Indian Journal of Chemical Technology Vol. 5, July 1998, pp. 199-208 Effect of preparation conditions of Raney Nickel on its catalytic properties for slurry phase hydrogenation of o-nitrophenol to o-aminophenol V R Choudhary'& M G Sane Chemical Engineering Division, National Chemical Laboratory, Pune 411 008, India Received 5 November 1997; accepted 10 June 1998 Influence of leaching conditions of Ni-Al alloy (50% AI) on the catalytic activity of Raney Nt (m the hydrogenation of o-nitrophenol at 308 K and H2-pressure of 1508 kPa) has been studied and optimum conditions for the preparation of Raney-Ni catalyst for the hydrogenation process have been obtained. The hydrogenation activity of Raney-Ni is found to be strongly influenced by its preparation conditions. Catalytic slurry phase hydrogenation of 0• nitrotoluene over Raney-Ni prepared under nitrophenol using Raney Ni catalyst is an different conditions4 has indicated a strong important commercial process for the production influence of leaching conditions of Ni-Al (50%, AI) of o-aminophenol, an important intermediate for alloy (viz. type of alkali, concentration of alkali, drugs, dyes and pesticides. Nickel aluminium alloy temperature and duration of leaching, and the is commonly used for the preparation of Raney• washing agent (viz. tap water, distilled water, nickel. The alloy contains NiAI3, Ni2A13, and Ni3AI deionised distilled water, 50% ethanol and 95% phases 1.2 and the composition of these phases ethanol) used in the washing of the leached alloy depends on the alloy composition. The non• on the hydrogen content and hydrogenation catalytic part of the alloy (i.e. AI) can be leached activity of Raney-Ni. out by hydrolysis with water, alkali or acid. The present investigation was undertaken to However, the leaching IS most commonly done by study systemati cally the effect of various alkali treatment. The catalytic activity of Raney preparation conditions of Raney nickel on the nickel is found to be strongly affected by leaching catalytic activity in the liquid phase hydrogenation conditions, viz. type of alkali used3.4, alkali of o-nitrophenol (ONP) to o-aminophenol (OAP) concentration4 , temperature4.5, duration of using methanol as a reaction media and arn ve at leaching4.6 and washing agent4. the optimum conditions for the preparation of The physico-chemical and surface properties of Raney-nickel catalyst giving maximum activity for Raney Ni, such as lattice parameters1, distributIon the hydrogenation process. This study was of hydrogen on the surfaceS, surface area4.9 crystal undertaken as a part of the development of Raney• size4, residual aluminium and hydrogen content4,9 Ni catalyst for the above process. are also strongly influenced by the conditions of Raney Ni preparation. It has been shown that Experimental Procedure Raney-Ni catalyst having its maximum activity for Preparation of Raney-Nickel Catalyst the hydrogenation of a substance has a definite The experimental setup for the preparation of crystal size characteristic of a substance, and hence Raney nickel is shown in Fig.I. It consisted of a it is impossible to prepare Raney nickel catalyst stirred jacketed reactor (made of stamless steel 15 which exhibits its highest activity to every cm diameter and 35 cm height), provided with a substance to. The effect of crystal size on catalytic cooling coil, a thermometer, H2 inlet tube and activity indicated that the activity is strongly provision for addition of the alloy. A known affected by the geometrical factors of the catalyst. volume of aqueous alkali solution (2000 cm\) was Earlier studies on the hydrogenation of p- taken in the reactor and maintained at the desired * For correspondence temperature by circulating water having constant 200 INDIAN 1. CHEM. TECHNOL., JULY 1998 Type of alkali used :NaOH and KOH Concentration of alkali (NaOH) :1.25-20.00 mol dm-3 Leaching temperature :283-358 K Leaching time :1-12h Washing agents :tap water, distilled water, r deionised distilled water, CHILLED .ATER 50% ethanol and 95% ethanol. WATER JACKET The temperature of the leaching could be ALKALI SOLUTION controlled within ±l dc. COOLIN8 COIL A number of Raney nickel catalysts were prepared by systematically varying one FLAT BLADE DISC TURBINE STIRRER preparation condition at a time while keeping all the other conditions the same. The catalyst prepared under different controlled conditions are listed in Table 1. L WATER FROM CONSTANT TEMP. BATH Measurement of Properties of Raney Nickel Fig. I-Experimental set-up for preparation of Raney nickel. Residual aluminium in the catalyst -I The residual aluminium in the Raney nickel temperature through the reactor jacket. The catalyst was determined by the method similar 'to solution was stirred at 1200 rpm and hydrogen gas that used by Schnyderl1• A known amount of (20-30 cm3 min-I) bubbled through it in order to catalyst about 3.0 g based on the weight was remove