Catalytic hydrogenation of vegetable oils: II. The activity of the prereduced copper chromite catalyst

The prereduction of copper chromite with hydrogen produces a strong deactivation of catalyst in soybean oil hydrogenation at 200 C and 6 atm. ESCA studies and kinetic data show that the decrement of the activity is correlated to the disappearance of Cu″ and Cu′ species and to the decrement of Cu/Cr ratio on the catalyst surface. The comparison of activity between original and prereduced catalysts allows a better elucidation of the role of Cu′ in promoting the double bond conjugation and of Cu° in catalyzing the conjugated double bond hydrogenation. For part I, see ref. 23.     

Kinetics of desorption of hydrogen from copper chromite catalyst

Isothermal desorption of hydrogen from copper chromite has been studied from 50 to 300°C. An empirical expression, β exp [—αq]= t, is found to fit the desorption data satisfactorily, while the application of the Elovich and the first order desorption rate expressions lead to the detection of three kinetic stages in the desorption process. The rate parameters obtained using these latter two models have a complex trend in their behaviour with temperature. The Elovich rate parameters are found to undergo undulatory changes with temperature like those of the adsorption isobar and their transition regions are very close to those of the adsorption isobar. Also, there seems to be a close relationship between the surface coverage at transition points and the adsorption isobars. The presence of the three kinetic stages in the desorption process may be accounted for by considering the three distinctly different types of adsorption sites on the reduced copper chromite.     

Computation of nickel catalyst activity in the hydrogenation of triacylglycerol oils

The development of a new method for a faster and more accurate computation of the nickel catalyst activity was studied. This catalyst is used in partial catalytic hydrogenation of vegetable oils for production of edible fats. In order to index the activity, a computer program, CATACT, was developed using FORTRAN language. This program uses 3 easily determined experimental values as input data (refractive index at 60 C, catalyst concentration and hydrogenation time). Output data are catalyst activity indexes either in word or numerical form. The hydrogenation data were gathered from a laboratory reactor under laboratory conditions. Using these data, we computed the activity of Ni catalysts which have been reused in oil hydrogenation under industrial conditions. The classical method of determining such activity by evaluating the melting point is, in view of the very low activity of such catalysts, inadequate to provide sufficient information for easy interpretation.     

Reclamation of nickel from spent nickel catalyst

Spent nickel catalyst containing an average 9.6% nickel was obtained locally from an oil hydrogenation industry. It was digested with 1–3N HCl, HNO₃, H₂SO₄ and mixtures thereof in one to three stages of durations ranging from one to three hr at 100°C using spent nickel catalyst to acid proportions of 1:3 to 1:8 (w/v). Nickel recoveries of over 94% were obtained when one part of spent catalyst was digested for three hr with six or more parts of 3N mixture of HCl and HNO₃ (3:1, v/v). Acid extracts of spent nickel catalyst obtained using HCl, H₂SO₄ and mixtures thereof were treated with NaOCl to convert their content of iron in the ferric form. The iron from the nickel extract was precipitated out in the form of ferric hydroxide at pH 6.0. Nickel from the iron-freed acid extracts was recovered at pH 8.5±0.5 as nickel hydroxide. Nickel formate was prepared by refluxing nickel hydroxide with 10% formic acid in about 6% excess to stoichiometric requirements for 30 min. The dried nickel formate was reduced in peanut oil at 230°C to 270°C for 0.25 to 2.75 hr. The reduction at 260°C on kieselguhr support, employing nickel formate:oil:support in ratio of 50:43:7, for two hr provided catalyst of maximum activity. The hydrogenation activity of the reclaimed catalyst, assessed by standard AOCS procedure, was greater than that of the parent catalyst. Presented at the AOCS Meeting in New Orleans, LA, in May 1987.     

沉淀条件对合成气镍基催化剂活性的影响

本文采用固定床微反装置考察共沉淀法制备的镍基催化剂天然气和CO2转化制备合成气的催化活性.并采用X-射线衍射(XRD)和催化剂程序升温还原(TPR)等技术表征催化剂.结果表明:共沉淀法制备的镍基催化剂具有较高的催化活性,最佳的沉淀条件是沉淀温度为室温、快速加料、搅拌0.5～1h、沉淀沉降1h、沉淀过滤、烘干、500℃焙烧,这样制备的催化剂活性较高.通过对焙烧温度的研究发现,高温焙烧能够使氧化镍从催化剂体相向表相移动.     

A study of the preactivation of a copper chromite catalyst

Copper chromite was studied for the reductive alkylation of aniline with acetone to N-isopropylaniline as a function of the catalyst prereduction conditions. In order to optimize prereduction conditions the catalyst was reduced in an atmosphere of hydrogen at different temperatures: 100, 150, 200, 250, 300, 350, 400 and 450°C and for different durations. The activity of reduced catalysts was determined. The X-ray diffractograms of all catalyst samples were taken. Partially reduced copper species were determined by chemical analysis. Prereduced catalyst having more Cu(I) species showed a greater activity than the fresh catalyst containing only Cu(II) ions and than that of the catalyst containing more Cu(0) ions. From these studies it was inferred that the active sites of the copper chromite catalyst used for reductive alkylation of amines are Cu(I) species.This paper is dedicated to the 60th birthday of Professor C.N. Pillai, Department of Chemistry, Indian Institute of Technology, Madras, India.     

