Dab tsi yog Compatibility ntawm Graphite Kub Exchangers nrog Oxidizing Acids Zoo li Nitric thiab Chromic?

Graphite's Achilles pob taws yog nws qhov cuam tshuam rau oxidising cov neeg ua haujlwm. PTFE yog inert rau txhua yam. Graphite, ntawm qhov tod tes, tuaj yeem tawm tsam sai los ntawm nitric acid, chromic acid, thiab txawm tias boiling concentrated sulfuric acid nyob rau hauv tej yam kev mob. Impervious graphite tshav kub exchangers muaj kev pab cuam lub neej zoo nyob rau hauv txo tej yam kev mob (xws li hydrochloric, dilute sulfuric, phosphoric acids) tab sis heev txwv compatibility nrog oxidising acids. Nws yog ib qho tseem ceeb kom nkag siab txog graphite compatibility nrog oxidising acids los tiv thaiv cov cuab yeej puas tsuaj thiab tsis tsim nyog downtime.

Oxidative Attack Mechanism
Graphite yog ib hom khoom carbon. Muaj zog oxidisers chemically tua cov pa roj carbon lattice, tig nws mus rau carbon dioxide (CO 2), carbon monoxide (CO) los yog lwm yam oxidised molecules. Tag nrho cov tshuaj tiv thaiv tej zaum yuav generalized raws li hauv qab no:

O2 + C(los ntawm oxidiser)=CO2 + O(los ntawm oxidiser)=COx

Cov txheej txheem no noj cov khoom siv graphite thiab maj mam hloov cov khoom carbon rau roj. Qhov no ua rau poob ntawm cov qauv kev ncaj ncees, nto pitting thiab thaum kawg perforation ntawm cov phab ntsa ntawm lub raj los yog thaiv cov channel. Kev tiv thaiv thawj zaug yog muab los ntawm impregnating resin (feem ntau yog phenolic), uas tsim kom muaj kev cuam tshuam ntawm oxidiser thiab graphite substrate. Tab sis cov resin nws tus kheej kuj nquag oxidation. Yog hais tias cov resin raug punctured - los ntawm tshuaj tua kab mob, microcracks, tshav kub cycling, thiab lwm yam - lub hauv paus graphite yog ncaj qha tawm tsam thiab sai sai puas.

Hauv ntau qhov kev pabcuam oxidising, tus nqi ntawm cov pa roj carbon monoxide poob sai heev uas cov khoom siv hluav taws xob graphite tuaj yeem ua tsis tiav hauv hnub lossis lub lis piam, tsis yog xyoo.

Common Oxidisers thiab tshwj xeeb incompatibilities
Graphite Compatibility Oxidising Acid PTFE Compatibility Comments
Nitric acid (HNO3) Poor; degraded at >5% concentration ntawm kub kub Zoo mus txog 110℃Dilute (<5%) nitric acid at room temperature can be tolerated for short durations, but is not suggested for continuous service
Chromic Acid (H₂CrO₄) pluag heev. Tag nrho cov concentrations thiab kub.Txog 110℃ExcellentChromic acid yog ib tug haib oxidiser. Graphite tsis qhia.
Sulphuric acid (H 2 SO 4 ) - concentrated, heated Limited; assaults start above 96% concentration and >150 CZoo rau 110 C (tsuas los ntawm qhov kub thiab txias) Graphite resistant rau dilute mus rau 96% H2SO4 rau ~ 150 C; ze 98% ntawm qhov kub thiab txias ua oxidising
Perchloric acid (HClO₄) Muaj phom sij; Cov tshuaj tiv thaiv muaj zog zoo heev (txias) Graphite yuav tsum tsis txhob siv nrog perchloric acid vim oxidation thiab tawg txaus ntshai
Cov kua qaub sib xyaw (aqua regia, nitrosulfuric acid) Tsis zoo; Kev tawm tsam nrawm Zoo heev txog li 110℃Oxidizing kev sib txuas ua haujlwm ntau dua li cov kua qaub
Nitric Acid: Concentration thiab Temperature Limits
Qhov txwv ntawm graphite compatibility nrog oxidising acids yog qhov hnyav heev rau nitric acid. Lub sij hawm luv luv raug rau ambient kub (tsawg dua los yog sib npaug li 30 degree) thiab qis dua li 5% concentration yuav ua rau me ntsis tshwm sim. Txawm li cas los xij, qhov nce hauv concentration lossis kub txhawb oxidation ntau heev. Graphite heat exchangers raug kev txom nyem deg deg hauv cov xuab moos ntawm 10-20% nitric acid thiab 50 degree. Ntawm 50% nitric acid thiab nyob ze ntawm kub kub, cov graphite tau noj sai.

