Zuwei Liao

Modeling and Multi-objective Optimization of Refinery Hydrogen Network

Abstract The demand of hydrogen in oil refinery is increasing as market forces and environmental legislation, so hydrogen network management is becoming increasingly important in refineries. Most studies focused on single- objective optimization problem for the hydrogen network, but few account for the multi-objective optimization problem. This paper presents a novel approach for modeling and multi-objective optimization for hydrogen network in refineries. An improved multi-objective optimization model is proposed based on the concept of superstructure. The optimization includes minimization of operating cost and minimization of investment cost of equipment. The proposed methodology for the multi-objective optimization of hydrogen network takes into account flow rate constraints, pressure constraints, purity constraints, impurity constraints, payback period, etc . The method considers all the feasible connections and subjects this to mixed-integer nonlinear programming (MINLP). A deterministic optimization method is applied to solve this multi-objective optimization problem. Finally, a real case study is introduced to illustrate the applicability of the approach.

Design Energy Efficient Water Utilization Systems Allowing Operation Split

Abstract This article deals with the design of energy efficient water utilization systems allowing operation split. Practical features such as operating flexibility and capital cost have made the number of sub operations an important parameter of the problem. By treating the direct and indirect heat transfers separately, target freshwater and energy consumption as well as the operation split conditions are first obtained. Subsequently, a mixed integer non-linear programming (MINLP) model is established for the design of water network and the heat exchanger network (HEN). The proposed systematic approach is limited to a single contaminant. Example from literature is used to illustrate the applicability of the approach.

Efficient Au 0/C catalyst synthesized by a new method for acetylene hydrochlorination

A new impregnation method, involving a mixture of solvents and a vacuum drying process, was used to prepare a gold catalyst (MIV-1Au/C1) for acetylene hydrochlorination. It was found that MIV-1Au/C1 was twice as active as the catalyst prepared through the traditional method (PI-1Au/C1). The new method is green, mild and simple. Moreover, it appears to be controllable by tuning solvent and temperature. Excellent Au dispersion in MIV-1Au/C1 was revealed by transmission electron microscopy (TEM). In addition, X-ray photoelectron spectroscopy (XPS) profiles proved that Au0 was the only active species of MIV-1Au/C1 at the initial/highest point of testing. Further XPS results showed that Au0 could be oxidized to Au3+ during the reaction along with the deactivation of MIV-1Au/C1. Thus, Au0 appeared to be preferred for the catalytic route. Our findings demonstrate that this new method has potential as a catalyst for acetylene hydrochlorination. Moreover, this study highlighted the importance of Au0 in this field.

Improvement of performance of a Au–Cu/AC catalyst using thiol for acetylene hydrochlorination reaction

In order to overcome problems of Au–Cu bimetallic catalysts for acetylene hydrochlorination reaction such as instability, Au–Cu–SH/AC catalysts were prepared through the introduction of thiol and tested to examine their activity and stability. It was found that performances of Au–Cu–SH/AC catalysts were quite excellent, with significantly higher catalytic activity and better stability than performances of Au/AC and Au–Cu/AC catalysts. The contents of Cu and thiol additives were also optimized and the optimum molar ratio of Au/Cu/SH was 1 : 1 : 10. Catalyst samples were characterized by scanning electron microscopy (SEM), nitrogen adsorption/desorption (BET), X-ray diffraction (XRD), transmission electronic microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the Au–Cu–SH/AC catalysts were Au0-based catalysts, due to thiol reducing Au3+ to Au0 species during the preparation process. Au0 species exhibited better catalytic activity than Au3+ species for acetylene hydrochlorination, according to the comparison with the composition of active species in different samples through XPS. Furthermore, the sulfhydryl of thiol could bond to the surface of gold nanoparticles (Au NPs). It helped in mitigating the oxidation of Au0 by HCl, protecting Au NPs from structure damage, stabilizing Au NPs in a nearly constant particle size and keeping a more active structure in the reaction environment. Thus, improved dispersity of active species and protection of the active structure of the Au NPs resulted in the better catalytic activity and stability of Au–Cu–SH/AC.

Promotional effect of Ti doping on the ketonization of acetic acid over a CeO2 catalyst

A series of Ce1−xTixO2−δ mixed oxide catalysts were synthesized using a homogeneous precipitation method and characterized, and then these catalysts were applied to convert acetic acid to acetone using a gas-phase ketonization reaction. Ti-doped Ce1−xTixO2−δ catalysts (x = 0.1–0.5) exhibited much better ketonization performance than their parent catalysts of CeO2 and TiO2, and such Ti-doping-induced catalysis improvement is attributed to the formation of a Ce–O–Ti structure depending on the Ti content. Among the different Ce1−xTixO2−δ catalysts, the Ce0.7Ti0.3O2−δ catalyst calcinated at 500 °C showed the best catalysis activity and high stability. A combination of techniques (i.e. TEM, FTIR, H2-TPR, NH3/CO2-TPD and XPS) further revealed that the formation of the Ce–O–Ti structure modified the surface acid–base properties and thus enhanced the redox properties. Moreover, the introduction of Ti into CeO2 also increased the number of oxygen vacancies on the catalysts’ surface that favored the ketonization of acid molecules. This work provides valuable insights into the design of highly efficient CeO2-based catalysts for acid removal in the upgrading process of bio-oil.

