Crude Terephthalic Acid Research Articles

Upcycling heavy impure crude terephthalic acid into porous carbons for adsorption of dye pollutants: The role of endogenous ferric groups

Crude terephthalic acid (CTA), a byproduct in the textile industry, is generated from the acid-precipitation process during the treatment of alkali-peeling (AP) wastewater. Due to its heavy impurity, CTA is typically disposed of as solid waste through incineration and landfilling, leading to severe pollution and resource wastage. In this work, an upcycling method was explored to convert CTA into carbonaceous adsorbent through pyrolysis at temperatures ranging from 400 to 800 °C. The carbonization mechanism of CTA to carbon was thoroughly investigated by using TGA-MS, FT-IR and XPS analyses. The resulting CTA carbons exhibited excellent adsorption performance for dye adsorption. For instance, the adsorption capacity for methylene blue (MB) reached 87.9 mg/g, surpassing the performance of several biochar adsorbents. Besides, it was found that the adsorption performance of CTA carbons was better than that of Fe-PTA carbons which have larger specific surface area and such result was attributed to the rich acidic functional groups on CTA carbon surface. Moreover, used CTA carbons could be recovered efficiently by self-activating low-concentration peroxydisulfate, achieving the regeneration rate of 82 %. Our work offers a promising eco-friendly approach for CTA upcycling in textile industry.

Purification of crude terephthalic acid using phosphomolybdic acid supported on MCM-41 and TiO2 photocatalysts

The present research introduces the photocatalytic process for the conversion of 4-carboxybenzaldehyde to terephthalic acid through the synthesis of phosphomolybdic acid (PMo) supported on TiO2 and MCM-41 as the new class of photocatalysts for this application. As synthesized photocatalysts were characterized through XRD, FT-IR, N2 adsorption–desorption, and FESEM-EDS. It was found that the maximum conversion of 4-carboxybenzaldehyde to para-toluic acid was achieved by 25% PMo/TiO2 photocatalyst with a value of 97.85%. To investigate the effect of parameters such as UV irradiation power intensity, temperature, catalyst dosage, and persulfate concentration, Response Surface Methodology (RSM) was used. Finally, the experimental results showed the UV irradiation power intensity of 2.3 W/mL, the temperature of 24 °C, and the concentration ratio of terephthalic acid to persulfate and catalyst of 3.1 mg/mg and 7.2 mg/mg, respectively as the optimum values. At this operating condition, the concentration of 4-carboxybenzaldehyde decreased from 1870 ppm to 40.2 ppm after 90 min.

Investigation of Crystal Size Distribution in Purification of Terephthalic Acid from Polyester Textile Industry Waste by Reactive Crystallization

The purification of terephthalic acid recovered from an alkali-reduction wastewater by reactive crystallization was investigated. The crude terephthalic acid was reacted with sodium hydroxide solution to form a salt of disodium terephthalate, then acidified with sulfuric acid to get the terephthalic acid with higher purity. Effects of time, pH, concentration, and flow rate of secondary feed solutions, temperature, and stirring rate on Crystal Size Distribution (CSD) of terephthalic acid precipitate were investigated. The results showed that CSD was influenced by the concentration of reactants and the pH solution. On the other hand, time, temperature, flow rate of secondary solution, and stirring rate had no significant effects on the CSD, which the mean size of crystals ±3 μm. The mean size of crystals at solution pH 5, 4, and 3 were 6.03, 9.42, and 10.34 μm, respectively; meanwhile, at concentrations of 0.5, 0.3, and 0.1 M, were 7.57, 3.24, and 3.09 μm, respectively. The semi-batch reactive crystallization with double-feeding at constant pH and temperature produced monodispersed crystals. However, this method needs to be carried out more than once for terephthalic acid purification, which is intended for polyethylene terephthalate (PET) polymerization.

Multicomponent Pt-based catalyst for highly efficient chemoselective hydrogenation of 4-carboxybenzaldehyde

The design of efficient nanostructured catalysts is highly desirable for promoting the hydrogenation of 4-carboxybenzaldehyde (4-CBA), which are the key process of hydrorefining of crude terephthalic acid (CTA) to pure terephthalic acid (PTA). Herein, the Pt-FeNi@C, Pt-Fe@C and Pt-Ni@C catalysts were developed and proved to be active for the selective hydrogenation of 4-CBA. As a result, the excellent 4-hydroxymethylbenzoic acid (4-HMBA) selectivity (85%) and benzoic acid (BA) selectivity (88%) were achieved on Pt-FeNi@C and Pt/C, respectively. In comparison with the commercial Pd/C catalyst, the Pt-FeNi@C catalyst exhibits excellent activity (97%) and reduces the occurrence of decarbonylation. Moreover, the Pt-FeNi@C catalyst exhibits excellent recyclability: the catalytic activity did not decrease significantly after four reaction cycles. In combination with detailed characterization, the Pt-FeNi@C catalyst has porous graphene core-shell architecture and remarkable electron transfer capacity. This work may provide some inspirations for the exploration of new PTA hydrofining catalysts.

