Product Slate Research Articles

Multi-linear model-based fault detection during process transitions

Process transitions due to startup, shutdown, product slate changes, and feedstock changes are frequent in the process industry. Experienced operators usually execute transitions in the manual mode as transitions may involve unusual conditions and nonlinear process behavior. Processes are therefore more prone to faults as well as inadvertent operator errors during transitions. Fault detection during transition is critical as faults can lead to abnormal situations and even cause accidents. This paper proposes a model-based fault detection scheme that involves decomposition of nonlinear transient systems into multiple linear modeling regimes. Kalman filters and open-loop observers are used for state estimation and residual generation based on the resulting linear models. Analysis of residuals using thresholds, faults tags, and logic charts enables on-line detection and isolation of faults. The multi-linear model-based fault detection technique has been implemented using Matlab and successfully tested to detect process faults and operator errors during the startup transition of highly nonlinear pH neutralization reactor in the laboratory.

NOVA REVAMPS STYRENICS

NOVA CHEMICALS, THE world's fourth-largest styrene and polystyrene producer, is making a series of capacity expansions in specialty styrenics and shutdowns in commodity polystyrene that it says will reduce costs and allow it to focus on more value-added products. Nova will close suspension polystyrene resin capacity in Breda, the Netherlands, and Chesapeake, Va., on Sept. 1. In Chesapeake, it will close a 100 million-lb-per-year plant, leaving 14 workers without jobs. In Breda, the closure of 75 million lb of capacity will mean the loss of 23 positions. Christopher Pappas, president of Nova's styrenics business, said at a press conference in New York City that Nova's goal is to increase the share of high-performance, high-growth products like its styrene copolymers and certain grades of polystyrene and expandable polystyrene (EPS) from 15% of its product slate today to 25% by 2004 and 30% by 2005. To this end, ...

Synthetic fuel for imitation of municipal solid waste in experimental studies of waste incineration

Supercritical fluid extraction, narrow-cut characterization of bitumen pitch, hydrocracker and once-through coker vacuum resids revealed the unexpected process chemistry of bitumen hydrocracking. Hydrocracking appears to prolong the coke formation process of the end-cut material of bitumen, by converting it to coke precursors. The conversion (or removal) mechanism for most key species (microcarbon residue (MCR), metals, N) in hydrocracking is by partitioning, which is similar to coking. Sulfur species that convert in hydrocracking are from the front-end of bitumen pitch; there is only a small sulfur reduction in the end-cut.Bitumen pitch and resid products have similar MCR distribution which is dependent on the “depth” of resid, not the conversion processes. Coke yield did not correlate with the MCR content of narrow-cut feed; coke yield was insignificant at the front-fractions and high at the end-cut. The sub-fractions of bitumen derived resid products have lower H/C ratios than those of bitumen pitch, but have the same MCR content. This can be explained by the pendant-core model, in which bitumen pitch and resid products have the same amount of aromatic cores (coke precursors). The inverse correlation of key species with H/C ratio is process dependent. The reaction products of end-cut (mainly asphaltenes) remained in resid product slate (524°C+ materials) in once-through coking and hydrocracking operations. The implications for the current commercial bitumen upgrading flowsheet are also discussed.

Improvement of technology for preparation of coal suspensions in water

Supercritical fluid extraction, narrow-cut characterization of bitumen pitch, hydrocracker and once-through coker vacuum resids revealed the unexpected process chemistry of bitumen hydrocracking. Hydrocracking appears to prolong the coke formation process of the end-cut material of bitumen, by converting it to coke precursors. The conversion (or removal) mechanism for most key species (microcarbon residue (MCR), metals, N) in hydrocracking is by partitioning, which is similar to coking. Sulfur species that convert in hydrocracking are from the front-end of bitumen pitch; there is only a small sulfur reduction in the end-cut.Bitumen pitch and resid products have similar MCR distribution which is dependent on the “depth” of resid, not the conversion processes. Coke yield did not correlate with the MCR content of narrow-cut feed; coke yield was insignificant at the front-fractions and high at the end-cut. The sub-fractions of bitumen derived resid products have lower H/C ratios than those of bitumen pitch, but have the same MCR content. This can be explained by the pendant-core model, in which bitumen pitch and resid products have the same amount of aromatic cores (coke precursors). The inverse correlation of key species with H/C ratio is process dependent. The reaction products of end-cut (mainly asphaltenes) remained in resid product slate (524°C+ materials) in once-through coking and hydrocracking operations. The implications for the current commercial bitumen upgrading flowsheet are also discussed.

