Kant did not reject the virtue of benevolence. He embraced it. He did argue that benevolence ought to be based on a sense of duty, rather than on mere sentiment (feeling, desire).
To be beneficent when we can is a duty; and besides this, there are many minds so sympathetically constituted that, without any other motive of vanity or self-interest, they find a pleasure in spreading joy around them and can take delight in the satisfaction of others so far as it is their own work. But I maintain that in such a case an action of this kind, however proper, however amiable it may be, has nevertheless no true moral worth, but is on a level with other inclinations, e.g., the inclination to honour, which, if it is happily directed to that which is in fact of public utility and accordant with duty and consequently honourable, deserves praise and encouragement, but not esteem. For the maxim lacks the moral import, namely, that such actions be done from duty, not from inclination. (Fundamental Principles of the Metaphysic of Morals "I. Transition from the common rational knowledge of morality to the philosophical.")
The point of benevolence as duty is that one acts from the free part of one's nature. Sentiments (feelings, desires) one just happens to have. They are not freely chosen.
It is in this manner, undoubtedly, that we are to understand those passages of Scripture also in which we are commanded to love our neighbour, even our enemy. For love, as an affection, cannot be commanded, but beneficence for duty's sake may. (Ibid.)
There is no one, not even the most consummate villain, provided only that he is otherwise accustomed to the use of reason, who, when we set before him examples of ... sympathy and general benevolence ... does not wish that he might also possess these qualities ... He proves by this that he transfers himself in thought with a will free from the impulses of the sensibility into an order of things wholly different from that of his desires. (Ibid. "How is a Categorical Imperative Possible?")