Nitrogen doped carbon for Pd-catalyzed hydropurification of crude terephthalic acid: roles of nitrogen species.

The purification of crude terephthalic acid was performed by the hydrogenation of 4-carboxybenzaldehyde (4-CBA) over activated carbon (AC) supported Pd catalysts in industry. However, traditional Pd/AC catalysts usually suffer from low hydrogenation activity and poor thermal stability. Herein, nitrogen was incorporated into AC via a simple hydrothermal treatment of AC with urea as the nitrogen resource. The N doped AC contained pyridinic N, pyrrolic N, graphitic N and oxidized N. Wide characterizations revealed that N doping not only effectively improved the dispersion of Pd NPs but also increased the proportion of Pd0. In addition, N doping also enhanced the dissociative adsorption capacity of molecular hydrogen. More importantly, the resistance to sintering of Pd NPs was efficiently suppressed after N doping. As a result, N doped AC supported Pd showed both higher activity and better thermal stability than the N-free one.

Product quality control in hydropurification process by monitoring reactor feed impurities: Dynamic mathematical modeling

Control of product quality plays a crucial role in petrochemical industries. In this paper, we propose a new strategy to control the quality of purified terephthalic acid (PTA) product. In this approach, the PTA quality is controlled by monitoring the concentration of the main impurity in the hydropurification process, which is 4-carboxybenzaldehyde (4-CBA) in the crude terephthalic acid (CTA) powder. To attain the research objectives, a dynamic dispersion model is developed in the face of catalyst deactivation, considering the vital operating parameters. The CTA powder streams with low and high 4-CBA concentrations can be effectively used through a proper (and controlled) mixing procedure. This strategy can be applied by controlling the ratio of the mass flowrates of the two streams, having high and low concentrations. The positive effect of H2 partial pressure on the system performance can be implemented by a small decrease in reactor temperature. Off-spec PTA powder can be used with the CTA powder having a high 4-CBA concentration. Increasing temperature accelerates the reduction rate of the Pd/C catalyst surface area, leading to an unfavorable sintering phenomenon. The decreased activity of Pd/C catalyst is in good agreement with the normalized ratio of decrease in the surface area of pure Pd with increasing temperature.

Cleaner production of purified terephthalic and isophthalic acids through exergy analysis

The purified terephthalic and isophthalic acids production process was improved through the exergy analysis approach demonstrated in this work. The overall exergy losses and low-exergy-efficient units were first identified and presented using visualised exergetic flowsheets. Recommendations were then proposed to reduce losses based on the main cause(s) of irreversibility. Three out of the five constituent blocks contained the highest exergy losses. The oxidation block was the main player where it was suggested that using several reactors in series with gradually decreasing temperatures could lower losses. The product refining block had the second-largest irreversibilities, where improving coolers' performances were recommended. The crude terephthalic acid crystallisation block was the third-largest loss producer, where isothermal and isobaric mixing in the solvent dehydrator was suggested to reduce losses. The approach used in this work can be adapted to improve the energy footprint of other chemical processes.

Synthesis of polyoxometalates supported on HZSM-5 for the photocatalytic purification of crude terephthalic acid under mild conditions

Phosphomolybdic (PMo) and vanadium-containing phosphomolybdic (PV2Mo) acids were synthesized and supported on HZSM-5 zeolite via a wet impregnation technique and used as photocatalysts for the purification of terephthalic acid (TA) via an economic process. Nowadays, purified TA can be obtained from crude TA due to their great commercial importance by separating 4-carboxybenzaldehyde (4-CBA), which represents high environmental toxicity and negatively affects the applications of TA. For these reasons, conversion of 4-CBA to TA is highly desirable for both enhancing the efficiency of purified TA production and environmental reasons. The synthesized catalysts were characterized by XRD, FTIR, Raman spectroscopy, BET, SEM, and TEM. The purification process was carried out by under different parameters as VUV irradiation, persulfate (PS), time, and different types of catalysts (PMo or PV2Mo)/HZSM-5. This kind of combination showed complete removal of the 4-CBA with a high yield of PTA in 2 h. The high efficiency attributed to the acidity of the polyoxometalates/HZSM-5, which increase the selectivity to oxidize 4-CBA at room temperature and much shorter reaction time compared to other common methods.

