Maleic Anhydride Yield Research Articles

In SituStudy of Redox and of p-Type Semiconducting Properties of Vanadyl Pyrophosphate and of V–P–O Catalysts during the Partial Oxidation ofn-Butane to Maleic Anhydride

In situelectrical conductivity measurements have been performed on vanadyl pyrophosphate samples as a function of their preparation temperature and on V–P–O catalysts as a function of their activation time. In agreement with X-ray diffraction results, electrical conductivity has shown that heat treatment of vanadyl pyrophosphates between 450 and 800°C results in a less conducting state corresponding to a very crystalline form. Such a stabilized form can already be reached at a temperature between 600 and 700°C. For V–P–O catalysts, electrical conductivity decreased as a function of the activation time,tact, under the reaction mixture, reaching a steady value fortact≥84 h. Both types of solids were found to be p-type semiconductors with positive holes as the main charge carriers. During subsequent exposures ton-butane and to oxygen at reaction temperature (400°C), it was confirmed that vanadyl pyrophosphate constitutes the main phase of efficient V–P–O catalysts working with some excess of surface oxygen probably in relation with the presence of V5+species. The recorded changes in conductivity upon exposure to reactants provide illustrative evidence of a redox (Mars and van Krevelen) mechanism. The long activation period necessary to produce a high yield of maleic anhydride corresponds to structural and chemical changes of the surface which accommodates the reaction mixture and gives rise to active and selective sites able to convertn-butane to maleic anhydride.

Vanadium-Phosphorus Catalysts Modified with Magnesium, Calcium and Barium

Vanadium-phosphorus catalysts specially modified with promotors can ensure an efficient and selective oxidation of C4 hydrocarbons, even also that of butane to maleic anhydride. The catalysts with incorporated Mg, Ca or Ba ions provide a higher conversion of butane, yield of maleic anhydride, and selectivity for the latter compound than the unmodified catalyst. The conversion of butane and yield of maleic anhydride decrease with increasing basicity of the incorporated modifiers in the order: Mg, Ca, Ba, however, the selectivity of formation of maleic anhydride increases in the opposite order, which is interpreted by the idea that on the modified V-P catalysts the conversion of butane decreases faster than the yield of the anhydride with the natural basicity of the above-mentioned modifiers.

Effect of compositions of promoted VPO catalysts on the selective oxidation of n-butane to maleic anhydride

A series of vanadium phosphate (VPO) catalysts with different P/V ratios and with or without indium and TEOS additives have been characterized by controlled-environment XRD, ICP, ESCA, TEM, SEM, BET and chemical titration and used for n-butane oxidation to maleic anhydride. The best catalyst contains slightly excess P over V with indium and TEOS promoters. It was found that excess P increases the resistance of catalyst precursors toward oxidation and results in VPO catalysts with a large exposed platelet face of a layer morphology. The promoters reduce the thickness of the platelet and facilitate the oxidation of the precursor which contains disordered VOHPO 4 · 0.5H 2O. The combination of the promoters and excess P results in a VPO catalyst with appropriate oxidizability and morphology and gives high yields of maleic anhydride.

Influence of zirconium phosphate on the properties of (VO)2P2O7catalysts for the selective oxidation of n-butane to maleic anhydride

The effect of zirconium phosphate on the catalytic, textural and structural properties of (VO)2P2O7 catalysts has been studied. Catalysts with different P/V and Zr/V ratios were prepared using different preparation methods and characterized by thermo-analytical and texture measurements, X-ray diffraction (XRD), potentiometric titration, FTIR, X-ray absorption [X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)] and laser Raman spectroscopy. The n-butane conversion and the maxima of maleic anhydride (MA) yield shift to lower reaction temperatures on modification of (VO)2P2O7 with zirconium phosphate. There is no correlation between catalytic and textural properties of the modified catalysts. The zirconium phosphate modification causes a partial amorphization of the (VO)2P2O7 catalysts and leads to an enhancement of the VOPO4 microdomains (α1-, β-VOPO4 and amorphous VOPO4).

Oxidation of Butane to Maleic Anhydride on Unmodified and Modified Vanadium-Phosphorus Catalysts

Properties of modified vanadium-phosphorus catalysts were studied and compared with the unmodified catalyst in the oxidation of butane. The highest promoting effect has been achieved by introducing cobalt to the catalyst lattice. At 90% conversion, the yield of maleic anhydride amounted to 59 mole per cent. The catalyst modified by cobalt increased the specific rate of butane oxidation and maleic anhydride formation three times compared to the unmodified catalyst. The specific activity of the catalysts decreased in the following order: Co > U ~ Ce > V-P-O > K ~ Mo.