Reactive distillation for toluene disproportionation: a technical and economic evaluation

The potential of reactive distillation for xylenes manufacture via the toluene disproportionation reaction is considered in detail. The conventional process is carried out in the vapour phase over a fixed bed catalyst at elevated temperature and pressure. Process design and flowsheeting were carried out for both the conventional and reactive distillation processes using the Aspen Plus simulation package, specifically using the facility for evaluation of simultaneous reaction and physical equilibrium within a distillation column calculation block. Using the flowsheeting based process and equipment designs, a detailed comparative cost assessment and economic analysis of the two processes was performed. The economic evaluation is equivocal, and the reactive distillation process does not appear to offer significant benefits. While the reactive distillation approach does allow significant flowsheet simplification, the design compromises required to enable simultaneous reaction and distillation, particularly relating to design pressure, negate the inherent process benefits. Further, changes in reaction selectivity between the two reaction environments influenced not only the process product slate but also forced process design features to suppress an unwanted (heavy) by-product.

Conversion of waste plastics into fuels: Recycling polyethylene in FCC

Low density polyethylene was dissolved into toluene and converted at 500 °C over three different commercial FCC catalysts in a laboratory Riser Simulator reactor. Short reaction-times up to 12 s were used. All the catalysts had qualitatively similar behaviors. The specific contribution of the polymer to the product slate of FCC was centered in hydrocarbons in the range of gasoline, with high aromatic content and highly olefinic C 3–C 4 gases. Saturated C 4–C 5 products were mainly isoparaffins. The additional coke formed by the polymer would make coke yields to increase moderately in relation to the standard operation. These facts confirmed that this recycling option, which is based on a proven technology, represents an interesting alternative to solve a major environmental problem.

Narrow-cut characterization reveals resid process chemistry

Supercritical fluid extraction, narrow-cut characterization of bitumen pitch, hydrocracker and once-through coker vacuum resids revealed the unexpected process chemistry of bitumen hydrocracking. Hydrocracking appears to prolong the coke formation process of the end-cut material of bitumen, by converting it to coke precursors. The conversion (or removal) mechanism for most key species (microcarbon residue (MCR), metals, N) in hydrocracking is by partitioning, which is similar to coking. Sulfur species that convert in hydrocracking are from the front-end of bitumen pitch; there is only a small sulfur reduction in the end-cut. Bitumen pitch and resid products have similar MCR distribution which is dependent on the “depth” of resid, not the conversion processes. Coke yield did not correlate with the MCR content of narrow-cut feed; coke yield was insignificant at the front-fractions and high at the end-cut. The sub-fractions of bitumen derived resid products have lower H/C ratios than those of bitumen pitch, but have the same MCR content. This can be explained by the pendant-core model, in which bitumen pitch and resid products have the same amount of aromatic cores (coke precursors). The inverse correlation of key species with H/C ratio is process dependent. The reaction products of end-cut (mainly asphaltenes) remained in resid product slate (524°C+ materials) in once-through coking and hydrocracking operations. The implications for the current commercial bitumen upgrading flowsheet are also discussed.

Quantum Chemical and RRKM Investigation of the Elementary Channels of the Reaction C6H6 + O (3P)

We performed a computational study of an important reaction in the combustion of hydrocarbons, C6H6, + O (3P), using ab initio and RRKM methods. Density functional theory (B3LYP) was used to optimize geometries and obtain molecular vibrational frequencies, and complete basis set extrapolation (CBS-QB3) was used to obtain the energies for the reactants several transition states and products. The initial formation of a stabilized adduct is characterized by a barrier of 4.9 kcal mol-1, in good agreement with the measured activation energy for this reaction. All product channels originate from rearrangement or decomposition of this adduct, which our calculations suggest is a triplet ground state. All of our ab initio calculations are thus conducted on the triplet surface. There are several products that are energetically accessible at combustion temperatures, but the formation of phenoxy radical, C6H5O, and H atom dominate the product slate at low temperatures. Rearrangement to form formylcyclopentadiene, C5H...