A Dynamic Heterogeneous Dispersion Model Evaluates Performance of Industrial Catalytic Hydrotreating Systems

Catalyst deactivation is one of the main challenges in industrial reaction operations. In this paper, a dynamic heterogeneous model is developed for the crude terephthalic acid hydropurification process. The model incorporates the effects of axial mixing and deactivation of the commercial catalyst of palladium supported on carbon on efficiency of the hydropurification operation. The transport phenomena governing equations lead to a series of partial differential equations which are simultaneously solved. The model validation is accomplished using the industrial data. The proposed model satisfactorily simulates the real process, and it is more accurate than the plug flow model to forecast the process behaviors. A decline in the catalyst particle size improves the catalyst performance; an increase in the catalyst porosity prolongs the catalyst lifetime, while maintaining an acceptable pressure drop in the catalyst bed. It is concluded that the effective control of p-xylene oxidation reactor (in terms of pro...

Selective hydrogenation of 4-carboxybenzaldehyde over palladium catalysts supported with different structural organization

The palladium-incorporated catalyst, (0.5% Pd/C) (nanospace engineering KOH-activated carbon material) catalyst with macro-structured carbon nanofibers aggregates and micro-nano-porous activated carbons, has been studied as a candidate for hydro-purification of crude terephthalic acid containing of 4- carboxybenzaldehyde (4-CBA) as an impurity. The efficiency of different carbon structures (macro/micro) was investigated over selectivity catalyst. The reaction products were analyzed by HPLC to determine the amounts of 4-CBA, benzoic acid (BA), 4-Hydroxymethyl benzoic acid (4-HMBA) and para-toluic acid (p-tol). It has been confirmed that 0.5% Pd/microporous catalyst gave an excellent performance to catalyze the hydrogenation of 4-CBA to para-toluic acid due to high micro-porous surface area and the most desirable selectivity to 4-HMBA was obtained with macro-structured carbon nanofibers. Pd/AC catalyst with more micro surface area (85.26%) achieved a maximum yield to the intermediate product of 4-HMBA only 30% whereas the macro-structured CNFs achieved typically 66%. The desired selectivity to para-toluic acid was found to be deep dependent on the micro-porous structure.

Preparation of pyromellitic anhydride and terephthalic acid from anthracite

Shanxi anthracite was subjected to oxygen-oxidation at 250°C in all aqueous solution of potassium hydroxide to produce solid benzene polycarboxylic acid (BPCA), and then the BPCA were selectively decarboxylated in the mixed medium of concentrated H2SO4 and KHSO4 to produce crude pyromellitic acid (PA). Pure PA was obtained by solvent recrystallization method, and the best solvent was 2-pentanone. Pure pyromellitic anhydride (PMDA) was gotton by heating pure pyromellitic acid in vacuum chamber at 260°C for 3 h. The remaining BPCA which through 2-pentanone recrystallization was isomerizated with consistent temperature at 420°C for 2 h. Appropriation pH of BPCA, initial pressure of carbon dioxide and cadmium carbonate catalyst were provided to produce crude terephthalic acid (TPA). Pure TPA was obtained by washing and drying the crude TPA precipitation.

Preparation of Pd/C nanocatalyst for hydropurification of terephthalic acid from aqueous colloid solution

An activated carbon-supported palladium catalyst for hydropurification of crude terephthalic acid was prepared by coating coconut activated carbon with Pd nanoparticles synthesized from colloid solution containing ternary surfactants. The performance and microstructure of catalysts were investigated by means of scanning electron microscope, high resolution transmission electron microscope, H2 chemisorption and high performance liquid chromatography. The results show that the Pd particles in colloidal dispersion have a narrow size distribution and the average size is about 6.45nm. The conversion rate of 4-carboxy benzaldehyde nearly reaches 100% under reaction temperature of 278°C, H2 partial pressure of 0.5MPa and reaction time of 1h. The catalyst remains nearly stable after five consecutive hydropurification tests. When the concentration of these surfactants is 0.67g/L, the catalytic performance of catalyst remains relatively high value. The ternary surfactants of Brij 35-Tween 80-CTAB provides a dense micellar layer which warps and minimizes the colloids particles and as a result the catalytic activity and stability of catalysts are increased.

