylene (LDPE) which is produced by the polymerization process of ethylene in the presence of initiators in a long tubular reactor is the most widely used in polymer industry. The highly exothermic nature of the LDPE polymerization process and the heating-cooling prerequisite in the tubular reactor can lead to various problems, particularly safety in terms of thermal runaway and productivity, i.e., decreasing monomer conversion. Therefore, model-based optimization of an industrial LDPE tubular reactor under thermal safety consideration is required to be implemented. A first principle model for this process is developed and validated using industrial data. Mass and energy balances have been derived from kinetics of LDPE polymerization. Thereafter, an expression of reactor temperature under critical condition is developed and incorporated in the reference model for the thermal safety study. In order to ensure the process is thermally safe and meets the desired product grade, the constrained dynamic optimization is proposed to maximize the conversion of the monomer using orthogonal collocation (OC). The dynamic optimization result shows that the maximum reaction temperature under critical condition constraint can be satisfied by optimizing the reactor jacket. Moreover, it is achieved without jeopardizing the monomer conversion and the product grade.

Effect of Fly Ash Based Geopolymer Reinforced Low Density Polyethylene (LDPE) Composite

Composite is commonly used today attributed to the distinctive characteristics that can be acquired from the mixture of the components in them. However, as time passes on, our globe is heading towards providing green technology for the sector to use environmentally friendly methods. In this study, Fly Ash geopolymer is used as filler, in the production of LDPE / FA composite, to be inserted in a low-density polyethylene matrix. To enhance bonding between the fly ash filler and the LDPE matrix, alkali activator therapy with the use of sodium hydroxide and sodium silicate at the molarity of NaOH is in range of 12M and the ratio for fly ash to alkali activator is about 2.0. In this research properties of these composites are investigate using tensile test, morphology analysis, thermal properties and infrared spectrum analysis, FTIR. The result found that the tensile strength and modulus of elasticity of the composite increased with increasing of filler loading but the percentage of elongation decrease due to filler loading increase while fly ash filler show the interfacial adhesion on LDPE matrix as evidenced by images of scanning electron microscopy (SEM) and this also proved by FTIR spectra explain that LDPE/FA charged with SiO which is fly ash composed with silica. Moreover, thermal properties explain that fly ash interface reaction which can change to amorphous crystallization during the temperature increase.

The effect of novel biodegradable films on agronomic performance of zucchini squash grown under open-field and greenhouse conditions

The soil mulching is an important agricultural practice for increasing crop productivity and earliness. Mulching can be made with natural or synthetic materials. The common films being used these days are usually made of low density polyethylene (LDPE), but its disposal can represent a serious environmental and economic problem. The biodegradable mulching can overcome these problems. Two experiments were carried out comparing the effects of biodegradable and LDPE mulching films on yield and quality of zucchini (Cucurbita pepo L.) grown in two environments (open-field vs. greenhouse). In both the environments a randomized complete block design was adopted. The treatments composed of no-mulched crop (control), soil covered by 15 microns black biodegradable film (MB15) and soil covered by 50 microns black LDPE film. The results showed that MB15 was able to maintain discrete technical proprieties until the end of cycle, especially in greenhouse, assuring a sufficient heating of soil, similar to LDPE. The soil heating promoted crop development. Furthermore, earliness was increased (84 in greenhouse vs. 99 days in open air) in greenhouse. The early production of zucchini grown on MB15 was similar to the one in LDPE production in greenhouse. The total marketable yield of plants grown on both films was not different but it was lower in open air. The biodegradable film significantly improved fruits quality, with higher values of firmness and total soluble solid than fruits grown on LDPE.

Icephobic Behaviour and Thermal Stability of Flame-Sprayed Polyethylene Coating: The Effect of Process Parameters

The present work investigates the effect of different process parameters on the production of low-density polyethylene (LDPE) coatings by flame spray technology. Previously, flame spraying of polymers has been successfully performed to obtain durable icephobic coatings, providing an interesting solution for applications facing icing problems, e.g. in marine, aviation, energy, and transportation industry. However, the fine tailoring of the process parameters represents a necessary strategy for optimising the coating production due to the unique thermal properties of each polymer. For this purpose, we vary the heat input of the process during flame spraying of the coating, by changing the transverse speed and the spraying distance. The results show that the variation in the process parameters strongly influenced the quality of the polymer coating, including its areal roughness, thickness, chemical composition, thermal stability, and degree of crystallinity. Furthermore, we demonstrate that these properties significantly affect the icephobic behaviour of the surface within the spray window of the chosen parameters. In conclusion, the relationship between the thermal degradation of the polymer and the icephobicity of the surface was defined. This highlights the importance of process parameter optimisation in order to achieve the desired icephobic performance of the LPDE coatings.