Selective oxidation of butane on phosphorus-modified silica supported vanadia catalysts

Triethylphosphate impregnation of 2.8 wt% V/SiO2 and subsequent controlled calcination produced phosphorus-modified supported vanadium catalysts. Phosphorus modification enhanced the yield of maleic anhydride in the partial oxidation of butane. Varying the phosphorus to vanadium atomic ratio from 0 to 2.8 increased the selectivity to maleic anhydride from 0 to approximately 48%. The selectivity was nearly constant up to 20% butane conversion and for different O2/C4H10 ratios. The Raman spectra of the phosphorus-modified samples had bands at 1040 and 930 cm−1, and broad unresolved bands between 580 and 540 cm−1. It was concluded that the active phases in these samples were α-VOPO4.

Acidity and catalytic behavior of vanadium-phosphorus-oxygen catalysts

The surface acidity of equilibrated and non-equilibrated vanadium-phosphorus oxide (VPO) catalysts was studied using basic probe molecules (ammonia, pyridine and acetonitrile) via Fourier transform-IR spectroscopy. The stronger bases detected the presence, in varying proportions, of both Lewis and Brønsted acid centers on all the solids assayed. All the catalysts used exhibited the X-ray diffraction pattern of vanadyl pyrophosphate and much higher Lewis/Brønsted ratios than the β-VOPO 4 compound. This indicates that the Lewis acidity observed on the used catalysts is not due to the presence of small amounts of V v species. The Lewis/Brønsted ratio almost invariably decreased with temperature, suggesting that the Brønsted sites are stronger than the Lewis centers. Acetonitrile served to differentiate Lewis centers of varying strength. The equilibrated catalysts which exhibited a better crystallized pyrophosphate phase showed an increase in very strong Lewis acidity whereas the stacking fold disordered non-equilibrated catalyst showed the presence of both medium strong and very strong Lewis centers. The oxidation of n-butane to maleic anhydride was studied using a plug flow reactor. Both the yield of maleic anhydride and the proportion of very strong Lewis sites increased with time-on-stream. These findings together with previous IR studies reported in the literature allow a better understanding of the relationship among structural features, acidity and catalytic behavior of VPO formulations.

Selective oxidation of n-butane to maleic anhydride: A comparative study between promoted and unpromoted VPO catalysts

A comparative study has been conducted between a promoted VPO catalyst (promoted with molybdenum and cerium added simultaneously) and an unpromoted VPO catalyst with respect to their characteristics and catalytic performance. It was observed that the promoted VPO catalyst produced higher yields of maleic anhydride (MA) as compared to the unpromoted one but at comparatively more severe conditions of operations (i.e., higher reaction temperature, higher contact time and higher inlet n-butane concentration). Characterization studies revealed that molybdenum prevents further reduction of V IV to V III, whose transformation was probably responsible for the production of oxides of carbon. As a result, promoted catalyst showed higher selectivity toward MA as compared to the unpromoted one.

Regeneration of a P [sbnd]V [sbnd]O [sbnd]Zn butane oxidation catalyst using chlorine containing hydrocarbons

A fresh V P O Zn (vanadyl phosphate) catalyst has a maximum molar yield of maleic anhydride of 52% (at 450°C) which eventually becomes a spent catalyst having a maximum yield of 44% (at 400°C). This catalyst can be regenerated by passing carbon tetrachloride (in an air or nitrogen carrier gas) over its surface at 300–450°C. The products in the effluent of the reactor are consistent with the decomposition of CCl 4, (CO, CO 2, VCl 4, unknown chlorine compounds) and with part of the catalyst surface being “stripped” off (VCl 4, O 2, unknown phosphorus containing compounds). Twenty-four hours after the CCl 4 regeneration, the catalytic properties of the regenerated and fresh catalysts are identical i.e. the conversion, selectivities, yields (as a function of temperature) as well as other physical properties - surface areas, XRD patterns, and bulk P/V ratios. The experimental data is consistent with the CCl 4 selectively reacting with the poisoned sites and removing the vanadium from them by forming VCl 4. A regenerated catalyst gives a XRD pattern consisting of a mixture of the catalyst precursor and the fresh catalyst indicating a bulk rearrangement (presumably topotactic). The regeneration procedure can be practiced a large number of times without a detrimental effect on the catalytic performance.

Kinetics and redox properties of vanadium phosphate catalysts for butane oxidation

The kinetics of butane oxidation over two vanadium phosphate catalysts of differing phosphorous to vanadium ratios (P/V = 1.0 and 1.1) were studied in order to assess the effects of phosphorous content on butane oxidation kinetics. These catalysts were prepared in an organic medium and demonstrated yields of maleic anhydride (MA) comparable to those claimed in commercial catalysts. The primary reaction products were MA and carbon oxides. The kinetic data were correlated by an eight parameter model which accounts for reaction inhibition by butane and MA. The PV1.0 catalyst was approximately twice as active as the PV1.1 catalyst, while the selectivities to MA were similar. Transient reaction experiments and redox titrations indicate that the redox processes taking place under reaction conditions are restricted to a near-surface region.