Copper catalysts in the selective hydrogenation of soybean and rapeseed oils: I. The activity of the copper chromite catalyst

In the hydrogenation of soybean and rapeseed oils with fresh copper chromite catalyst, the rate of reaction −d(IV)/dt varies extensively with time. These variations are ascribable to changes in phase composition of the catalyst during its reduction. This reduction is not restricted to an initial period but proceeds in two steps during the major part of a normal hydrogenation for the reduction of the linolenate content of the oil. Variations of the catalyst activity followed by experimental measurements have been related to the changes of the catalyst composition.     

Regeneration of used nickel catalyst

Regeneration of used nickel catalyst from a hydrogenation plant has been achieved by converting the nickel content of slurry into NiO and Ni(OH)₂, and the subsequent reduction of these compounds by hydrogen gas at temperatures of 450 C and 290 C respectively. A laboratory and plant apparatus for reduction are designed. Activity of regenerated catalyst was measured in comparison with reference catalyst (G15). Pretreatment of discarded catalyst prior to reduction is described.     

Kinetics of nickel catalyst poisoning

Hydrogenation was done in a “dead-end” type of reactor with automatic recording of hydrogen absorption. In order to determine the poisoning rates of various nickel catalysts with phospholipids, allyl isothiocyanate (AITC), free fatty acids, sodium soaps and products of lipid oxidation, these poisons were added to the reaction system while the reaction was approaching the highest rate. The kinetic curves show that, at the moment of inhibitor addition, the reaction rate decreases immediately; for AITC, the reaction is even stopped for a certain period of time. This observation proves inhibitors are adsorbed at the metal surface immediately after introduction to the system. In some cases, after decreasing the reaction rate, we have observed subsequent acceleration of the reaction that may result from depoisoning processes at the catalyst surface.     

Supported nickel catalyst from hydroxycarbonate of nickel and aluminium

The hydroxycarbonate of nickel and aluminium (Ni/ Al = 3) with a hydrotalcite-like structure is an outstanding precursor of the active component of supported nickel catalysts. Good mechanical strength and suitable nickel content of these catalysts, which are necessary for practical applications, can be achieved by mechanical mixing of this compound with an additional support. The catalyst prepared from a mixture of 56.5 wt-% of nickel-aluminium hydroxycarbonate and 43.5 wt-% of γ-alumina was proven to have a stable catalytic activity in the methanation reaction at 2 MPa and 800 K.     

Separation of nickel catalyst by microfiltration

Ceramic membranes with pore size of 0.1 and 0.2 µm are used for the separation of nickel catalyst. Effect of trans‐membrane pressure (TMP), linear velocity, temperature and nickel content (solute) on flux and rejection has been investigated. The flux increased with increase in pore size of the membrane. The rejection characteristics were similar for 0.1 and 0.2 µm membranes. The nickel content and iodine value of the membrane‐filtered oil was comparable with that of conventional processes. Permeate flux increased with increase in temperature. Flux increased with increase in linear velocity and a marginal rise was observed above 2.09 m/s. The rejection characteristics were only slightly affected by higher linear velocity. The flux improved after back flushing. The average flux was higher with back flushing as compared to continuous (with out back flushing) filtration process. The results indicated that the secondary layer effect was more pronounced in microfiltration. The flux decreased with increase in solute concentration. The rejection characteristics were not affected by solute concentration. The rejection characteristic of the membranes remained unaltered after membranes were repeatedly cleaned with sodium hydroxide and HCl solutions, however, the flux was decreased marginally.     

硫酸镍做催化剂测定COD

对化学需氧量(COD)的测定,在国标方法中是以硫酸银做催化剂.试验研究表明,以硫酸镍替代硫酸银做催化剂,测定理论值分别为500、250 mg/L的COD标准溶液(邻苯二甲酸氢钾溶液),相对标准偏差为O.9%~2.7%;测定含氯离子1 000 mg/L、COD理论值分别为500、250/L的COD标准溶液(含氯离子1 000 mg/L的邻苯二甲酸氢钾溶液),相对标准偏差为1.9%~3.7%;测定某工业废水,与用硫酸银做催化剂相比较,相对误差为-1.5%:对理论值为250 mg/L的COD标准溶液做加标实验,加标量分别为100、200mg/L,加标回收率为99%~101%.试验结果的重复性、准确度和加标回收率均符合实验室质量控制指标的要求.     

