By Luciana Magalhaes SAO PAULO (Reuters) -Brazilian conglomerate Cosan's plan to raise up to 10 billion reais ($1.9 billion) through public offerings will go towards alleviating the company's debt, an executive said on Monday, adding none of the funds would go to helping Raizen, its embattled joint venture with oil major Shell. Although analysts welcomed the move, Cosan's shares plunged 21%, on track for their worst day ever. The losses wiped off around 3 billion reais from its market cap. Raizen's share ...