Pycnometer

A method for determining the density of a particulate porous polymer which consists essentially of the steps of:

• a. placing a sample of a particulate porous olefin polymer in a sample container of known weight,
• b. placing the filled sample container in a sample cell of known volume which has a gas inlet and a gas outlet,
• c. placing the sample cell of (b) in open gas communication with a gas reservoir of known volume which has a gas inlet and a gas outlet,
• d. passing helium through the gas reservoir and the sample cell to sweep the gas reservoir and sample cell free of gases other than helium, including any gases absorbed on the polymer sample,
• e. closing the inlet and the outlet of the sample cell,
• f. weighing the sample container and determining the weight of the polymer sample,
• g. pressurizing the gas reservoir to superatmospheric pressure with helium, sealing the inlet to the gas reservoir, and determining the helium pressure within the gas reservoir,
• h. opening the gas reservoir to gas communication with the sample cell and determining the equalized helium pressure in the gas reservoir and the sample cell,
• i. determining the free gas volume in the gas reservoir and the sample cell from the pressures measured in steps (g) and (h),
• j. determining the volume of the polymer sample by subtracting the free gas volume determined in step (i) from the known combined volume of the gas reservoir and the sample cell, and
• k. determining the density of the polymer sample by dividing the weight of the polymer determined in step (f) by the volume of the polymer determined in step (j).

A method for determining the density of a particulare porous olefin polymer having hydrocarbon and/or air absorbed in the pores thereof which consists essentially of:

• a. placing a sample of the porous particulate olefin polymer in a sample container of known weight,
• b. placing the sample container of step (a) in a gas tight sample cell of known volume,
• c. pressurizng the sample cell with helium under superatmospheric pressure to displace hydrocarbon and/or air from the pores of the polymer,
• d. venting helium from the sample cell,
• e. repeating steps (c) and (d) until the polymer sample reaches constant weight,
• f. determining the weight of the polymer sample after step (e),
• g. charging a gas reservoir of known volume with helium under superatmospheric pressure and measuring the pressure thereof,
• h. admitting helium from the gas reservoir to the sample cell and measuring the equalized pressure established in the gas reservoir and the sample cell,
• i. determining the free gas volume of the gas reservoir and the sample cell containing the polymer sample from the pressures measured in steps (g) and (h),
• j. determining the volume of the polymer sample by subtracting the free gas volume determined in step (i) from the known combined volume of the gas reservoir and the sample cell, and
• k. determining the density of the polymer from the sample volume determined in step (j) and the sample weight determined in step (f).

In a continuous process for preparing a copolymer of ethylene and a mono-1-olefin containing three or more carbon atoms by a particle form process, the improvement of maintaining the polymer density within a narrow preselected range of density which consists essentially of:

• a. withdrawing a slurry of polymer particles from the polymerization reactor,
• b. transferring the sample from (a) to a sample container of known weight, said sample container being placed in a sample cell of known volume,
• c. pressuring the sample cell with helium under superatmospheric pressure,
• d. venting helium from the sample cell,
• e. repeating steps (c) and (d) until the polymer sample reaches constant weight,
• f. determining the weight of the polymer sample after step (e),
• g. charging a gas reservoir of known volume with helium under superatmospheric pressure and measuring the pressure thereof,
• h. admitting helium from the gas reservoir to the sample cell and measuring the equalized pressure in the gas reservoir and the sample cell,
• i. determining the free gas volume of the gas reservoir and the sample cell containing the polymer sample from the pressures measured in steps (g) and (h),
• j. determining the volume of the polymer sample by subtracting the free gas volume determined in step (i) from the known combined volume of the gas reservoir and the sample cell,
• k. determining the true density of the polymer from the sample volume determined in step (j) and the sample weight determined in step (f),
• l. making any required adjustment in the rate of feed of the mono-1-olefin to the reactor to bring the density of the ethylene/mono-1-olefin copolymer within the preselected range, and
• m. repeating steps (a) - (l) on a periodic basis.