Ring-cleavage Reactions of Aromatic Hydrocarbons Studied by FT–IR Spectroscopy. I. Photooxidation of Toluene and Benzene in the NOx–Air System

Abstract The products of the atmospheric photooxidation reactions of toluene and benzene were analyzed quantitatively using long-path FT–IR spectroscopy. Methylglyoxal (only in the case of toluene), glyoxal and maleic anhydride were observed as aromatic ring-cleavage products. In the toluene photooxidation, yields of methylglyoxal, glyoxal, and maleic anhydride were 14±4, 15±4, and 4.0±0.4% (mole/mole), respectively. The formation of small molecules, formaldehyde and formic acid, was observed. It is suggested that the precursor of the ring-cleavage reaction is OH–aromatics–O2 adducts, and that the α-dicarbonyls and unsaturated γ-dicarbonyls are produced by ring cleavage after cyclization of the OH–aromatics–O2 adduct. The observation of maleic anhydride is considered as an evidence of the aromatic ring cleavage into C2 and C4 fragments. The fraction of the ring cleavage process in the total reaction is 29 and 15–20% in the cases of toluene and benzene, respectively.

Study of n-butane oxidation to maleic anhydride in a tubular flow stacked-pellet reactor. Influence of phosphorus on the selectivity.

The influence of phosphorus on the selectivity in maleic anhydride from n-butane is examined on vanadium-phosphorus catalysts prepared in an organic medium. A deficiency of phosphorus with respect to a P:V atomic ratio of 1.0 enhances the rate of maleic anhydride decomposition, consequently leading to lower yields of maleic anhydride at high conversion. An excess of phosphorus limits the rate of maleic anhydride decomposition, but decreases both the activity of the catalyst and the ratio of the two parallel rates of maleic anhydride and carbon oxides formation from n-butane.

Catalytic properties of defective brannerite-type vanadates: III. Oxidation of o-xylene on Mn 1 − xφxV 2 − 2 xMo 2 xO 6

Part I of this series (J. Catal. 81, 298 (1983)) described the catalytic anisotropy of Mn 1 − x φ x V 2 − 2 x Mo 2 x O 6 solid solutions in the oxidation of propylene. In Part II (J. Catal. 81, 311 (1983) a new model of sites active in oxidation reactions has been proposed to explain this phenomenon. This model, designated BSMAS, is based on crystallochemical considerations and on the assumption that the individual catalytic activity of a given surface oxygen atom is proportional to its reciprocal bond-strength sum. In this paper the studies are extended to the oxidation of o-xylene. The conversion and yield of phthalic anhydride, tolualdehyde, phthalide, maleic anhydride, CO, and CO 2 have been determined as a function of temperature, contact time, catalyst composition, and type of preferentially exposed crystallographic plane ((201) or (202̄)). It is shown that the reaction scheme is composed of “one-stage” total combustion and of a one-site “rake-reaction” along which C 8 products are formed. The scheme is common for both planes and it does not alter with catalyst composition, but, as is shown by results from changes of conversion, yields, and selectivities to different products, the rate constant of the elementary steps does depend on the plane exposed and on the composition of the solid. Discussion in terms of the BSMAS model makes it possible to indicate the structure of active sites on which the abovementioned reactions may take place and to explain the plane effect and the dependence of the reaction pattern on catalyst composition.

Effect of various modifying elements on the catalytic properties of vanadium-phosphorus catalysts in oxidation of butane

The flow-through method was applied to a study of the catalytic properties of vanadium-phosphorus catalysts (V: P = 1 : 1.2) prepared by the method of interaction of H3PO4 with V2O2 solution in HCl to which a Li, Ba, Mn, Fe, Co, Ni, Cu, Zn, Pd, Cd, Sn, or Ce salt was added as a modifying substance. The catalysts were ordered in a sequence according to the selectivity found in oxidation of butane. Catalysts with modifying elements whose ions possess an incomplete outer electron shell exhibit higher selectivity and yields of maleic anhydride than those in which the introduced ions possess a complete outer electron shell.

The surface chemistry of VP mixed oxide

The surface chemistry of VP mixed oxides has been investigated by ESR, UV and Vis spectroscopy. The results are correlated with the yield of maleic anhydride in the oxidation of 1-butene. High yields of maleic anhydride are observed for catalysts that contain V5+ and V4+.

