FREEZING POINT ANALYZER MODEL 1470

Introduction

The Model 1470 Freezing Point Anolyax I:, u continuous process analyzer that rne~sures the freezing point of liquids as CI means of purity determination. On-stream analysis eliminates laboratory time and cost of performing purity tests by the standard ASTM D 1015-55 method. Correction of off-specification products can be made manually or through closed control loops obviating the necessity of holding tanks. The purity specification margin can be held closer with a corresponding increase in yield. A liquid sample is supercooled below its freezing point and then caused to partially fuse into a solid by mechanical impact. The exact freezing point temperature is indicated and recorded by a two-pen strip chart recorder. This method is simpler and more reliable than the comparable ASTM test. Stirring of the sample during cooldown is not required.

Applications Determination of p u r i t y is applicable to essentially pure compounds such as benzene, toluene, ethylbenzene, o-xylene, p-xylene and probably many other compounds with known freezing points for zero impurity and cryo- scopic constants. The samples must be water-free and capable of being supercooled. Corrosive solvents may require a special sample cell (consult factory).

Operation

A representative dry sample is introduced into the copper sample cell through a timer-controlled solenoid valve. The valve is opened for approximately 30 seconds to purge the cell of the previous sample and to raise the cell temperature to the required starting level. A thermo- electric cooler is energized to cool the sample a+ a rate of about 6°C. per minute. As cooling progresses, the blue and red pens of the ttiu-ysn recorder move down- scale to the left ~1s the sample temperature is sensed by CI thermistor centrally immersed in the cell. When both have reached the left full scale position, which represents the required amount of supercooling, a knocker solenoid is energized which mechanically shocks the sample into freezing. The frozen material along the walls of the cell thermally insulates the liquid center core. This central portion of the sample remains at the freezing temperature for several minutes. The freezing point tem.perature, and thus the percent purity, is indicated and recorded by the red pen of the recorder which is calibrated in the range of 98% to 100% purity, or as required. When the display period is completed, the programmer automatically opens the solen- oid valve to flush the cell with fresh, warm sample and the cycle repeats. The time of one cycle con vary depending on the product being measured but several tests per hour can normolly be expected.

General Description

The instrument is composed of two separate "nits; analyzer and recorder. An explosion-proof box houses the sample cell, thermo-electric cooler, power supply and water-cooled heat sink, solenoid valve, knocker solenoid and thermistor temperature detector plus the electronic control chassis. This unit should be located close to the main process stream from which the sample is to be drawn.

The recorder is o modified Bristol Z-pen recorder and is usually mounted in a control house remote to the sample point. included in the recorder case ore the timer-programmer, pen-controlled switches, and therm- istor bridge circuits.

Description of Components

Housings

Sample Cell

General Specifications

Sample flow rate:

Installation:

Maximum line pressure:

Cycle frequency:

Cooling rate:

SUperCOOl:

Cooling water:

Utilities:

Thermal cutout:

Sp0n: Repeatability: The housing for the sample cell, thermoelectric cooler and electronics is on explosion-proof enclosure designed for "se in Gloss 1, Group D, Division 1 areas. The recorder case is not explosion-proof and is designated for in- stallation in a control house.

Copper with 15 ml volume (standard) or copper with 5.5. liner for corrosive liquids [at extra cost).

Maximum possible in sweepstream. Total flow through sample cell depends on product. With p-xylene, sample must be 70-F. and dry. Pressure drop across cell is approximately 1 to 2 psi with 30.second flushing period.

Analyzer mounted in vibration-free area near main process stream. Cooling water is required for thermoelectric cooler heat sink.

200 psi.

Varies with product. Approximately 11 minutes for p-xytene.

Varies with product, about 6'C./min. for p-xylene

Varies with product, 5OC. below freezing point for p-xylene

5.10 gph at 65.80°F

115 volt, 60 cycle, single phase

Thermoswitch deenergizes cooler if module rises above 135°F. due to loss of or inadequate flow of cooling water.

As needed depending upon product. O.B'C. (red pen] for 98.100% purity of of p-xylene (100 % = 13.26'C.) For benzene, 0.5'C. corresponds to 99x.- 100% purity (100% = 5.53"C.) Phthalic onhydride, 1'C. corresponds to 98% 100% purity (100% = 131.1"C.)

Better than % 0.004'C. with p-xylene.