制备条件对低Ni／Al2O3催化活性的影响

用含Ｐ、Ｍｏ的改性剂处理工业γ－Ａｌ２Ｏ３载体,制备了一种性能很好的低Ｎｉ／Ａｌ２Ｏ３催化剂,并考察了制备条件对其催化活性的影响,得到最佳的制备条件。     

Hydrogenation of cyclopentadiene on a nickel catalyst

The hydrogenation of cyclopentadiene on Ni catalyst was carried out with a fixed bed reactor. The initial reaction rates were expressed by the following equations. The activation energies of overall-and surface-reaction rates were, respectively, 1.9 and 6.5 kcal/mol and the heats of adsorption of hydrogen and cyclopentadiene were, respectively, 5.6 and 1.6 kcal/mol. The hydrogenation of cyclopentadiene on Ni catalyst is a consecutive reaction passing through cyclopentene, where the activation energy of the 1st stage is higher than that of the 2nd one, namely, E₁ > E₂. At the lower ratio of P_H/P_C, cyclopentene is produced with 100% selectivity, whereas, increasing P_H/P_C or W/F₀, the selectivity decreases. At the intermediate reaction temperature, there appears the minimum selectivity. This phenomenon is considered to be due to E₁ > E₂.     

新型固定床Raney Ni催化剂的制备、表征及苯加氢活性评价

将镍铝合金粉、拟薄水铝石和田菁粉捏合、成型,在空气中高温焙烧,然后用苛性碱溶液充分浸取,制备出可应用于固定床加氢的活性Raney Ni催化剂.实验结果表明,成型合金焙烧过程中,富铝合金相逐渐转化为贫铝相,同时小部分金属铝氧化生成α-Al₂O₃,可提高催化剂的颗粒强度.BET和SEM分析表明,催化剂表面具有较宽的缝隙和丰富的大孔结构.苯加氢活性评价表明,在一定反应条件下,该新型固定床Raney Ni催化剂活性高于传统负载型镍催化剂,也高于按照专利方法制备的同类型催化剂.     

Cyclohexane dehydrogenation on a nickel catalyst: Kinetics and catalyst fouling

The main reaction and deactivation kinetics of cyclohexane dehydrogenation in the presence of hydrogen has been investigated at atmospheric pressure over a nickel kieselguhr catalyst in the temperature range 583–623 K. The rate of reaction for the fresh catalyst increased with increasing temperature, cyclohexane and hydrogen partial pressures whereas it decreased with an increase in the benzene partial pressure. The experimental data could be adequately modelled by a power law rate expression. The catalyst activity decreased with run time due to catalyst fouling by coke deposition. The rate of deactivation was independent of cyclohexane partial pressure, increased with increasing benzene concentration and decreased with increasing hydrogen partial pressure. It is postulated that coke is most likely formed by the successive dehydrogenation of benzene.     

Recovery of nickel from chromite overburden, Sukinda using Aspergillus niger supplemented with manganese

Oxalic acid is a prominent metabolite secreted by several fungi under specific conditions, which acts as a metal chelating agent. Amongst different fungal species, Aspergillus niger is favored as the best option for microbial production of oxalic acid. The present study deals with the oxalic acid over production by A. niger in response to manganese supplement to its growth medium, which in turn improves the recovery of nickel from pre-treated chromite overburden(COB) during fungal bioleaching. The metabolic pathway in oxalate bio-synthesis by A. niger involves one prominent cytoplasmic enzyme oxaloacetate acetylhydrolase (OAH), which catalyzes the breakdown of oxaloacetate metabolic intermediate to oxalate and acetate. Oxalic acid production was increased due to supplement of manganese to the culture medium of the A. niger. Manganese acts as cofactor for OAH enzyme; further, it enhances the catalytic activity of OAH to produce more oxalate. With oxalic acid production by A. niger, nickel recovery from pre-treated COB was improved. During the study, a maximum of nickel recovery was achieved up to 38.6% from pre-treated COB by adding 80 ppm of manganese to the culture media, whereas 24.0% of nickel was recovered without supplement of manganese (experiments were performed at 30 °C and the COB pulp density 2% w/v).     

The preparation and sintering of a high area supported nickel oxide catalyst

A detailed study has been made on the preparation and consequent heat treatment of various active nickel oxide—alumina catalysts. The techniques used in this study were surface area measurements, pore size analysis and density determinations. Three methods were employed for catalyst preparation, these being impregnation; co-precipitation and bulk fusion of the metal nitrates. The results indicate that the catalyst prepared by co-precipitation was the most suitable. By following surface area changes with temperature and time as variables two modes of sintering were noted, one occurring in the temperature range 1100 to 1164 K giving an activation energy of 98 kJ mol^?1, and the other occurring in the temperature range 1182 to 1200 K giving an activation energy of 460 kJ mol^?1. It is thought that the mechanism controlling the sintering in the first case is a direct result of surface diffusion, whilst that occurring in the second range is governed by volume diffusion. The decrease in the number of particles as a trend in sintering is calculated for the sample sintered at 1182 K using surface area and density data.     

The structure of tartaric acid adsorbed over nickel catalyst observed by FT-IRAS

The structure of the L-tartaric acid adsorbed on the surface of a nickel metal catalyst with or without NaBr was studied by FT-IRAS. The carboxylic acid and carboxylate type adsorbed species were observed on nickel surface which was treated with only tartaric acid, while only one type of carboxylate ion was observed on the nickel surface which was treated with tartaric acid and NaBr.