Control structure design of an industrial crude terephthalic acid hydropurification process with catalyst deactivation

Purified terephthalic acid (PTA) is a fundamental raw material for polyester and textile industry. The p-xylene oxidation process and crude terephthalic acid (CTA) hydropurification process are the two main sections of industrial PTA production. 4-Carboxybenzaldehyde is a byproduct of the first section that can lower the polymerization rate and the average molecular weight of the polymer. In this work, an improved complete plant dynamic model of the second section, CTA hydropurification with catalyst deactivation, was developed based on Aspen Dynamics. The present contribution considered the performance of the proposed catalyst deactivation model (Azarpour and Zahedi, 2012). Moreover, we designed a control structure for this process with catalyst deactivation, and the performance of the resulting control structure was analyzed using several criteria. Results showed that the proposed system provides a better control system and higher profit for the process.

Hydrogenation of crude terephthalic acid by supported Pd and Pd–Sn catalysts on functionalized multiwall carbon nanotubes

Liquid phase hydro-purification of crude terephthalic acid (CTA) was performed using supported Pd and Pd–Sn catalysts on functionalized multi-wall carbon nanotubes (FMWCNT). Pd/FMWCNT catalysts were prepared by wet impregnation with Pd loadings of 0.05 to 0.6wt.%. Pd–Sn/FMWCNT catalysts were prepared by co-impregnation (CI) and successive impregnation (SI) using 0.3wt.% Pd loading and Sn/Pd molar ratios of 0.1 and 0.35 for the CI method and 0.05 to 0.35 for the SI method. Pd loading of 0.3wt.% for Pd/FMWCNT was sufficient to decrease the 4-carboxybenzaldehyde (4-CBA) content of CTA from 2100ppm to 5.5ppm without excessive hydrogenation of terephthalic acid (TA). The commercial catalyst containing 0.5wt.% Pd on activated carbon decreased the 4-CBA content to 23ppm and showed excessive hydrogenation of TA leading to a lower selectivity. The Pd–Sn/FMWCNT had lower CTA hydrogenation activity compared with Pd/FMWCNT possibly due to alloy formation and palladium surface blocking due to Sn addition. Sn addition also led to a decrease in the decarbonylation rate of 4-CBA thus enhancing the product selectivity. Pd–Sn/FMWCNT prepared by the SI method and Sn/Pd ratio of 0.1 resulted in 99%+ removal of 4-CBA as well as enhanced selectivity compared with Pd/FMWCNT.

Synthesis of Reduced Graphene Oxide-Carbon Nanotubes (rGO–CNT) Composite and Its Use As a Novel Catalyst Support for Hydro-Purification of Crude Terephthalic Acid

Palladium nanocatalysts supported on reduced graphene oxide (rGO), multi walled carbon nanotubes (MWCNT), and rGO/CNT composite were synthesized by a wet impregnation method using PdCl2 as a precursor. Palladium loading was 0.3 wt %, and the catalysts were reduced at 300 °C. The catalysts were characterized by inductively coupled plasma, Brunauer−Emmett−Teller (BET) analysis, Fourier transform infrared spectroscopy, X-ray powder diffraction, transmission electron microscopy, temperatue-programmed reduction, temperatue-programmed desorption, and Raman spectroscopy. The performance of the catalysts was investigated for hydro-purification of crude terephthalic acid (CTA) containing 2100 ppm 4-carboxybenzaldehyde (4-CBA) as an impurity. The reaction products were analyzed by HPLC to determine the amounts of 4-CBA, benzoic acid, and p-toluic acid. Pd/rGO–CNT catalyst had excellent performance in terms of both selectivity and 4-CBA conversion. All catalysts exhibited more than 99% removal of 4-CBA. The most desired selectivity, however, was obtained for the catalyst with rGO–CNT as a support. Comparison with the performance of the commercial catalyst (0.5 wt % palladium on activated carbon) indicated that the Pd/rGO–CNT catalyst had a better performance.

Hydro-purification of crude terephthalic acid using palladium catalyst supported on multi-wall carbon nanotubes

Palladium catalysts supported on functionalized multi-wall carbon nanotubes were synthesized for hydro-purification of crude terephthalic acid containing 2100ppm 4-carboxybenzaldehyde (4-CBA) as impurity. PdCl2 and Pd(OAc)2 were used as precursors. Palladium loadings were 0.05 to 0.6wt.% with catalysts reduced at 200 to 400°C. Catalysts prepared from both precursors with least 0.3wt.% palladium resulted in 99%+ removal of 4-CBA. The most desired selectivity was obtained for the catalyst with PdCl2 as precursor, reduction temperature of 300°C, and palladium loading of 0.3wt.%. This catalyst had slightly better performance than the commercial catalyst (0.5wt.% of palladium on activated carbon).