The effect of bismuth addition to the molybdenum-phosphorus oxide catalyst on the partial oxidation of butene, butadiene, and furan

The vapor-phase air oxidation of cis-2-butene, butadiene, furan, and maleic anhydride was carried out over various MoBiP oxide catalysts with different Bi Mo ratios ( P Mo = 0.2 atomic ratio) at the concentration of about 0.66%, in order to elucidate the effect of the Bi 2O 3 addition to the MoO 3P 2O 5 catalyst on the activity and selectivity for the oxidation of each reactant. The oxidation activity for butene, butadiene, and furan increases with an increase in Bi 2O 3 content and goes through a maximum at Bi Mo = 0.10. With a further increase in Bi 2O 3, it decreases. However, the activity for maleic anhydride sharply increases with Bi 2O 3 content. We attempted to explain the result by using the acid-base nature of reactant and catalyst. The highest yields of maleic anhydride are obtained at Bi Mo = 0.1 in the oxidations of butene, butadiene, and furan, and reach 30, 60, and 76 mole %, respectively, based on the reactants fed in. When Bi Mo is over 0.1, the yields decrease remarkably. This is attributable to the fact that the activity for the secondary oxidation of maleic anhydride grows to a significant extent, thus no longer being negligible.

Preparation of Maleic Anhydride by Catalytic Air Oxidation of C<sub>5</sub>-Hydrocarbons

C5-hydrocarbons were oxidized on V2O5-MoO3 catalyst by air using a fixed bed reactor. Reaction conditions such as temperature, flow rate of gas and concentration of hydrocarbon were examined in order to obtain maleic anhydride in a good yield. Maximum yields obtained from 1, 3-pentadiene, cyclopentene, n-pentene-1 and C5-fraction of cracked naphtha were 35, 40, 15 and 29mol%, respectively under the optimum reaction condition. Yield of maleic anhydride from C5-fraction agreed with the yield calculated based on the assumption that each component was oxidized independently.

A Study of the Catalytic Partial Oxidation of Hydrocarbons. VI. The Effect of Molybdenum Addition to the Vanadium Oxide Catalyst on the Oxidation of Butene to Maleic Anhydride

Abstract In the present work, the vapor-phase partial oxidation of cis-2-butene was carried out using V2O5-MoO3 catalysts with different compositions, at 350°C, and at a butene content of 0.65% in air, in order to elucidate the effect of the addition of MoO3 to the V2O5 catalyst on the selectivity and the mechanism for maleic anhydride formation. Two types of catalytic specificities were found, depending upon the Mo content: in the range of less than 20 atom% Mo, the specificity was similar to that of V2O5 alone, while in the range of more than 50 atom% Mo, a different specificity was observed, one which gave 1.2 times the yield of maleic anhydride than did V2O5 alone or the Mo-poor catalysts. The increase in the selectivity of butene to maleic anhydride which occurred when a large amount of MoO3 was doped is considered to be caused by the increase in the selectivity of the C4H4O→MA step, not in that of the C4H8→C4H6 or C4H6→C4H4O step. The selectivity of the side pathway in the C4H8→C4H6step was so great that no satisfactory maleic anhydride yield from butene can be expected by the use of the V2O5-MoO3 catalyst.

Oxidation of butenes in maleic anhydride with vanadium-phosphorus catalysts prepared by coprecipitation with colloidal SiO 2

A study was made of the oxidation of n-butenes in maleic anhydride with V–P catalysts prepared by coprecipitation with colloidal silica. With an optimum SiO 2 content in the catalysts of 60% wt. the yield of maleic anhydride was 75 mole%.

Gas Phase Air Oxidation of Durene with V-P-O Catalysts

Gas phase air oxidation of durene to pyromellitic dianhydride (PMDA) has been studied with catalysts of vanadium oxide on porous alundum. Simple V2O5 catalysts had some selectivity for formation of PMDA, and by addition of a little amount of P2O5-component the selectivity increased though the activity for oxidation slightly decreased. The optimum amount of P2O5 to be added was 15% on the weight of V2O5, and the addition of the P2O5 in excess of the optimum amount resulted only in the decrease of the oxidation-activity.Formation of PMDA on V-P-O catalyst proceeded mainly via 3, 4-dimethylphthalic anhydride. Trimethylbenzene carboxylic acid and monomethylbenzene tricarboxylic acid expected to come from durene were formed in small quantities, and most of the adjacent methyl groups in the molecule of durene seemed to be oxidized at the same time.Oxidation of durene was compared with those of toluene, o-xylene and pseudocumene, and the following results were obtained. (1) Oxidizability was in the order: durene>pseudocumene>o-xylene_??_toluene. (2) Yields of benzene carboxylic acids, φ-(COOH)n (or anhydrides), in oxidation of the hydrocarbons, φ-(CH3)n, were in the order: o-xylene>durene>toluene>pseudocumene. Good yield of PMDA may be at least partly due to the high stability of the anhydride-structure to oxidation. (3) Yield of maleic anhydride was in the order: toluene>o-xylene>pseudocumene>durene.