Dupont, conoco and the biodegradable grease project: Using innovation to turn chemical by-products into a new product

Conoco manufactures lubricants and oils from petroleum and markets them to the mining, trasportation, recreation, construction and related industries. In the wake of the 1990 amendments to the Clean Air Act, the company became concerned that certain customers would be obligated to discontinue the use of lubricants that contained chlorinated solvents. Specifically, Conoco realized that numerous state and local environmental quality standards were becoming stricter with respect to open gear lubricants dropping to the ground from the gears on large power shovels and drag lines used in mining and construction. Although these applications were often in avid regions, groundwater contamination was an issue in other regions. Therefore, if the company did not initiate the development of alternatives to current products, it might lose market share to competitor's products. Fortuitously, a new line of feedstocks came to the attention of Conoco in the form of a chemical by-product stream from a business unit of its parent company, DuPont. The two companies ultimately used this chemical by-product stream to develop a new product to solve the problem. In this case study, we describe a DuPont/Conoco effort to develop a more environmentally friendly niche lubrication product that could be used to mitigate certain heavy machinery environmental problems and create a more competitive slate of products to facilitate sales of an entire line of lubricants. Likewise we examine how Conoco employed part of a chemical by-product stream from another part of the company as feedstock for the new product.

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 5. Feedstocks Derived from Lagomedio, a Venezuelan Crude†

The fluid catalytic cracking (FCC) behavior of compound types present in the >650 °F resid from Lagomedio crude was investigated. Distillation and liquid chromatography were employed for separation of selected compound type fractions from the resid; the resulting fractions were then cracked using a bench-scale FCC unit. The FCC behavior for each compound type was defined in terms of the resulting product distribution (yields of gas, gasoline, etc.); sulfur, nitrogen, nickel, and vanadium partitioning; and in selected cases, gasoline composition. Results obtained from Lagomedio fractions were compared to those obtained from earlier FCC studies of compound types from Wilmington, CA, Maya (Mexican), and Brass River (Nigerian) >650 °F resids. An equation is presented for prediction of gasoline yield for feedstocks derived from Lagomedio as well as other crudes. Gasoline yield (wt % of feed) is calculated from these feedstock parameters: the atomic ratio of hydrogen divided by carbon plus sulfur (H/(C + S)), ...

ANOVA Analysis of Two-Stage Coprocessing of Low-Density Polyethylene, Coal, and Petroleum Resid

The sequencing of reactants and reaction parameters in the two-stage coprocessing of coal with low-density polyethylene (LDPE) and petroleum resid was investigated using two fractional factorial designs and analyses of variance (ANOVA). The experiments were designed to determine the sequence of reactants and the reaction conditions that were required to achieve the highest level of conversion of the solid reactants, and to achieve a desirable product slate in terms of product solubility and boiling point distribution. The reaction system that yielded the highest amount of hexane solubles regardless of the reaction temperature sequence or extraction after the first stage was the catalytic liquefaction of LDPE in the first stage, with the reaction products being added to coal and heavy resid in the second stage, which was also reacted catalytically. Examination of the effect of coal content and H2 pressure in the first and second stages showed that the H2 pressure affected the amount of coal conversion achi...

