Motorised syringes

In order to obtain very low flow rates without pulsation (e.g. 1 pl/min), pumps based on the principle of high volume motorised syringes are used. The piston, activated by a pneumatic amplifier, moves at a constant linear velocity. These pumps are still in widespread use. 

The alkylation of aniline with methanol was carried out in a down-flow reactor (Ld. 6 mm, length 120 mm) and at atmospheric pressure. Catalyst samples (co. 120 mg, <0.149 mm) were pretreated for 1 h at 523 K in a nitrogen flow (3 L h , 99.999%). The aniline-methanol mixtine (1-10 M) was feed from the top through a calibrated motorised syringe (Harward 44) to achieve different WHSV and different aniline conversion levels. Experiments were carried out at temperatures in the range 523-673 K (mostly 523 K). Blanks runs at 673 K showed that the thermal reaction could be neglected. 

Onto the supports HTl, HT2, HT3, HT4 and HT5 acidified solution containing PdCb was impregnated so as to get lwt% of Pd on the support. Different palladium precursors were used to load Iwt% of palladium on HTl support. Characterisation and catalytic activity The above supports and supported metal catalysts were characterised by XRD, sur ce area and CO chemisorption. The catalytic activity was studied for phenol hydrogenation at 4S3 K in a vertical down flow reactor. The reaction mixture containing phenol and cyclohexane (1 4 wtAvt) was added fi om the top of the reactor at a controlled rate with the help of a motorised syringe. H/Phenol (mol/mol) was maintained at 4. The experimental setup and conditions are given elsewhere (12). 

A teflon tube (cf. Fig. 1.20) of inner diameter 0.5 mm is connected to a syringe filled with air and the latter is placed on a motorised syringe plunger. A droplet of an alkane (nonane, dodecane or hexadecane) is deposited at the end of the tube. The syringe piston moves forward steadily and the air pushes the droplet along at constant speed. Speeds between 10 pm/s and 1 cm/s can be obtained in this way. 

Although the B.P, specifies that the extracts should be made at the rate of 1 g of drug to 10 ml of 80 per cent ethanol it has always appeared more convenient to use sufficient ethanol to produce an extract containing 1 u/ml. If the samples being tested are treated similarly it is then much simpler to keep the ethanolic concentrations equal in the subsequent dilutions with saline. The B,P, method prescribes that the preparation be injected at a slow uniform rate and this can readily be done by means of a motorised syringe if such an apparatus is not available and the infusion made from a burette it has been found easier to infuse 0 5 ml within a few seconds at intervals of thirty seconds. 

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