ASTM_D_4824_-_13.pdf

Designation:D482413Standard Test Method forDetermination of Catalyst Acidity by AmmoniaChemisorption1This standard is issued under the fixed designation D4824;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method involves the measurement of total catalyst acidity by chemisorption of ammoniain a static volumetric system.Acidity is a very important property in determining catalyst activity andselectivity in many commercial reactions.Zeolite based catalysts used in the petroleum industry forcatalytic cracking are a prime example.This test method describes a simple procedure employinginexpensive equipment that could readily be assembled in most laboratories.1.Scope1.1 This test method covers the determination of acidity ofcatalysts and catalyst carriers by ammonia chemisorption.Avolumetric measuring system is used to obtain the amount ofchemisorbed ammonia.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D3766 Terminology Relating to Catalysts and CatalysisE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsSee Terminology D3766.3.2 Symbols:Vk=calibrated expansion volume,cm3.T1=temperature of Vkat initial ammonia pressure,K.T2=temperature of Vkat final ammonia pressure,K.P1=initial ammonia pressure,torr.P2=final ammonia pressure,torr.Ws=mass of sample,g.W1=tare of sample tube,g.W2=sample mass plus tare of tube,g.P1T=initial ammonia pressure corrected to standardtemperature,torr.P2T=final ammonia pressure corrected to standardtemperature,torr.4.Summary of Test Method4.1 A sample is degassed by heating in a vacuum to removeadsorbed vapors from the surface.The sample is then exposedto an excess of gaseous ammonia and the excess ammonia isremoved by freezing it into a trap cooled with liquid nitrogen.The chemisorbed ammonia is calculated as the differencebetween the volume of ammonia before exposure and thevolume recovered in the liquid nitrogen trap.5.Significance and Use5.1 This test method can be used to determine the acidity ofcatalysts and catalyst carriers by ammonia chemisorption formaterials specifications,manufacturing control,and researchand development in the evaluation of catalysts.6.Apparatus6.1 A schematic diagram of one type of apparatus is shownin Fig.1.It may be constructed of glass or metal and mayoperate manually or automatically.It has the following fea-tures:1This test method is under the jurisdiction of ASTM Committee D32 onCatalysts and is the direct responsibility of Subcommittee D32.01 on Physical-Chemical Properties.Current edition approved April 1,2013.Published August 2013.Originallyapproved in 1988.Last previous edition approved in 2008 as D4824 03(2008).DOI:10.1520/D4824-13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.1.1 Vacuum System,capable of attaining and maintainingpressures below 104torr(0.01 Pa)in the absence of catalyst.6.1.2 Expansion Vessel,having a volume between 300 to500 cm3(Vk)known to the nearest 0.01 cm3(Note 1).Thisvolume is defined as the volume between stopcocks V7and V8and includes the pressure gage and ammonia bulb.NOTE1An expansion vessel of smaller volume is recommended formaterials of low surface area or smaller sample size.6.1.3 Pressure Sensing Device or Pressure Transducer,capable of measuring 0 to 250 torr to the nearest 101torr(10Pa).6.1.4 Pressure Sensing Device or Pressure Transducer,capable of measuring 0 to 1000 torr to the nearest 103torr(0.1Pa).6.1.5 Valve,(V8)from ammonia supply to the expansionvolume.6.1.6 Sample Tubes,with volume between 5 and 25 cm3.The sample tube(s)may be connected to the apparatus withstandard taper joints,glass-to-glass seals,or compressionfittings.6.1.7 Dewar Flask(s),for immersion of ammonia(freeze-back bulb)in liquid nitrogen.6.1.8 Thermometer or Thermocouple,for measuring thetemperature of the expansion volume,Vk.Alternatively,theexpansion volume may be thermostatted a few degrees aboveambient to obviate the necessity of recording this temperature.6.1.9 Heating Mantle or Small Furnace,for each sampletu