<p>Hello again! <br /><br />For simplicity, I'll respond to both of your questions in this thread. <br /><br />1. For the first question, it should remain as is unless you put a subject clarifying who/what is doing the cooling. The simplified sentence would be, "Siloxanes separate from the biogas once it cools". You could, if you wish, explain what is cooling it, e.g. "Researchers separate siloxanes from the biogas by cooling...". Otherwise, I would recommend keeping it in active voice. <br /><br />2. There is a small typo: "known" should be "know". I had changed that, but the document must not have saved it for some reason. The phrase "neither...nor" is a phrase for mentioning two negatives for the same subject: "Billy neither knows how to get to the store nor how to buy groceries." Grammatically, it unites the sentence.<br /><br />Hope this helps,</p>
<p>EE</p>
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