Abstract: A method of testing a substrate monolith (1), the substrate monolith (1) comprising: i) a plurality of channels extending longitudinally along a Z-axis of the substrate monolith (1); and ii) an array of walls extending along the Z-axis and forming partitions between adjacent channels; wherein the array of walls comprises first walls (10) orientated parallel to a first-axis of the substrate monolith (1) and second walls (11) orientated parallel to a second-axis of the substrate monolith (1), the first-axis and the second-axis both being orthogonal to the Z-axis; the method comprising the steps of: a) applying an impulse (J) to the substrate monolith (1) with an impact tool (22) to induce mechanical vibrations in the substrate monolith (1); b) sensing the mechanical vibrations of the substrate monolith (1); c) determining a fundamental frequency of the sensed mechanical vibrations; and d) comparing the fundamental frequency of the sensed mechanical vibrations to a fundamental frequency obtained from testing

Abstract: A process for the production of heterocyclic quaternary ammonium salts or hydroxides is disclosed. The process comprises a continuous hydrogenation step, in which an unsaturated heterocyclic amine is reacted with hydrogen to form a saturated heterocyclic amine; a first continuous N-alkylation step, in which the saturated heterocyclic amine is alkylated to produce an intermediate saturated heterocyclic amine having an increased degree of substitution compared to the saturated heterocyclic amine; and one or more further N-alkylation steps in which the intermediate saturated heterocyclic amine is N-alkylated to the heterocyclic quaternary ammonium salt or hydroxide. A process of producing a saturated heterocyclic amine is also disclosed. The process comprises reacting an unsaturated heterocyclic amine with hydrogen in a vapour phase reaction at a pressure of not more than 70 bar and a temperature in the range of from 150° C. to 350° C. A process of N-alkylating a saturated heterocyclic amine is also disclosed.