Effect of process conditions on co-liquefaction kinetics of waste tire and coal

Thermal and catalytic liquefactions of waste (recycled) tire and coal were studied both separately and using mixtures with different tire/coal ratios. Runs were made in a batch tubing bomb reactor at 350–425°C. The effect of hydrogen pressure on the product slate was also studied. Mixtures of tire components and coal were used in order to understand the role of the tire as a solvent in co-liquefaction. In the catalytic runs, a ferric-sulfide-based catalyst impregnated in situ in the coal was used. Both the tire components and the entire tire exhibit a synergistic effect on coal conversion. The extent of synergism depends on temperature, H 2 pressure and the tire/coal ratio. Experiments with coal and tire components show that the synergistic effect of tire is due to the rubber portion of the tire and not the carbon black. The synergism mainly leads to an increase in the yields of asphaltenes, which are nearly double those in the coal-only runs at 400°C. The conversion of coal increases dramatically using the catalyst, but the catalytic effect is attenuated somewhat in the presence of tire, especially at high tire/coal ratios. The data were analyzed using a consecutive reaction scheme for the liquefaction of coal to asphaltenes and thence to oil+gas, both reactions being of second order; a second-order conversion of tire to oil+gas; and an additional synergism reaction when both coal and tire are present, first-order in both coal and tire. Parallel schemes were assumed for thermal (uncatalyzed) and catalyzed reactions. The uncatalyzed liquefaction of coal has a low apparent activation energy, 36 kJ/mol, compared to those for the synergism reaction (84 kJ/mol) and the catalytic coal liquefaction (158 kJ/mol). The conversion of asphaltenes to oil+gas is relatively independent of temperature and of the presence of the catalyst. The catalyst appears to play a significant role in the conversion of coal to asphaltenes, but a negligible role in the synergism reaction.

Design of multipurpose batch chemical plants using a genetic algorithm

In this paper, we introduce the development and implementation of a Genetic Algorithm for the preliminary design of a multipurpose chemical batch plant. A two-stage approach combining a Discrete Event Simulation Model (D.E.S. model) and a Genetic Algorithm (G.A.) for optimal design is proposed. The goal is to minimise equipment investment cost for a fixed product slate and production level.

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 4. An Extended Pendant−Core Model for Gasoline Composition

The pendant−core concept has been used previously to predict product slates from catalytic cracking. In this concept, alkyl side chains and analogous moieties are defined as “pendants”, which are attached to a cluster of aromatic and/or naphthenic rings which is referred to as the “core”. This work extends the pendant−core concept via a model which correlates feed composition (19 main component types determined by mass spectroscopy) to nine product subclasses (both gasoline and non-gasoline) by adding product distribution functions. These product distribution functions depend upon the feed component class (saturates, aromatics, and sulfur compounds) and upon the core−pendant ratio. For example, the production of light gas and coke increases with the core−pendant ratio since the probability of coke formation increases with core size and the average pendant chain length decreases as the proportion of carbon in pendants decreases. Using these component distribution functions, and the mass spectroscopic analysis of feeds, one can calculate anticipated yields of nine product subclasses: light gas, C3/C4 gas, light cycle oils, heavy cycle oils, coke, and gasoline range: paraffins, olefins, aromatics, and naphthenes. The product distribution functions were developed from data on four feedstocks. For the four feedstocks used in the correlation, plus a fifth feedstock, the predicted product quantities are within 2 wt % of the experimental values. The present form of the model does not address effects of polar (acidic or basic) compounds in feeds on product slate.

Adsorption and Reaction of Aldehydes on Pd Surfaces

Aldehydes have been proposed as important intermediates during alcohol synthesis on supported transition metal catalysts. To develop insights into higher oxygenate syntheses, adsorption and reaction of aldehydes on transition metal surfaces and the surface structure dependence of these processes are considered here. In this work, the adsorption and reactions of acetaldehyde and propionaldehyde on Pd(110) surfaces were investigated with temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy techniques. The slate of desorption products observed in TPD experiments following acetaldehyde adsorption on the clean Pd(111) and Pd(110) surfaces was the same: CO, H2, CH4, and CH3CHO were observed in both cases. Likewise, propionaldehyde decomposition gave rise to CO, H2, C2H4, and C2H6 on both surfaces. However, acetaldehyde isotope-labeling experiments indicated that methyl groups were released following decarbonylation reactions of acetaldehyde on Pd(110), in contrast with ...

A MODEL STUDY OF THE OXIDATION OF UNDECYLENIC ACID BY TERT-BUTYL HYDROPEROXIDE: FUEL INSTABILITY REACTIONS

ABSTRACT The subject of fuel instability reactions is usually complicated in that no one species is entirely responsible. Thus multi-component model systems need to be employed to simplify the study of alternate mechanisms and pathways. If the system is too complicated, the reaction pathways are too varied and complicated to discern. Additionally, the suite of heteroatoms present in a finished fuel depends on the source of the crude. Model systems thus represent a reasonable alternative. The model system employed in this study consists of tert-butyl hydroperoxide, and undecylenic acid in benzene solvent. Although radical mechanisms are complex, the slate of products was explainable by a few competing reactions.