Yog li ntawd, kev xyaum ua lag luam tsis suav nrog graphite rau kev siv nrog nitric acid tshwj tsis yog cov kua qaub diluted heev, txias thiab siv rau hauv daim ntawv thov tsis yog -tseem ceeb. Tseem, PTFE lossis lwm yam ntaub ntawv (ceramics, tantalum, zirconium) tau pom zoo.

Chromic Acid: Tsis sib haum xeeb
Chromic acid (H 2 CrO 4) yog ib qho ntawm cov khoom muaj zog tshaj plaws ntawm cov tshuaj oxidizing pom nyob rau hauv kev lag luam. Nws yog siv hauv cov hlau polishing thiab anodising da dej. Nws tawm tsam graphite ntawm tag nrho cov concentrations thiab tag nrho cov kub nrog rau txias dilute daws. Tsis muaj kev tiv thaiv resin npog yuav zam chromic acid rau lub sijhawm ntev. Txhua qhov graphite, cov khoom siv hluav taws xob, lub valve lossis sparger, raug chromic acid yuav tawg nrawm, feem ntau nyob rau hauv hnub. Yog tias qhov ntsuas kub qis dua qhov txwv ntawm PTFE (kwv yees li 110 C) ces PTFE cov khoom siv hluav taws xob yog cov qauv rau chromic acid cua sov lossis cua txias ua haujlwm.

Kub Concentrated Sulfuric Acid: Ib Qhov Kev Kawm Txog Kev Hloov Pauv
Graphite has found wide and successful usage in sulphuric acid service over much of the concentration range. Low (0-70%) and medium (70-93%) concentrations of sulphuric acid are well handled at temperatures up to 150-180°C. Concentrated sulphuric acid (>96%) yog haum rau nruab nrab kub (<=100°C). However, the oxidising power of sulphuric acid increases as the concentration near 98% and the temperature exceeds about 150°C. The acid then begins to function as an oxidiser and attacks the graphite lattice, not as a reducing acid. This is a well-known boundary: graphite oxidises and loses weight rapidly at 180°C and 98% H₂SO₄.

Rau cov haujlwm zoo li no (xws li sulfuric acid concentrators lossis oleum kev pabcuam) PTFE tsis yog qhov kev xaiv ua tau raws li qhov kub thiab txias siab tshaj qhov kev txwv. Hloov chaw, ceramic (iav, silicon carbide) los yog tantalum heat exchangers yog siv.

Vim li cas PTFE zoo dua rau Oxidising Acids
Poly (tetrafluoroethylene) (PTFE) muaj cov pa roj carbon -fluorine qaum. Cov pa roj carbon muaj zog- fluorine txuas ua rau PTFE inert rau yuav luag txhua yam khoom xws li cov oxidisers muaj zog xws li nitric, chromic thiab kub concentrated sulfuric acid (ntawm qhov kub nruab nrab). Nyob rau hauv cov xwm txheej no, PTFE tsis oxidise lossis deteriorate. Qhov kev txwv ib leeg ntawm PTFE yog qhov siab tshaj plaws ua haujlwm kub kub uas yog kwv yees li 110-120℃rau cov khoom PTFE hauv cov ntawv siv hluav taws xob. PTFE yog cov khoom ntawm kev xaiv rau oxidising acid lub luag hauj lwm nyob rau hauv uas kub ntau yam.

Ib qho kev qhia zoo heev yog tias graphite yuav tsum tsis txhob siv rau hauv txhua qhov kev pabcuam uas muaj cov oxidiser muaj zog muaj nyob rau ntawm qhov xav tau ntau thiab kub dhau. Qhov no yog ib thaj tsam ntawm cov tshuaj tawv tawv: cov qauv carbon ntawm graphite tsis tuaj yeem tiv taus oxidation, txawm tias cov resin impregnation.

Dilute Oxidant Conditions thiab Exceptions
 

Kev ntsuas oxidative puas tsuaj