CITIC Securities Co. Ltd. on Tuesday estimated its net profit in the first half of this year had a year-on-year growth of more than 50%, Reuters reported.   The company posted a net profit of 66.22 million yuan in the first half of 2006.   Earnings at Chinese brokerages have climbed this year because of a recovery in the overall stock market. The benchmark Shanghai stock index is up more than 40 percent since the start of the year, while turnover has more than doubled, Reuters wrote.