Effect of metal on the methanol to aromatics conversion over modified ZSM-5 in the presence of carbon dioxide

To improve the aromatics yield of methanol to aromatics conversion (MTA) over zeolite, which has become a potential route for producing aromatics, modified ZSM-5 catalysts with equimolar metals denoted as EM-X/ZSM-5 (X = Zn, Cu, Ag, and Ni) were investigated under CO2 and N2 flow for MTA in a fixed-bed reactor. The physicochemical properties were characterized by atomic absorption spectroscopy (AAS), N2 adsorption–desorption isotherms, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (NH3-TPD). Comparison with the results obtained in pure N2 flow showed that catalysts doped with Zn, Ni, and Ag could promote aromatization activity and BTX yield in the presence of CO2. Among these, EM-Zn/ZSM-5 showed an aromatics yield of 59.05%, with an increase of 8.1%, whereas EM-Cu/ZSM-5 was found to reduce the aromatization activity in the presence of CO2. Moreover, the interaction mechanism of the active sites of the catalysts with CO2 for the MTA reaction was explored on the basis of the absorbability of the catalysts for CO2, which was studied by CO2 temperature-programmed desorption (CO2-TPD); the activation ability for CO2 to combine with hydrogen was investigated by the catalytic reaction of CO2 + H2, and the verification experiments for the coupling behavior of ZSM-5 doped with different contents of Zn in the presence of CO2 were carried out.

Simultaneous optimization of hydrogen network with desulfurization processes embedded

In refineries, hydrogen purification techniques include hydrocarbon removal units and hydrogen sulfide (H2S) removal units. Hydrocarbon removal units such as membrane separation and pressure swing adsorption (PSA) are frequently employed in the hydrogen network integration (HNI) study. However, the possibility of integrating H2S removal units into HNI study has been overlooked until recently. In the present work, an improved modeling and optimization approach has been developed to integrate H2S removal units into HNI. By introducing a desulfurization ratio, RdSpl j, simplified mass exchange network (MEN) is incorporated into hydrogen distribution network. Total annual cost (TAC) is employed as the optimizing object to investigate the tradeoffs between hydrogen distribution network cost and MEN cost. A practical case study is used to illustrate the application and effectiveness of the proposed method.

Topological properties of refinery system: A complex network approach

Recent development in complex network theory has boosted the exploration of topological properties of various natural and man-made complex systems. Refinery system is a typical complex system in process industry. However, only plant at equipment level has been studied by the complex network theory. This article treats the whole refinery system at plant level as a network. Study illustrates that the refinery network is a small-world network with heterogeneous distributions of node degree and betweenness centrality. The robustness of the refinery network under different attack strategies is evaluated by efficiency of network performance. Vulnerability study demonstrates the different importance of vertices in keeping the network structural efficiency. This study provides a good example to explain the structure-activity relationship in process industry.

Preparation of Aryloxy-aluminoxanes and Their Use as Activators in the Bis(imino)pyridyl Iron-catalyzed Oligomerization of Ethylene

In this study, a series of aryloxy-aluminoxanes originated directly from the hydrolysis of reaction products of AlMe3 and phenols were synthesized, which could serve as effective polymer-retarding activators for the iron-catalyzed ethylene oligomerization. The molar ratios of [PhOH]/[AlMe3] and [H2O]/[Al] during the preparation were explored and their impacts on the oligomerization activity and product distribution were discussed. To obtain the effective activators with good polymer-retarding effect and relatively high activity, the optimized conditions were proposed to be [PhOH]/[AlMe3] = 0.5 and [H2O]/[Al] = 0.7. Various aluminoxanes with different [―OH] sources confirmed the importance of using phenols in preparing the effective polymer-retarding activators. By utilizing these aryloxy-aluminoxanes, the mass fraction of polymers in the total products could be reduced to lower than 1.0 wt%, which is much lower than that of the MAO-activated systems (> 30 wt%). This is a potential benefit for the industrial application of the iron-catalyzed oligomerization process.

A heuristic approach to grade transition strategy of the HDPE slurry process in different operation modes

To satisfy fast changing market demands, polymer plants are forced to operate under frequent grade transition polices which produce a huge amount of off-specification product and waste the time of normal production. In the present study, a model of grade transition is presented for the industrial continuous high-density polyethylene (HDPE) slurry process, which includes two stirred reactors connected in either parallel mode or series mode. The objective of the study is to maximize the economic benefit and minimize the negative environmental impact of the process. Different objective functions are constructed according to the different operation modes. The trajectories of the operating variables can be optimized successfully with the desired polymer quality targets. A heuristic combined strategy is proposed to solve the unstable problem caused by mathematical optimization during the transition between parallel mode and series mode. The problem is solved from three aspects: temperature, operating variables, and material flow. The result indicates that the heuristic combined grade transition takes longer time, but is more feasible in the restriction of the manipulated variables and therefore more effective in controlling the instantaneous properties of the polymer produced.