the dissolved oxygen. The hydrogen flow warmed with 10 cc of dilute hydrochloric acid was continued throughout the leaching period. (3M). After the complete dissolution of the When the temperature of the alkali solution catalyst, dilute ammonium hydroxide was added reached the desired value, a known amount of until the turbidity cleared and 1 or 2 drops of the Raney alloy (50 g, particle size: 30-60 1-1) was acid were added in excess. To the solution, 100 added to it in small portions in a period of 10 min. cm3 of 6% succinic acid solution, 10 g ammonium The reaction temperature was maintained by chloride and 4 g urea were added successively. The removing the exothermic heat of reaction by resulting solution was made upto about 400 cm3 adjusting the flow of the chilled water through the with distilled water. It was then boiled for 2 hand cooling coil. cooled to room temperature. The precipitate After the alloy was added for the period, the formed was filtered and washed with a 1% stirring was stopped and the catalyst particles were succinic acid solution neutralised by ammonium allowed to settle. The supernatant solution was hydroxide. The precipitate along with the filter removed by suction and the catalyst particles were paper was ignited at 1473 K in a platinum crucible washed with the desired washing agent and the residual alumina (AI203) was estimated (presaturated with hydrogen) at 303-308 K till free gravimetrically. The weight percent of the residual from alkali (as shown by litmus paper test). The aluminium in the catalyst was obtained as, duration of washing was 20-25 min. The catalyst was then stored under hydrogen atmosphere in the same liquid medium as that used for the washing. 26.97 x w x 100 The catalyst was subjected to the activity test Residual Al (wt %) = 101.04 X (w3 - w4) after the storage period of 45-50 h. The leaching and washing variables were, where, w is the amount of A1203 (g), W3 is the 'I ,. III I CHOUDHARY & SANE: EFFECT OF PREPARATION CONDITIONS OF RANEY-Ni ON ITS PROPERTIES 201 Table 1- Preparation conditions of Raney Nicke] catalysts Volume of alkali solution - 2000 cm3, Composition of Raney Nickel alloy - Ni (50 wt %) - Al (50 wt %), Particle size of alloy (av) - 30-60 f.l, Amount of Raney alloy - 50 g, Stirring speed - 1200 rpm Catalyst Concentration Temperature Time of Washing Storage of NaOH of Leaching Leaching agent Conditions mol dm-3 K h " """" " " Effect of alkali95%50%distilledHzDistilledDistilledwaterFilteredHzFiltereddeioniseddistilled313298328343358under1250%95%4268Stored at at3136DeionisedStoredin2836Deionised1 ethanol room room Hz water tapin water temp.at deionised temp. under water room under under20.0010.0012.503.756.252.501.25 RN2 AllEffectRN21RN catalysts 222010 of alkali were concentration stored for 45-50RNEffect 151816 17h beforeof washing measuringEffectRN agent 1213]1 oftheir leaching catalyticEffectRN6RN7RN8RN periodRN4 activity. 5 of Temperaturetapdistilledethanolwater water temperatureroomunderRN9RN 319I14 temp. Hz at weight of the wet catalyst, and W4 is the weight of Solid phase density (Ps)-The Raney nickel, water contained in the wet catalyst as determined along with methanol, was introduced in to the by the Karl Fisher method. The residual alumilJ.ium catalyst bulb by removing the cap of the Rotaflow was determined in the catalyst Rn-l, 14, 17 and 18 stopcock. The cap was replaced and the methanol prepared at different leaching periods. in the catalyst bulb was evaporated very carefully at room temperature by applying suction to the Solid phase and particle density and porosity of bulb. The Rotaflow stopcock was closed and the the catalyst apparatus weighed. This procedure was repeated These properties of the catalyst were determined till a constant weight was obtained. The graduated using the apparatus shown in Fig.2. tube was filled with cyclohexane up to the level 202 INDIAN J CHEM. TECHNOL, JULY 1998 marked A (Fig.2) and the reading A noted. Gas TO ATMOSPHERE bubbles, [1' any present in the liquid column, were t removed by applying a slight suction. The system was connected to atmosphere by the two way -- TO VACUUM stopcock. The liquid was introduced in the evacuakd catalyst bulb, the rota flow stopcock TWO WAY STOPCOCK closed and the reading of the liquid level B in the graduated tube noted. A similar experiment was performed without the catalyst. The \ olume of the solid phase of the catalyst could be obtamed as the difference between (A-B) withoUi catalyst and (A -B) with catalyst from whIch the solid phase density (pJ could be calculated (p, = weight of the catalyst/volume of s(,!;d phase of the catalyst). l'article density - For determining the particle B density, mercury was used instead of cyclohexane as it does not penetrate the pores at atmospheric pressure. In thIs case the difference between (A -B) without catalyst and (A -B) with catalyst gave the ioltlmc of the particles of the catalyst.