The invention relates to a defoamer composition. The invention also relates to a method for reducing or preventing foam in an aqueous composition. The defoamer composition of the invention comprises at least one hydrophobic liquid; and at least one modified polyacrylate polymer. The modified polyacrylate polymer is obtainable by a process comprising 1. polymerizing at least one acrylate monomer selected from substituted or unsubstituted C.sub.1-C.sub.22 alkyl acrylates, substituted or unsubstituted C.sub.4-C.sub.22 cycloalkyl acrylates, substituted or unsubstituted C.sub.1-C.sub.22 acrylamides, esters of acrylic acid with polyalkylether alcohol, or combinations of two or more thereof, to obtain at least one polyacrylate polymer; and 2. modifying the at least one polyacrylate polymer obtained in step (i) by transesterification with at least one alcohol selected from (c1) at least one unsubstituted C.sub.8-C.sub.36 alcohol, (c2) at least one polyalkylether alcohol, or combinations of two or more thereof.

Miscible antifoams are provided that do not separate out of a target liquid and that are easy to incorporate in the target liquid. A method or system involves mixing a liquid (a miscible antifoam) into a target foaming liquid. This miscible antifoam is engineered/chosen such that it has both a higher surface tension and is more volatile than the target liquid, or engineered such that it has both a lower surface tension and is less volatility than the target liquid. The miscible antifoam leads to surface tension gradients that cause bubble rupture up to 10 times faster than the target liquid without the antifoam. Further, the miscible antifoams are easy to incorporate and do not separate out from the target liquid during operationboth of which are key limitations faced by existing antifoams.

The present invention relates to a defoamer oil compound that contains an organopolysiloxane (A), a fine silica powder (B), and a group (C) that is represented by the organopolysiloxanes of formulas (I) and/or (II)

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(in the formulas, c, d, and e are each an integer of 0 or more, and at least one of X.sup.1 to X.sup.3 is the group represented by formula (i)). The component (C) is used as a surface treatment agent for the component (B). The present invention makes it possible to obtain a silicone-based defoamer composition that imparts good initial defoaming properties even in an alkaline foaming liquid, that exhibits very little loss in performance over time, and that has excellent defoaming performance.

A method of defoaming a system subject to foaming by using a defoamer composition is disclosed. The defoamer composition contains (a) 80 to 100 wt. % of a decarboxylated rosin acid (DCR) having a density of 0.9 to 1.0 g/cm.sup.3, a flash point of 135 to 175 C., an acid value of <50 mg KOH/g, measured according to ASTM D465, and a viscosity of 15 to 60 cSt at 40 C., measured according to ASTM D-445; and (b) 0 to 20 wt. % based on total weight of the defoamer composition of at least one component selected from the group consisting of nanoparticles, surfactants, hydrophobic compounds, and mixtures thereof. The defoamer composition is very effective in controlling unwanted foam formation or reduce already formed foam in the system.

The present disclosure provides methods and compositions for reducing an amount of foam in a medium. A method may include adding a composition to the medium and reducing the amount of foam in the medium. The composition may include an anti-foam composition that includes an imide-containing compound. The anti-foam composition may comprise, for example, a detacking composition, a fuel cloud point depressant, and/or a crude oil pour point depressant.