Development of Mathematical Model Based on Artificial Neural Network to Predict Density in Polymerization Process of Styrene

In the chemical industry is important to control the process in order to guarantee the quality and repeatability of the final product. Using sensors in the industrial plant allows a large volume of data to be captured regarding the process. These data can be used for modelling to better understanding and predict the properties of the product in the process. In this work, two types of Artificial Neural Networks (ANN) and the hybrid model Adaptive Neuro Fuzzy Inference System (ANFIS) were used to predict the density of polystyrene along the styrene polymerization process. The dataset used was extracted from the batch of polymerization reactions performed in open-loop, manual control and closed-loop and monitored in each 5 seconds. The Feedforward and Elman ANN has coefficient of correlation (R) equal 94.2%. However, the best topology obtained to Feedforward ANN presents 2 hidden layers and error index RMSE (Root Mean Squared Error) equal to 2.69x10-2. The Elman ANN presents only 1 hidden layer and RMSE of 3.39x10-2. The ANFIS model, in turn, presented R equal to 91% and RMSE of 0.2123. Therefore, ANFIS model did not prove to be the most adequate for the prediction of the polystyrene density in the studied process.Polymerization process pose significant challenges to the industrial community as it is difficult to control with high nonlinearity behaviour and fast dynamic response. The monitoring and control of polymer processes guarantee to the final product the qualities required by the market. Muhammad and Aziz (2017), for instance, studied the production of low density polyethylene (LDPE) and presented a review of the control strategies developed for the LDPE process. The strategies presented were developed in tubular and autoclave reactors and highlights the importance of nonlinear control in polymerization process.The use of sensors to monitor production allows a large volume of process data to be collected. Therefore, it is necessary to construct mathematical models of prediction to interpret and correlate significant patterns, indispensable to assist in the management of decisions and risk analysis.The development of phenomenological models for polymerization is complex and requires deep knowledge about the processes involved in each step. Modelling using artificial intelligence is a strategy that can provide valuable information about the process and allows the construction of an intelligent model capable of predicting process response based on parameters provided. ANN and ANFIS are artificial intelligence tools that can be used to build predictive models. In supervised learning, the data are presented to the network and its main objective is to provide a model that correctly correlates the pairs inputs - outputs of the problems. The use of ANN and ANFIS to predict the density of the polystyrene produced in the process becomes attractive since it is a type of non-linear modelling.Jumari and Mohd-Yusof (2017) presents models to measure melt flow index (MFI) in industrial polypropylene loop reactors using first principle (FP) model and ANN model. The authors state that the prediction of the ANN model is more accurate compare to the MFI calculated by the FP model. Furthermore, the CPU time recorded that ANN model is much faster than FP model.This work aims to develop direct and recursive ANN and ANFIS models from a set of experimental data from a controlled styrene polymerization plant capable of predicting the density of the product satisfactorily.

حساب الحجب الإشعاعي للأشعة السينية لبوليمر البولي اثيلين واطئ الكثافة والمطعم بمسحوق قشور المحار المستخرج من بحر قزوين