Dynamic modeling and control of industrial crude terephthalic acid hydropurification process

Purified terephthalic acid (PTA) is critical to the development of the polyester industry. PTA production consists of p-xylene oxidation reaction and crude terephthalic acid (CTA) hydropurification. The hydropurification process is necessary to eliminate 4-carboxybenzaldehyde (4-CBA), which is a harmful byproduct of the oxidation reaction process. Based on the dynamic model of the hydropurification process, two control systems are studied using Aspen Dynamics. The first system is the ratio control system, in which the mass flows of CTA and deionized water are controlled. The second system is the multivariable predictive control-proportional-integral-derivative cascade control strategy, in which the concentrations of 4-CBA and carbon monoxide are chosen as control variables and the reaction temperature and hydrogen flow are selected as manipulated variables. A detailed dynamic behavior is investigated through simulation. Results show that the developed control strategies exhibit good control performances, thereby providing theoretical guidance for advanced control of industry-scale PTA production.

Experimental Investigation of Viscous Surfactant Based Enhanced Oil Recovery

Crude terephthalic acid (CTA) as a chemical compound is used for flooding here as an alternative to the traditional hydrolyzed polyacrylamide (HPAM) because of its availability and economical aspects and higher efficiency. Crude oil samples from an Iranian oil field were used during the flooding tests. Sand packed models using two different sizes of sand mainly 50 and 100 meshes were employed in this investigation. A comparison between water flooding and CTA flooding as a secondary oil recovery process revealed that the oil recovery factor was improved by 10% OOIP when CTA after water flooding was used in secondary state. The effect of various injection rates and different concentration of chemical solutions on the recovery factor have been checked. Besides, experimental results improved the surfactant behavior of the CTA solution in water. Experiments showed that oil recovery factor increased by 5% OOIP when SDS solution was used in tertiary state. Experiments were performed in laboratory temperature and pressure around 10 bars.

Preparation of Terephthalic Acid (TPA) and Dioctyl Terephthalate (DOTP) by Anthracite's Alkali Oxygen Oxidation

TPA was synthesized by a two step reaction. Firstly, water-soluble coal acids (CA) was obtained by oxygen-oxidation at 260°C in all aqueous solution of potassium hydroxide, and then crud TPA was got by isomerization of the CA with the existence of CdCO3 catalyst and CO2 pressure. The optimum reaction conditions to get crude TPA were 4% amount of CdCO3 catalyst, and reacted at 420°C with initial 3.0MPa CO2 pressure. Pure TPA was obtained by a separation step and the yield of pure TPA is 37.16% (based on CA). Furthermore, DOTP was synthesized by the refined TPA and isooctanol. The influence of mole ratio of TPA and isooctanol, amount of catalyst and reaction time on the final yield of DOTP were discussed. The purity of TPA was detected by HPLC and DOTP was detected by FT-IR, 1H-NMR to get confirmatory results.

Performance analysis of crude terephthalic acid hydropurification in an industrial trickle-bed reactor experiencing catalyst deactivation

In this work, a dynamic model of an industrial trickle-bed reactor for hydrogenation reactions of 4-carboxybenzaldehyde has been developed. In this case, a heterogeneous plug-flow model has been considered to predict the dynamic behavior of the catalytic hydropurification reactor of Purified Terephthalic Acid production plant. Furthermore, deactivation model of carbon coated palladium catalyst of the reactor (0.5wt.% Pd/C, type D3065, supplied by Chimet SpA) has been devised based on the actual plant data. The catalyst of the proposed industrial reactor is deactivated after 360days. The simulation results indicate that the concentration of 4-carboxybenzaldehyde is very influential. In addition, concentration of para-toluic is not as destructive as that of 4-carboxybenzaldehyde so that it lessens the lifetime of catalyst about 40days if its concentration in normal operation builds up more than 1.6 times. Besides, the concentration of reactor feed should not be increased to boost the rate of production since this makes the lifetime of the catalyst shorter. If the production rate enhances about 18%, the lifetime of the catalyst drops more than 6months. The hydropurification reactor control is the most crucial part of the purification unit operation. Thus, in addition to the reactor operation assessment, this dynamic model can be used to evaluate the purification section performance at any time to continue producing on-spec product. Also, it might be used in future in the formulation of model based control strategies for the reactor control.