97/00999 Use of dispersed catalysts for direct coal liquefaction

With dwindling supplies of petroleum products, efforts to utilize alternative energy feedstocks such as coal, is essential. Several areas in coal conversion technology have been identified that, if improved, could make coal liquefaction more cost competitive with petroleum. The objectives of this project are to address possible improvements in the economics by utilizing low-rank coals, new precursors to dispersed catalysts, and processing variations such as using syngas atmospheres. The purpose of the dispersed catalysts is to better control retrogressive reactions and avoid char formation, while the purpose of the carbon monoxide atmosphere is to improve the economics by simplifying or totally eliminating a separate water-gas-shift step, and perhaps help remove oxygen in the product slate. These possible improvements are being examined and evaluated for potential use in a 2-stage liquefaction process with the goal of converting coal to distillable liquids at a cost competitive to petroleum of $25/bbl. To evaluate our catalysts and process conditions, we used three types of laboratory-scale operations. In the first operation, we compared the reaction chemistry of various ranks of coals and catalysts in synthetic solvents such as hexadecane. This method allowed us to better compare our catalysts without the complications of solvent initiated chemistry.more » Once the catalysts were tested in this manner, they were examined for the conversions of a Black Thunder subbituminous coal using a recycle vehicle derived from the same coal as the solvent. Finally, we upgraded selected first-stage conversion products using a conventional hydrotreating catalyst to compare with recent results in two-stage coal liquefaction development. The results were evaluated for economic feasibility through a subcontract with Bechtel Corp.« less

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 3. Feedstocks Derived from Maya, a Mexican Crude

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 3. Feedstocks Derived from Maya, a Mexican Crude

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 2. Feedstocks Derived from Brass River, a High-Quality Nigerian Crude

The fluid catalytic cracking (FCC) behavior of compound types present in the >650 °F resid from Brass River (Nigerian) crude was investigated. Liquid chromatography and distillation were employed for separation of selected compound type fractions from the resid; the resulting fractions were then cracked using a bench scale FCC unit. The FCC behavior for each compound type was defined in terms of the resulting product distribution (yields of gas, gasoline, etc.) sulfur and nitrogen partitioning, and in selected cases, gasoline composition. Results obtained from Brass River fractions were compared to those obtained from an earlier FCC study of compound types from Wilmington, CA, >650 °F resid. Correlations were derived for gasoline and coke yields from feedstocks derived from either crude. Brass River is a sweet, paraffinic crude which gives rise to a >650 °F resid with very favorable FCC characteristics. Although the bulk of the FCC gasoline was produced from cracking hydrocarbon types present, significant...

Quantitation of Employee Exposure to Emission Products Generated by Commercial-Scale Processing of Polyethylene

Although considerable research has been performed on the thermal degradation products of polyethylene, no data that can be compared to occupational exposure limits have been reported on the exposure of workers in commercial polyethylene extrusion operations. In this study, the actual airborne concentrations of previously identified analytes were measured during the commercial-scale processing of polyethylene resins. Nine polyethylene resins, spanning LDPE, LLDPE, and HDPE product slates were processed under commercial-scale conditions appropriate to their application: blown film, extrusion coating, blow molding, pipe extrusion, and rotational molding. Air samples were taken from operator breathing zones and of representative workplace air and contained air (inside film bubbles and molded parts) using recognized occupational health and safety protocols. The compounds selected for monitoring consisted of aldehydes (formaldehyde, acetaldehyde, acrolein, butyraldehyde, crotonaldehyde, and benzaldehyde), aromatics (benzene, toluene, xylenes, and styrene), formic and acetic acids, furan and tetrahydrofuran, and acetone. Airborne particulates also were measured. Of the 450 concentrations measured from workplace air and operator breathing zones, 440 were below detection limits. Nine of the remaining ten concentrations were <10% of the established exposure limits, while one particulate measurement was <50% of the established exposure limit. As well, 180 contained-air samples were taken. Off-gases trapped inside film bubbles and molded parts accumulated to concentrations above those measured in the ambient air. It was concluded that polyethylene extrusion presents minimal inhalation hazards in a moderately ventilated environment.