في هذا البحث تم دراسة حجب الأشعة السينية (توهين الأشعة) باستخدام عينات من بوليمر البولي اثيلين واطى الكثافة والمصنع في معمل البتر وكيمياويات في البصرة - العراق، والمضاف اليه مسحوق قشور المحار المستخرج من بحر قزوين في إيران كحشوات مالئة وبنسب وزنيه (2.5% ,5 % ,10 % ,15% ,20%) وعند حجم دقائق للحشوات مساو أو أقل من (0.25mm) إذ تمت دراسة معامل التوهين الخطي (μ) ومعدل المسار الحر (λ)، وبينت النتائج العملية بأن قشور المحار تعمل على تقليل الفراغات بين السلال البوليمرية وخاصة عند النسب العالية (%20-%10) مما يعكس إمكانية البوليمر مع المضاف عند هذه النسب بحجب قسم كبير من الأشعة السينية المسلطة على النماذج، حيث تمت الدراسة العملية بتسليط حزمة من الأشعة بطاقة مقدارها (30 KV) وباستخدام وحدة الأشعة السينية (x- ray unit) مع أنبوبتي توليد الأشعة ومنظومة كاشف عداد كايكر - موللر (G-M detector) وبطاقة مقدارها (V VG.M =600) ومن خلال القيم العلمية في هذا البحث نستنتج بأن قيم معدل المسار الحر (λ) تتناسب تناسبا عكسيا مع النسب الوزنية للمادة المتراكبة وان القيم العملية لمعامل التوهين الخطي (μ) تتناسب تناسبا طرديا مع النسب الوزنية للمادة المتراكبة (البوليمر المضاف إليه مسحوق قشور المحار) وخاصة عند النسب الوزنية العالية. فتم الحصول على أعلى قيمة لمعدل المسار الحر عند النسبة الوزنية (%2.5) وهي (2.1 cm (بينما كانت أقل قيمة لمعدل المسار الحر وهي (0.40 cm) عند النسبة الوزنية (%20). وتم الحصول على أعلى قيمة لمعامل التوهين الخطي وهي (2.44 cm-1) عند النسبة الوزنية للمادة المتراكبة وهي (%20)، وأقل قيمة كانت عند النسبة الوزنية (%2.5) وهي (0.49 cm-1).

Soot Production and Radiative Heat Transfer in Opposed Flame Spread over a Polyethylene Insulated Wire in Microgravity

Flame spread over an insulated electrical wire is identified as a fire scenario in space vehicles. In such microgravity configurations, the contribution of thermal radiation from gaseous participating species and soot to the wire burning rate and flame spread is not fully understood and the present paper addresses this question both experimentally and numerically. A non-buoyant opposed-flow flame spread configuration over a nickel–chrome wire coated by Low Density PolyEthylene (LDPE) is considered with an O2/N2 oxidizer composed of 19% of oxygen in volume and a flow velocity of 200 mm/s. Flame spread rate, pyrolysis rate, stand-off distance, soot volume fraction, and soot temperature are experimentally determined based on optical diagnostics that capture the flame spread in parabolic flights. The numerical model uses the measured spread and pyrolysis rates as input data and solves transport equations for mass, momentum, species, energy, and soot number density and mass fraction in an axisymmetric flame-fixed coordinate system in conjunction with a simple degradation model for the LDPE and a state-of-the-art radiation model. The model considers two assumptions. First, pure ethylene results from the decomposition of LDPE and, second, an acetylene/benzene based-soot model, initially validated for C1–C3 hydrocarbons, can be extended with minor modifications to model soot production of LDPE. Comparisons between model predictions and experimental data in terms of flame structure and soot volume fraction support these assumptions. The major finding of this study is that radiation contributes negatively to the surface heat balance along the LDPE molten surface and the coating ahead of the molten front. This shows that the convective heat transfer from the flame is the main contribution to sustain the pyrolysis process and the flame spread is mainly ensured owing to the combined contribution of convection from flame and conduction inside the condensed phase. The maximum incident radiative flux along the molten ball is 17.5 kW/m2 and is reached at the molten ball trailing edge whereas the radiant fraction is about 0.25. Neglecting flame self-absorption affects these values by less than 5%, showing that the optically-thin approximation is valid for this flame. In addition, soot radiation dominates the radiative heat transfer in this flame, contributing for about two-third of the total radiation. Finally, model results show that the usually-used thermally-thin assumption throughout the LDPE coating is not strictly valid.

LDPE Production in Tubular Reactors: Comprehensive Model for the Prediction of the Joint Molecular Weight-Short (Long) Chain Branching Distributions

Good control on molecular properties, and as a consequence on end-use properties, is very important for low-density polyethylene (LDPE) manufacturers. However, the connection between the architecture of polymer chains and the kinetic mechanism and polymerization conditions is still a subject of study. In this work, we present a comprehensive model of the polymerization of ethylene in high-pressure tubular reactors. In addition to the usual predictions of conversion, temperature profiles, and average molecular properties, this model also provides bivariate distributions such as molecular-weight–long-chain branching distribution and molecular-weight–short-chain branching distribution of LDPE produced under different operating conditions. The 2D probability-generating function technique is applied to obtain the bivariate distributions. This is a deterministic technique that allows the calculation of the distributions without any prior assumption of their shape.