METHOD FOR PREPARATION OF PHENOL-FORMALDEHYDE RESINS OF THE NOVOLAK TYPE - CZECHOSLOVAK INVENTION SPECIFICATION 171578

Sep 21, 2026

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A method is described for preparing phenol-formaldehyde novolak resins by condensing phenols with formaldehyde using an acid catalyst formed by oxalic acid. The process addresses limitations of conventional practice where reactions are not completed before withdrawing condensate, and describes dehydration under vacuum, which strongly affects resin properties due to side reactions. It further explains that foaming during dehydration complicates processing at higher temperatures and proposes stabilizing the reaction mixture with oxides of Group II and III metals that form suitable salts with oxalic acid.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages28

Reading Time1 h 11 min

AccessFree to download

Inventive Specification Overview

Acid-catalyzed Condensation Process

Dehydration and Its Effect on Resin Properties

Problems: Side Reactions and Foaming During High-Temperature Dehydration

Stabilization Using Group II and III Metal Oxides

Ciernik,J. Method for preparation of phenol-formaldehyde resins of the novolak type.8 p. Patent(Czechoelowak)No.171578(1978)·Filed: TRANSLATION NO.4415 (2)R0e Czechoslovak Patent No.171578 # CZECHOSLOVAK SOCIALIST REPUBLICINVENTION SPECIFICATION PERTAINING TO ACERTIFICATE OF AUTHORSHIP NO.171578 Int.c₁.²: C 08 G 8/10Filed:November ll,1974Application No.:PV 7639-74Open to Public Inspection:February 27,1976Published:February 15,1978Inventor:Jan Ciernik,Brno # METHOD FOR PREPARATION OF PHENOL-FORMALDEHYDE RESINS OFTHE NOVOLAK TYPE The invention pertains to a method for preparation ofphenol-formaldehyde resins of the novolak type by condensationof phenols with formaldehyde by means of an acid catalystformed by oxalic acid. Phenolic resins of the novolak type are now producedby reacting phenols with formaldehyde in the presence of acidcatalysts,most often hydrochloric acid or oxalic acid. Thereaction is always run with a molar excess of phenol. Incommercial practice the molar ratio of phenol to formaldehydeis close to 1:0.9. ? Digitized by the Internet Archivein 2019 https://archive.org/details/methodforprepera00cier_0 Page 2 The time required for reaction of all the formaldehydein the reaction mixture is long and depends on the molarratio of phenol to formaldehyde. In current practice foreconomic reasons (utilization of the capacity of the processinstallation)it is not waited until all the formaldehyde hasreacted,but the withdrawn condensate is heated under areflux condenser after a certain period of time that depends(at a specified molar ratio of phenol to formaldehyde)onthe desired molecular rate of the novolak and which is merelya fraction of the time required before complete reaction offormaldehyde. Oxalic acid as reaction catalyst in novolakproduction is sometimes combined with other stronger acids,for example sulfuric acid or hydrochloric acid which aregenerally added to the reaction mixture in the second condensation stage(after the reaction mixture becomes turbid)in order to accelerate the reaction. Isolation of the novolak resin then begins by dehydrationof the reaction mixture under vacuum at lower temperatures.Dehydration is often carried out so that an oily layer fromthe reaction mixture is separated from the aqueous layer andthis is then dehydrated in evaporators by distillation of thevolatile fractions using vacuum or atmospheric distillationor combined distillation. The dehydration time is dictatedby the temperature,the degree of vacuum and by the thickness ofthe deposits on the walls of the reactor.This period rangesfrom 2 to 5 hours.Its length significantly influences theultimate properties of the resin,since reaction of phenolwith formaldehyde in the presence of oxalic acid also occursduring dehydration.During dehydration undesireable reactions Page 3 occur that cause an increase in the degree of gelation and adeterioration in the flow properties of the novolak resinmelt. The differences in properties of individual productsare greater,the more different the dehydration time. Another disadvantage of preparation of novolaks withoxalic acid as catalyst is that during preparation of novolakswith higher softening points it is necessary to run dehydrationunder vacuum and to high final temperatures of the reactionmixture -above 130℃. At these and higher temperaturessignificant foaming of the reaction mixture occurs whichhampers and substantially complicates subsequent novolakprocessing.Major difficulties occur in the vessels wheresignificant foaming occurs in the case of novolaks with lowersoftening points when the melt is heated above 130℃. Themelt then flocculates with considerable difficulty,or whendischarged into a cooling bath or onto a cooling band,theresultant foam on the surface greatly complicates and lengthensthe cooling process. It has been found that these undesirable phenomena,aswell as changes in novolak characteristics during dehydrationand foaming of the r

FAQs

How does the method prepare novolak resins from phenol and formaldehyde?

It condenses phenols with formaldehyde using an acid catalyst formed by oxalic acid to produce phenol-formaldehyde novolak resins.

Why is the dehydration step critical in the process?

Dehydration time and conditions affect final resin properties because reactions involving phenol and formaldehyde in the presence of oxalic acid continue during dehydration.

What stabilization approach is proposed to prevent undesirable dehydration and foaming phenomena?

Stabilizing the reaction mixture before or during distillation with at least an equimolar amount of Group II and III metal oxides—such as aluminum, zinc, calcium, or magnesium oxide—prevents the negative effects related to oxalic acid behavior.

Sep 21, 2026

Uploaded by Eliana